[compiler] Update fixtures for new inference

2025-06-18 13:00:42 -07:00
1249 changed files with 18799 additions and 60744 deletions
--- a/.eslintignore
+++ b/.eslintignore
@@ -28,6 +28,3 @@ packages/react-devtools-shared/src/hooks/__tests__/__source__/__untransformed__/
 packages/react-devtools-shell/dist
 packages/react-devtools-timeline/dist
 packages/react-devtools-timeline/static
-
-# Imported third-party Flow types
-flow-typed/
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -468,14 +468,13 @@ module.exports = {
      files: ['packages/react-server-dom-webpack/**/*.js'],
      globals: {
        __webpack_chunk_load__: 'readonly',
-        __webpack_get_script_filename__: 'readonly',
        __webpack_require__: 'readonly',
      },
    },
    {
      files: ['packages/react-server-dom-turbopack/**/*.js'],
      globals: {
-        __turbopack_load_by_url__: 'readonly',
+        __turbopack_load__: 'readonly',
        __turbopack_require__: 'readonly',
      },
    },
@@ -547,10 +546,13 @@ module.exports = {
  },

  globals: {
+    $Call: 'readonly',
+    $ElementType: 'readonly',
    $Flow$ModuleRef: 'readonly',
    $FlowFixMe: 'readonly',
    $Keys: 'readonly',
    $NonMaybeType: 'readonly',
+    $PropertyType: 'readonly',
    $ReadOnly: 'readonly',
    $ReadOnlyArray: 'readonly',
    $ArrayBufferView: 'readonly',
@@ -565,7 +567,6 @@ module.exports = {
    BigInt: 'readonly',
    BigInt64Array: 'readonly',
    BigUint64Array: 'readonly',
-    CacheType: 'readonly',
    Class: 'readonly',
    ClientRect: 'readonly',
    CopyInspectedElementPath: 'readonly',
@@ -580,15 +581,13 @@ module.exports = {
    IteratorResult: 'readonly',
    JSONValue: 'readonly',
    JSResourceReference: 'readonly',
-    mixin$Animatable: 'readonly',
    MouseEventHandler: 'readonly',
    NavigateEvent: 'readonly',
-    PerformanceMeasureOptions: 'readonly',
    PropagationPhases: 'readonly',
    PropertyDescriptor: 'readonly',
-    PropertyDescriptorMap: 'readonly',
-    Proxy$traps: 'readonly',
+    React$AbstractComponent: 'readonly',
    React$Component: 'readonly',
+    React$ComponentType: 'readonly',
    React$Config: 'readonly',
    React$Context: 'readonly',
    React$Element: 'readonly',
@@ -609,7 +608,6 @@ module.exports = {
    symbol: 'readonly',
    SyntheticEvent: 'readonly',
    SyntheticMouseEvent: 'readonly',
-    SyntheticPointerEvent: 'readonly',
    Thenable: 'readonly',
    TimeoutID: 'readonly',
    WheelEventHandler: 'readonly',
@@ -620,10 +618,10 @@ module.exports = {
    PropertyIndexedKeyframes: 'readonly',
    KeyframeAnimationOptions: 'readonly',
    GetAnimationsOptions: 'readonly',
+    Animatable: 'readonly',
    ScrollTimeline: 'readonly',
    EventListenerOptionsOrUseCapture: 'readonly',
    FocusOptions: 'readonly',
-    OptionalEffectTiming: 'readonly',

    spyOnDev: 'readonly',
    spyOnDevAndProd: 'readonly',
--- a/.github/workflows/compiler_playground.yml
+++ b/.github/workflows/compiler_playground.yml
@@ -57,6 +57,8 @@ jobs:
          key: playwright-browsers-v6-${{ runner.arch }}-${{ runner.os }}-${{ steps.playwright_version.outputs.playwright_version }}
      - run: npx playwright install --with-deps chromium
        if: steps.cache_playwright_browsers.outputs.cache-hit != 'true'
+      - run: npx playwright install-deps
+        if: steps.cache_playwright_browsers.outputs.cache-hit == 'true'
      - run: CI=true yarn test
      - run: ls -R test-results
        if: '!cancelled()'
--- a/.github/workflows/runtime_build_and_test.yml
+++ b/.github/workflows/runtime_build_and_test.yml
@@ -6,12 +6,6 @@ on:
  pull_request:
    paths-ignore:
      - compiler/**
-  workflow_dispatch:
-    inputs:
-      commit_sha:
-        required: false
-        type: string
-        default: ''

 permissions: {}

@@ -34,7 +28,7 @@ jobs:
    steps:
      - uses: actions/checkout@v4
        with:
-          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.pull_request.head.sha || github.sha }}
      - name: Check cache hit
        uses: actions/cache/restore@v4
        id: node_modules
@@ -75,7 +69,7 @@ jobs:
    steps:
      - uses: actions/checkout@v4
        with:
-          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.pull_request.head.sha || github.sha }}
      - name: Check cache hit
        uses: actions/cache/restore@v4
        id: node_modules
@@ -123,7 +117,7 @@ jobs:
    steps:
      - uses: actions/checkout@v4
        with:
-          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.pull_request.head.sha || github.sha }}
      - uses: actions/github-script@v7
        id: set-matrix
        with:
@@ -142,7 +136,7 @@ jobs:
    steps:
      - uses: actions/checkout@v4
        with:
-          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.pull_request.head.sha || github.sha }}
      - uses: actions/setup-node@v4
        with:
          node-version-file: '.nvmrc'
@@ -172,7 +166,7 @@ jobs:
    steps:
      - uses: actions/checkout@v4
        with:
-          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.pull_request.head.sha || github.sha }}
      - uses: actions/setup-node@v4
        with:
          node-version-file: '.nvmrc'
@@ -204,7 +198,7 @@ jobs:
    steps:
      - uses: actions/checkout@v4
        with:
-          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.pull_request.head.sha || github.sha }}
      - uses: actions/setup-node@v4
        with:
          node-version-file: '.nvmrc'
@@ -260,7 +254,7 @@ jobs:
    steps:
      - uses: actions/checkout@v4
        with:
-          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.pull_request.head.sha || github.sha }}
      - uses: actions/setup-node@v4
        with:
          node-version-file: '.nvmrc'
@@ -307,16 +301,14 @@ jobs:
          path: |
            **/node_modules
          key: runtime-and-compiler-node_modules-v6-${{ runner.arch }}-${{ runner.os }}-${{ hashFiles('yarn.lock', 'compiler/yarn.lock') }}
-      - name: Install runtime dependencies
-        run: yarn install --frozen-lockfile
-        if: steps.node_modules.outputs.cache-hit != 'true'
-      - name: Install compiler dependencies
-        run: yarn install --frozen-lockfile
-        working-directory: compiler
+          restore-keys: |
+            runtime-and-compiler-node_modules-v6-${{ runner.arch }}-${{ runner.os }}-
+            runtime-and-compiler-node_modules-v6-
+      - run: yarn install --frozen-lockfile
        if: steps.node_modules.outputs.cache-hit != 'true'
      - run: ./scripts/react-compiler/build-compiler.sh && ./scripts/react-compiler/link-compiler.sh
      - run: yarn workspace eslint-plugin-react-hooks test
-
+        
  # ----- BUILD -----
  build_and_lint:
    name: yarn build and lint
@@ -331,7 +323,7 @@ jobs:
    steps:
      - uses: actions/checkout@v4
        with:
-          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.pull_request.head.sha || github.sha }}
      - uses: actions/setup-node@v4
        with:
          node-version-file: '.nvmrc'
@@ -426,7 +418,7 @@ jobs:
    steps:
      - uses: actions/checkout@v4
        with:
-          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.pull_request.head.sha || github.sha }}
      - uses: actions/setup-node@v4
        with:
          node-version-file: '.nvmrc'
@@ -471,7 +463,7 @@ jobs:
    steps:
      - uses: actions/checkout@v4
        with:
-          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.pull_request.head.sha || github.sha }}
      - uses: actions/setup-node@v4
        with:
          node-version-file: '.nvmrc'
@@ -499,7 +491,7 @@ jobs:
          merge-multiple: true
      - name: Display structure of build
        run: ls -R build
-      - run: echo ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }} >> build/COMMIT_SHA
+      - run: echo ${{ github.event.pull_request.head.sha || github.sha }} >> build/COMMIT_SHA
      - name: Scrape warning messages
        run: |
          mkdir -p ./build/__test_utils__
@@ -536,7 +528,7 @@ jobs:
    steps:
      - uses: actions/checkout@v4
        with:
-          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.pull_request.head.sha || github.sha }}
      - uses: actions/setup-node@v4
        with:
          node-version-file: '.nvmrc'
@@ -576,7 +568,7 @@ jobs:
    steps:
      - uses: actions/checkout@v4
        with:
-          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.pull_request.head.sha || github.sha }}
      - uses: actions/setup-node@v4
        with:
          node-version-file: '.nvmrc'
@@ -613,7 +605,7 @@ jobs:
    steps:
      - uses: actions/checkout@v4
        with:
-          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.pull_request.head.sha || github.sha }}
      - uses: actions/setup-node@v4
        with:
          node-version-file: '.nvmrc'
@@ -654,7 +646,7 @@ jobs:
    steps:
      - uses: actions/checkout@v4
        with:
-          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.pull_request.head.sha || github.sha }}
      - uses: actions/setup-node@v4
        with:
          node-version-file: '.nvmrc'
@@ -728,7 +720,7 @@ jobs:
    steps:
      - uses: actions/checkout@v4
        with:
-          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.pull_request.head.sha || github.sha }}
      - uses: actions/setup-node@v4
        with:
          node-version-file: '.nvmrc'
@@ -785,7 +777,7 @@ jobs:
    steps:
      - uses: actions/checkout@v4
        with:
-          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.pull_request.head.sha || github.sha }}
      - uses: actions/setup-node@v4
        with:
          node-version-file: '.nvmrc'
@@ -811,18 +803,9 @@ jobs:
          pattern: _build_*
          path: build
          merge-multiple: true
-      - name: Check Playwright version
-        id: playwright_version
-        run: echo "playwright_version=$(npm ls @playwright/test | grep @playwright | sed 's/.*@//' | head -1)" >> "$GITHUB_OUTPUT"
-      - name: Cache Playwright Browsers for version ${{ steps.playwright_version.outputs.playwright_version }}
-        id: cache_playwright_browsers
-        uses: actions/cache@v4
-        with:
-          path: ~/.cache/ms-playwright
-          key: playwright-browsers-v6-${{ runner.arch }}-${{ runner.os }}-${{ steps.playwright_version.outputs.playwright_version }}
-      - name: Playwright install deps
-        if: steps.cache_playwright_browsers.outputs.cache-hit != 'true'
-        run: npx playwright install --with-deps chromium
+      - run: |
+          npx playwright install
+          sudo npx playwright install-deps
      - run: ./scripts/ci/run_devtools_e2e_tests.js
        env:
          RELEASE_CHANNEL: experimental
@@ -839,7 +822,7 @@ jobs:
    steps:
      - uses: actions/checkout@v4
        with:
-          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.pull_request.head.sha || github.sha }}
      - uses: actions/setup-node@v4
        with:
          node-version-file: '.nvmrc'
@@ -888,7 +871,7 @@ jobs:
          node ./scripts/print-warnings/print-warnings.js > build/__test_utils__/ReactAllWarnings.js
      - name: Display structure of build for PR
        run: ls -R build
-      - run: echo ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }} >> build/COMMIT_SHA
+      - run: echo ${{ github.event.pull_request.head.sha || github.sha }} >> build/COMMIT_SHA
      - run: node ./scripts/tasks/danger
      - name: Archive sizebot results
        uses: actions/upload-artifact@v4
--- a/.github/workflows/runtime_prereleases.yml
+++ b/.github/workflows/runtime_prereleases.yml
@@ -85,7 +85,7 @@ jobs:
            --skipTests \
            --tags=${{ inputs.dist_tag }} \
            --onlyPackages=${{ inputs.only_packages }} ${{ (inputs.dry && '') || '\'}}
-            ${{ inputs.dry && '--dry' || '' }}
+            ${{ inputs.dry && '--dry'}}
      - if: '${{ inputs.skip_packages }}'
        name: 'Publish all packages EXCEPT ${{ inputs.skip_packages }}'
        run: |
@@ -94,19 +94,19 @@ jobs:
            --skipTests \
            --tags=${{ inputs.dist_tag }} \
            --skipPackages=${{ inputs.skip_packages }} ${{ (inputs.dry && '') || '\'}}
-            ${{ inputs.dry && '--dry' || '' }}
+            ${{ inputs.dry && '--dry'}}
      - if: '${{ !(inputs.skip_packages && inputs.only_packages) }}'
        name: 'Publish all packages'
        run: |
          scripts/release/publish.js \
            --ci \
            --tags=${{ inputs.dist_tag }} ${{ (inputs.dry && '') || '\'}}
-            ${{ inputs.dry && '--dry' || '' }}
+            ${{ inputs.dry && '--dry'}}
      - name: Notify Discord on failure
        if: failure() && inputs.enableFailureNotification == true
        uses: tsickert/discord-webhook@86dc739f3f165f16dadc5666051c367efa1692f4
        with:
          webhook-url: ${{ secrets.DISCORD_WEBHOOK_URL }}
          embed-author-name: "GitHub Actions"
-          embed-title: '[Runtime] Publish of ${{ inputs.release_channel }}@${{ inputs.dist_tag}} release failed'
+          embed-title: 'Publish of $${{ inputs.release_channel }} release failed'
          embed-url: ${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}/attempts/${{ github.run_attempt }}
--- a/.github/workflows/runtime_releases_from_npm_manual.yml
+++ b/.github/workflows/runtime_releases_from_npm_manual.yml
@@ -110,7 +110,7 @@ jobs:
            --tags=${{ inputs.tags }} \
            --publishVersion=${{ inputs.version_to_publish }} \
            --onlyPackages=${{ inputs.only_packages }} ${{ (inputs.dry && '') || '\'}}
-            ${{ inputs.dry && '--dry' || '' }}
+            ${{ inputs.dry && '--dry'}}
      - if: '${{ inputs.skip_packages }}'
        name: 'Publish all packages EXCEPT ${{ inputs.skip_packages }}'
        run: |
@@ -119,7 +119,7 @@ jobs:
            --tags=${{ inputs.tags }} \
            --publishVersion=${{ inputs.version_to_publish }} \
            --skipPackages=${{ inputs.skip_packages }} ${{ (inputs.dry && '') || '\'}}
-            ${{ inputs.dry && '--dry' || '' }}
+            ${{ inputs.dry && '--dry'}}
      - name: Archive released package for debugging
        uses: actions/upload-artifact@v4
        with:
--- a/.github/workflows/shared_close_direct_sync_branch_prs.yml
+++ b/.github/workflows/shared_close_direct_sync_branch_prs.yml
@@ -18,7 +18,6 @@ jobs:
    permissions:
      # Used to create a review and close PRs
      pull-requests: write
-      contents: write
    steps:
      - name: Close PR
        uses: actions/github-script@v7
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,8 +1,3 @@
-## 19.1.1 (July 28, 2025)
-
-### React
-* Fixed Owner Stacks to work with ES2015 function.name semantics ([#33680](https://github.com/facebook/react/pull/33680) by @hoxyq)
-
 ## 19.1.0 (March 28, 2025)

 ### Owner Stack
@@ -24,11 +19,11 @@ An Owner Stack is a string representing the components that are directly respons
 * Updated `useId` to use valid CSS selectors, changing format from `:r123:` to `«r123»`. [#32001](https://github.com/facebook/react/pull/32001)
 * Added a dev-only warning for null/undefined created in useEffect, useInsertionEffect, and useLayoutEffect. [#32355](https://github.com/facebook/react/pull/32355)
 * Fixed a bug where dev-only methods were exported in production builds. React.act is no longer available in production builds. [#32200](https://github.com/facebook/react/pull/32200)
-* Improved consistency across prod and dev to improve compatibility with Google Closure Compiler and bindings [#31808](https://github.com/facebook/react/pull/31808)
+* Improved consistency across prod and dev to improve compatibility with Google Closure Complier and bindings [#31808](https://github.com/facebook/react/pull/31808)
 * Improve passive effect scheduling for consistent task yielding. [#31785](https://github.com/facebook/react/pull/31785)
 * Fixed asserts in React Native when passChildrenWhenCloningPersistedNodes is enabled for OffscreenComponent rendering. [#32528](https://github.com/facebook/react/pull/32528)
 * Fixed component name resolution for Portal [#32640](https://github.com/facebook/react/pull/32640)
-* Added support for beforetoggle and toggle events on the dialog element. [#32479](https://github.com/facebook/react/pull/32479)
+* Added support for beforetoggle and toggle events on the dialog element. #32479 [#32479](https://github.com/facebook/react/pull/32479)

 ### React DOM
 * Fixed double warning when the `href` attribute is an empty string [#31783](https://github.com/facebook/react/pull/31783)
--- a/babel.config-ts.js
+++ b/babel.config-ts.js
@@ -8,7 +8,6 @@ module.exports = {
    '@babel/plugin-syntax-jsx',
    '@babel/plugin-transform-flow-strip-types',
    ['@babel/plugin-transform-class-properties', {loose: true}],
-    ['@babel/plugin-transform-private-methods', {loose: true}],
    '@babel/plugin-transform-classes',
  ],
  presets: [
--- a/compiler/apps/playground/tests/e2e/snapshots/page.spec.ts/compilationMode-all-output.txt
+++ b/compiler/apps/playground/tests/e2e/snapshots/page.spec.ts/compilationMode-all-output.txt
@@ -1,5 +1,5 @@
 import { c as _c } from "react/compiler-runtime"; // 
-@compilationMode:"all"
+        @compilationMode:"all"
 function nonReactFn() {
   const $ = _c(1);
   let t0;
--- a/compiler/apps/playground/components/Editor/ConfigEditor.tsx
+++ b/compiler/apps/playground/components/Editor/ConfigEditor.tsx
@@ -1,103 +0,0 @@
-/**
- * Copyright (c) Meta Platforms, Inc. and affiliates.
- *
- * This source code is licensed under the MIT license found in the
- * LICENSE file in the root directory of this source tree.
- */
-
-import MonacoEditor, {loader, type Monaco} from '@monaco-editor/react';
-import {parseConfigPragmaAsString} from 'babel-plugin-react-compiler';
-import type {editor} from 'monaco-editor';
-import * as monaco from 'monaco-editor';
-import parserBabel from 'prettier/plugins/babel';
-import * as prettierPluginEstree from 'prettier/plugins/estree';
-import * as prettier from 'prettier/standalone';
-import {useState, useEffect} from 'react';
-import {Resizable} from 're-resizable';
-import {useStore} from '../StoreContext';
-import {monacoOptions} from './monacoOptions';
-
-loader.config({monaco});
-
-export default function ConfigEditor(): JSX.Element {
-  const [, setMonaco] = useState<Monaco | null>(null);
-  const store = useStore();
-
-  // Parse string-based override config from pragma comment and format it
-  const [configJavaScript, setConfigJavaScript] = useState('');
-
-  useEffect(() => {
-    const pragma = store.source.substring(0, store.source.indexOf('\n'));
-    const configString = `(${parseConfigPragmaAsString(pragma)})`;
-
-    prettier
-      .format(configString, {
-        semi: true,
-        parser: 'babel-ts',
-        plugins: [parserBabel, prettierPluginEstree],
-      })
-      .then(formatted => {
-        setConfigJavaScript(formatted);
-      })
-      .catch(error => {
-        console.error('Error formatting config:', error);
-        setConfigJavaScript('({})'); // Return empty object if not valid for now
-        //TODO: Add validation and error handling for config
-      });
-    console.log('Config:', configString);
-  }, [store.source]);
-
-  const handleChange: (value: string | undefined) => void = value => {
-    if (!value) return;
-
-    // TODO: Implement sync logic to update pragma comments in the source
-    console.log('Config changed:', value);
-  };
-
-  const handleMount: (
-    _: editor.IStandaloneCodeEditor,
-    monaco: Monaco,
-  ) => void = (_, monaco) => {
-    setMonaco(monaco);
-
-    const uri = monaco.Uri.parse(`file:///config.js`);
-    const model = monaco.editor.getModel(uri);
-    if (model) {
-      model.updateOptions({tabSize: 2});
-    }
-  };
-
-  return (
-    <div className="relative flex flex-col flex-none border-r border-gray-200">
-      <h2 className="p-4 duration-150 ease-in border-b cursor-default border-grey-200 font-light text-secondary">
-        Config Overrides
-      </h2>
-      <Resizable
-        minWidth={300}
-        maxWidth={600}
-        defaultSize={{width: 350, height: 'auto'}}
-        enable={{right: true}}
-        className="!h-[calc(100vh_-_3.5rem_-_4rem)]">
-        <MonacoEditor
-          path={'config.js'}
-          language={'javascript'}
-          value={configJavaScript}
-          onMount={handleMount}
-          onChange={handleChange}
-          options={{
-            ...monacoOptions,
-            readOnly: true,
-            lineNumbers: 'off',
-            folding: false,
-            renderLineHighlight: 'none',
-            scrollBeyondLastLine: false,
-            hideCursorInOverviewRuler: true,
-            overviewRulerBorder: false,
-            overviewRulerLanes: 0,
-            fontSize: 12,
-          }}
-        />
-      </Resizable>
-    </div>
-  );
-}
--- a/compiler/apps/playground/components/Editor/EditorImpl.tsx
+++ b/compiler/apps/playground/components/Editor/EditorImpl.tsx
@@ -11,7 +11,6 @@ import * as t from '@babel/types';
 import BabelPluginReactCompiler, {
  CompilerError,
  CompilerErrorDetail,
-  CompilerDiagnostic,
  Effect,
  ErrorSeverity,
  parseConfigPragmaForTests,
@@ -37,7 +36,6 @@ import {
  type Store,
 } from '../../lib/stores';
 import {useStore, useStoreDispatch} from '../StoreContext';
-import ConfigEditor from './ConfigEditor';
 import Input from './Input';
 import {
  CompilerOutput,
@@ -46,8 +44,6 @@ import {
  PrintedCompilerPipelineValue,
 } from './Output';
 import {transformFromAstSync} from '@babel/core';
-import {LoggerEvent} from 'babel-plugin-react-compiler/dist/Entrypoint';
-import {useSearchParams} from 'next/navigation';

 function parseInput(
  input: string,
@@ -144,13 +140,9 @@ const COMMON_HOOKS: Array<[string, Hook]> = [
  ],
 ];

-function compile(
-  source: string,
-  mode: 'compiler' | 'linter',
-): [CompilerOutput, 'flow' | 'typescript'] {
+function compile(source: string): [CompilerOutput, 'flow' | 'typescript'] {
  const results = new Map<string, Array<PrintedCompilerPipelineValue>>();
  const error = new CompilerError();
-  const otherErrors: Array<CompilerErrorDetail | CompilerDiagnostic> = [];
  const upsert: (result: PrintedCompilerPipelineValue) => void = result => {
    const entry = results.get(result.name);
    if (Array.isArray(entry)) {
@@ -209,23 +201,6 @@ function compile(
    };
    const parsedOptions = parseConfigPragmaForTests(pragma, {
      compilationMode: 'infer',
-      environment:
-        mode === 'linter'
-          ? {
-              // enabled in compiler
-              validateRefAccessDuringRender: false,
-              // enabled in linter
-              validateNoSetStateInRender: true,
-              validateNoSetStateInEffects: true,
-              validateNoJSXInTryStatements: true,
-              validateNoImpureFunctionsInRender: true,
-              validateStaticComponents: true,
-              validateNoFreezingKnownMutableFunctions: true,
-              validateNoVoidUseMemo: true,
-            }
-          : {
-              /* use defaults for compiler mode */
-            },
    });
    const opts: PluginOptions = parsePluginOptions({
      ...parsedOptions,
@@ -235,11 +210,7 @@ function compile(
      },
      logger: {
        debugLogIRs: logIR,
-        logEvent: (_filename: string | null, event: LoggerEvent) => {
-          if (event.kind === 'CompileError') {
-            otherErrors.push(event.detail);
-          }
-        },
+        logEvent: () => {},
      },
    });
    transformOutput = invokeCompiler(source, language, opts);
@@ -249,7 +220,7 @@ function compile(
     * (i.e. object shape that is not CompilerError)
     */
    if (err instanceof CompilerError && err.details.length > 0) {
-      error.merge(err);
+      error.details.push(...err.details);
    } else {
      /**
       * Handle unexpected failures by logging (to get a stack trace)
@@ -266,17 +237,10 @@ function compile(
      );
    }
  }
-  // Only include logger errors if there weren't other errors
-  if (!error.hasErrors() && otherErrors.length !== 0) {
-    otherErrors.forEach(e => error.details.push(e));
-  }
  if (error.hasErrors()) {
-    return [{kind: 'err', results, error}, language];
+    return [{kind: 'err', results, error: error}, language];
  }
-  return [
-    {kind: 'ok', results, transformOutput, errors: error.details},
-    language,
-  ];
+  return [{kind: 'ok', results, transformOutput}, language];
 }

 export default function Editor(): JSX.Element {
@@ -285,21 +249,11 @@ export default function Editor(): JSX.Element {
  const dispatchStore = useStoreDispatch();
  const {enqueueSnackbar} = useSnackbar();
  const [compilerOutput, language] = useMemo(
-    () => compile(deferredStore.source, 'compiler'),
+    () => compile(deferredStore.source),
    [deferredStore.source],
  );
-  const [linterOutput] = useMemo(
-    () => compile(deferredStore.source, 'linter'),
-    [deferredStore.source],
-  );
-
-  // TODO: Remove this once the config editor is more stable
-  const searchParams = useSearchParams();
-  const search = searchParams.get('showConfig');
-  const shouldShowConfig = search === 'true';

  useMountEffect(() => {
-    // Initialize store
    let mountStore: Store;
    try {
      mountStore = initStoreFromUrlOrLocalStorage();
@@ -321,27 +275,19 @@ export default function Editor(): JSX.Element {
    });
  });

-  let mergedOutput: CompilerOutput;
-  let errors: Array<CompilerErrorDetail | CompilerDiagnostic>;
-  if (compilerOutput.kind === 'ok') {
-    errors = linterOutput.kind === 'ok' ? [] : linterOutput.error.details;
-    mergedOutput = {
-      ...compilerOutput,
-      errors,
-    };
-  } else {
-    mergedOutput = compilerOutput;
-    errors = compilerOutput.error.details;
-  }
  return (
    <>
      <div className="relative flex basis top-14">
-        {shouldShowConfig && <ConfigEditor />}
        <div className={clsx('relative sm:basis-1/4')}>
-          <Input language={language} errors={errors} />
+          <Input
+            language={language}
+            errors={
+              compilerOutput.kind === 'err' ? compilerOutput.error.details : []
+            }
+          />
        </div>
        <div className={clsx('flex sm:flex flex-wrap')}>
-          <Output store={deferredStore} compilerOutput={mergedOutput} />
+          <Output store={deferredStore} compilerOutput={compilerOutput} />
        </div>
      </div>
    </>
--- a/compiler/apps/playground/components/Editor/Input.tsx
+++ b/compiler/apps/playground/components/Editor/Input.tsx
@@ -36,18 +36,13 @@ export default function Input({errors, language}: Props): JSX.Element {
    const uri = monaco.Uri.parse(`file:///index.js`);
    const model = monaco.editor.getModel(uri);
    invariant(model, 'Model must exist for the selected input file.');
-    renderReactCompilerMarkers({
-      monaco,
-      model,
-      details: errors,
-      source: store.source,
-    });
+    renderReactCompilerMarkers({monaco, model, details: errors});
    /**
     * N.B. that `tabSize` is a model property, not an editor property.
     * So, the tab size has to be set per model.
     */
    model.updateOptions({tabSize: 2});
-  }, [monaco, errors, store.source]);
+  }, [monaco, errors]);

  useEffect(() => {
    /**
--- a/compiler/apps/playground/components/Editor/Output.tsx
+++ b/compiler/apps/playground/components/Editor/Output.tsx
@@ -11,11 +11,7 @@ import {
  InformationCircleIcon,
 } from '@heroicons/react/outline';
 import MonacoEditor, {DiffEditor} from '@monaco-editor/react';
-import {
-  CompilerErrorDetail,
-  CompilerDiagnostic,
-  type CompilerError,
-} from 'babel-plugin-react-compiler';
+import {type CompilerError} from 'babel-plugin-react-compiler';
 import parserBabel from 'prettier/plugins/babel';
 import * as prettierPluginEstree from 'prettier/plugins/estree';
 import * as prettier from 'prettier/standalone';
@@ -48,7 +44,6 @@ export type CompilerOutput =
      kind: 'ok';
      transformOutput: CompilerTransformOutput;
      results: Map<string, Array<PrintedCompilerPipelineValue>>;
-      errors: Array<CompilerErrorDetail | CompilerDiagnostic>;
    }
  | {
      kind: 'err';
@@ -128,36 +123,10 @@ async function tabify(
      parser: transformOutput.language === 'flow' ? 'babel-flow' : 'babel-ts',
      plugins: [parserBabel, prettierPluginEstree],
    });
-
-    let output: string;
-    let language: string;
-    if (compilerOutput.errors.length === 0) {
-      output = code;
-      language = 'javascript';
-    } else {
-      language = 'markdown';
-      output = `
-# Summary
-
-React Compiler compiled this function successfully, but there are lint errors that indicate potential issues with the original code.
-
-## ${compilerOutput.errors.length} Lint Errors
-
-${compilerOutput.errors.map(e => e.printErrorMessage(source, {eslint: false})).join('\n\n')}
-
-## Output
-
-\`\`\`js
-${code}
-\`\`\`
-`.trim();
-    }
-
    reorderedTabs.set(
-      'Output',
+      'JS',
      <TextTabContent
-        output={output}
-        language={language}
+        output={code}
        diff={null}
        showInfoPanel={false}></TextTabContent>,
    );
@@ -173,18 +142,6 @@ ${code}
        </>,
      );
    }
-  } else if (compilerOutput.kind === 'err') {
-    const errors = compilerOutput.error.printErrorMessage(source, {
-      eslint: false,
-    });
-    reorderedTabs.set(
-      'Output',
-      <TextTabContent
-        output={errors}
-        language="markdown"
-        diff={null}
-        showInfoPanel={false}></TextTabContent>,
-    );
  }
  tabs.forEach((tab, name) => {
    reorderedTabs.set(name, tab);
@@ -205,32 +162,17 @@ function getSourceMapUrl(code: string, map: string): string | null {
 }

 function Output({store, compilerOutput}: Props): JSX.Element {
-  const [tabsOpen, setTabsOpen] = useState<Set<string>>(
-    () => new Set(['Output']),
-  );
+  const [tabsOpen, setTabsOpen] = useState<Set<string>>(() => new Set(['JS']));
  const [tabs, setTabs] = useState<Map<string, React.ReactNode>>(
    () => new Map(),
  );
-
-  /*
-   * Update the active tab back to the output or errors tab when the compilation state
-   * changes between success/failure.
-   */
-  const [previousOutputKind, setPreviousOutputKind] = useState(
-    compilerOutput.kind,
-  );
-  if (compilerOutput.kind !== previousOutputKind) {
-    setPreviousOutputKind(compilerOutput.kind);
-    setTabsOpen(new Set(['Output']));
-  }
-
  useEffect(() => {
    tabify(store.source, compilerOutput).then(tabs => {
      setTabs(tabs);
    });
  }, [store.source, compilerOutput]);

-  const changedPasses: Set<string> = new Set(['Output', 'HIR']); // Initial and final passes should always be bold
+  const changedPasses: Set<string> = new Set(['JS', 'HIR']); // Initial and final passes should always be bold
  let lastResult: string = '';
  for (const [passName, results] of compilerOutput.results) {
    for (const result of results) {
@@ -254,6 +196,20 @@ function Output({store, compilerOutput}: Props): JSX.Element {
        tabs={tabs}
        changedPasses={changedPasses}
      />
+      {compilerOutput.kind === 'err' ? (
+        <div
+          className="flex flex-wrap absolute bottom-0 bg-white grow border-y border-grey-200 transition-all ease-in"
+          style={{width: 'calc(100vw - 650px)'}}>
+          <div className="w-full p-4 basis-full border-b">
+            <h2>COMPILER ERRORS</h2>
+          </div>
+          <pre
+            className="p-4 basis-full text-red-600 overflow-y-scroll whitespace-pre-wrap"
+            style={{width: 'calc(100vw - 650px)', height: '150px'}}>
+            <code>{compilerOutput.error.toString()}</code>
+          </pre>
+        </div>
+      ) : null}
    </>
  );
 }
@@ -262,12 +218,10 @@ function TextTabContent({
  output,
  diff,
  showInfoPanel,
-  language,
 }: {
  output: string;
  diff: string | null;
  showInfoPanel: boolean;
-  language: string;
 }): JSX.Element {
  const [diffMode, setDiffMode] = useState(false);
  return (
@@ -318,7 +272,7 @@ function TextTabContent({
        />
      ) : (
        <MonacoEditor
-          language={language ?? 'javascript'}
+          defaultLanguage="javascript"
          value={output}
          options={{
            ...monacoOptions,
--- a/compiler/apps/playground/components/Editor/monacoOptions.ts
+++ b/compiler/apps/playground/components/Editor/monacoOptions.ts
@@ -28,5 +28,5 @@ export const monacoOptions: Partial<EditorProps['options']> = {

  automaticLayout: true,
  wordWrap: 'on',
-  wrappingIndent: 'same',
+  wrappingIndent: 'deepIndent',
 };
--- a/compiler/apps/playground/lib/reactCompilerMonacoDiagnostics.ts
+++ b/compiler/apps/playground/lib/reactCompilerMonacoDiagnostics.ts
@@ -6,11 +6,7 @@
 */

 import {Monaco} from '@monaco-editor/react';
-import {
-  CompilerDiagnostic,
-  CompilerErrorDetail,
-  ErrorSeverity,
-} from 'babel-plugin-react-compiler';
+import {CompilerErrorDetail, ErrorSeverity} from 'babel-plugin-react-compiler';
 import {MarkerSeverity, type editor} from 'monaco-editor';

 function mapReactCompilerSeverityToMonaco(
@@ -26,46 +22,38 @@ function mapReactCompilerSeverityToMonaco(
 }

 function mapReactCompilerDiagnosticToMonacoMarker(
-  detail: CompilerErrorDetail | CompilerDiagnostic,
+  detail: CompilerErrorDetail,
  monaco: Monaco,
-  source: string,
 ): editor.IMarkerData | null {
-  const loc = detail.primaryLocation();
-  if (loc == null || typeof loc === 'symbol') {
+  if (detail.loc == null || typeof detail.loc === 'symbol') {
    return null;
  }
  const severity = mapReactCompilerSeverityToMonaco(detail.severity, monaco);
-  let message = detail.printErrorMessage(source, {eslint: true});
+  let message = detail.printErrorMessage();
  return {
    severity,
    message,
-    startLineNumber: loc.start.line,
-    startColumn: loc.start.column + 1,
-    endLineNumber: loc.end.line,
-    endColumn: loc.end.column + 1,
+    startLineNumber: detail.loc.start.line,
+    startColumn: detail.loc.start.column + 1,
+    endLineNumber: detail.loc.end.line,
+    endColumn: detail.loc.end.column + 1,
  };
 }

 type ReactCompilerMarkerConfig = {
  monaco: Monaco;
  model: editor.ITextModel;
-  details: Array<CompilerErrorDetail | CompilerDiagnostic>;
-  source: string;
+  details: Array<CompilerErrorDetail>;
 };
 let decorations: Array<string> = [];
 export function renderReactCompilerMarkers({
  monaco,
  model,
  details,
-  source,
 }: ReactCompilerMarkerConfig): void {
  const markers: Array<editor.IMarkerData> = [];
  for (const detail of details) {
-    const marker = mapReactCompilerDiagnosticToMonacoMarker(
-      detail,
-      monaco,
-      source,
-    );
+    const marker = mapReactCompilerDiagnosticToMonacoMarker(detail, monaco);
    if (marker == null) {
      continue;
    }
--- a/compiler/package.json
+++ b/compiler/package.json
@@ -19,8 +19,7 @@
    "test": "yarn workspaces run test",
    "snap": "yarn workspace babel-plugin-react-compiler run snap",
    "snap:build": "yarn workspace snap run build",
-    "npm:publish": "node scripts/release/publish",
-    "eslint-docs": "yarn workspace babel-plugin-react-compiler build && node scripts/build-eslint-docs.js"
+    "npm:publish": "node scripts/release/publish"
  },
  "dependencies": {
    "fs-extra": "^4.0.2",
--- a/compiler/packages/babel-plugin-react-compiler/src/Babel/BabelPlugin.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Babel/BabelPlugin.ts
@@ -12,7 +12,6 @@ import {
  pipelineUsesReanimatedPlugin,
 } from '../Entrypoint/Reanimated';
 import validateNoUntransformedReferences from '../Entrypoint/ValidateNoUntransformedReferences';
-import {CompilerError} from '..';

 const ENABLE_REACT_COMPILER_TIMINGS =
  process.env['ENABLE_REACT_COMPILER_TIMINGS'] === '1';
@@ -35,58 +34,51 @@ export default function BabelPluginReactCompiler(
       */
      Program: {
        enter(prog, pass): void {
-          try {
-            const filename = pass.filename ?? 'unknown';
-            if (ENABLE_REACT_COMPILER_TIMINGS === true) {
-              performance.mark(`${filename}:start`, {
-                detail: 'BabelPlugin:Program:start',
-              });
-            }
-            let opts = parsePluginOptions(pass.opts);
-            const isDev =
-              (typeof __DEV__ !== 'undefined' && __DEV__ === true) ||
-              process.env['NODE_ENV'] === 'development';
-            if (
-              opts.enableReanimatedCheck === true &&
-              pipelineUsesReanimatedPlugin(pass.file.opts.plugins)
-            ) {
-              opts = injectReanimatedFlag(opts);
-            }
-            if (
-              opts.environment.enableResetCacheOnSourceFileChanges !== false &&
-              isDev
-            ) {
-              opts = {
-                ...opts,
-                environment: {
-                  ...opts.environment,
-                  enableResetCacheOnSourceFileChanges: true,
-                },
-              };
-            }
-            const result = compileProgram(prog, {
-              opts,
-              filename: pass.filename ?? null,
-              comments: pass.file.ast.comments ?? [],
-              code: pass.file.code,
+          const filename = pass.filename ?? 'unknown';
+          if (ENABLE_REACT_COMPILER_TIMINGS === true) {
+            performance.mark(`${filename}:start`, {
+              detail: 'BabelPlugin:Program:start',
+            });
+          }
+          let opts = parsePluginOptions(pass.opts);
+          const isDev =
+            (typeof __DEV__ !== 'undefined' && __DEV__ === true) ||
+            process.env['NODE_ENV'] === 'development';
+          if (
+            opts.enableReanimatedCheck === true &&
+            pipelineUsesReanimatedPlugin(pass.file.opts.plugins)
+          ) {
+            opts = injectReanimatedFlag(opts);
+          }
+          if (
+            opts.environment.enableResetCacheOnSourceFileChanges !== false &&
+            isDev
+          ) {
+            opts = {
+              ...opts,
+              environment: {
+                ...opts.environment,
+                enableResetCacheOnSourceFileChanges: true,
+              },
+            };
+          }
+          const result = compileProgram(prog, {
+            opts,
+            filename: pass.filename ?? null,
+            comments: pass.file.ast.comments ?? [],
+            code: pass.file.code,
+          });
+          validateNoUntransformedReferences(
+            prog,
+            pass.filename ?? null,
+            opts.logger,
+            opts.environment,
+            result,
+          );
+          if (ENABLE_REACT_COMPILER_TIMINGS === true) {
+            performance.mark(`${filename}:end`, {
+              detail: 'BabelPlugin:Program:end',
            });
-            validateNoUntransformedReferences(
-              prog,
-              pass.filename ?? null,
-              opts.logger,
-              opts.environment,
-              result,
-            );
-            if (ENABLE_REACT_COMPILER_TIMINGS === true) {
-              performance.mark(`${filename}:end`, {
-                detail: 'BabelPlugin:Program:end',
-              });
-            }
-          } catch (e) {
-            if (e instanceof CompilerError) {
-              throw e.withPrintedMessage(pass.file.code, {eslint: false});
-            }
-            throw e;
          }
        },
        exit(_, pass): void {
--- a/compiler/packages/babel-plugin-react-compiler/src/CompilerError.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/CompilerError.ts
@@ -5,12 +5,9 @@
 * LICENSE file in the root directory of this source tree.
 */

-import * as t from '@babel/types';
-import {codeFrameColumns} from '@babel/code-frame';
-import {type SourceLocation} from './HIR';
+import type {SourceLocation} from './HIR';
 import {Err, Ok, Result} from './Utils/Result';
 import {assertExhaustive} from './Utils/utils';
-import invariant from 'invariant';

 export enum ErrorSeverity {
  /**
@@ -18,11 +15,6 @@ export enum ErrorSeverity {
   * misunderstanding on the user’s part.
   */
  InvalidJS = 'InvalidJS',
-  /**
-   * JS syntax that is not supported and which we do not plan to support. Developers should
-   * rewrite to use supported forms.
-   */
-  UnsupportedJS = 'UnsupportedJS',
  /**
   * Code that breaks the rules of React.
   */
@@ -47,29 +39,6 @@ export enum ErrorSeverity {
  Invariant = 'Invariant',
 }

-export type CompilerDiagnosticOptions = {
-  category: ErrorCategory;
-  severity: ErrorSeverity;
-  reason: string;
-  description: string;
-  details: Array<CompilerDiagnosticDetail>;
-  suggestions?: Array<CompilerSuggestion> | null | undefined;
-};
-
-export type CompilerDiagnosticDetail =
-  /**
-   * A/the source of the error
-   */
-  | {
-      kind: 'error';
-      loc: SourceLocation | null;
-      message: string;
-    }
-  | {
-      kind: 'hint';
-      message: string;
-    };
-
 export enum CompilerSuggestionOperation {
  InsertBefore,
  InsertAfter,
@@ -93,124 +62,13 @@ export type CompilerSuggestion =
    };

 export type CompilerErrorDetailOptions = {
-  category: ErrorCategory;
-  severity: ErrorSeverity;
  reason: string;
  description?: string | null | undefined;
+  severity: ErrorSeverity;
  loc: SourceLocation | null;
  suggestions?: Array<CompilerSuggestion> | null | undefined;
 };

-export type PrintErrorMessageOptions = {
-  /**
-   * ESLint uses 1-indexed columns and prints one error at a time
-   * So it doesn't require the "Found # error(s)" text
-   */
-  eslint: boolean;
-};
-
-export class CompilerDiagnostic {
-  options: CompilerDiagnosticOptions;
-
-  constructor(options: CompilerDiagnosticOptions) {
-    this.options = options;
-  }
-
-  static create(
-    options: Omit<CompilerDiagnosticOptions, 'details'>,
-  ): CompilerDiagnostic {
-    return new CompilerDiagnostic({...options, details: []});
-  }
-
-  get reason(): CompilerDiagnosticOptions['reason'] {
-    return this.options.reason;
-  }
-  get description(): CompilerDiagnosticOptions['description'] {
-    return this.options.description;
-  }
-  get severity(): CompilerDiagnosticOptions['severity'] {
-    return this.options.severity;
-  }
-  get suggestions(): CompilerDiagnosticOptions['suggestions'] {
-    return this.options.suggestions;
-  }
-  get category(): ErrorCategory {
-    return this.options.category;
-  }
-
-  withDetail(detail: CompilerDiagnosticDetail): CompilerDiagnostic {
-    this.options.details.push(detail);
-    return this;
-  }
-
-  primaryLocation(): SourceLocation | null {
-    const firstErrorDetail = this.options.details.filter(
-      d => d.kind === 'error',
-    )[0];
-    return firstErrorDetail != null && firstErrorDetail.kind === 'error'
-      ? firstErrorDetail.loc
-      : null;
-  }
-
-  printErrorMessage(source: string, options: PrintErrorMessageOptions): string {
-    const buffer = [
-      printErrorSummary(this.severity, this.reason),
-      '\n\n',
-      this.description,
-    ];
-    for (const detail of this.options.details) {
-      switch (detail.kind) {
-        case 'error': {
-          const loc = detail.loc;
-          if (loc == null || typeof loc === 'symbol') {
-            continue;
-          }
-          let codeFrame: string;
-          try {
-            codeFrame = printCodeFrame(source, loc, detail.message);
-          } catch (e) {
-            codeFrame = detail.message;
-          }
-          buffer.push('\n\n');
-          if (loc.filename != null) {
-            const line = loc.start.line;
-            const column = options.eslint
-              ? loc.start.column + 1
-              : loc.start.column;
-            buffer.push(`${loc.filename}:${line}:${column}\n`);
-          }
-          buffer.push(codeFrame);
-          break;
-        }
-        case 'hint': {
-          buffer.push('\n\n');
-          buffer.push(detail.message);
-          break;
-        }
-        default: {
-          assertExhaustive(
-            detail,
-            `Unexpected detail kind ${(detail as any).kind}`,
-          );
-        }
-      }
-    }
-    return buffer.join('');
-  }
-
-  toString(): string {
-    const buffer = [printErrorSummary(this.severity, this.reason)];
-    if (this.description != null) {
-      buffer.push(`. ${this.description}.`);
-    }
-    const loc = this.primaryLocation();
-    if (loc != null && typeof loc !== 'symbol') {
-      buffer.push(` (${loc.start.line}:${loc.start.column})`);
-    }
-    return buffer.join('');
-  }
-}
-
 /*
 * Each bailout or invariant in HIR lowering creates an {@link CompilerErrorDetail}, which is then
 * aggregated into a single {@link CompilerError} later.
@@ -237,66 +95,35 @@ export class CompilerErrorDetail {
  get suggestions(): CompilerErrorDetailOptions['suggestions'] {
    return this.options.suggestions;
  }
-  get category(): ErrorCategory {
-    return this.options.category;
-  }

-  primaryLocation(): SourceLocation | null {
-    return this.loc;
-  }
-
-  printErrorMessage(source: string, options: PrintErrorMessageOptions): string {
-    const buffer = [printErrorSummary(this.severity, this.reason)];
+  printErrorMessage(): string {
+    const buffer = [`${this.severity}: ${this.reason}`];
    if (this.description != null) {
-      buffer.push(`\n\n${this.description}.`);
+      buffer.push(`. ${this.description}`);
    }
-    const loc = this.loc;
-    if (loc != null && typeof loc !== 'symbol') {
-      let codeFrame: string;
-      try {
-        codeFrame = printCodeFrame(source, loc, this.reason);
-      } catch (e) {
-        codeFrame = '';
-      }
-      buffer.push(`\n\n`);
-      if (loc.filename != null) {
-        const line = loc.start.line;
-        const column = options.eslint ? loc.start.column + 1 : loc.start.column;
-        buffer.push(`${loc.filename}:${line}:${column}\n`);
-      }
-      buffer.push(codeFrame);
-      buffer.push('\n\n');
+    if (this.loc != null && typeof this.loc !== 'symbol') {
+      buffer.push(` (${this.loc.start.line}:${this.loc.end.line})`);
    }
    return buffer.join('');
  }

  toString(): string {
-    const buffer = [printErrorSummary(this.severity, this.reason)];
-    if (this.description != null) {
-      buffer.push(`. ${this.description}.`);
-    }
-    const loc = this.loc;
-    if (loc != null && typeof loc !== 'symbol') {
-      buffer.push(` (${loc.start.line}:${loc.start.column})`);
-    }
-    return buffer.join('');
+    return this.printErrorMessage();
  }
 }

 export class CompilerError extends Error {
-  details: Array<CompilerErrorDetail | CompilerDiagnostic> = [];
-  printedMessage: string | null = null;
+  details: Array<CompilerErrorDetail> = [];

  static invariant(
    condition: unknown,
-    options: Omit<CompilerErrorDetailOptions, 'severity' | 'category'>,
+    options: Omit<CompilerErrorDetailOptions, 'severity'>,
  ): asserts condition {
    if (!condition) {
      const errors = new CompilerError();
      errors.pushErrorDetail(
        new CompilerErrorDetail({
          ...options,
-          category: ErrorCategory.Invariant,
          severity: ErrorSeverity.Invariant,
        }),
      );
@@ -304,35 +131,24 @@ export class CompilerError extends Error {
    }
  }

-  static throwDiagnostic(options: CompilerDiagnosticOptions): never {
-    const errors = new CompilerError();
-    errors.pushDiagnostic(new CompilerDiagnostic(options));
-    throw errors;
-  }
-
  static throwTodo(
-    options: Omit<CompilerErrorDetailOptions, 'severity' | 'category'>,
+    options: Omit<CompilerErrorDetailOptions, 'severity'>,
  ): never {
    const errors = new CompilerError();
    errors.pushErrorDetail(
-      new CompilerErrorDetail({
-        ...options,
-        severity: ErrorSeverity.Todo,
-        category: ErrorCategory.Todo,
-      }),
+      new CompilerErrorDetail({...options, severity: ErrorSeverity.Todo}),
    );
    throw errors;
  }

  static throwInvalidJS(
-    options: Omit<CompilerErrorDetailOptions, 'severity' | 'category'>,
+    options: Omit<CompilerErrorDetailOptions, 'severity'>,
  ): never {
    const errors = new CompilerError();
    errors.pushErrorDetail(
      new CompilerErrorDetail({
        ...options,
        severity: ErrorSeverity.InvalidJS,
-        category: ErrorCategory.Syntax,
      }),
    );
    throw errors;
@@ -352,14 +168,13 @@ export class CompilerError extends Error {
  }

  static throwInvalidConfig(
-    options: Omit<CompilerErrorDetailOptions, 'severity' | 'category'>,
+    options: Omit<CompilerErrorDetailOptions, 'severity'>,
  ): never {
    const errors = new CompilerError();
    errors.pushErrorDetail(
      new CompilerErrorDetail({
        ...options,
        severity: ErrorSeverity.InvalidConfig,
-        category: ErrorCategory.Config,
      }),
    );
    throw errors;
@@ -378,52 +193,20 @@ export class CompilerError extends Error {
  }

  override get message(): string {
-    return this.printedMessage ?? this.toString();
+    return this.toString();
  }

  override set message(_message: string) {}

  override toString(): string {
-    if (this.printedMessage) {
-      return this.printedMessage;
-    }
    if (Array.isArray(this.details)) {
      return this.details.map(detail => detail.toString()).join('\n\n');
    }
    return this.name;
  }

-  withPrintedMessage(
-    source: string,
-    options: PrintErrorMessageOptions,
-  ): CompilerError {
-    this.printedMessage = this.printErrorMessage(source, options);
-    return this;
-  }
-
-  printErrorMessage(source: string, options: PrintErrorMessageOptions): string {
-    if (options.eslint && this.details.length === 1) {
-      return this.details[0].printErrorMessage(source, options);
-    }
-    return (
-      `Found ${this.details.length} error${this.details.length === 1 ? '' : 's'}:\n\n` +
-      this.details
-        .map(detail => detail.printErrorMessage(source, options).trim())
-        .join('\n\n')
-    );
-  }
-
-  merge(other: CompilerError): void {
-    this.details.push(...other.details);
-  }
-
-  pushDiagnostic(diagnostic: CompilerDiagnostic): void {
-    this.details.push(diagnostic);
-  }
-
  push(options: CompilerErrorDetailOptions): CompilerErrorDetail {
    const detail = new CompilerErrorDetail({
-      category: options.category,
      reason: options.reason,
      description: options.description ?? null,
      severity: options.severity,
@@ -458,424 +241,13 @@ export class CompilerError extends Error {
        case ErrorSeverity.InvalidJS:
        case ErrorSeverity.InvalidReact:
        case ErrorSeverity.InvalidConfig:
-        case ErrorSeverity.UnsupportedJS: {
          return true;
-        }
        case ErrorSeverity.CannotPreserveMemoization:
-        case ErrorSeverity.Todo: {
+        case ErrorSeverity.Todo:
          return false;
-        }
-        default: {
+        default:
          assertExhaustive(detail.severity, 'Unhandled error severity');
-        }
      }
    });
  }
 }
-
-function printCodeFrame(
-  source: string,
-  loc: t.SourceLocation,
-  message: string,
-): string {
-  return codeFrameColumns(
-    source,
-    {
-      start: {
-        line: loc.start.line,
-        column: loc.start.column + 1,
-      },
-      end: {
-        line: loc.end.line,
-        column: loc.end.column + 1,
-      },
-    },
-    {
-      message,
-    },
-  );
-}
-
-function printErrorSummary(severity: ErrorSeverity, message: string): string {
-  let severityCategory: string;
-  switch (severity) {
-    case ErrorSeverity.InvalidConfig:
-    case ErrorSeverity.InvalidJS:
-    case ErrorSeverity.InvalidReact:
-    case ErrorSeverity.UnsupportedJS: {
-      severityCategory = 'Error';
-      break;
-    }
-    case ErrorSeverity.CannotPreserveMemoization: {
-      severityCategory = 'Memoization';
-      break;
-    }
-    case ErrorSeverity.Invariant: {
-      severityCategory = 'Invariant';
-      break;
-    }
-    case ErrorSeverity.Todo: {
-      severityCategory = 'Todo';
-      break;
-    }
-    default: {
-      assertExhaustive(severity, `Unexpected severity '${severity}'`);
-    }
-  }
-  return `${severityCategory}: ${message}`;
-}
-
-/**
- * See getRuleForCategory() for how these map to ESLint rules
- */
-export enum ErrorCategory {
-  // Checking for valid hooks usage (non conditional, non-first class, non reactive, etc)
-  Hooks = 'Hooks',
-
-  // Checking for no capitalized calls (not definitively an error, hence separating)
-  CapitalizedCalls = 'CapitalizedCalls',
-
-  // Checking for static components
-  StaticComponents = 'StaticComponents',
-
-  // Checking for valid usage of manual memoization
-  UseMemo = 'UseMemo',
-
-  // Checking for higher order functions acting as factories for components/hooks
-  Factories = 'Factories',
-
-  // Checks that manual memoization is preserved
-  PreserveManualMemo = 'PreserveManualMemo',
-
-  // Checking for no mutations of props, hook arguments, hook return values
-  Immutability = 'Immutability',
-
-  // Checking for assignments to globals
-  Globals = 'Globals',
-
-  // Checking for valid usage of refs, ie no access during render
-  Refs = 'Refs',
-
-  // Checks for memoized effect deps
-  EffectDependencies = 'EffectDependencies',
-
-  // Checks for no setState in effect bodies
-  EffectSetState = 'EffectSetState',
-
-  EffectDerivationsOfState = 'EffectDerivationsOfState',
-
-  // Validates against try/catch in place of error boundaries
-  ErrorBoundaries = 'ErrorBoundaries',
-
-  // Checking for pure functions
-  Purity = 'Purity',
-
-  // Validates against setState in render
-  RenderSetState = 'RenderSetState',
-
-  // Internal invariants
-  Invariant = 'Invariant',
-
-  // Todos
-  Todo = 'Todo',
-
-  // Syntax errors
-  Syntax = 'Syntax',
-
-  // Checks for use of unsupported syntax
-  UnsupportedSyntax = 'UnsupportedSyntax',
-
-  // Config errors
-  Config = 'Config',
-
-  // Gating error
-  Gating = 'Gating',
-
-  // Suppressions
-  Suppression = 'Suppression',
-
-  // Issues with auto deps
-  AutomaticEffectDependencies = 'AutomaticEffectDependencies',
-
-  // Issues with `fire`
-  Fire = 'Fire',
-
-  // fbt-specific issues
-  FBT = 'FBT',
-}
-
-export type LintRule = {
-  // Stores the category the rule corresponds to, used to filter errors when reporting
-  category: ErrorCategory;
-
-  /**
-   * The "name" of the rule as it will be used by developers to enable/disable, eg
-   * "eslint-disable-nest line <name>"
-   */
-  name: string;
-
-  /**
-   * A description of the rule that appears somewhere in ESLint. This does not affect
-   * how error messages are formatted
-   */
-  description: string;
-
-  /**
-   * If true, this rule will automatically appear in the default, "recommended" ESLint
-   * rule set. Otherwise it will be part of an `allRules` export that developers can
-   * use to opt-in to showing output of all possible rules.
-   *
-   * NOTE: not all validations are enabled by default! Setting this flag only affects
-   * whether a given rule is part of the recommended set. The corresponding validation
-   * also should be enabled by default if you want the error to actually show up!
-   */
-  recommended: boolean;
-};
-
-const RULE_NAME_PATTERN = /^[a-z]+(-[a-z]+)*$/;
-
-export function getRuleForCategory(category: ErrorCategory): LintRule {
-  const rule = getRuleForCategoryImpl(category);
-  invariant(
-    RULE_NAME_PATTERN.test(rule.name),
-    `Invalid rule name, got '${rule.name}' but rules must match ${RULE_NAME_PATTERN.toString()}`,
-  );
-  return rule;
-}
-
-function getRuleForCategoryImpl(category: ErrorCategory): LintRule {
-  switch (category) {
-    case ErrorCategory.AutomaticEffectDependencies: {
-      return {
-        category,
-        name: 'automatic-effect-dependencies',
-        description:
-          'Verifies that automatic effect dependencies are compiled if opted-in',
-        recommended: false,
-      };
-    }
-    case ErrorCategory.CapitalizedCalls: {
-      return {
-        category,
-        name: 'capitalized-calls',
-        description:
-          'Validates against calling capitalized functions/methods instead of using JSX',
-        recommended: false,
-      };
-    }
-    case ErrorCategory.Config: {
-      return {
-        category,
-        name: 'config',
-        description: 'Validates the compiler configuration options',
-        recommended: true,
-      };
-    }
-    case ErrorCategory.EffectDependencies: {
-      return {
-        category,
-        name: 'memoized-effect-dependencies',
-        description: 'Validates that effect dependencies are memoized',
-        recommended: false,
-      };
-    }
-    case ErrorCategory.EffectDerivationsOfState: {
-      return {
-        category,
-        name: 'no-deriving-state-in-effects',
-        description:
-          'Validates against deriving values from state in an effect',
-        recommended: false,
-      };
-    }
-    case ErrorCategory.EffectSetState: {
-      return {
-        category,
-        name: 'set-state-in-effect',
-        description:
-          'Validates against calling setState synchronously in an effect, which can lead to re-renders that degrade performance',
-        recommended: true,
-      };
-    }
-    case ErrorCategory.ErrorBoundaries: {
-      return {
-        category,
-        name: 'error-boundaries',
-        description:
-          'Validates usage of error boundaries instead of try/catch for errors in child components',
-        recommended: true,
-      };
-    }
-    case ErrorCategory.Factories: {
-      return {
-        category,
-        name: 'component-hook-factories',
-        description:
-          'Validates against higher order functions defining nested components or hooks. ' +
-          'Components and hooks should be defined at the module level',
-        recommended: true,
-      };
-    }
-    case ErrorCategory.FBT: {
-      return {
-        category,
-        name: 'fbt',
-        description: 'Validates usage of fbt',
-        recommended: false,
-      };
-    }
-    case ErrorCategory.Fire: {
-      return {
-        category,
-        name: 'fire',
-        description: 'Validates usage of `fire`',
-        recommended: false,
-      };
-    }
-    case ErrorCategory.Gating: {
-      return {
-        category,
-        name: 'gating',
-        description:
-          'Validates configuration of [gating mode](https://react.dev/reference/react-compiler/gating)',
-        recommended: true,
-      };
-    }
-    case ErrorCategory.Globals: {
-      return {
-        category,
-        name: 'globals',
-        description:
-          'Validates against assignment/mutation of globals during render, part of ensuring that ' +
-          '[side effects must render outside of render](https://react.dev/reference/rules/components-and-hooks-must-be-pure#side-effects-must-run-outside-of-render)',
-        recommended: true,
-      };
-    }
-    case ErrorCategory.Hooks: {
-      return {
-        category,
-        name: 'hooks',
-        description: 'Validates the rules of hooks',
-        /**
-         * TODO: the "Hooks" rule largely reimplements the "rules-of-hooks" non-compiler rule.
-         * We need to dedeupe these (moving the remaining bits into the compiler) and then enable
-         * this rule.
-         */
-        recommended: false,
-      };
-    }
-    case ErrorCategory.Immutability: {
-      return {
-        category,
-        name: 'immutability',
-        description:
-          'Validates against mutating props, state, and other values that [are immutable](https://react.dev/reference/rules/components-and-hooks-must-be-pure#props-and-state-are-immutable)',
-        recommended: true,
-      };
-    }
-    case ErrorCategory.Invariant: {
-      return {
-        category,
-        name: 'invariant',
-        description: 'Internal invariants',
-        recommended: false,
-      };
-    }
-    case ErrorCategory.PreserveManualMemo: {
-      return {
-        category,
-        name: 'preserve-manual-memoization',
-        description:
-          'Validates that existing manual memoized is preserved by the compiler. ' +
-          'React Compiler will only compile components and hooks if its inference ' +
-          '[matches or exceeds the existing manual memoization](https://react.dev/learn/react-compiler/introduction#what-should-i-do-about-usememo-usecallback-and-reactmemo)',
-        recommended: true,
-      };
-    }
-    case ErrorCategory.Purity: {
-      return {
-        category,
-        name: 'purity',
-        description:
-          'Validates that [components/hooks are pure](https://react.dev/reference/rules/components-and-hooks-must-be-pure) by checking that they do not call known-impure functions',
-        recommended: true,
-      };
-    }
-    case ErrorCategory.Refs: {
-      return {
-        category,
-        name: 'refs',
-        description:
-          'Validates correct usage of refs, not reading/writing during render. See the "pitfalls" section in [`useRef()` usage](https://react.dev/reference/react/useRef#usage)',
-        recommended: true,
-      };
-    }
-    case ErrorCategory.RenderSetState: {
-      return {
-        category,
-        name: 'set-state-in-render',
-        description:
-          'Validates against setting state during render, which can trigger additional renders and potential infinite render loops',
-        recommended: true,
-      };
-    }
-    case ErrorCategory.StaticComponents: {
-      return {
-        category,
-        name: 'static-components',
-        description:
-          'Validates that components are static, not recreated every render. Components that are recreated dynamically can reset state and trigger excessive re-rendering',
-        recommended: true,
-      };
-    }
-    case ErrorCategory.Suppression: {
-      return {
-        category,
-        name: 'rule-suppression',
-        description: 'Validates against suppression of other rules',
-        recommended: false,
-      };
-    }
-    case ErrorCategory.Syntax: {
-      return {
-        category,
-        name: 'syntax',
-        description: 'Validates against invalid syntax',
-        recommended: false,
-      };
-    }
-    case ErrorCategory.Todo: {
-      return {
-        category,
-        name: 'todo',
-        description: 'Unimplemented features',
-        recommended: false,
-      };
-    }
-    case ErrorCategory.UnsupportedSyntax: {
-      return {
-        category,
-        name: 'unsupported-syntax',
-        description:
-          'Validates against syntax that we do not plan to support in React Compiler',
-        recommended: true,
-      };
-    }
-    case ErrorCategory.UseMemo: {
-      return {
-        category,
-        name: 'use-memo',
-        description:
-          'Validates usage of the useMemo() hook against common mistakes. See [`useMemo()` docs](https://react.dev/reference/react/useMemo) for more information.',
-        recommended: true,
-      };
-    }
-    default: {
-      assertExhaustive(category, `Unsupported category ${category}`);
-    }
-  }
-}
-
-export const LintRules: Array<LintRule> = Object.keys(ErrorCategory).map(
-  category => getRuleForCategory(category as any),
-);
--- a/compiler/packages/babel-plugin-react-compiler/src/Entrypoint/Imports.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Entrypoint/Imports.ts
@@ -9,7 +9,7 @@ import {NodePath} from '@babel/core';
 import * as t from '@babel/types';
 import {Scope as BabelScope} from '@babel/traverse';

-import {CompilerError, ErrorCategory, ErrorSeverity} from '../CompilerError';
+import {CompilerError, ErrorSeverity} from '../CompilerError';
 import {
  EnvironmentConfig,
  GeneratedSource,
@@ -38,7 +38,6 @@ export function validateRestrictedImports(
    ImportDeclaration(importDeclPath) {
      if (restrictedImports.has(importDeclPath.node.source.value)) {
        error.push({
-          category: ErrorCategory.Todo,
          severity: ErrorSeverity.Todo,
          reason: 'Bailing out due to blocklisted import',
          description: `Import from module ${importDeclPath.node.source.value}`,
@@ -206,7 +205,6 @@ export class ProgramContext {
    }
    const error = new CompilerError();
    error.push({
-      category: ErrorCategory.Todo,
      severity: ErrorSeverity.Todo,
      reason: 'Encountered conflicting global in generated program',
      description: `Conflict from local binding ${name}`,
--- a/compiler/packages/babel-plugin-react-compiler/src/Entrypoint/Options.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Entrypoint/Options.ts
@@ -7,12 +7,7 @@

 import * as t from '@babel/types';
 import {z} from 'zod';
-import {
-  CompilerDiagnostic,
-  CompilerError,
-  CompilerErrorDetail,
-  CompilerErrorDetailOptions,
-} from '../CompilerError';
+import {CompilerError, CompilerErrorDetailOptions} from '../CompilerError';
 import {
  EnvironmentConfig,
  ExternalFunction,
@@ -229,7 +224,7 @@ export type LoggerEvent =
 export type CompileErrorEvent = {
  kind: 'CompileError';
  fnLoc: t.SourceLocation | null;
-  detail: CompilerErrorDetail | CompilerDiagnostic;
+  detail: CompilerErrorDetailOptions;
 };
 export type CompileDiagnosticEvent = {
  kind: 'CompileDiagnostic';
--- a/compiler/packages/babel-plugin-react-compiler/src/Entrypoint/Pipeline.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Entrypoint/Pipeline.ts
@@ -33,7 +33,9 @@ import {findContextIdentifiers} from '../HIR/FindContextIdentifiers';
 import {
  analyseFunctions,
  dropManualMemoization,
+  inferMutableRanges,
  inferReactivePlaces,
+  inferReferenceEffects,
  inlineImmediatelyInvokedFunctionExpressions,
  inferEffectDependencies,
 } from '../Inference';
@@ -90,19 +92,20 @@ import {
 } from '../Validation';
 import {validateLocalsNotReassignedAfterRender} from '../Validation/ValidateLocalsNotReassignedAfterRender';
 import {outlineFunctions} from '../Optimization/OutlineFunctions';
+import {propagatePhiTypes} from '../TypeInference/PropagatePhiTypes';
 import {lowerContextAccess} from '../Optimization/LowerContextAccess';
-import {validateNoSetStateInEffects} from '../Validation/ValidateNoSetStateInEffects';
+import {validateNoSetStateInPassiveEffects} from '../Validation/ValidateNoSetStateInPassiveEffects';
 import {validateNoJSXInTryStatement} from '../Validation/ValidateNoJSXInTryStatement';
 import {propagateScopeDependenciesHIR} from '../HIR/PropagateScopeDependenciesHIR';
 import {outlineJSX} from '../Optimization/OutlineJsx';
 import {optimizePropsMethodCalls} from '../Optimization/OptimizePropsMethodCalls';
 import {transformFire} from '../Transform';
 import {validateNoImpureFunctionsInRender} from '../Validation/ValidateNoImpureFunctionsInRender';
+import {CompilerError} from '..';
 import {validateStaticComponents} from '../Validation/ValidateStaticComponents';
 import {validateNoFreezingKnownMutableFunctions} from '../Validation/ValidateNoFreezingKnownMutableFunctions';
 import {inferMutationAliasingEffects} from '../Inference/InferMutationAliasingEffects';
 import {inferMutationAliasingRanges} from '../Inference/InferMutationAliasingRanges';
-import {validateNoDerivedComputationsInEffects} from '../Validation/ValidateNoDerivedComputationsInEffects';

 export type CompilerPipelineValue =
  | {kind: 'ast'; name: string; value: CodegenFunction}
@@ -171,7 +174,7 @@ function runWithEnvironment(
    !env.config.disableMemoizationForDebugging &&
    !env.config.enableChangeDetectionForDebugging
  ) {
-    dropManualMemoization(hir).unwrap();
+    dropManualMemoization(hir);
    log({kind: 'hir', name: 'DropManualMemoization', value: hir});
  }

@@ -226,12 +229,26 @@ function runWithEnvironment(
  analyseFunctions(hir);
  log({kind: 'hir', name: 'AnalyseFunctions', value: hir});

-  const mutabilityAliasingErrors = inferMutationAliasingEffects(hir);
-  log({kind: 'hir', name: 'InferMutationAliasingEffects', value: hir});
-  if (env.isInferredMemoEnabled) {
-    if (mutabilityAliasingErrors.isErr()) {
-      throw mutabilityAliasingErrors.unwrapErr();
+  if (!env.config.enableNewMutationAliasingModel) {
+    const fnEffectErrors = inferReferenceEffects(hir);
+    if (env.isInferredMemoEnabled) {
+      if (fnEffectErrors.length > 0) {
+        CompilerError.throw(fnEffectErrors[0]);
+      }
    }
+    log({kind: 'hir', name: 'InferReferenceEffects', value: hir});
+  } else {
+    const mutabilityAliasingErrors = inferMutationAliasingEffects(hir);
+    log({kind: 'hir', name: 'InferMutationAliasingEffects', value: hir});
+    if (env.isInferredMemoEnabled) {
+      if (mutabilityAliasingErrors.isErr()) {
+        throw mutabilityAliasingErrors.unwrapErr();
+      }
+    }
+  }
+
+  if (!env.config.enableNewMutationAliasingModel) {
+    validateLocalsNotReassignedAfterRender(hir);
  }

  // Note: Has to come after infer reference effects because "dead" code may still affect inference
@@ -246,15 +263,20 @@ function runWithEnvironment(
  pruneMaybeThrows(hir);
  log({kind: 'hir', name: 'PruneMaybeThrows', value: hir});

-  const mutabilityAliasingRangeErrors = inferMutationAliasingRanges(hir, {
-    isFunctionExpression: false,
-  });
-  log({kind: 'hir', name: 'InferMutationAliasingRanges', value: hir});
-  if (env.isInferredMemoEnabled) {
-    if (mutabilityAliasingRangeErrors.isErr()) {
-      throw mutabilityAliasingRangeErrors.unwrapErr();
+  if (!env.config.enableNewMutationAliasingModel) {
+    inferMutableRanges(hir);
+    log({kind: 'hir', name: 'InferMutableRanges', value: hir});
+  } else {
+    const mutabilityAliasingErrors = inferMutationAliasingRanges(hir, {
+      isFunctionExpression: false,
+    });
+    log({kind: 'hir', name: 'InferMutationAliasingRanges', value: hir});
+    if (env.isInferredMemoEnabled) {
+      if (mutabilityAliasingErrors.isErr()) {
+        throw mutabilityAliasingErrors.unwrapErr();
+      }
+      validateLocalsNotReassignedAfterRender(hir);
    }
-    validateLocalsNotReassignedAfterRender(hir);
  }

  if (env.isInferredMemoEnabled) {
@@ -270,12 +292,8 @@ function runWithEnvironment(
      validateNoSetStateInRender(hir).unwrap();
    }

-    if (env.config.validateNoDerivedComputationsInEffects) {
-      validateNoDerivedComputationsInEffects(hir);
-    }
-
-    if (env.config.validateNoSetStateInEffects) {
-      env.logErrors(validateNoSetStateInEffects(hir));
+    if (env.config.validateNoSetStateInPassiveEffects) {
+      env.logErrors(validateNoSetStateInPassiveEffects(hir));
    }

    if (env.config.validateNoJSXInTryStatements) {
@@ -286,7 +304,12 @@ function runWithEnvironment(
      validateNoImpureFunctionsInRender(hir).unwrap();
    }

-    validateNoFreezingKnownMutableFunctions(hir).unwrap();
+    if (
+      env.config.validateNoFreezingKnownMutableFunctions ||
+      env.config.enableNewMutationAliasingModel
+    ) {
+      validateNoFreezingKnownMutableFunctions(hir).unwrap();
+    }
  }

  inferReactivePlaces(hir);
@@ -299,6 +322,13 @@ function runWithEnvironment(
    value: hir,
  });

+  propagatePhiTypes(hir);
+  log({
+    kind: 'hir',
+    name: 'PropagatePhiTypes',
+    value: hir,
+  });
+
  if (env.isInferredMemoEnabled) {
    if (env.config.validateStaticComponents) {
      env.logErrors(validateStaticComponents(hir));
--- a/compiler/packages/babel-plugin-react-compiler/src/Entrypoint/Program.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Entrypoint/Program.ts
@@ -10,7 +10,6 @@ import * as t from '@babel/types';
 import {
  CompilerError,
  CompilerErrorDetail,
-  ErrorCategory,
  ErrorSeverity,
 } from '../CompilerError';
 import {ExternalFunction, ReactFunctionType} from '../HIR/Environment';
@@ -106,7 +105,6 @@ function findDirectivesDynamicGating(
          reason: `Dynamic gating directive is not a valid JavaScript identifier`,
          description: `Found '${directive.value.value}'`,
          severity: ErrorSeverity.InvalidReact,
-          category: ErrorCategory.Gating,
          loc: directive.loc ?? null,
          suggestions: null,
        });
@@ -123,7 +121,6 @@ function findDirectivesDynamicGating(
        .map(r => r.directive.value.value)
        .join(', ')}]`,
      severity: ErrorSeverity.InvalidReact,
-      category: ErrorCategory.Gating,
      loc: result[0].directive.loc ?? null,
      suggestions: null,
    });
@@ -184,7 +181,7 @@ function logError(
        context.opts.logger.logEvent(context.filename, {
          kind: 'CompileError',
          fnLoc,
-          detail,
+          detail: detail.options,
        });
      }
    } else {
@@ -459,7 +456,6 @@ export function compileProgram(
          reason:
            'Unexpected compiled functions when module scope opt-out is present',
          severity: ErrorSeverity.Invariant,
-          category: ErrorCategory.Invariant,
          loc: null,
        }),
      );
@@ -494,20 +490,7 @@ function findFunctionsToCompile(
 ): Array<CompileSource> {
  const queue: Array<CompileSource> = [];
  const traverseFunction = (fn: BabelFn, pass: CompilerPass): void => {
-    // In 'all' mode, compile only top level functions
-    if (
-      pass.opts.compilationMode === 'all' &&
-      fn.scope.getProgramParent() !== fn.scope.parent
-    ) {
-      return;
-    }
-
    const fnType = getReactFunctionType(fn, pass);
-
-    if (pass.opts.environment.validateNoDynamicallyCreatedComponentsOrHooks) {
-      validateNoDynamicallyCreatedComponentsOrHooks(fn, pass, programContext);
-    }
-
    if (fnType === null || programContext.alreadyCompiled.has(fn.node)) {
      return;
    }
@@ -828,7 +811,6 @@ function shouldSkipCompilation(
          description:
            "When the 'sources' config options is specified, the React compiler will only compile files with a name",
          severity: ErrorSeverity.InvalidConfig,
-          category: ErrorCategory.Config,
          loc: null,
        }),
      );
@@ -852,73 +834,6 @@ function shouldSkipCompilation(
  return false;
 }

-/**
- * Validates that Components/Hooks are always defined at module level. This prevents scope reference
- * errors that occur when the compiler attempts to optimize the nested component/hook while its
- * parent function remains uncompiled.
- */
-function validateNoDynamicallyCreatedComponentsOrHooks(
-  fn: BabelFn,
-  pass: CompilerPass,
-  programContext: ProgramContext,
-): void {
-  const parentNameExpr = getFunctionName(fn);
-  const parentName =
-    parentNameExpr !== null && parentNameExpr.isIdentifier()
-      ? parentNameExpr.node.name
-      : '<anonymous>';
-
-  const validateNestedFunction = (
-    nestedFn: NodePath<
-      t.FunctionDeclaration | t.FunctionExpression | t.ArrowFunctionExpression
-    >,
-  ): void => {
-    if (
-      nestedFn.node === fn.node ||
-      programContext.alreadyCompiled.has(nestedFn.node)
-    ) {
-      return;
-    }
-
-    if (nestedFn.scope.getProgramParent() !== nestedFn.scope.parent) {
-      const nestedFnType = getReactFunctionType(nestedFn as BabelFn, pass);
-      const nestedFnNameExpr = getFunctionName(nestedFn as BabelFn);
-      const nestedName =
-        nestedFnNameExpr !== null && nestedFnNameExpr.isIdentifier()
-          ? nestedFnNameExpr.node.name
-          : '<anonymous>';
-      if (nestedFnType === 'Component' || nestedFnType === 'Hook') {
-        CompilerError.throwDiagnostic({
-          category: ErrorCategory.Factories,
-          severity: ErrorSeverity.InvalidReact,
-          reason: `Components and hooks cannot be created dynamically`,
-          description: `The function \`${nestedName}\` appears to be a React ${nestedFnType.toLowerCase()}, but it's defined inside \`${parentName}\`. Components and Hooks should always be declared at module scope`,
-          details: [
-            {
-              kind: 'error',
-              message: 'this function dynamically created a component/hook',
-              loc: parentNameExpr?.node.loc ?? fn.node.loc ?? null,
-            },
-            {
-              kind: 'error',
-              message: 'the component is created here',
-              loc: nestedFnNameExpr?.node.loc ?? nestedFn.node.loc ?? null,
-            },
-          ],
-        });
-      }
-    }
-
-    nestedFn.skip();
-  };
-
-  fn.traverse({
-    FunctionDeclaration: validateNestedFunction,
-    FunctionExpression: validateNestedFunction,
-    ArrowFunctionExpression: validateNestedFunction,
-  });
-}
-
 function getReactFunctionType(
  fn: BabelFn,
  pass: CompilerPass,
@@ -957,6 +872,11 @@ function getReactFunctionType(
      return componentSyntaxType;
    }
    case 'all': {
+      // Compile only top level functions
+      if (fn.scope.getProgramParent() !== fn.scope.parent) {
+        return null;
+      }
+
      return getComponentOrHookLike(fn, hookPattern) ?? 'Other';
    }
    default: {
--- a/compiler/packages/babel-plugin-react-compiler/src/Entrypoint/Suppression.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Entrypoint/Suppression.ts
@@ -8,10 +8,9 @@
 import {NodePath} from '@babel/core';
 import * as t from '@babel/types';
 import {
-  CompilerDiagnostic,
  CompilerError,
+  CompilerErrorDetail,
  CompilerSuggestionOperation,
-  ErrorCategory,
  ErrorSeverity,
 } from '../CompilerError';
 import {assertExhaustive} from '../Utils/utils';
@@ -182,12 +181,12 @@ export function suppressionsToCompilerError(
          'Unhandled suppression source',
        );
    }
-    error.pushDiagnostic(
-      CompilerDiagnostic.create({
-        reason: reason,
-        description: `React Compiler only works when your components follow all the rules of React, disabling them may result in unexpected or incorrect behavior. Found suppression \`${suppressionRange.disableComment.value.trim()}\``,
+    error.pushErrorDetail(
+      new CompilerErrorDetail({
+        reason: `${reason}. React Compiler only works when your components follow all the rules of React, disabling them may result in unexpected or incorrect behavior`,
+        description: suppressionRange.disableComment.value.trim(),
        severity: ErrorSeverity.InvalidReact,
-        category: ErrorCategory.Suppression,
+        loc: suppressionRange.disableComment.loc ?? null,
        suggestions: [
          {
            description: suggestion,
@@ -198,10 +197,6 @@ export function suppressionsToCompilerError(
            op: CompilerSuggestionOperation.Remove,
          },
        ],
-      }).withDetail({
-        kind: 'error',
-        loc: suppressionRange.disableComment.loc ?? null,
-        message: 'Found React rule suppression',
      }),
    );
  }
--- a/compiler/packages/babel-plugin-react-compiler/src/Entrypoint/ValidateNoUntransformedReferences.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Entrypoint/ValidateNoUntransformedReferences.ts
@@ -8,67 +8,35 @@
 import {NodePath} from '@babel/core';
 import * as t from '@babel/types';

-import {CompilerError, EnvironmentConfig, ErrorSeverity, Logger} from '..';
+import {
+  CompilerError,
+  CompilerErrorDetailOptions,
+  EnvironmentConfig,
+  ErrorSeverity,
+  Logger,
+} from '..';
 import {getOrInsertWith} from '../Utils/utils';
-import {Environment, GeneratedSource} from '../HIR';
+import {Environment} from '../HIR';
 import {DEFAULT_EXPORT} from '../HIR/Environment';
 import {CompileProgramMetadata} from './Program';
-import {
-  CompilerDiagnostic,
-  CompilerDiagnosticOptions,
-  ErrorCategory,
-} from '../CompilerError';

 function throwInvalidReact(
-  options: Omit<CompilerDiagnosticOptions, 'severity'>,
+  options: Omit<CompilerErrorDetailOptions, 'severity'>,
  {logger, filename}: TraversalState,
 ): never {
-  const detail: CompilerDiagnosticOptions = {
-    severity: ErrorSeverity.InvalidReact,
+  const detail: CompilerErrorDetailOptions = {
    ...options,
+    severity: ErrorSeverity.InvalidReact,
  };
  logger?.logEvent(filename, {
    kind: 'CompileError',
    fnLoc: null,
-    detail: new CompilerDiagnostic(detail),
+    detail,
  });
-  CompilerError.throwDiagnostic(detail);
-}
-
-function isAutodepsSigil(
-  arg: NodePath<t.ArgumentPlaceholder | t.SpreadElement | t.Expression>,
-): boolean {
-  // Check for AUTODEPS identifier imported from React
-  if (arg.isIdentifier() && arg.node.name === 'AUTODEPS') {
-    const binding = arg.scope.getBinding(arg.node.name);
-    if (binding && binding.path.isImportSpecifier()) {
-      const importSpecifier = binding.path.node as t.ImportSpecifier;
-      if (importSpecifier.imported.type === 'Identifier') {
-        return (importSpecifier.imported as t.Identifier).name === 'AUTODEPS';
-      }
-    }
-    return false;
-  }
-
-  // Check for React.AUTODEPS member expression
-  if (arg.isMemberExpression() && !arg.node.computed) {
-    const object = arg.get('object');
-    const property = arg.get('property');
-
-    if (
-      object.isIdentifier() &&
-      object.node.name === 'React' &&
-      property.isIdentifier() &&
-      property.node.name === 'AUTODEPS'
-    ) {
-      return true;
-    }
-  }
-
-  return false;
+  CompilerError.throw(detail);
 }
 function assertValidEffectImportReference(
-  autodepsIndex: number,
+  numArgs: number,
  paths: Array<NodePath<t.Node>>,
  context: TraversalState,
 ): void {
@@ -81,10 +49,11 @@ function assertValidEffectImportReference(
        maybeCalleeLoc != null &&
        context.inferredEffectLocations.has(maybeCalleeLoc);
      /**
-       * Error on effect calls that still have AUTODEPS in their args
+       * Only error on untransformed references of the form `useMyEffect(...)`
+       * or `moduleNamespace.useMyEffect(...)`, with matching argument counts.
+       * TODO: do we also want a mode to also hard error on non-call references?
       */
-      const hasAutodepsArg = args.some(isAutodepsSigil);
-      if (hasAutodepsArg && !hasInferredEffect) {
+      if (args.length === numArgs && !hasInferredEffect) {
        const maybeErrorDiagnostic = matchCompilerDiagnostic(
          path,
          context.transformErrors,
@@ -96,19 +65,14 @@ function assertValidEffectImportReference(
         */
        throwInvalidReact(
          {
-            category: ErrorCategory.AutomaticEffectDependencies,
            reason:
-              'Cannot infer dependencies of this effect. This will break your build!',
-            description:
-              'To resolve, either pass a dependency array or fix reported compiler bailout diagnostics.' +
-              (maybeErrorDiagnostic ? ` ${maybeErrorDiagnostic}` : ''),
-            details: [
-              {
-                kind: 'error',
-                message: 'Cannot infer dependencies',
-                loc: parent.node.loc ?? GeneratedSource,
-              },
-            ],
+              '[InferEffectDependencies] React Compiler is unable to infer dependencies of this effect. ' +
+              'This will break your build! ' +
+              'To resolve, either pass your own dependency array or fix reported compiler bailout diagnostics.',
+            description: maybeErrorDiagnostic
+              ? `(Bailout reason: ${maybeErrorDiagnostic})`
+              : null,
+            loc: parent.node.loc ?? null,
          },
          context,
        );
@@ -128,20 +92,13 @@ function assertValidFireImportReference(
    );
    throwInvalidReact(
      {
-        category: ErrorCategory.Fire,
-        reason: '[Fire] Untransformed reference to compiler-required feature.',
-        description:
-          'Either remove this `fire` call or ensure it is successfully transformed by the compiler' +
-          maybeErrorDiagnostic
-            ? ` ${maybeErrorDiagnostic}`
-            : '',
-        details: [
-          {
-            kind: 'error',
-            message: 'Untransformed `fire` call',
-            loc: paths[0].node.loc ?? GeneratedSource,
-          },
-        ],
+        reason:
+          '[Fire] Untransformed reference to compiler-required feature. ' +
+          'Either remove this `fire` call or ensure it is successfully transformed by the compiler',
+        description: maybeErrorDiagnostic
+          ? `(Bailout reason: ${maybeErrorDiagnostic})`
+          : null,
+        loc: paths[0].node.loc ?? null,
      },
      context,
    );
@@ -171,12 +128,12 @@ export default function validateNoUntransformedReferences(
  if (env.inferEffectDependencies) {
    for (const {
      function: {source, importSpecifierName},
-      autodepsIndex,
+      numRequiredArgs,
    } of env.inferEffectDependencies) {
      const module = getOrInsertWith(moduleLoadChecks, source, () => new Map());
      module.set(
        importSpecifierName,
-        assertValidEffectImportReference.bind(null, autodepsIndex),
+        assertValidEffectImportReference.bind(null, numRequiredArgs),
      );
    }
  }
--- a/compiler/packages/babel-plugin-react-compiler/src/Flood/FlowTypes.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Flood/FlowTypes.ts
@@ -1,752 +0,0 @@
-/**
- * TypeScript definitions for Flow type JSON representations
- * Based on the output of /data/sandcastle/boxes/fbsource/fbcode/flow/src/typing/convertTypes.ml
- */
-
-// Base type for all Flow types with a kind field
-export interface BaseFlowType {
-  kind: string;
-}
-
-// Type for representing polarity
-export type Polarity = 'positive' | 'negative' | 'neutral';
-
-// Type for representing a name that might be null
-export type OptionalName = string | null;
-
-// Open type
-export interface OpenType extends BaseFlowType {
-  kind: 'Open';
-}
-
-// Def type
-export interface DefType extends BaseFlowType {
-  kind: 'Def';
-  def: DefT;
-}
-
-// Eval type
-export interface EvalType extends BaseFlowType {
-  kind: 'Eval';
-  type: FlowType;
-  destructor: Destructor;
-}
-
-// Generic type
-export interface GenericType extends BaseFlowType {
-  kind: 'Generic';
-  name: string;
-  bound: FlowType;
-  no_infer: boolean;
-}
-
-// ThisInstance type
-export interface ThisInstanceType extends BaseFlowType {
-  kind: 'ThisInstance';
-  instance: InstanceT;
-  is_this: boolean;
-  name: string;
-}
-
-// ThisTypeApp type
-export interface ThisTypeAppType extends BaseFlowType {
-  kind: 'ThisTypeApp';
-  t1: FlowType;
-  t2: FlowType;
-  t_list?: Array<FlowType>;
-}
-
-// TypeApp type
-export interface TypeAppType extends BaseFlowType {
-  kind: 'TypeApp';
-  type: FlowType;
-  targs: Array<FlowType>;
-  from_value: boolean;
-  use_desc: boolean;
-}
-
-// FunProto type
-export interface FunProtoType extends BaseFlowType {
-  kind: 'FunProto';
-}
-
-// ObjProto type
-export interface ObjProtoType extends BaseFlowType {
-  kind: 'ObjProto';
-}
-
-// NullProto type
-export interface NullProtoType extends BaseFlowType {
-  kind: 'NullProto';
-}
-
-// FunProtoBind type
-export interface FunProtoBindType extends BaseFlowType {
-  kind: 'FunProtoBind';
-}
-
-// Intersection type
-export interface IntersectionType extends BaseFlowType {
-  kind: 'Intersection';
-  members: Array<FlowType>;
-}
-
-// Union type
-export interface UnionType extends BaseFlowType {
-  kind: 'Union';
-  members: Array<FlowType>;
-}
-
-// Maybe type
-export interface MaybeType extends BaseFlowType {
-  kind: 'Maybe';
-  type: FlowType;
-}
-
-// Optional type
-export interface OptionalType extends BaseFlowType {
-  kind: 'Optional';
-  type: FlowType;
-  use_desc: boolean;
-}
-
-// Keys type
-export interface KeysType extends BaseFlowType {
-  kind: 'Keys';
-  type: FlowType;
-}
-
-// Annot type
-export interface AnnotType extends BaseFlowType {
-  kind: 'Annot';
-  type: FlowType;
-  use_desc: boolean;
-}
-
-// Opaque type
-export interface OpaqueType extends BaseFlowType {
-  kind: 'Opaque';
-  opaquetype: {
-    opaque_id: string;
-    underlying_t: FlowType | null;
-    super_t: FlowType | null;
-    opaque_type_args: Array<{
-      name: string;
-      type: FlowType;
-      polarity: Polarity;
-    }>;
-    opaque_name: string;
-  };
-}
-
-// Namespace type
-export interface NamespaceType extends BaseFlowType {
-  kind: 'Namespace';
-  namespace_symbol: {
-    symbol: string;
-  };
-  values_type: FlowType;
-  types_tmap: PropertyMap;
-}
-
-// Any type
-export interface AnyType extends BaseFlowType {
-  kind: 'Any';
-}
-
-// StrUtil type
-export interface StrUtilType extends BaseFlowType {
-  kind: 'StrUtil';
-  op: 'StrPrefix' | 'StrSuffix';
-  prefix?: string;
-  suffix?: string;
-  remainder?: FlowType;
-}
-
-// TypeParam definition
-export interface TypeParam {
-  name: string;
-  bound: FlowType;
-  polarity: Polarity;
-  default: FlowType | null;
-}
-
-// EnumInfo types
-export type EnumInfo = ConcreteEnum | AbstractEnum;
-
-export interface ConcreteEnum {
-  kind: 'ConcreteEnum';
-  enum_name: string;
-  enum_id: string;
-  members: Array<string>;
-  representation_t: FlowType;
-  has_unknown_members: boolean;
-}
-
-export interface AbstractEnum {
-  kind: 'AbstractEnum';
-  representation_t: FlowType;
-}
-
-// CanonicalRendersForm types
-export type CanonicalRendersForm =
-  | InstrinsicRenders
-  | NominalRenders
-  | StructuralRenders
-  | DefaultRenders;
-
-export interface InstrinsicRenders {
-  kind: 'InstrinsicRenders';
-  name: string;
-}
-
-export interface NominalRenders {
-  kind: 'NominalRenders';
-  renders_id: string;
-  renders_name: string;
-  renders_super: FlowType;
-}
-
-export interface StructuralRenders {
-  kind: 'StructuralRenders';
-  renders_variant: 'RendersNormal' | 'RendersMaybe' | 'RendersStar';
-  renders_structural_type: FlowType;
-}
-
-export interface DefaultRenders {
-  kind: 'DefaultRenders';
-}
-
-// InstanceT definition
-export interface InstanceT {
-  inst: InstType;
-  static: FlowType;
-  super: FlowType;
-  implements: Array<FlowType>;
-}
-
-// InstType definition
-export interface InstType {
-  class_name: string | null;
-  class_id: string;
-  type_args: Array<{
-    name: string;
-    type: FlowType;
-    polarity: Polarity;
-  }>;
-  own_props: PropertyMap;
-  proto_props: PropertyMap;
-  call_t: null | {
-    id: number;
-    call: FlowType;
-  };
-}
-
-// DefT types
-export type DefT =
-  | NumGeneralType
-  | StrGeneralType
-  | BoolGeneralType
-  | BigIntGeneralType
-  | EmptyType
-  | MixedType
-  | NullType
-  | VoidType
-  | SymbolType
-  | FunType
-  | ObjType
-  | ArrType
-  | ClassType
-  | InstanceType
-  | SingletonStrType
-  | NumericStrKeyType
-  | SingletonNumType
-  | SingletonBoolType
-  | SingletonBigIntType
-  | TypeType
-  | PolyType
-  | ReactAbstractComponentType
-  | RendersType
-  | EnumValueType
-  | EnumObjectType;
-
-export interface NumGeneralType extends BaseFlowType {
-  kind: 'NumGeneral';
-}
-
-export interface StrGeneralType extends BaseFlowType {
-  kind: 'StrGeneral';
-}
-
-export interface BoolGeneralType extends BaseFlowType {
-  kind: 'BoolGeneral';
-}
-
-export interface BigIntGeneralType extends BaseFlowType {
-  kind: 'BigIntGeneral';
-}
-
-export interface EmptyType extends BaseFlowType {
-  kind: 'Empty';
-}
-
-export interface MixedType extends BaseFlowType {
-  kind: 'Mixed';
-}
-
-export interface NullType extends BaseFlowType {
-  kind: 'Null';
-}
-
-export interface VoidType extends BaseFlowType {
-  kind: 'Void';
-}
-
-export interface SymbolType extends BaseFlowType {
-  kind: 'Symbol';
-}
-
-export interface FunType extends BaseFlowType {
-  kind: 'Fun';
-  static: FlowType;
-  funtype: FunTypeObj;
-}
-
-export interface ObjType extends BaseFlowType {
-  kind: 'Obj';
-  objtype: ObjTypeObj;
-}
-
-export interface ArrType extends BaseFlowType {
-  kind: 'Arr';
-  arrtype: ArrTypeObj;
-}
-
-export interface ClassType extends BaseFlowType {
-  kind: 'Class';
-  type: FlowType;
-}
-
-export interface InstanceType extends BaseFlowType {
-  kind: 'Instance';
-  instance: InstanceT;
-}
-
-export interface SingletonStrType extends BaseFlowType {
-  kind: 'SingletonStr';
-  from_annot: boolean;
-  value: string;
-}
-
-export interface NumericStrKeyType extends BaseFlowType {
-  kind: 'NumericStrKey';
-  number: string;
-  string: string;
-}
-
-export interface SingletonNumType extends BaseFlowType {
-  kind: 'SingletonNum';
-  from_annot: boolean;
-  number: string;
-  string: string;
-}
-
-export interface SingletonBoolType extends BaseFlowType {
-  kind: 'SingletonBool';
-  from_annot: boolean;
-  value: boolean;
-}
-
-export interface SingletonBigIntType extends BaseFlowType {
-  kind: 'SingletonBigInt';
-  from_annot: boolean;
-  value: string;
-}
-
-export interface TypeType extends BaseFlowType {
-  kind: 'Type';
-  type_kind: TypeTKind;
-  type: FlowType;
-}
-
-export type TypeTKind =
-  | 'TypeAliasKind'
-  | 'TypeParamKind'
-  | 'OpaqueKind'
-  | 'ImportTypeofKind'
-  | 'ImportClassKind'
-  | 'ImportEnumKind'
-  | 'InstanceKind'
-  | 'RenderTypeKind';
-
-export interface PolyType extends BaseFlowType {
-  kind: 'Poly';
-  tparams: Array<TypeParam>;
-  t_out: FlowType;
-  id: string;
-}
-
-export interface ReactAbstractComponentType extends BaseFlowType {
-  kind: 'ReactAbstractComponent';
-  config: FlowType;
-  renders: FlowType;
-  instance: ComponentInstance;
-  component_kind: ComponentKind;
-}
-
-export type ComponentInstance =
-  | {kind: 'RefSetterProp'; type: FlowType}
-  | {kind: 'Omitted'};
-
-export type ComponentKind =
-  | {kind: 'Structural'}
-  | {kind: 'Nominal'; id: string; name: string; types: Array<FlowType> | null};
-
-export interface RendersType extends BaseFlowType {
-  kind: 'Renders';
-  form: CanonicalRendersForm;
-}
-
-export interface EnumValueType extends BaseFlowType {
-  kind: 'EnumValue';
-  enum_info: EnumInfo;
-}
-
-export interface EnumObjectType extends BaseFlowType {
-  kind: 'EnumObject';
-  enum_value_t: FlowType;
-  enum_info: EnumInfo;
-}
-
-// ObjKind types
-export type ObjKind =
-  | {kind: 'Exact'}
-  | {kind: 'Inexact'}
-  | {kind: 'Indexed'; dicttype: DictType};
-
-// DictType definition
-export interface DictType {
-  dict_name: string | null;
-  key: FlowType;
-  value: FlowType;
-  dict_polarity: Polarity;
-}
-
-// ArrType types
-export type ArrTypeObj = ArrayAT | TupleAT | ROArrayAT;
-
-export interface ArrayAT {
-  kind: 'ArrayAT';
-  elem_t: FlowType;
-}
-
-export interface TupleAT {
-  kind: 'TupleAT';
-  elem_t: FlowType;
-  elements: Array<TupleElement>;
-  min_arity: number;
-  max_arity: number;
-  inexact: boolean;
-}
-
-export interface ROArrayAT {
-  kind: 'ROArrayAT';
-  elem_t: FlowType;
-}
-
-// TupleElement definition
-export interface TupleElement {
-  name: string | null;
-  t: FlowType;
-  polarity: Polarity;
-  optional: boolean;
-}
-
-// Flags definition
-export interface Flags {
-  obj_kind: ObjKind;
-}
-
-// Property types
-export type Property =
-  | FieldProperty
-  | GetProperty
-  | SetProperty
-  | GetSetProperty
-  | MethodProperty;
-
-export interface FieldProperty {
-  kind: 'Field';
-  type: FlowType;
-  polarity: Polarity;
-}
-
-export interface GetProperty {
-  kind: 'Get';
-  type: FlowType;
-}
-
-export interface SetProperty {
-  kind: 'Set';
-  type: FlowType;
-}
-
-export interface GetSetProperty {
-  kind: 'GetSet';
-  get_type: FlowType;
-  set_type: FlowType;
-}
-
-export interface MethodProperty {
-  kind: 'Method';
-  type: FlowType;
-}
-
-// PropertyMap definition
-export interface PropertyMap {
-  [key: string]: Property; // For other properties in the map
-}
-
-// ObjType definition
-export interface ObjTypeObj {
-  flags: Flags;
-  props: PropertyMap;
-  proto_t: FlowType;
-  call_t: number | null;
-}
-
-// FunType definition
-export interface FunTypeObj {
-  this_t: {
-    type: FlowType;
-    status: ThisStatus;
-  };
-  params: Array<{
-    name: string | null;
-    type: FlowType;
-  }>;
-  rest_param: null | {
-    name: string | null;
-    type: FlowType;
-  };
-  return_t: FlowType;
-  type_guard: null | {
-    inferred: boolean;
-    param_name: string;
-    type_guard: FlowType;
-    one_sided: boolean;
-  };
-  effect: Effect;
-}
-
-// ThisStatus types
-export type ThisStatus =
-  | {kind: 'This_Method'; unbound: boolean}
-  | {kind: 'This_Function'};
-
-// Effect types
-export type Effect =
-  | {kind: 'HookDecl'; id: string}
-  | {kind: 'HookAnnot'}
-  | {kind: 'ArbitraryEffect'}
-  | {kind: 'AnyEffect'};
-
-// Destructor types
-export type Destructor =
-  | NonMaybeTypeDestructor
-  | PropertyTypeDestructor
-  | ElementTypeDestructor
-  | OptionalIndexedAccessNonMaybeTypeDestructor
-  | OptionalIndexedAccessResultTypeDestructor
-  | ExactTypeDestructor
-  | ReadOnlyTypeDestructor
-  | PartialTypeDestructor
-  | RequiredTypeDestructor
-  | SpreadTypeDestructor
-  | SpreadTupleTypeDestructor
-  | RestTypeDestructor
-  | ValuesTypeDestructor
-  | ConditionalTypeDestructor
-  | TypeMapDestructor
-  | ReactElementPropsTypeDestructor
-  | ReactElementConfigTypeDestructor
-  | ReactCheckComponentConfigDestructor
-  | ReactDRODestructor
-  | MakeHooklikeDestructor
-  | MappedTypeDestructor
-  | EnumTypeDestructor;
-
-export interface NonMaybeTypeDestructor {
-  kind: 'NonMaybeType';
-}
-
-export interface PropertyTypeDestructor {
-  kind: 'PropertyType';
-  name: string;
-}
-
-export interface ElementTypeDestructor {
-  kind: 'ElementType';
-  index_type: FlowType;
-}
-
-export interface OptionalIndexedAccessNonMaybeTypeDestructor {
-  kind: 'OptionalIndexedAccessNonMaybeType';
-  index: OptionalIndexedAccessIndex;
-}
-
-export type OptionalIndexedAccessIndex =
-  | {kind: 'StrLitIndex'; name: string}
-  | {kind: 'TypeIndex'; type: FlowType};
-
-export interface OptionalIndexedAccessResultTypeDestructor {
-  kind: 'OptionalIndexedAccessResultType';
-}
-
-export interface ExactTypeDestructor {
-  kind: 'ExactType';
-}
-
-export interface ReadOnlyTypeDestructor {
-  kind: 'ReadOnlyType';
-}
-
-export interface PartialTypeDestructor {
-  kind: 'PartialType';
-}
-
-export interface RequiredTypeDestructor {
-  kind: 'RequiredType';
-}
-
-export interface SpreadTypeDestructor {
-  kind: 'SpreadType';
-  target: SpreadTarget;
-  operands: Array<SpreadOperand>;
-  operand_slice: Slice | null;
-}
-
-export type SpreadTarget =
-  | {kind: 'Value'; make_seal: 'Sealed' | 'Frozen' | 'As_Const'}
-  | {kind: 'Annot'; make_exact: boolean};
-
-export type SpreadOperand = {kind: 'Type'; type: FlowType} | Slice;
-
-export interface Slice {
-  kind: 'Slice';
-  prop_map: PropertyMap;
-  generics: Array<string>;
-  dict: DictType | null;
-  reachable_targs: Array<{
-    type: FlowType;
-    polarity: Polarity;
-  }>;
-}
-
-export interface SpreadTupleTypeDestructor {
-  kind: 'SpreadTupleType';
-  inexact: boolean;
-  resolved_rev: string;
-  unresolved: string;
-}
-
-export interface RestTypeDestructor {
-  kind: 'RestType';
-  merge_mode: RestMergeMode;
-  type: FlowType;
-}
-
-export type RestMergeMode =
-  | {kind: 'SpreadReversal'}
-  | {kind: 'ReactConfigMerge'; polarity: Polarity}
-  | {kind: 'Omit'};
-
-export interface ValuesTypeDestructor {
-  kind: 'ValuesType';
-}
-
-export interface ConditionalTypeDestructor {
-  kind: 'ConditionalType';
-  distributive_tparam_name: string | null;
-  infer_tparams: string;
-  extends_t: FlowType;
-  true_t: FlowType;
-  false_t: FlowType;
-}
-
-export interface TypeMapDestructor {
-  kind: 'ObjectKeyMirror';
-}
-
-export interface ReactElementPropsTypeDestructor {
-  kind: 'ReactElementPropsType';
-}
-
-export interface ReactElementConfigTypeDestructor {
-  kind: 'ReactElementConfigType';
-}
-
-export interface ReactCheckComponentConfigDestructor {
-  kind: 'ReactCheckComponentConfig';
-  props: {
-    [key: string]: Property;
-  };
-}
-
-export interface ReactDRODestructor {
-  kind: 'ReactDRO';
-  dro_type:
-    | 'HookReturn'
-    | 'HookArg'
-    | 'Props'
-    | 'ImmutableAnnot'
-    | 'DebugAnnot';
-}
-
-export interface MakeHooklikeDestructor {
-  kind: 'MakeHooklike';
-}
-
-export interface MappedTypeDestructor {
-  kind: 'MappedType';
-  homomorphic: Homomorphic;
-  distributive_tparam_name: string | null;
-  property_type: FlowType;
-  mapped_type_flags: {
-    variance: Polarity;
-    optional: 'MakeOptional' | 'RemoveOptional' | 'KeepOptionality';
-  };
-}
-
-export type Homomorphic =
-  | {kind: 'Homomorphic'}
-  | {kind: 'Unspecialized'}
-  | {kind: 'SemiHomomorphic'; type: FlowType};
-
-export interface EnumTypeDestructor {
-  kind: 'EnumType';
-}
-
-// Union of all possible Flow types
-export type FlowType =
-  | OpenType
-  | DefType
-  | EvalType
-  | GenericType
-  | ThisInstanceType
-  | ThisTypeAppType
-  | TypeAppType
-  | FunProtoType
-  | ObjProtoType
-  | NullProtoType
-  | FunProtoBindType
-  | IntersectionType
-  | UnionType
-  | MaybeType
-  | OptionalType
-  | KeysType
-  | AnnotType
-  | OpaqueType
-  | NamespaceType
-  | AnyType
-  | StrUtilType;
--- a/compiler/packages/babel-plugin-react-compiler/src/Flood/TypeErrors.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Flood/TypeErrors.ts
@@ -1,131 +0,0 @@
-import {CompilerError, SourceLocation} from '..';
-import {
-  ConcreteType,
-  printConcrete,
-  printType,
-  StructuralValue,
-  Type,
-  VariableId,
-} from './Types';
-
-export function unsupportedLanguageFeature(
-  desc: string,
-  loc: SourceLocation,
-): never {
-  CompilerError.throwInvalidJS({
-    reason: `Typedchecker does not currently support language feature: ${desc}`,
-    loc,
-  });
-}
-
-export type UnificationError =
-  | {
-      kind: 'TypeUnification';
-      left: ConcreteType<Type>;
-      right: ConcreteType<Type>;
-    }
-  | {
-      kind: 'StructuralUnification';
-      left: StructuralValue;
-      right: ConcreteType<Type>;
-    };
-
-function printUnificationError(err: UnificationError): string {
-  if (err.kind === 'TypeUnification') {
-    return `${printConcrete(err.left, printType)} is incompatible with ${printConcrete(err.right, printType)}`;
-  } else {
-    return `structural ${err.left.kind} is incompatible with ${printConcrete(err.right, printType)}`;
-  }
-}
-
-export function raiseUnificationErrors(
-  errs: null | Array<UnificationError>,
-  loc: SourceLocation,
-): void {
-  if (errs != null) {
-    if (errs.length === 0) {
-      CompilerError.invariant(false, {
-        reason: 'Should not have array of zero errors',
-        loc,
-      });
-    } else if (errs.length === 1) {
-      CompilerError.throwInvalidJS({
-        reason: `Unable to unify types because ${printUnificationError(errs[0])}`,
-        loc,
-      });
-    } else {
-      const messages = errs
-        .map(err => `\t* ${printUnificationError(err)}`)
-        .join('\n');
-      CompilerError.throwInvalidJS({
-        reason: `Unable to unify types because:\n${messages}`,
-        loc,
-      });
-    }
-  }
-}
-
-export function unresolvableTypeVariable(
-  id: VariableId,
-  loc: SourceLocation,
-): never {
-  CompilerError.throwInvalidJS({
-    reason: `Unable to resolve free variable ${id} to a concrete type`,
-    loc,
-  });
-}
-
-export function cannotAddVoid(explicit: boolean, loc: SourceLocation): never {
-  if (explicit) {
-    CompilerError.throwInvalidJS({
-      reason: `Undefined is not a valid operand of \`+\``,
-      loc,
-    });
-  } else {
-    CompilerError.throwInvalidJS({
-      reason: `Value may be undefined, which is not a valid operand of \`+\``,
-      loc,
-    });
-  }
-}
-
-export function unsupportedTypeAnnotation(
-  desc: string,
-  loc: SourceLocation,
-): never {
-  CompilerError.throwInvalidJS({
-    reason: `Typedchecker does not currently support type annotation: ${desc}`,
-    loc,
-  });
-}
-
-export function checkTypeArgumentArity(
-  desc: string,
-  expected: number,
-  actual: number,
-  loc: SourceLocation,
-): void {
-  if (expected !== actual) {
-    CompilerError.throwInvalidJS({
-      reason: `Expected ${desc} to have ${expected} type parameters, got ${actual}`,
-      loc,
-    });
-  }
-}
-
-export function notAFunction(desc: string, loc: SourceLocation): void {
-  CompilerError.throwInvalidJS({
-    reason: `Cannot call ${desc} because it is not a function`,
-    loc,
-  });
-}
-
-export function notAPolymorphicFunction(
-  desc: string,
-  loc: SourceLocation,
-): void {
-  CompilerError.throwInvalidJS({
-    reason: `Cannot call ${desc} with type arguments because it is not a polymorphic function`,
-    loc,
-  });
-}
--- a/compiler/packages/babel-plugin-react-compiler/src/Flood/TypeUtils.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Flood/TypeUtils.ts
@@ -1,312 +0,0 @@
-import {GeneratedSource} from '../HIR';
-import {assertExhaustive} from '../Utils/utils';
-import {unsupportedLanguageFeature} from './TypeErrors';
-import {
-  ConcreteType,
-  ResolvedType,
-  TypeParameter,
-  TypeParameterId,
-  DEBUG,
-  printConcrete,
-  printType,
-} from './Types';
-
-export function substitute(
-  type: ConcreteType<ResolvedType>,
-  typeParameters: Array<TypeParameter<ResolvedType>>,
-  typeArguments: Array<ResolvedType>,
-): ResolvedType {
-  const substMap = new Map<TypeParameterId, ResolvedType>();
-  for (let i = 0; i < typeParameters.length; i++) {
-    // TODO: Length checks to make sure type params match up with args
-    const typeParameter = typeParameters[i];
-    const typeArgument = typeArguments[i];
-    substMap.set(typeParameter.id, typeArgument);
-  }
-  const substitutionFunction = (t: ResolvedType): ResolvedType => {
-    // TODO: We really want a stateful mapper or visitor here so that we can model nested polymorphic types
-    if (t.type.kind === 'Generic' && substMap.has(t.type.id)) {
-      const substitutedType = substMap.get(t.type.id)!;
-      return substitutedType;
-    }
-
-    return {
-      kind: 'Concrete',
-      type: mapType(substitutionFunction, t.type),
-      platform: t.platform,
-    };
-  };
-
-  const substituted = mapType(substitutionFunction, type);
-
-  if (DEBUG) {
-    let substs = '';
-    for (let i = 0; i < typeParameters.length; i++) {
-      const typeParameter = typeParameters[i];
-      const typeArgument = typeArguments[i];
-      substs += `[${typeParameter.name}${typeParameter.id} := ${printType(typeArgument)}]`;
-    }
-    console.log(
-      `${printConcrete(type, printType)}${substs} = ${printConcrete(substituted, printType)}`,
-    );
-  }
-
-  return {kind: 'Concrete', type: substituted, platform: /* TODO */ 'shared'};
-}
-
-export function mapType<T, U>(
-  f: (t: T) => U,
-  type: ConcreteType<T>,
-): ConcreteType<U> {
-  switch (type.kind) {
-    case 'Mixed':
-    case 'Number':
-    case 'String':
-    case 'Boolean':
-    case 'Void':
-      return type;
-
-    case 'Nullable':
-      return {
-        kind: 'Nullable',
-        type: f(type.type),
-      };
-
-    case 'Array':
-      return {
-        kind: 'Array',
-        element: f(type.element),
-      };
-
-    case 'Set':
-      return {
-        kind: 'Set',
-        element: f(type.element),
-      };
-
-    case 'Map':
-      return {
-        kind: 'Map',
-        key: f(type.key),
-        value: f(type.value),
-      };
-
-    case 'Function':
-      return {
-        kind: 'Function',
-        typeParameters:
-          type.typeParameters?.map(param => ({
-            id: param.id,
-            name: param.name,
-            bound: f(param.bound),
-          })) ?? null,
-        params: type.params.map(f),
-        returnType: f(type.returnType),
-      };
-
-    case 'Component': {
-      return {
-        kind: 'Component',
-        children: type.children != null ? f(type.children) : null,
-        props: new Map([...type.props.entries()].map(([k, v]) => [k, f(v)])),
-      };
-    }
-
-    case 'Generic':
-      return {
-        kind: 'Generic',
-        id: type.id,
-        bound: f(type.bound),
-      };
-
-    case 'Object':
-      return type;
-
-    case 'Tuple':
-      return {
-        kind: 'Tuple',
-        id: type.id,
-        members: type.members.map(f),
-      };
-
-    case 'Structural':
-      return type;
-
-    case 'Enum':
-    case 'Union':
-    case 'Instance':
-      unsupportedLanguageFeature(type.kind, GeneratedSource);
-
-    default:
-      assertExhaustive(type, 'Unknown type kind');
-  }
-}
-
-export function diff<R, T>(
-  a: ConcreteType<T>,
-  b: ConcreteType<T>,
-  onChild: (a: T, b: T) => R,
-  onChildMismatch: (child: R, cur: R) => R,
-  onMismatch: (a: ConcreteType<T>, b: ConcreteType<T>, cur: R) => R,
-  init: R,
-): R {
-  let errors = init;
-
-  // Check if kinds match
-  if (a.kind !== b.kind) {
-    errors = onMismatch(a, b, errors);
-    return errors;
-  }
-
-  // Based on kind, check other properties
-  switch (a.kind) {
-    case 'Mixed':
-    case 'Number':
-    case 'String':
-    case 'Boolean':
-    case 'Void':
-      // Simple types, no further checks needed
-      break;
-
-    case 'Nullable':
-      // Check the nested type
-      errors = onChildMismatch(onChild(a.type, (b as typeof a).type), errors);
-      break;
-
-    case 'Array':
-    case 'Set':
-      // Check the element type
-      errors = onChildMismatch(
-        onChild(a.element, (b as typeof a).element),
-        errors,
-      );
-      break;
-
-    case 'Map':
-      // Check both key and value types
-      errors = onChildMismatch(onChild(a.key, (b as typeof a).key), errors);
-      errors = onChildMismatch(onChild(a.value, (b as typeof a).value), errors);
-      break;
-
-    case 'Function': {
-      const bFunc = b as typeof a;
-
-      // Check type parameters
-      if ((a.typeParameters == null) !== (bFunc.typeParameters == null)) {
-        errors = onMismatch(a, b, errors);
-      }
-
-      if (a.typeParameters != null && bFunc.typeParameters != null) {
-        if (a.typeParameters.length !== bFunc.typeParameters.length) {
-          errors = onMismatch(a, b, errors);
-        }
-
-        // Type parameters are just numbers, so we can compare them directly
-        for (let i = 0; i < a.typeParameters.length; i++) {
-          if (a.typeParameters[i] !== bFunc.typeParameters[i]) {
-            errors = onMismatch(a, b, errors);
-          }
-        }
-      }
-
-      // Check parameters
-      if (a.params.length !== bFunc.params.length) {
-        errors = onMismatch(a, b, errors);
-      }
-
-      for (let i = 0; i < a.params.length; i++) {
-        errors = onChildMismatch(onChild(a.params[i], bFunc.params[i]), errors);
-      }
-
-      // Check return type
-      errors = onChildMismatch(onChild(a.returnType, bFunc.returnType), errors);
-      break;
-    }
-
-    case 'Component': {
-      const bComp = b as typeof a;
-
-      // Check children
-      if (a.children !== bComp.children) {
-        errors = onMismatch(a, b, errors);
-      }
-
-      // Check props
-      if (a.props.size !== bComp.props.size) {
-        errors = onMismatch(a, b, errors);
-      }
-
-      for (const [k, v] of a.props) {
-        const bProp = bComp.props.get(k);
-        if (bProp == null) {
-          errors = onMismatch(a, b, errors);
-        } else {
-          errors = onChildMismatch(onChild(v, bProp), errors);
-        }
-      }
-
-      break;
-    }
-
-    case 'Generic': {
-      // Check that the type parameter IDs match
-      if (a.id !== (b as typeof a).id) {
-        errors = onMismatch(a, b, errors);
-      }
-      break;
-    }
-    case 'Structural': {
-      const bStruct = b as typeof a;
-
-      // Check that the structural IDs match
-      if (a.id !== bStruct.id) {
-        errors = onMismatch(a, b, errors);
-      }
-      break;
-    }
-    case 'Object': {
-      const bNom = b as typeof a;
-
-      // Check that the nominal IDs match
-      if (a.id !== bNom.id) {
-        errors = onMismatch(a, b, errors);
-      }
-      break;
-    }
-
-    case 'Tuple': {
-      const bTuple = b as typeof a;
-
-      // Check that the tuple IDs match
-      if (a.id !== bTuple.id) {
-        errors = onMismatch(a, b, errors);
-      }
-      for (let i = 0; i < a.members.length; i++) {
-        errors = onChildMismatch(
-          onChild(a.members[i], bTuple.members[i]),
-          errors,
-        );
-      }
-
-      break;
-    }
-
-    case 'Enum':
-    case 'Instance':
-    case 'Union': {
-      unsupportedLanguageFeature(a.kind, GeneratedSource);
-    }
-
-    default:
-      assertExhaustive(a, 'Unknown type kind');
-  }
-
-  return errors;
-}
-
-export function filterOptional(t: ResolvedType): ResolvedType {
-  if (t.kind === 'Concrete' && t.type.kind === 'Nullable') {
-    return t.type.type;
-  }
-  return t;
-}
--- a/compiler/packages/babel-plugin-react-compiler/src/Flood/Types.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Flood/Types.ts
--- a/compiler/packages/babel-plugin-react-compiler/src/HIR/BuildHIR.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/HIR/BuildHIR.ts
@@ -9,10 +9,8 @@ import {NodePath, Scope} from '@babel/traverse';
 import * as t from '@babel/types';
 import invariant from 'invariant';
 import {
-  CompilerDiagnostic,
  CompilerError,
  CompilerSuggestionOperation,
-  ErrorCategory,
  ErrorSeverity,
 } from '../CompilerError';
 import {Err, Ok, Result} from '../Utils/Result';
@@ -74,7 +72,7 @@ export function lower(
  env: Environment,
  // Bindings captured from the outer function, in case lower() is called recursively (for lambdas)
  bindings: Bindings | null = null,
-  capturedRefs: Map<t.Identifier, SourceLocation> = new Map(),
+  capturedRefs: Array<t.Identifier> = [],
 ): Result<HIRFunction, CompilerError> {
  const builder = new HIRBuilder(env, {
    bindings,
@@ -82,13 +80,13 @@ export function lower(
  });
  const context: HIRFunction['context'] = [];

-  for (const [ref, loc] of capturedRefs ?? []) {
+  for (const ref of capturedRefs ?? []) {
    context.push({
      kind: 'Identifier',
      identifier: builder.resolveBinding(ref),
      effect: Effect.Unknown,
      reactive: false,
-      loc,
+      loc: ref.loc ?? GeneratedSource,
    });
  }

@@ -106,18 +104,12 @@ export function lower(
    if (param.isIdentifier()) {
      const binding = builder.resolveIdentifier(param);
      if (binding.kind !== 'Identifier') {
-        builder.errors.pushDiagnostic(
-          CompilerDiagnostic.create({
-            severity: ErrorSeverity.Invariant,
-            category: ErrorCategory.Invariant,
-            reason: 'Could not find binding',
-            description: `[BuildHIR] Could not find binding for param \`${param.node.name}\`.`,
-          }).withDetail({
-            kind: 'error',
-            loc: param.node.loc ?? null,
-            message: 'Could not find binding',
-          }),
-        );
+        builder.errors.push({
+          reason: `(BuildHIR::lower) Could not find binding for param \`${param.node.name}\``,
+          severity: ErrorSeverity.Invariant,
+          loc: param.node.loc ?? null,
+          suggestions: null,
+        });
        return;
      }
      const place: Place = {
@@ -171,18 +163,12 @@ export function lower(
        'Assignment',
      );
    } else {
-      builder.errors.pushDiagnostic(
-        CompilerDiagnostic.create({
-          severity: ErrorSeverity.Todo,
-          category: ErrorCategory.Todo,
-          reason: `Handle ${param.node.type} parameters`,
-          description: `[BuildHIR] Add support for ${param.node.type} parameters.`,
-        }).withDetail({
-          kind: 'error',
-          loc: param.node.loc ?? null,
-          message: 'Unsupported parameter type',
-        }),
-      );
+      builder.errors.push({
+        reason: `(BuildHIR::lower) Handle ${param.node.type} params`,
+        severity: ErrorSeverity.Todo,
+        loc: param.node.loc ?? null,
+        suggestions: null,
+      });
    }
  });

@@ -192,7 +178,6 @@ export function lower(
    const fallthrough = builder.reserve('block');
    const terminal: ReturnTerminal = {
      kind: 'return',
-      returnVariant: 'Implicit',
      loc: GeneratedSource,
      value: lowerExpressionToTemporary(builder, body),
      id: makeInstructionId(0),
@@ -203,18 +188,13 @@ export function lower(
    lowerStatement(builder, body);
    directives = body.get('directives').map(d => d.node.value.value);
  } else {
-    builder.errors.pushDiagnostic(
-      CompilerDiagnostic.create({
-        severity: ErrorSeverity.InvalidJS,
-        category: ErrorCategory.Syntax,
-        reason: `Unexpected function body kind`,
-        description: `Expected function body to be an expression or a block statement, got \`${body.type}\`.`,
-      }).withDetail({
-        kind: 'error',
-        loc: body.node.loc ?? null,
-        message: 'Expected a block statement or expression',
-      }),
-    );
+    builder.errors.push({
+      severity: ErrorSeverity.InvalidJS,
+      reason: `Unexpected function body kind`,
+      description: `Expected function body to be an expression or a block statement, got \`${body.type}\``,
+      loc: body.node.loc ?? null,
+      suggestions: null,
+    });
  }

  if (builder.errors.hasErrors()) {
@@ -224,7 +204,6 @@ export function lower(
  builder.terminate(
    {
      kind: 'return',
-      returnVariant: 'Void',
      loc: GeneratedSource,
      value: lowerValueToTemporary(builder, {
        kind: 'Primitive',
@@ -242,6 +221,7 @@ export function lower(
    params,
    fnType: bindings == null ? env.fnType : 'Other',
    returnTypeAnnotation: null, // TODO: extract the actual return type node if present
+    returnType: makeType(),
    returns: createTemporaryPlace(env, func.node.loc ?? GeneratedSource),
    body: builder.build(),
    context,
@@ -277,7 +257,6 @@ function lowerStatement(
          reason:
            '(BuildHIR::lowerStatement) Support ThrowStatement inside of try/catch',
          severity: ErrorSeverity.Todo,
-          category: ErrorCategory.Todo,
          loc: stmt.node.loc ?? null,
          suggestions: null,
        });
@@ -309,7 +288,6 @@ function lowerStatement(
      }
      const terminal: ReturnTerminal = {
        kind: 'return',
-        returnVariant: 'Explicit',
        loc: stmt.node.loc ?? GeneratedSource,
        value,
        id: makeInstructionId(0),
@@ -465,7 +443,6 @@ function lowerStatement(
          } else if (!binding.path.isVariableDeclarator()) {
            builder.errors.push({
              severity: ErrorSeverity.Todo,
-              category: ErrorCategory.Todo,
              reason: 'Unsupported declaration type for hoisting',
              description: `variable "${binding.identifier.name}" declared with ${binding.path.type}`,
              suggestions: null,
@@ -475,7 +452,6 @@ function lowerStatement(
          } else {
            builder.errors.push({
              severity: ErrorSeverity.Todo,
-              category: ErrorCategory.Todo,
              reason: 'Handle non-const declarations for hoisting',
              description: `variable "${binding.identifier.name}" declared with ${binding.kind}`,
              suggestions: null,
@@ -556,7 +532,6 @@ function lowerStatement(
            reason:
              '(BuildHIR::lowerStatement) Handle non-variable initialization in ForStatement',
            severity: ErrorSeverity.Todo,
-            category: ErrorCategory.Todo,
            loc: stmt.node.loc ?? null,
            suggestions: null,
          });
@@ -629,7 +604,6 @@ function lowerStatement(
        builder.errors.push({
          reason: `(BuildHIR::lowerStatement) Handle empty test in ForStatement`,
          severity: ErrorSeverity.Todo,
-          category: ErrorCategory.Todo,
          loc: stmt.node.loc ?? null,
          suggestions: null,
        });
@@ -781,7 +755,6 @@ function lowerStatement(
            builder.errors.push({
              reason: `Expected at most one \`default\` branch in a switch statement, this code should have failed to parse`,
              severity: ErrorSeverity.InvalidJS,
-              category: ErrorCategory.Syntax,
              loc: case_.node.loc ?? null,
              suggestions: null,
            });
@@ -854,7 +827,6 @@ function lowerStatement(
        builder.errors.push({
          reason: `(BuildHIR::lowerStatement) Handle ${nodeKind} kinds in VariableDeclaration`,
          severity: ErrorSeverity.Todo,
-          category: ErrorCategory.Todo,
          loc: stmt.node.loc ?? null,
          suggestions: null,
        });
@@ -883,7 +855,6 @@ function lowerStatement(
            builder.errors.push({
              reason: `(BuildHIR::lowerAssignment) Could not find binding for declaration.`,
              severity: ErrorSeverity.Invariant,
-              category: ErrorCategory.Invariant,
              loc: id.node.loc ?? null,
              suggestions: null,
            });
@@ -901,7 +872,6 @@ function lowerStatement(
                builder.errors.push({
                  reason: `Expect \`const\` declaration not to be reassigned`,
                  severity: ErrorSeverity.InvalidJS,
-                  category: ErrorCategory.Syntax,
                  loc: id.node.loc ?? null,
                  suggestions: [
                    {
@@ -949,7 +919,6 @@ function lowerStatement(
            reason: `Expected variable declaration to be an identifier if no initializer was provided`,
            description: `Got a \`${id.type}\``,
            severity: ErrorSeverity.InvalidJS,
-            category: ErrorCategory.Syntax,
            loc: stmt.node.loc ?? null,
            suggestions: null,
          });
@@ -1058,7 +1027,6 @@ function lowerStatement(
        builder.errors.push({
          reason: `(BuildHIR::lowerStatement) Handle for-await loops`,
          severity: ErrorSeverity.Todo,
-          category: ErrorCategory.Todo,
          loc: stmt.node.loc ?? null,
          suggestions: null,
        });
@@ -1291,7 +1259,6 @@ function lowerStatement(
        builder.errors.push({
          reason: `(BuildHIR::lowerStatement) Handle TryStatement without a catch clause`,
          severity: ErrorSeverity.Todo,
-          category: ErrorCategory.Todo,
          loc: stmt.node.loc ?? null,
          suggestions: null,
        });
@@ -1301,7 +1268,6 @@ function lowerStatement(
        builder.errors.push({
          reason: `(BuildHIR::lowerStatement) Handle TryStatement with a finalizer ('finally') clause`,
          severity: ErrorSeverity.Todo,
-          category: ErrorCategory.Todo,
          loc: stmt.node.loc ?? null,
          suggestions: null,
        });
@@ -1390,89 +1356,13 @@ function lowerStatement(

      return;
    }
-    case 'WithStatement': {
-      builder.errors.push({
-        reason: `JavaScript 'with' syntax is not supported`,
-        description: `'with' syntax is considered deprecated and removed from JavaScript standards, consider alternatives`,
-        severity: ErrorSeverity.UnsupportedJS,
-        category: ErrorCategory.UnsupportedSyntax,
-        loc: stmtPath.node.loc ?? null,
-        suggestions: null,
-      });
-      lowerValueToTemporary(builder, {
-        kind: 'UnsupportedNode',
-        loc: stmtPath.node.loc ?? GeneratedSource,
-        node: stmtPath.node,
-      });
-      return;
-    }
-    case 'ClassDeclaration': {
-      /**
-       * In theory we could support inline class declarations, but this is rare enough in practice
-       * and complex enough to support that we don't anticipate supporting anytime soon. Developers
-       * are encouraged to lift classes out of component/hook declarations.
-       */
-      builder.errors.push({
-        reason: 'Inline `class` declarations are not supported',
-        description: `Move class declarations outside of components/hooks`,
-        severity: ErrorSeverity.UnsupportedJS,
-        category: ErrorCategory.UnsupportedSyntax,
-        loc: stmtPath.node.loc ?? null,
-        suggestions: null,
-      });
-      lowerValueToTemporary(builder, {
-        kind: 'UnsupportedNode',
-        loc: stmtPath.node.loc ?? GeneratedSource,
-        node: stmtPath.node,
-      });
-      return;
-    }
-    case 'EnumDeclaration':
-    case 'TSEnumDeclaration': {
-      lowerValueToTemporary(builder, {
-        kind: 'UnsupportedNode',
-        loc: stmtPath.node.loc ?? GeneratedSource,
-        node: stmtPath.node,
-      });
-      return;
-    }
-    case 'ExportAllDeclaration':
-    case 'ExportDefaultDeclaration':
-    case 'ExportNamedDeclaration':
-    case 'ImportDeclaration':
-    case 'TSExportAssignment':
-    case 'TSImportEqualsDeclaration': {
-      builder.errors.push({
-        reason:
-          'JavaScript `import` and `export` statements may only appear at the top level of a module',
-        severity: ErrorSeverity.InvalidJS,
-        category: ErrorCategory.Syntax,
-        loc: stmtPath.node.loc ?? null,
-        suggestions: null,
-      });
-      lowerValueToTemporary(builder, {
-        kind: 'UnsupportedNode',
-        loc: stmtPath.node.loc ?? GeneratedSource,
-        node: stmtPath.node,
-      });
-      return;
-    }
-    case 'TSNamespaceExportDeclaration': {
-      builder.errors.push({
-        reason:
-          'TypeScript `namespace` statements may only appear at the top level of a module',
-        severity: ErrorSeverity.InvalidJS,
-        category: ErrorCategory.Syntax,
-        loc: stmtPath.node.loc ?? null,
-        suggestions: null,
-      });
-      lowerValueToTemporary(builder, {
-        kind: 'UnsupportedNode',
-        loc: stmtPath.node.loc ?? GeneratedSource,
-        node: stmtPath.node,
-      });
+    case 'TypeAlias':
+    case 'TSInterfaceDeclaration':
+    case 'TSTypeAliasDeclaration': {
+      // We do not preserve type annotations/syntax through transformation
      return;
    }
+    case 'ClassDeclaration':
    case 'DeclareClass':
    case 'DeclareExportAllDeclaration':
    case 'DeclareExportDeclaration':
@@ -1483,14 +1373,31 @@ function lowerStatement(
    case 'DeclareOpaqueType':
    case 'DeclareTypeAlias':
    case 'DeclareVariable':
+    case 'EnumDeclaration':
+    case 'ExportAllDeclaration':
+    case 'ExportDefaultDeclaration':
+    case 'ExportNamedDeclaration':
+    case 'ImportDeclaration':
    case 'InterfaceDeclaration':
    case 'OpaqueType':
    case 'TSDeclareFunction':
-    case 'TSInterfaceDeclaration':
+    case 'TSEnumDeclaration':
+    case 'TSExportAssignment':
+    case 'TSImportEqualsDeclaration':
    case 'TSModuleDeclaration':
-    case 'TSTypeAliasDeclaration':
-    case 'TypeAlias': {
-      // We do not preserve type annotations/syntax through transformation
+    case 'TSNamespaceExportDeclaration':
+    case 'WithStatement': {
+      builder.errors.push({
+        reason: `(BuildHIR::lowerStatement) Handle ${stmtPath.type} statements`,
+        severity: ErrorSeverity.Todo,
+        loc: stmtPath.node.loc ?? null,
+        suggestions: null,
+      });
+      lowerValueToTemporary(builder, {
+        kind: 'UnsupportedNode',
+        loc: stmtPath.node.loc ?? GeneratedSource,
+        node: stmtPath.node,
+      });
      return;
    }
    default: {
@@ -1541,7 +1448,6 @@ function lowerObjectPropertyKey(
      builder.errors.push({
        reason: `(BuildHIR::lowerExpression) Expected Identifier, got ${key.type} key in ObjectExpression`,
        severity: ErrorSeverity.Todo,
-        category: ErrorCategory.Todo,
        loc: key.node.loc ?? null,
        suggestions: null,
      });
@@ -1567,7 +1473,6 @@ function lowerObjectPropertyKey(
  builder.errors.push({
    reason: `(BuildHIR::lowerExpression) Expected Identifier, got ${key.type} key in ObjectExpression`,
    severity: ErrorSeverity.Todo,
-    category: ErrorCategory.Todo,
    loc: key.node.loc ?? null,
    suggestions: null,
  });
@@ -1625,7 +1530,6 @@ function lowerExpression(
            builder.errors.push({
              reason: `(BuildHIR::lowerExpression) Handle ${valuePath.type} values in ObjectExpression`,
              severity: ErrorSeverity.Todo,
-              category: ErrorCategory.Todo,
              loc: valuePath.node.loc ?? null,
              suggestions: null,
            });
@@ -1652,7 +1556,6 @@ function lowerExpression(
            builder.errors.push({
              reason: `(BuildHIR::lowerExpression) Handle ${propertyPath.node.kind} functions in ObjectExpression`,
              severity: ErrorSeverity.Todo,
-              category: ErrorCategory.Todo,
              loc: propertyPath.node.loc ?? null,
              suggestions: null,
            });
@@ -1674,7 +1577,6 @@ function lowerExpression(
          builder.errors.push({
            reason: `(BuildHIR::lowerExpression) Handle ${propertyPath.type} properties in ObjectExpression`,
            severity: ErrorSeverity.Todo,
-            category: ErrorCategory.Todo,
            loc: propertyPath.node.loc ?? null,
            suggestions: null,
          });
@@ -1708,7 +1610,6 @@ function lowerExpression(
          builder.errors.push({
            reason: `(BuildHIR::lowerExpression) Handle ${element.type} elements in ArrayExpression`,
            severity: ErrorSeverity.Todo,
-            category: ErrorCategory.Todo,
            loc: element.node.loc ?? null,
            suggestions: null,
          });
@@ -1729,7 +1630,6 @@ function lowerExpression(
          reason: `Expected an expression as the \`new\` expression receiver (v8 intrinsics are not supported)`,
          description: `Got a \`${calleePath.node.type}\``,
          severity: ErrorSeverity.InvalidJS,
-          category: ErrorCategory.Syntax,
          loc: calleePath.node.loc ?? null,
          suggestions: null,
        });
@@ -1756,7 +1656,6 @@ function lowerExpression(
        builder.errors.push({
          reason: `Expected Expression, got ${calleePath.type} in CallExpression (v8 intrinsics not supported). This error is likely caused by a bug in React Compiler. Please file an issue`,
          severity: ErrorSeverity.Todo,
-          category: ErrorCategory.Todo,
          loc: calleePath.node.loc ?? null,
          suggestions: null,
        });
@@ -1791,7 +1690,6 @@ function lowerExpression(
        builder.errors.push({
          reason: `(BuildHIR::lowerExpression) Expected Expression, got ${leftPath.type} lval in BinaryExpression`,
          severity: ErrorSeverity.Todo,
-          category: ErrorCategory.Todo,
          loc: leftPath.node.loc ?? null,
          suggestions: null,
        });
@@ -1804,7 +1702,6 @@ function lowerExpression(
        builder.errors.push({
          reason: `(BuildHIR::lowerExpression) Pipe operator not supported`,
          severity: ErrorSeverity.Todo,
-          category: ErrorCategory.Todo,
          loc: leftPath.node.loc ?? null,
          suggestions: null,
        });
@@ -1834,7 +1731,6 @@ function lowerExpression(
          builder.errors.push({
            reason: `Expected sequence expression to have at least one expression`,
            severity: ErrorSeverity.InvalidJS,
-            category: ErrorCategory.Syntax,
            loc: expr.node.loc ?? null,
            suggestions: null,
          });
@@ -2047,7 +1943,6 @@ function lowerExpression(
            reason: `(BuildHIR::lowerExpression) Unsupported syntax on the left side of an AssignmentExpression`,
            description: `Expected an LVal, got: ${left.type}`,
            severity: ErrorSeverity.Todo,
-            category: ErrorCategory.Todo,
            loc: left.node.loc ?? null,
            suggestions: null,
          });
@@ -2076,7 +1971,6 @@ function lowerExpression(
        builder.errors.push({
          reason: `(BuildHIR::lowerExpression) Handle ${operator} operators in AssignmentExpression`,
          severity: ErrorSeverity.Todo,
-          category: ErrorCategory.Todo,
          loc: expr.node.loc ?? null,
          suggestions: null,
        });
@@ -2176,7 +2070,6 @@ function lowerExpression(
          builder.errors.push({
            reason: `(BuildHIR::lowerExpression) Expected Identifier or MemberExpression, got ${expr.type} lval in AssignmentExpression`,
            severity: ErrorSeverity.Todo,
-            category: ErrorCategory.Todo,
            loc: expr.node.loc ?? null,
            suggestions: null,
          });
@@ -2216,7 +2109,6 @@ function lowerExpression(
          builder.errors.push({
            reason: `(BuildHIR::lowerExpression) Handle ${attribute.type} attributes in JSXElement`,
            severity: ErrorSeverity.Todo,
-            category: ErrorCategory.Todo,
            loc: attribute.node.loc ?? null,
            suggestions: null,
          });
@@ -2230,7 +2122,6 @@ function lowerExpression(
            builder.errors.push({
              reason: `(BuildHIR::lowerExpression) Unexpected colon in attribute name \`${propName}\``,
              severity: ErrorSeverity.Todo,
-              category: ErrorCategory.Todo,
              loc: namePath.node.loc ?? null,
              suggestions: null,
            });
@@ -2261,7 +2152,6 @@ function lowerExpression(
            builder.errors.push({
              reason: `(BuildHIR::lowerExpression) Handle ${valueExpr.type} attribute values in JSXElement`,
              severity: ErrorSeverity.Todo,
-              category: ErrorCategory.Todo,
              loc: valueExpr.node?.loc ?? null,
              suggestions: null,
            });
@@ -2272,7 +2162,6 @@ function lowerExpression(
            builder.errors.push({
              reason: `(BuildHIR::lowerExpression) Handle ${expression.type} expressions in JSXExpressionContainer within JSXElement`,
              severity: ErrorSeverity.Todo,
-              category: ErrorCategory.Todo,
              loc: valueExpr.node.loc ?? null,
              suggestions: null,
            });
@@ -2328,18 +2217,11 @@ function lowerExpression(
        });
        for (const [name, locations] of Object.entries(fbtLocations)) {
          if (locations.length > 1) {
-            CompilerError.throwDiagnostic({
-              severity: ErrorSeverity.Todo,
-              category: ErrorCategory.FBT,
-              reason: 'Support duplicate fbt tags',
-              description: `Support \`<${tagName}>\` tags with multiple \`<${tagName}:${name}>\` values`,
-              details: locations.map(loc => {
-                return {
-                  kind: 'error',
-                  message: `Multiple \`<${tagName}:${name}>\` tags found`,
-                  loc,
-                };
-              }),
+            CompilerError.throwTodo({
+              reason: `Support <${tagName}> tags with multiple <${tagName}:${name}> values`,
+              loc: locations.at(-1) ?? GeneratedSource,
+              description: null,
+              suggestions: null,
            });
          }
        }
@@ -2392,7 +2274,6 @@ function lowerExpression(
          reason:
            '(BuildHIR::lowerExpression) Handle tagged template with interpolations',
          severity: ErrorSeverity.Todo,
-          category: ErrorCategory.Todo,
          loc: exprPath.node.loc ?? null,
          suggestions: null,
        });
@@ -2411,7 +2292,6 @@ function lowerExpression(
          reason:
            '(BuildHIR::lowerExpression) Handle tagged template where cooked value is different from raw value',
          severity: ErrorSeverity.Todo,
-          category: ErrorCategory.Todo,
          loc: exprPath.node.loc ?? null,
          suggestions: null,
        });
@@ -2434,7 +2314,6 @@ function lowerExpression(
        builder.errors.push({
          reason: `Unexpected quasi and subexpression lengths in template literal`,
          severity: ErrorSeverity.InvalidJS,
-          category: ErrorCategory.Syntax,
          loc: exprPath.node.loc ?? null,
          suggestions: null,
        });
@@ -2445,7 +2324,6 @@ function lowerExpression(
        builder.errors.push({
          reason: `(BuildHIR::lowerAssignment) Handle TSType in TemplateLiteral.`,
          severity: ErrorSeverity.Todo,
-          category: ErrorCategory.Todo,
          loc: exprPath.node.loc ?? null,
          suggestions: null,
        });
@@ -2488,7 +2366,6 @@ function lowerExpression(
          builder.errors.push({
            reason: `Only object properties can be deleted`,
            severity: ErrorSeverity.InvalidJS,
-            category: ErrorCategory.Syntax,
            loc: expr.node.loc ?? null,
            suggestions: [
              {
@@ -2504,7 +2381,6 @@ function lowerExpression(
        builder.errors.push({
          reason: `Throw expressions are not supported`,
          severity: ErrorSeverity.InvalidJS,
-          category: ErrorCategory.Syntax,
          loc: expr.node.loc ?? null,
          suggestions: [
            {
@@ -2626,7 +2502,6 @@ function lowerExpression(
        builder.errors.push({
          reason: `(BuildHIR::lowerExpression) Handle UpdateExpression with ${argument.type} argument`,
          severity: ErrorSeverity.Todo,
-          category: ErrorCategory.Todo,
          loc: exprPath.node.loc ?? null,
          suggestions: null,
        });
@@ -2635,7 +2510,6 @@ function lowerExpression(
        builder.errors.push({
          reason: `(BuildHIR::lowerExpression) Handle UpdateExpression to variables captured within lambdas.`,
          severity: ErrorSeverity.Todo,
-          category: ErrorCategory.Todo,
          loc: exprPath.node.loc ?? null,
          suggestions: null,
        });
@@ -2656,7 +2530,6 @@ function lowerExpression(
          builder.errors.push({
            reason: `(BuildHIR::lowerExpression) Found an invalid UpdateExpression without a previously reported error`,
            severity: ErrorSeverity.Invariant,
-            category: ErrorCategory.Invariant,
            loc: exprLoc,
            suggestions: null,
          });
@@ -2666,7 +2539,6 @@ function lowerExpression(
        builder.errors.push({
          reason: `(BuildHIR::lowerExpression) Support UpdateExpression where argument is a global`,
          severity: ErrorSeverity.Todo,
-          category: ErrorCategory.Todo,
          loc: exprLoc,
          suggestions: null,
        });
@@ -2722,7 +2594,6 @@ function lowerExpression(
      builder.errors.push({
        reason: `(BuildHIR::lowerExpression) Handle MetaProperty expressions other than import.meta`,
        severity: ErrorSeverity.Todo,
-        category: ErrorCategory.Todo,
        loc: exprPath.node.loc ?? null,
        suggestions: null,
      });
@@ -2732,7 +2603,6 @@ function lowerExpression(
      builder.errors.push({
        reason: `(BuildHIR::lowerExpression) Handle ${exprPath.type} expressions`,
        severity: ErrorSeverity.Todo,
-        category: ErrorCategory.Todo,
        loc: exprPath.node.loc ?? null,
        suggestions: null,
      });
@@ -3030,7 +2900,6 @@ function lowerReorderableExpression(
    builder.errors.push({
      reason: `(BuildHIR::node.lowerReorderableExpression) Expression type \`${expr.type}\` cannot be safely reordered`,
      severity: ErrorSeverity.Todo,
-      category: ErrorCategory.Todo,
      loc: expr.node.loc ?? null,
      suggestions: null,
    });
@@ -3078,8 +2947,6 @@ function isReorderableExpression(
        }
      }
    }
-    case 'TSAsExpression':
-    case 'TSNonNullExpression':
    case 'TypeCastExpression': {
      return isReorderableExpression(
        builder,
@@ -3227,7 +3094,6 @@ function lowerArguments(
      builder.errors.push({
        reason: `(BuildHIR::lowerExpression) Handle ${argPath.type} arguments in CallExpression`,
        severity: ErrorSeverity.Todo,
-        category: ErrorCategory.Todo,
        loc: argPath.node.loc ?? null,
        suggestions: null,
      });
@@ -3263,7 +3129,6 @@ function lowerMemberExpression(
      builder.errors.push({
        reason: `(BuildHIR::lowerMemberExpression) Handle ${propertyNode.type} property`,
        severity: ErrorSeverity.Todo,
-        category: ErrorCategory.Todo,
        loc: propertyNode.node.loc ?? null,
        suggestions: null,
      });
@@ -3285,7 +3150,6 @@ function lowerMemberExpression(
      builder.errors.push({
        reason: `(BuildHIR::lowerMemberExpression) Expected Expression, got ${propertyNode.type} property`,
        severity: ErrorSeverity.Todo,
-        category: ErrorCategory.Todo,
        loc: propertyNode.node.loc ?? null,
        suggestions: null,
      });
@@ -3345,7 +3209,6 @@ function lowerJsxElementName(
        reason: `Expected JSXNamespacedName to have no colons in the namespace or name`,
        description: `Got \`${namespace}\` : \`${name}\``,
        severity: ErrorSeverity.InvalidJS,
-        category: ErrorCategory.Syntax,
        loc: exprPath.node.loc ?? null,
        suggestions: null,
      });
@@ -3360,7 +3223,6 @@ function lowerJsxElementName(
    builder.errors.push({
      reason: `(BuildHIR::lowerJsxElementName) Handle ${exprPath.type} tags`,
      severity: ErrorSeverity.Todo,
-      category: ErrorCategory.Todo,
      loc: exprPath.node.loc ?? null,
      suggestions: null,
    });
@@ -3459,7 +3321,6 @@ function lowerJsxElement(
    builder.errors.push({
      reason: `(BuildHIR::lowerJsxElement) Unhandled JsxElement, got: ${exprPath.type}`,
      severity: ErrorSeverity.Todo,
-      category: ErrorCategory.Todo,
      loc: exprPath.node.loc ?? null,
      suggestions: null,
    });
@@ -3578,16 +3439,15 @@ function lowerFunction(
   * This isn't a problem in practice because use Babel's scope analysis to
   * identify the correct references.
   */
-  const lowering = lower(
-    expr,
-    builder.environment,
-    builder.bindings,
-    new Map([...builder.context, ...capturedContext]),
-  );
+  const lowering = lower(expr, builder.environment, builder.bindings, [
+    ...builder.context,
+    ...capturedContext,
+  ]);
  let loweredFunc: HIRFunction;
  if (lowering.isErr()) {
-    const functionErrors = lowering.unwrapErr();
-    builder.errors.merge(functionErrors);
+    lowering
+      .unwrapErr()
+      .details.forEach(detail => builder.errors.pushErrorDetail(detail));
    return null;
  }
  loweredFunc = lowering.unwrap();
@@ -3641,17 +3501,6 @@ function lowerIdentifier(
      return place;
    }
    default: {
-      if (binding.kind === 'Global' && binding.name === 'eval') {
-        builder.errors.push({
-          reason: `The 'eval' function is not supported`,
-          description:
-            'Eval is an anti-pattern in JavaScript, and the code executed cannot be evaluated by React Compiler',
-          severity: ErrorSeverity.UnsupportedJS,
-          category: ErrorCategory.UnsupportedSyntax,
-          loc: exprPath.node.loc ?? null,
-          suggestions: null,
-        });
-      }
      return lowerValueToTemporary(builder, {
        kind: 'LoadGlobal',
        binding,
@@ -3704,7 +3553,6 @@ function lowerIdentifierForAssignment(
      builder.errors.push({
        reason: `(BuildHIR::lowerAssignment) Could not find binding for declaration.`,
        severity: ErrorSeverity.Invariant,
-        category: ErrorCategory.Invariant,
        loc: path.node.loc ?? null,
        suggestions: null,
      });
@@ -3717,7 +3565,6 @@ function lowerIdentifierForAssignment(
    builder.errors.push({
      reason: `Cannot reassign a \`const\` variable`,
      severity: ErrorSeverity.InvalidJS,
-      category: ErrorCategory.Syntax,
      loc: path.node.loc ?? null,
      description:
        binding.identifier.name != null
@@ -3775,7 +3622,6 @@ function lowerAssignment(
          builder.errors.push({
            reason: `Expected \`const\` declaration not to be reassigned`,
            severity: ErrorSeverity.InvalidJS,
-            category: ErrorCategory.Syntax,
            loc: lvalue.node.loc ?? null,
            suggestions: null,
          });
@@ -3790,7 +3636,6 @@ function lowerAssignment(
          builder.errors.push({
            reason: `Unexpected context variable kind`,
            severity: ErrorSeverity.InvalidJS,
-            category: ErrorCategory.Syntax,
            loc: lvalue.node.loc ?? null,
            suggestions: null,
          });
@@ -3862,7 +3707,6 @@ function lowerAssignment(
          builder.errors.push({
            reason: `(BuildHIR::lowerAssignment) Handle ${property.type} properties in MemberExpression`,
            severity: ErrorSeverity.Todo,
-            category: ErrorCategory.Todo,
            loc: property.node.loc ?? null,
            suggestions: null,
          });
@@ -3875,7 +3719,6 @@ function lowerAssignment(
            reason:
              '(BuildHIR::lowerAssignment) Expected private name to appear as a non-computed property',
            severity: ErrorSeverity.Todo,
-            category: ErrorCategory.Todo,
            loc: property.node.loc ?? null,
            suggestions: null,
          });
@@ -3941,7 +3784,6 @@ function lowerAssignment(
            } else if (identifier.kind === 'Global') {
              builder.errors.push({
                severity: ErrorSeverity.Todo,
-                category: ErrorCategory.Todo,
                reason:
                  'Expected reassignment of globals to enable forceTemporaries',
                loc: element.node.loc ?? GeneratedSource,
@@ -3981,7 +3823,6 @@ function lowerAssignment(
          } else if (identifier.kind === 'Global') {
            builder.errors.push({
              severity: ErrorSeverity.Todo,
-              category: ErrorCategory.Todo,
              reason:
                'Expected reassignment of globals to enable forceTemporaries',
              loc: element.node.loc ?? GeneratedSource,
@@ -4055,7 +3896,6 @@ function lowerAssignment(
            builder.errors.push({
              reason: `(BuildHIR::lowerAssignment) Handle ${argument.node.type} rest element in ObjectPattern`,
              severity: ErrorSeverity.Todo,
-              category: ErrorCategory.Todo,
              loc: argument.node.loc ?? null,
              suggestions: null,
            });
@@ -4087,7 +3927,6 @@ function lowerAssignment(
            } else if (identifier.kind === 'Global') {
              builder.errors.push({
                severity: ErrorSeverity.Todo,
-                category: ErrorCategory.Todo,
                reason:
                  'Expected reassignment of globals to enable forceTemporaries',
                loc: property.node.loc ?? GeneratedSource,
@@ -4105,7 +3944,6 @@ function lowerAssignment(
            builder.errors.push({
              reason: `(BuildHIR::lowerAssignment) Handle ${property.type} properties in ObjectPattern`,
              severity: ErrorSeverity.Todo,
-              category: ErrorCategory.Todo,
              loc: property.node.loc ?? null,
              suggestions: null,
            });
@@ -4115,7 +3953,6 @@ function lowerAssignment(
            builder.errors.push({
              reason: `(BuildHIR::lowerAssignment) Handle computed properties in ObjectPattern`,
              severity: ErrorSeverity.Todo,
-              category: ErrorCategory.Todo,
              loc: property.node.loc ?? null,
              suggestions: null,
            });
@@ -4130,7 +3967,6 @@ function lowerAssignment(
            builder.errors.push({
              reason: `(BuildHIR::lowerAssignment) Expected object property value to be an LVal, got: ${element.type}`,
              severity: ErrorSeverity.Todo,
-              category: ErrorCategory.Todo,
              loc: element.node.loc ?? null,
              suggestions: null,
            });
@@ -4153,7 +3989,6 @@ function lowerAssignment(
            } else if (identifier.kind === 'Global') {
              builder.errors.push({
                severity: ErrorSeverity.Todo,
-                category: ErrorCategory.Todo,
                reason:
                  'Expected reassignment of globals to enable forceTemporaries',
                loc: element.node.loc ?? GeneratedSource,
@@ -4303,7 +4138,6 @@ function lowerAssignment(
      builder.errors.push({
        reason: `(BuildHIR::lowerAssignment) Handle ${lvaluePath.type} assignments`,
        severity: ErrorSeverity.Todo,
-        category: ErrorCategory.Todo,
        loc: lvaluePath.node.loc ?? null,
        suggestions: null,
      });
@@ -4326,11 +4160,6 @@ function captureScopes({from, to}: {from: Scope; to: Scope}): Set<Scope> {
  return scopes;
 }

-/**
- * Returns a mapping of "context" identifiers — references to free variables that
- * will become part of the function expression's `context` array — along with the
- * source location of their first reference within the function.
- */
 function gatherCapturedContext(
  fn: NodePath<
    | t.FunctionExpression
@@ -4339,8 +4168,8 @@ function gatherCapturedContext(
    | t.ObjectMethod
  >,
  componentScope: Scope,
-): Map<t.Identifier, SourceLocation> {
-  const capturedIds = new Map<t.Identifier, SourceLocation>();
+): Array<t.Identifier> {
+  const capturedIds = new Set<t.Identifier>();

  /*
   * Capture all the scopes from the parent of this function up to and including
@@ -4383,15 +4212,8 @@ function gatherCapturedContext(

    // Add the base identifier binding as a dependency.
    const binding = baseIdentifier.scope.getBinding(baseIdentifier.node.name);
-    if (
-      binding !== undefined &&
-      pureScopes.has(binding.scope) &&
-      !capturedIds.has(binding.identifier)
-    ) {
-      capturedIds.set(
-        binding.identifier,
-        path.node.loc ?? binding.identifier.loc ?? GeneratedSource,
-      );
+    if (binding !== undefined && pureScopes.has(binding.scope)) {
+      capturedIds.add(binding.identifier);
    }
  }

@@ -4428,7 +4250,7 @@ function gatherCapturedContext(
    },
  });

-  return capturedIds;
+  return [...capturedIds.keys()];
 }

 function notNull<T>(value: T | null): value is T {
--- a/compiler/packages/babel-plugin-react-compiler/src/HIR/Environment.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/HIR/Environment.ts
@@ -49,7 +49,6 @@ import {
 } from './ObjectShape';
 import {Scope as BabelScope, NodePath} from '@babel/traverse';
 import {TypeSchema} from './TypeSchema';
-import {FlowTypeEnv} from '../Flood/Types';

 export const ReactElementSymbolSchema = z.object({
  elementSymbol: z.union([
@@ -245,10 +244,9 @@ export const EnvironmentConfigSchema = z.object({
  enableUseTypeAnnotations: z.boolean().default(false),

  /**
-   * Allows specifying a function that can populate HIR with type information from
-   * Flow
+   * Enable a new model for mutability and aliasing inference
   */
-  flowTypeProvider: z.nullable(z.function().args(z.string())).default(null),
+  enableNewMutationAliasingModel: z.boolean().default(false),

  /**
   * Enables inference of optional dependency chains. Without this flag
@@ -267,19 +265,21 @@ export const EnvironmentConfigSchema = z.object({
   *   {
   *     module: 'react',
   *     imported: 'useEffect',
-   *     autodepsIndex: 1,
+   *     numRequiredArgs: 1,
   *   },{
   *     module: 'MyExperimentalEffectHooks',
   *     imported: 'useExperimentalEffect',
-   *     autodepsIndex: 2,
+   *     numRequiredArgs: 2,
   *   },
   * ]
   * would insert dependencies for calls of `useEffect` imported from `react` and calls of
   * useExperimentalEffect` from `MyExperimentalEffectHooks`.
   *
-   * `autodepsIndex` tells the compiler which index we expect the AUTODEPS to appear in.
-   *  With the configuration above, we'd insert dependencies for `useEffect` if it has two
-   *  arguments, and the second is AUTODEPS.
+   * `numRequiredArgs` tells the compiler the amount of arguments required to append a dependency
+   *  array to the end of the call. With the configuration above, we'd insert dependencies for
+   *  `useEffect` if it is only given a single argument and it would be appended to the argument list.
+   *
+   * numRequiredArgs must always be greater than 0, otherwise there is no function to analyze for dependencies
   *
   * Still experimental.
   */
@@ -288,7 +288,7 @@ export const EnvironmentConfigSchema = z.object({
      z.array(
        z.object({
          function: ExternalFunctionSchema,
-          autodepsIndex: z.number().min(1, 'autodepsIndex must be > 0'),
+          numRequiredArgs: z.number().min(1, 'numRequiredArgs must be > 0'),
        }),
      ),
    )
@@ -320,16 +320,10 @@ export const EnvironmentConfigSchema = z.object({
  validateNoSetStateInRender: z.boolean().default(true),

  /**
-   * Validates that setState is not called synchronously within an effect (useEffect and friends).
+   * Validates that setState is not called directly within a passive effect (useEffect).
   * Scheduling a setState (with an event listener, subscription, etc) is valid.
   */
-  validateNoSetStateInEffects: z.boolean().default(false),
-
-  /**
-   * Validates that effects are not used to calculate derived data which could instead be computed
-   * during render.
-   */
-  validateNoDerivedComputationsInEffects: z.boolean().default(false),
+  validateNoSetStateInPassiveEffects: z.boolean().default(false),

  /**
   * Validates against creating JSX within a try block and recommends using an error boundary
@@ -616,7 +610,7 @@ export const EnvironmentConfigSchema = z.object({
   *
   * Here the variables `ref` and `myRef` will be typed as Refs.
   */
-  enableTreatRefLikeIdentifiersAsRefs: z.boolean().default(true),
+  enableTreatRefLikeIdentifiersAsRefs: z.boolean().default(false),

  /*
   * If specified a value, the compiler lowers any calls to `useContext` to use
@@ -639,24 +633,6 @@ export const EnvironmentConfigSchema = z.object({
   * ```
   */
  lowerContextAccess: ExternalFunctionSchema.nullable().default(null),
-
-  /**
-   * If enabled, will validate useMemos that don't return any values:
-   *
-   * Valid:
-   *   useMemo(() => foo, [foo]);
-   *   useMemo(() => { return foo }, [foo]);
-   * Invalid:
-   *   useMemo(() => { ... }, [...]);
-   */
-  validateNoVoidUseMemo: z.boolean().default(false),
-
-  /**
-   * Validates that Components/Hooks are always defined at module level. This prevents scope
-   * reference errors that occur when the compiler attempts to optimize the nested component/hook
-   * while its parent function remains uncompiled.
-   */
-  validateNoDynamicallyCreatedComponentsOrHooks: z.boolean().default(false),
 });

 export type EnvironmentConfig = z.infer<typeof EnvironmentConfigSchema>;
@@ -706,8 +682,6 @@ export class Environment {
  #hoistedIdentifiers: Set<t.Identifier>;
  parentFunction: NodePath<t.Function>;

-  #flowTypeEnvironment: FlowTypeEnv | null;
-
  constructor(
    scope: BabelScope,
    fnType: ReactFunctionType,
@@ -776,26 +750,6 @@ export class Environment {
    this.parentFunction = parentFunction;
    this.#contextIdentifiers = contextIdentifiers;
    this.#hoistedIdentifiers = new Set();
-
-    if (config.flowTypeProvider != null) {
-      this.#flowTypeEnvironment = new FlowTypeEnv();
-      CompilerError.invariant(code != null, {
-        reason:
-          'Expected Environment to be initialized with source code when a Flow type provider is specified',
-        loc: null,
-      });
-      this.#flowTypeEnvironment.init(this, code);
-    } else {
-      this.#flowTypeEnvironment = null;
-    }
-  }
-
-  get typeContext(): FlowTypeEnv {
-    CompilerError.invariant(this.#flowTypeEnvironment != null, {
-      reason: 'Flow type environment not initialized',
-      loc: null,
-    });
-    return this.#flowTypeEnvironment;
  }

  get isInferredMemoEnabled(): boolean {
--- a/compiler/packages/babel-plugin-react-compiler/src/HIR/Globals.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/HIR/Globals.ts
@@ -5,11 +5,10 @@
 * LICENSE file in the root directory of this source tree.
 */

-import {Effect, ValueKind, ValueReason} from './HIR';
+import {Effect, makeIdentifierId, ValueKind, ValueReason} from './HIR';
 import {
  BUILTIN_SHAPES,
  BuiltInArrayId,
-  BuiltInAutodepsId,
  BuiltInFireFunctionId,
  BuiltInFireId,
  BuiltInMapId,
@@ -35,6 +34,7 @@ import {
  addFunction,
  addHook,
  addObject,
+  signatureArgument,
 } from './ObjectShape';
 import {BuiltInType, ObjectType, PolyType} from './Types';
 import {TypeConfig} from './TypeSchema';
@@ -114,99 +114,6 @@ const TYPED_GLOBALS: Array<[string, BuiltInType]> = [
          returnValueKind: ValueKind.Mutable,
        }),
      ],
-      [
-        'entries',
-        addFunction(DEFAULT_SHAPES, [], {
-          positionalParams: [Effect.Capture],
-          restParam: null,
-          returnType: {kind: 'Object', shapeId: BuiltInArrayId},
-          calleeEffect: Effect.Read,
-          returnValueKind: ValueKind.Mutable,
-          aliasing: {
-            receiver: '@receiver',
-            params: ['@object'],
-            rest: null,
-            returns: '@returns',
-            temporaries: [],
-            effects: [
-              {
-                kind: 'Create',
-                into: '@returns',
-                reason: ValueReason.KnownReturnSignature,
-                value: ValueKind.Mutable,
-              },
-              // Object values are captured into the return
-              {
-                kind: 'Capture',
-                from: '@object',
-                into: '@returns',
-              },
-            ],
-          },
-        }),
-      ],
-      [
-        'keys',
-        addFunction(DEFAULT_SHAPES, [], {
-          positionalParams: [Effect.Read],
-          restParam: null,
-          returnType: {kind: 'Object', shapeId: BuiltInArrayId},
-          calleeEffect: Effect.Read,
-          returnValueKind: ValueKind.Mutable,
-          aliasing: {
-            receiver: '@receiver',
-            params: ['@object'],
-            rest: null,
-            returns: '@returns',
-            temporaries: [],
-            effects: [
-              {
-                kind: 'Create',
-                into: '@returns',
-                reason: ValueReason.KnownReturnSignature,
-                value: ValueKind.Mutable,
-              },
-              // Only keys are captured, and keys are immutable
-              {
-                kind: 'ImmutableCapture',
-                from: '@object',
-                into: '@returns',
-              },
-            ],
-          },
-        }),
-      ],
-      [
-        'values',
-        addFunction(DEFAULT_SHAPES, [], {
-          positionalParams: [Effect.Capture],
-          restParam: null,
-          returnType: {kind: 'Object', shapeId: BuiltInArrayId},
-          calleeEffect: Effect.Read,
-          returnValueKind: ValueKind.Mutable,
-          aliasing: {
-            receiver: '@receiver',
-            params: ['@object'],
-            rest: null,
-            returns: '@returns',
-            temporaries: [],
-            effects: [
-              {
-                kind: 'Create',
-                into: '@returns',
-                reason: ValueReason.KnownReturnSignature,
-                value: ValueKind.Mutable,
-              },
-              // Object values are captured into the return
-              {
-                kind: 'Capture',
-                from: '@object',
-                into: '@returns',
-              },
-            ],
-          },
-        }),
-      ],
    ]),
  ],
  [
@@ -739,35 +646,35 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
        hookKind: 'useEffect',
        returnValueKind: ValueKind.Frozen,
        aliasing: {
-          receiver: '@receiver',
+          receiver: makeIdentifierId(0),
          params: [],
-          rest: '@rest',
-          returns: '@returns',
-          temporaries: ['@effect'],
+          rest: makeIdentifierId(1),
+          returns: makeIdentifierId(2),
+          temporaries: [signatureArgument(3)],
          effects: [
            // Freezes the function and deps
            {
              kind: 'Freeze',
-              value: '@rest',
+              value: signatureArgument(1),
              reason: ValueReason.Effect,
            },
            // Internally creates an effect object that captures the function and deps
            {
              kind: 'Create',
-              into: '@effect',
+              into: signatureArgument(3),
              value: ValueKind.Frozen,
              reason: ValueReason.KnownReturnSignature,
            },
            // The effect stores the function and dependencies
            {
              kind: 'Capture',
-              from: '@rest',
-              into: '@effect',
+              from: signatureArgument(1),
+              into: signatureArgument(3),
            },
            // Returns undefined
            {
              kind: 'Create',
-              into: '@returns',
+              into: signatureArgument(2),
              value: ValueKind.Primitive,
              reason: ValueReason.KnownReturnSignature,
            },
@@ -874,7 +781,6 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
      BuiltInUseEffectEventId,
    ),
  ],
-  ['AUTODEPS', addObject(DEFAULT_SHAPES, BuiltInAutodepsId, [])],
 ];

 TYPED_GLOBALS.push(
@@ -1000,7 +906,6 @@ export function installTypeConfig(
        noAlias: typeConfig.noAlias === true,
        mutableOnlyIfOperandsAreMutable:
          typeConfig.mutableOnlyIfOperandsAreMutable === true,
-        aliasing: typeConfig.aliasing,
      });
    }
    case 'hook': {
@@ -1018,7 +923,6 @@ export function installTypeConfig(
        ),
        returnValueKind: typeConfig.returnValueKind ?? ValueKind.Frozen,
        noAlias: typeConfig.noAlias === true,
-        aliasing: typeConfig.aliasing,
      });
    }
    case 'object': {
--- a/compiler/packages/babel-plugin-react-compiler/src/HIR/HIR.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/HIR/HIR.ts
@@ -7,14 +7,13 @@

 import {BindingKind} from '@babel/traverse';
 import * as t from '@babel/types';
-import {CompilerError} from '../CompilerError';
+import {CompilerError, CompilerErrorDetailOptions} from '../CompilerError';
 import {assertExhaustive} from '../Utils/utils';
 import {Environment, ReactFunctionType} from './Environment';
 import type {HookKind} from './ObjectShape';
 import {Type, makeType} from './Types';
 import {z} from 'zod';
 import type {AliasingEffect} from '../Inference/AliasingEffects';
-import {isReservedWord} from '../Utils/Keyword';

 /*
 * *******************************************************************************************
@@ -280,15 +279,33 @@ export type HIRFunction = {
  env: Environment;
  params: Array<Place | SpreadPattern>;
  returnTypeAnnotation: t.FlowType | t.TSType | null;
+  returnType: Type;
  returns: Place;
  context: Array<Place>;
+  effects: Array<FunctionEffect> | null;
  body: HIR;
  generator: boolean;
  async: boolean;
  directives: Array<string>;
-  aliasingEffects: Array<AliasingEffect> | null;
+  aliasingEffects?: Array<AliasingEffect> | null;
 };

+export type FunctionEffect =
+  | {
+      kind: 'GlobalMutation';
+      error: CompilerErrorDetailOptions;
+    }
+  | {
+      kind: 'ReactMutation';
+      error: CompilerErrorDetailOptions;
+    }
+  | {
+      kind: 'ContextMutation';
+      places: ReadonlySet<Place>;
+      effect: Effect;
+      loc: SourceLocation;
+    };
+
 /*
 * Each reactive scope may have its own control-flow, so the instructions form
 * a control-flow graph. The graph comprises a set of basic blocks which reference
@@ -430,20 +447,8 @@ export type ThrowTerminal = {
 };
 export type Case = {test: Place | null; block: BlockId};

-export type ReturnVariant = 'Void' | 'Implicit' | 'Explicit';
 export type ReturnTerminal = {
  kind: 'return';
-  /**
-   * Void:
-   *   () => { ... }
-   *   function() { ... }
-   * Implicit (ArrowFunctionExpression only):
-   *   () => foo
-   * Explicit:
-   *   () => { return ... }
-   *   function () { return ... }
-   */
-  returnVariant: ReturnVariant;
  loc: SourceLocation;
  value: Place;
  id: InstructionId;
@@ -1304,21 +1309,12 @@ export function forkTemporaryIdentifier(
 * original source code.
 */
 export function makeIdentifierName(name: string): ValidatedIdentifier {
-  if (isReservedWord(name)) {
-    CompilerError.throwInvalidJS({
-      reason: 'Expected a non-reserved identifier name',
-      loc: GeneratedSource,
-      description: `\`${name}\` is a reserved word in JavaScript and cannot be used as an identifier name`,
-      suggestions: null,
-    });
-  } else {
-    CompilerError.invariant(t.isValidIdentifier(name), {
-      reason: `Expected a valid identifier name`,
-      loc: GeneratedSource,
-      description: `\`${name}\` is not a valid JavaScript identifier`,
-      suggestions: null,
-    });
-  }
+  CompilerError.invariant(t.isValidIdentifier(name), {
+    reason: `Expected a valid identifier name`,
+    loc: GeneratedSource,
+    description: `\`${name}\` is not a valid JavaScript identifier`,
+    suggestions: null,
+  });
  return {
    kind: 'named',
    value: name as ValidIdentifierName,
@@ -1392,16 +1388,6 @@ export enum ValueReason {
   */
  JsxCaptured = 'jsx-captured',

-  /**
-   * Argument to a hook
-   */
-  HookCaptured = 'hook-captured',
-
-  /**
-   * Return value of a hook
-   */
-  HookReturn = 'hook-return',
-
  /**
   * Passed to an effect
   */
@@ -1457,20 +1443,6 @@ export const ValueKindSchema = z.enum([
  ValueKind.Context,
 ]);

-export const ValueReasonSchema = z.enum([
-  ValueReason.Context,
-  ValueReason.Effect,
-  ValueReason.Global,
-  ValueReason.HookCaptured,
-  ValueReason.HookReturn,
-  ValueReason.JsxCaptured,
-  ValueReason.KnownReturnSignature,
-  ValueReason.Other,
-  ValueReason.ReactiveFunctionArgument,
-  ValueReason.ReducerState,
-  ValueReason.State,
-]);
-
 // The effect with which a value is modified.
 export enum Effect {
  // Default value: not allowed after lifetime inference
@@ -1774,10 +1746,6 @@ export function isUseStateType(id: Identifier): boolean {
  return id.type.kind === 'Object' && id.type.shapeId === 'BuiltInUseState';
 }

-export function isJsxType(type: Type): boolean {
-  return type.kind === 'Object' && type.shapeId === 'BuiltInJsx';
-}
-
 export function isRefOrRefValue(id: Identifier): boolean {
  return isUseRefType(id) || isRefValueType(id);
 }
--- a/compiler/packages/babel-plugin-react-compiler/src/HIR/HIRBuilder.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/HIR/HIRBuilder.ts
@@ -7,7 +7,7 @@

 import {Binding, NodePath} from '@babel/traverse';
 import * as t from '@babel/types';
-import {CompilerError, ErrorCategory, ErrorSeverity} from '../CompilerError';
+import {CompilerError} from '../CompilerError';
 import {Environment} from './Environment';
 import {
  BasicBlock,
@@ -106,7 +106,7 @@ export default class HIRBuilder {
  #current: WipBlock;
  #entry: BlockId;
  #scopes: Array<Scope> = [];
-  #context: Map<t.Identifier, SourceLocation>;
+  #context: Array<t.Identifier>;
  #bindings: Bindings;
  #env: Environment;
  #exceptionHandlerStack: Array<BlockId> = [];
@@ -121,7 +121,7 @@ export default class HIRBuilder {
    return this.#env.nextIdentifierId;
  }

-  get context(): Map<t.Identifier, SourceLocation> {
+  get context(): Array<t.Identifier> {
    return this.#context;
  }

@@ -137,13 +137,13 @@ export default class HIRBuilder {
    env: Environment,
    options?: {
      bindings?: Bindings | null;
-      context?: Map<t.Identifier, SourceLocation>;
+      context?: Array<t.Identifier>;
      entryBlockKind?: BlockKind;
    },
  ) {
    this.#env = env;
    this.#bindings = options?.bindings ?? new Map();
-    this.#context = options?.context ?? new Map();
+    this.#context = options?.context ?? [];
    this.#entry = makeBlockId(env.nextBlockId);
    this.#current = newBlock(this.#entry, options?.entryBlockKind ?? 'block');
  }
@@ -308,35 +308,9 @@ export default class HIRBuilder {

  resolveBinding(node: t.Identifier): Identifier {
    if (node.name === 'fbt') {
-      CompilerError.throwDiagnostic({
-        severity: ErrorSeverity.Todo,
-        category: ErrorCategory.FBT,
-        reason: 'Support local variables named `fbt`',
-        description:
-          'Local variables named `fbt` may conflict with the fbt plugin and are not yet supported',
-        details: [
-          {
-            kind: 'error',
-            message: 'Rename to avoid conflict with fbt plugin',
-            loc: node.loc ?? GeneratedSource,
-          },
-        ],
-      });
-    }
-    if (node.name === 'this') {
-      CompilerError.throwDiagnostic({
-        severity: ErrorSeverity.UnsupportedJS,
-        category: ErrorCategory.UnsupportedSyntax,
-        reason: '`this` is not supported syntax',
-        description:
-          'React Compiler does not support compiling functions that use `this`',
-        details: [
-          {
-            kind: 'error',
-            message: '`this` was used here',
-            loc: node.loc ?? GeneratedSource,
-          },
-        ],
+      CompilerError.throwTodo({
+        reason: 'Support local variables named "fbt"',
+        loc: node.loc ?? null,
      });
    }
    const originalName = node.name;
--- a/compiler/packages/babel-plugin-react-compiler/src/HIR/MergeConsecutiveBlocks.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/HIR/MergeConsecutiveBlocks.ts
@@ -107,17 +107,6 @@ export function mergeConsecutiveBlocks(fn: HIRFunction): void {
    merged.merge(block.id, predecessorId);
    fn.body.blocks.delete(block.id);
  }
-  for (const [, block] of fn.body.blocks) {
-    for (const phi of block.phis) {
-      for (const [predecessorId, operand] of phi.operands) {
-        const mapped = merged.get(predecessorId);
-        if (mapped !== predecessorId) {
-          phi.operands.delete(predecessorId);
-          phi.operands.set(mapped, operand);
-        }
-      }
-    }
-  }
  markPredecessors(fn.body);
  for (const [, {terminal}] of fn.body.blocks) {
    if (terminalHasFallthrough(terminal)) {
--- a/compiler/packages/babel-plugin-react-compiler/src/HIR/ObjectShape.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/HIR/ObjectShape.ts
@@ -6,18 +6,14 @@
 */

 import {CompilerError} from '../CompilerError';
-import {AliasingEffect, AliasingSignature} from '../Inference/AliasingEffects';
-import {assertExhaustive} from '../Utils/utils';
+import {AliasingSignature} from '../Inference/AliasingEffects';
 import {
  Effect,
  GeneratedSource,
-  Hole,
  makeDeclarationId,
  makeIdentifierId,
  makeInstructionId,
  Place,
-  SourceLocation,
-  SpreadPattern,
  ValueKind,
  ValueReason,
 } from './HIR';
@@ -29,7 +25,6 @@ import {
  PolyType,
  PrimitiveType,
 } from './Types';
-import {AliasingEffectConfig, AliasingSignatureConfig} from './TypeSchema';

 /*
 * This file exports types and defaults for JavaScript object shapes. These are
@@ -58,20 +53,13 @@ function createAnonId(): string {
 export function addFunction(
  registry: ShapeRegistry,
  properties: Iterable<[string, BuiltInType | PolyType]>,
-  fn: Omit<FunctionSignature, 'hookKind' | 'aliasing'> & {
-    aliasing?: AliasingSignatureConfig | null | undefined;
-  },
+  fn: Omit<FunctionSignature, 'hookKind'>,
  id: string | null = null,
  isConstructor: boolean = false,
 ): FunctionType {
  const shapeId = id ?? createAnonId();
-  const aliasing =
-    fn.aliasing != null
-      ? parseAliasingSignatureConfig(fn.aliasing, '<builtin>', GeneratedSource)
-      : null;
  addShape(registry, shapeId, properties, {
    ...fn,
-    aliasing,
    hookKind: null,
  });
  return {
@@ -89,18 +77,11 @@ export function addFunction(
 */
 export function addHook(
  registry: ShapeRegistry,
-  fn: Omit<FunctionSignature, 'aliasing'> & {
-    hookKind: HookKind;
-    aliasing?: AliasingSignatureConfig | null | undefined;
-  },
+  fn: FunctionSignature & {hookKind: HookKind},
  id: string | null = null,
 ): FunctionType {
  const shapeId = id ?? createAnonId();
-  const aliasing =
-    fn.aliasing != null
-      ? parseAliasingSignatureConfig(fn.aliasing, '<builtin>', GeneratedSource)
-      : null;
-  addShape(registry, shapeId, [], {...fn, aliasing});
+  addShape(registry, shapeId, [], fn);
  return {
    kind: 'Function',
    return: fn.returnType,
@@ -109,130 +90,6 @@ export function addHook(
  };
 }

-function parseAliasingSignatureConfig(
-  typeConfig: AliasingSignatureConfig,
-  moduleName: string,
-  loc: SourceLocation,
-): AliasingSignature {
-  const lifetimes = new Map<string, Place>();
-  function define(temp: string): Place {
-    CompilerError.invariant(!lifetimes.has(temp), {
-      reason: `Invalid type configuration for module`,
-      description: `Expected aliasing signature to have unique names for receiver, params, rest, returns, and temporaries in module '${moduleName}'`,
-      loc,
-    });
-    const place = signatureArgument(lifetimes.size);
-    lifetimes.set(temp, place);
-    return place;
-  }
-  function lookup(temp: string): Place {
-    const place = lifetimes.get(temp);
-    CompilerError.invariant(place != null, {
-      reason: `Invalid type configuration for module`,
-      description: `Expected aliasing signature effects to reference known names from receiver/params/rest/returns/temporaries, but '${temp}' is not a known name in '${moduleName}'`,
-      loc,
-    });
-    return place;
-  }
-  const receiver = define(typeConfig.receiver);
-  const params = typeConfig.params.map(define);
-  const rest = typeConfig.rest != null ? define(typeConfig.rest) : null;
-  const returns = define(typeConfig.returns);
-  const temporaries = typeConfig.temporaries.map(define);
-  const effects = typeConfig.effects.map(
-    (effect: AliasingEffectConfig): AliasingEffect => {
-      switch (effect.kind) {
-        case 'ImmutableCapture':
-        case 'CreateFrom':
-        case 'Capture':
-        case 'Alias':
-        case 'Assign': {
-          const from = lookup(effect.from);
-          const into = lookup(effect.into);
-          return {
-            kind: effect.kind,
-            from,
-            into,
-          };
-        }
-        case 'Mutate':
-        case 'MutateTransitiveConditionally': {
-          const value = lookup(effect.value);
-          return {kind: effect.kind, value};
-        }
-        case 'Create': {
-          const into = lookup(effect.into);
-          return {
-            kind: 'Create',
-            into,
-            reason: effect.reason,
-            value: effect.value,
-          };
-        }
-        case 'Freeze': {
-          const value = lookup(effect.value);
-          return {
-            kind: 'Freeze',
-            value,
-            reason: effect.reason,
-          };
-        }
-        case 'Impure': {
-          const place = lookup(effect.place);
-          return {
-            kind: 'Impure',
-            place,
-            error: CompilerError.throwTodo({
-              reason: 'Support impure effect declarations',
-              loc: GeneratedSource,
-            }),
-          };
-        }
-        case 'Apply': {
-          const receiver = lookup(effect.receiver);
-          const fn = lookup(effect.function);
-          const args: Array<Place | SpreadPattern | Hole> = effect.args.map(
-            arg => {
-              if (typeof arg === 'string') {
-                return lookup(arg);
-              } else if (arg.kind === 'Spread') {
-                return {kind: 'Spread', place: lookup(arg.place)};
-              } else {
-                return arg;
-              }
-            },
-          );
-          const into = lookup(effect.into);
-          return {
-            kind: 'Apply',
-            receiver,
-            function: fn,
-            mutatesFunction: effect.mutatesFunction,
-            args,
-            into,
-            loc,
-            signature: null,
-          };
-        }
-        default: {
-          assertExhaustive(
-            effect,
-            `Unexpected effect kind '${(effect as any).kind}'`,
-          );
-        }
-      }
-    },
-  );
-  return {
-    receiver: receiver.identifier.id,
-    params: params.map(p => p.identifier.id),
-    rest: rest != null ? rest.identifier.id : null,
-    returns: returns.identifier.id,
-    temporaries,
-    effects,
-  };
-}
-
 /*
 * Add an object to an existing ShapeRegistry.
 *
@@ -335,7 +192,8 @@ export type FunctionSignature = {

  canonicalName?: string;

-  aliasing?: AliasingSignature | null | undefined;
+  aliasing?: AliasingSignature | null;
+  todo_aliasing?: AliasingSignature | null;
 };

 /*
@@ -385,7 +243,6 @@ export const BuiltInFireId = 'BuiltInFire';
 export const BuiltInFireFunctionId = 'BuiltInFireFunction';
 export const BuiltInUseEffectEventId = 'BuiltInUseEffectEvent';
 export const BuiltinEffectEventId = 'BuiltInEffectEventFunction';
-export const BuiltInAutodepsId = 'BuiltInAutoDepsId';

 // See getReanimatedModuleType() in Globals.ts — this is part of supporting Reanimated's ref-like types
 export const ReanimatedSharedValueId = 'ReanimatedSharedValueId';
@@ -463,24 +320,24 @@ addObject(BUILTIN_SHAPES, BuiltInArrayId, [
      calleeEffect: Effect.Store,
      returnValueKind: ValueKind.Primitive,
      aliasing: {
-        receiver: '@receiver',
+        receiver: makeIdentifierId(0),
        params: [],
-        rest: '@rest',
-        returns: '@returns',
+        rest: makeIdentifierId(1),
+        returns: makeIdentifierId(2),
        temporaries: [],
        effects: [
          // Push directly mutates the array itself
-          {kind: 'Mutate', value: '@receiver'},
+          {kind: 'Mutate', value: signatureArgument(0)},
          // The arguments are captured into the array
          {
            kind: 'Capture',
-            from: '@rest',
-            into: '@receiver',
+            from: signatureArgument(1),
+            into: signatureArgument(0),
          },
          // Returns the new length, a primitive
          {
            kind: 'Create',
-            into: '@returns',
+            into: signatureArgument(2),
            value: ValueKind.Primitive,
            reason: ValueReason.KnownReturnSignature,
          },
@@ -517,56 +374,58 @@ addObject(BUILTIN_SHAPES, BuiltInArrayId, [
      noAlias: true,
      mutableOnlyIfOperandsAreMutable: true,
      aliasing: {
-        receiver: '@receiver',
-        params: ['@callback'],
+        receiver: makeIdentifierId(0),
+        params: [makeIdentifierId(1)],
        rest: null,
-        returns: '@returns',
+        returns: makeIdentifierId(2),
        temporaries: [
          // Temporary representing captured items of the receiver
-          '@item',
+          signatureArgument(3),
          // Temporary representing the result of the callback
-          '@callbackReturn',
+          signatureArgument(4),
          /*
           * Undefined `this` arg to the callback. Note the signature does not
           * support passing an explicit thisArg second param
           */
-          '@thisArg',
+          signatureArgument(5),
        ],
        effects: [
          // Map creates a new mutable array
          {
            kind: 'Create',
-            into: '@returns',
+            into: signatureArgument(2),
            value: ValueKind.Mutable,
            reason: ValueReason.KnownReturnSignature,
          },
          // The first arg to the callback is an item extracted from the receiver array
          {
            kind: 'CreateFrom',
-            from: '@receiver',
-            into: '@item',
+            from: signatureArgument(0),
+            into: signatureArgument(3),
          },
          // The undefined this for the callback
          {
            kind: 'Create',
-            into: '@thisArg',
+            into: signatureArgument(5),
            value: ValueKind.Primitive,
            reason: ValueReason.KnownReturnSignature,
          },
          // calls the callback, returning the result into a temporary
          {
            kind: 'Apply',
-            receiver: '@thisArg',
-            args: ['@item', {kind: 'Hole'}, '@receiver'],
-            function: '@callback',
-            into: '@callbackReturn',
+            receiver: signatureArgument(5),
+            args: [signatureArgument(3), {kind: 'Hole'}, signatureArgument(0)],
+            function: signatureArgument(1),
+            into: signatureArgument(4),
+            signature: null,
            mutatesFunction: false,
+            loc: GeneratedSource,
          },
          // captures the result of the callback into the return array
          {
            kind: 'Capture',
-            from: '@callbackReturn',
-            into: '@returns',
+            from: signatureArgument(4),
+            into: signatureArgument(2),
          },
        ],
      },
@@ -718,28 +577,28 @@ addObject(BUILTIN_SHAPES, BuiltInSetId, [
      // returnValueKind is technically dependent on the ValueKind of the set itself
      returnValueKind: ValueKind.Mutable,
      aliasing: {
-        receiver: '@receiver',
+        receiver: makeIdentifierId(0),
        params: [],
-        rest: '@rest',
-        returns: '@returns',
+        rest: makeIdentifierId(1),
+        returns: makeIdentifierId(2),
        temporaries: [],
        effects: [
          // Set.add returns the receiver Set
          {
            kind: 'Assign',
-            from: '@receiver',
-            into: '@returns',
+            from: signatureArgument(0),
+            into: signatureArgument(2),
          },
          // Set.add mutates the set itself
          {
            kind: 'Mutate',
-            value: '@receiver',
+            value: signatureArgument(0),
          },
          // Captures the rest params into the set
          {
            kind: 'Capture',
-            from: '@rest',
-            into: '@receiver',
+            from: signatureArgument(1),
+            into: signatureArgument(0),
          },
        ],
      },
@@ -1212,8 +1071,6 @@ addObject(BUILTIN_SHAPES, BuiltInRefValueId, [
  ['*', {kind: 'Object', shapeId: BuiltInRefValueId}],
 ]);

-addObject(BUILTIN_SHAPES, ReanimatedSharedValueId, []);
-
 addFunction(
  BUILTIN_SHAPES,
  [],
@@ -1445,34 +1302,6 @@ export const DefaultNonmutatingHook = addHook(
    calleeEffect: Effect.Read,
    hookKind: 'Custom',
    returnValueKind: ValueKind.Frozen,
-    aliasing: {
-      receiver: '@receiver',
-      params: [],
-      rest: '@rest',
-      returns: '@returns',
-      temporaries: [],
-      effects: [
-        // Freeze the arguments
-        {
-          kind: 'Freeze',
-          value: '@rest',
-          reason: ValueReason.HookCaptured,
-        },
-        // Returns a frozen value
-        {
-          kind: 'Create',
-          into: '@returns',
-          value: ValueKind.Frozen,
-          reason: ValueReason.HookReturn,
-        },
-        // May alias any arguments into the return
-        {
-          kind: 'Alias',
-          from: '@rest',
-          into: '@returns',
-        },
-      ],
-    },
  },
  'DefaultNonmutatingHook',
 );
--- a/compiler/packages/babel-plugin-react-compiler/src/HIR/PrintHIR.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/HIR/PrintHIR.ts
@@ -5,6 +5,7 @@
 * LICENSE file in the root directory of this source tree.
 */

+import generate from '@babel/generator';
 import {CompilerError} from '../CompilerError';
 import {printReactiveScopeSummary} from '../ReactiveScopes/PrintReactiveFunction';
 import DisjointSet from '../Utils/DisjointSet';
@@ -53,8 +54,6 @@ export function printFunction(fn: HIRFunction): string {
  let definition = '';
  if (fn.id !== null) {
    definition += fn.id;
-  } else {
-    definition += '<<anonymous>>';
  }
  if (fn.params.length !== 0) {
    definition +=
@@ -72,8 +71,10 @@ export function printFunction(fn: HIRFunction): string {
  } else {
    definition += '()';
  }
-  definition += `: ${printPlace(fn.returns)}`;
-  output.push(definition);
+  if (definition.length !== 0) {
+    output.push(definition);
+  }
+  output.push(`: ${printType(fn.returnType)} @ ${printPlace(fn.returns)}`);
  output.push(...fn.directives);
  output.push(printHIR(fn.body));
  return output.join('\n');
@@ -215,7 +216,7 @@ export function printTerminal(terminal: Terminal): Array<string> | string {
      break;
    }
    case 'return': {
-      value = `[${terminal.id}] Return ${terminal.returnVariant}${
+      value = `[${terminal.id}] Return${
        terminal.value != null ? ' ' + printPlace(terminal.value) : ''
      }`;
      if (terminal.effects != null) {
@@ -465,7 +466,7 @@ export function printInstructionValue(instrValue: ReactiveValue): string {
      break;
    }
    case 'UnsupportedNode': {
-      value = `UnsupportedNode ${instrValue.node.type}`;
+      value = `UnsupportedNode(${generate(instrValue.node).code})`;
      break;
    }
    case 'LoadLocal': {
@@ -554,11 +555,23 @@ export function printInstructionValue(instrValue: ReactiveValue): string {
      const context = instrValue.loweredFunc.func.context
        .map(dep => printPlace(dep))
        .join(',');
+      const effects =
+        instrValue.loweredFunc.func.effects
+          ?.map(effect => {
+            if (effect.kind === 'ContextMutation') {
+              return `ContextMutation places=[${[...effect.places]
+                .map(place => printPlace(place))
+                .join(', ')}] effect=${effect.effect}`;
+            } else {
+              return `GlobalMutation`;
+            }
+          })
+          .join(', ') ?? '';
      const aliasingEffects =
        instrValue.loweredFunc.func.aliasingEffects
          ?.map(printAliasingEffect)
          ?.join(', ') ?? '';
-      value = `${kind} ${name} @context[${context}] @aliasingEffects=[${aliasingEffects}]\n${fn}`;
+      value = `${kind} ${name} @context[${context}] @effects[${effects}] @aliasingEffects=[${aliasingEffects}]\n${fn}`;
      break;
    }
    case 'TaggedTemplateExpression': {
@@ -702,7 +715,7 @@ export function printInstructionValue(instrValue: ReactiveValue): string {
      break;
    }
    case 'FinishMemoize': {
-      value = `FinishMemoize decl=${printPlace(instrValue.decl)}${instrValue.pruned ? ' pruned' : ''}`;
+      value = `FinishMemoize decl=${printPlace(instrValue.decl)}`;
      break;
    }
    default: {
@@ -880,8 +893,7 @@ export function printType(type: Type): string {
  if (type.kind === 'Object' && type.shapeId != null) {
    return `:T${type.kind}<${type.shapeId}>`;
  } else if (type.kind === 'Function' && type.shapeId != null) {
-    const returnType = printType(type.return);
-    return `:T${type.kind}<${type.shapeId}>()${returnType !== '' ? `:  ${returnType}` : ''}`;
+    return `:T${type.kind}<${type.shapeId}>`;
  } else {
    return `:T${type.kind}`;
  }
@@ -932,10 +944,7 @@ export function printAliasingEffect(effect: AliasingEffect): string {
      return `Assign ${printPlaceForAliasEffect(effect.into)} = ${printPlaceForAliasEffect(effect.from)}`;
    }
    case 'Alias': {
-      return `Alias ${printPlaceForAliasEffect(effect.into)} <- ${printPlaceForAliasEffect(effect.from)}`;
-    }
-    case 'MaybeAlias': {
-      return `MaybeAlias ${printPlaceForAliasEffect(effect.into)} <- ${printPlaceForAliasEffect(effect.from)}`;
+      return `Alias ${printPlaceForAliasEffect(effect.into)} = ${printPlaceForAliasEffect(effect.from)}`;
    }
    case 'Capture': {
      return `Capture ${printPlaceForAliasEffect(effect.into)} <- ${printPlaceForAliasEffect(effect.from)}`;
@@ -984,7 +993,7 @@ export function printAliasingEffect(effect: AliasingEffect): string {
    case 'MutateConditionally':
    case 'MutateTransitive':
    case 'MutateTransitiveConditionally': {
-      return `${effect.kind} ${printPlaceForAliasEffect(effect.value)}${effect.kind === 'Mutate' && effect.reason?.kind === 'AssignCurrentProperty' ? ' (assign `.current`)' : ''}`;
+      return `${effect.kind} ${printPlaceForAliasEffect(effect.value)}`;
    }
    case 'MutateFrozen': {
      return `MutateFrozen ${printPlaceForAliasEffect(effect.place)} reason=${JSON.stringify(effect.error.reason)}`;
--- a/compiler/packages/babel-plugin-react-compiler/src/HIR/TypeSchema.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/HIR/TypeSchema.ts
@@ -8,12 +8,7 @@
 import {isValidIdentifier} from '@babel/types';
 import {z} from 'zod';
 import {Effect, ValueKind} from '..';
-import {
-  EffectSchema,
-  ValueKindSchema,
-  ValueReason,
-  ValueReasonSchema,
-} from './HIR';
+import {EffectSchema, ValueKindSchema} from './HIR';

 export type ObjectPropertiesConfig = {[key: string]: TypeConfig};
 export const ObjectPropertiesSchema: z.ZodType<ObjectPropertiesConfig> = z
@@ -36,209 +31,6 @@ export const ObjectTypeSchema: z.ZodType<ObjectTypeConfig> = z.object({
  properties: ObjectPropertiesSchema.nullable(),
 });

-export const LifetimeIdSchema = z.string().refine(id => id.startsWith('@'), {
-  message: "Placeholder names must start with '@'",
-});
-
-export type FreezeEffectConfig = {
-  kind: 'Freeze';
-  value: string;
-  reason: ValueReason;
-};
-
-export const FreezeEffectSchema: z.ZodType<FreezeEffectConfig> = z.object({
-  kind: z.literal('Freeze'),
-  value: LifetimeIdSchema,
-  reason: ValueReasonSchema,
-});
-
-export type MutateEffectConfig = {
-  kind: 'Mutate';
-  value: string;
-};
-
-export const MutateEffectSchema: z.ZodType<MutateEffectConfig> = z.object({
-  kind: z.literal('Mutate'),
-  value: LifetimeIdSchema,
-});
-
-export type MutateTransitiveConditionallyConfig = {
-  kind: 'MutateTransitiveConditionally';
-  value: string;
-};
-
-export const MutateTransitiveConditionallySchema: z.ZodType<MutateTransitiveConditionallyConfig> =
-  z.object({
-    kind: z.literal('MutateTransitiveConditionally'),
-    value: LifetimeIdSchema,
-  });
-
-export type CreateEffectConfig = {
-  kind: 'Create';
-  into: string;
-  value: ValueKind;
-  reason: ValueReason;
-};
-
-export const CreateEffectSchema: z.ZodType<CreateEffectConfig> = z.object({
-  kind: z.literal('Create'),
-  into: LifetimeIdSchema,
-  value: ValueKindSchema,
-  reason: ValueReasonSchema,
-});
-
-export type AssignEffectConfig = {
-  kind: 'Assign';
-  from: string;
-  into: string;
-};
-
-export const AssignEffectSchema: z.ZodType<AssignEffectConfig> = z.object({
-  kind: z.literal('Assign'),
-  from: LifetimeIdSchema,
-  into: LifetimeIdSchema,
-});
-
-export type AliasEffectConfig = {
-  kind: 'Alias';
-  from: string;
-  into: string;
-};
-
-export const AliasEffectSchema: z.ZodType<AliasEffectConfig> = z.object({
-  kind: z.literal('Alias'),
-  from: LifetimeIdSchema,
-  into: LifetimeIdSchema,
-});
-
-export type ImmutableCaptureEffectConfig = {
-  kind: 'ImmutableCapture';
-  from: string;
-  into: string;
-};
-
-export const ImmutableCaptureEffectSchema: z.ZodType<ImmutableCaptureEffectConfig> =
-  z.object({
-    kind: z.literal('ImmutableCapture'),
-    from: LifetimeIdSchema,
-    into: LifetimeIdSchema,
-  });
-
-export type CaptureEffectConfig = {
-  kind: 'Capture';
-  from: string;
-  into: string;
-};
-
-export const CaptureEffectSchema: z.ZodType<CaptureEffectConfig> = z.object({
-  kind: z.literal('Capture'),
-  from: LifetimeIdSchema,
-  into: LifetimeIdSchema,
-});
-
-export type CreateFromEffectConfig = {
-  kind: 'CreateFrom';
-  from: string;
-  into: string;
-};
-
-export const CreateFromEffectSchema: z.ZodType<CreateFromEffectConfig> =
-  z.object({
-    kind: z.literal('CreateFrom'),
-    from: LifetimeIdSchema,
-    into: LifetimeIdSchema,
-  });
-
-export type ApplyArgConfig =
-  | string
-  | {kind: 'Spread'; place: string}
-  | {kind: 'Hole'};
-
-export const ApplyArgSchema: z.ZodType<ApplyArgConfig> = z.union([
-  LifetimeIdSchema,
-  z.object({
-    kind: z.literal('Spread'),
-    place: LifetimeIdSchema,
-  }),
-  z.object({
-    kind: z.literal('Hole'),
-  }),
-]);
-
-export type ApplyEffectConfig = {
-  kind: 'Apply';
-  receiver: string;
-  function: string;
-  mutatesFunction: boolean;
-  args: Array<ApplyArgConfig>;
-  into: string;
-};
-
-export const ApplyEffectSchema: z.ZodType<ApplyEffectConfig> = z.object({
-  kind: z.literal('Apply'),
-  receiver: LifetimeIdSchema,
-  function: LifetimeIdSchema,
-  mutatesFunction: z.boolean(),
-  args: z.array(ApplyArgSchema),
-  into: LifetimeIdSchema,
-});
-
-export type ImpureEffectConfig = {
-  kind: 'Impure';
-  place: string;
-};
-
-export const ImpureEffectSchema: z.ZodType<ImpureEffectConfig> = z.object({
-  kind: z.literal('Impure'),
-  place: LifetimeIdSchema,
-});
-
-export type AliasingEffectConfig =
-  | FreezeEffectConfig
-  | CreateEffectConfig
-  | CreateFromEffectConfig
-  | AssignEffectConfig
-  | AliasEffectConfig
-  | CaptureEffectConfig
-  | ImmutableCaptureEffectConfig
-  | ImpureEffectConfig
-  | MutateEffectConfig
-  | MutateTransitiveConditionallyConfig
-  | ApplyEffectConfig;
-
-export const AliasingEffectSchema: z.ZodType<AliasingEffectConfig> = z.union([
-  FreezeEffectSchema,
-  CreateEffectSchema,
-  CreateFromEffectSchema,
-  AssignEffectSchema,
-  AliasEffectSchema,
-  CaptureEffectSchema,
-  ImmutableCaptureEffectSchema,
-  ImpureEffectSchema,
-  MutateEffectSchema,
-  MutateTransitiveConditionallySchema,
-  ApplyEffectSchema,
-]);
-
-export type AliasingSignatureConfig = {
-  receiver: string;
-  params: Array<string>;
-  rest: string | null;
-  returns: string;
-  effects: Array<AliasingEffectConfig>;
-  temporaries: Array<string>;
-};
-
-export const AliasingSignatureSchema: z.ZodType<AliasingSignatureConfig> =
-  z.object({
-    receiver: LifetimeIdSchema,
-    params: z.array(LifetimeIdSchema),
-    rest: LifetimeIdSchema.nullable(),
-    returns: LifetimeIdSchema,
-    effects: z.array(AliasingEffectSchema),
-    temporaries: z.array(LifetimeIdSchema),
-  });
-
 export type FunctionTypeConfig = {
  kind: 'function';
  positionalParams: Array<Effect>;
@@ -250,7 +42,6 @@ export type FunctionTypeConfig = {
  mutableOnlyIfOperandsAreMutable?: boolean | null | undefined;
  impure?: boolean | null | undefined;
  canonicalName?: string | null | undefined;
-  aliasing?: AliasingSignatureConfig | null | undefined;
 };
 export const FunctionTypeSchema: z.ZodType<FunctionTypeConfig> = z.object({
  kind: z.literal('function'),
@@ -263,7 +54,6 @@ export const FunctionTypeSchema: z.ZodType<FunctionTypeConfig> = z.object({
  mutableOnlyIfOperandsAreMutable: z.boolean().nullable().optional(),
  impure: z.boolean().nullable().optional(),
  canonicalName: z.string().nullable().optional(),
-  aliasing: AliasingSignatureSchema.nullable().optional(),
 });

 export type HookTypeConfig = {
@@ -273,7 +63,6 @@ export type HookTypeConfig = {
  returnType: TypeConfig;
  returnValueKind?: ValueKind | null | undefined;
  noAlias?: boolean | null | undefined;
-  aliasing?: AliasingSignatureConfig | null | undefined;
 };
 export const HookTypeSchema: z.ZodType<HookTypeConfig> = z.object({
  kind: z.literal('hook'),
@@ -282,7 +71,6 @@ export const HookTypeSchema: z.ZodType<HookTypeConfig> = z.object({
  returnType: z.lazy(() => TypeSchema),
  returnValueKind: ValueKindSchema.nullable().optional(),
  noAlias: z.boolean().nullable().optional(),
-  aliasing: AliasingSignatureSchema.nullable().optional(),
 });

 export type BuiltInTypeConfig =
--- a/compiler/packages/babel-plugin-react-compiler/src/HIR/visitors.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/HIR/visitors.ts
@@ -345,51 +345,6 @@ export function* eachPatternOperand(pattern: Pattern): Iterable<Place> {
  }
 }

-export function* eachPatternItem(
-  pattern: Pattern,
-): Iterable<Place | SpreadPattern> {
-  switch (pattern.kind) {
-    case 'ArrayPattern': {
-      for (const item of pattern.items) {
-        if (item.kind === 'Identifier') {
-          yield item;
-        } else if (item.kind === 'Spread') {
-          yield item;
-        } else if (item.kind === 'Hole') {
-          continue;
-        } else {
-          assertExhaustive(
-            item,
-            `Unexpected item kind \`${(item as any).kind}\``,
-          );
-        }
-      }
-      break;
-    }
-    case 'ObjectPattern': {
-      for (const property of pattern.properties) {
-        if (property.kind === 'ObjectProperty') {
-          yield property.place;
-        } else if (property.kind === 'Spread') {
-          yield property;
-        } else {
-          assertExhaustive(
-            property,
-            `Unexpected item kind \`${(property as any).kind}\``,
-          );
-        }
-      }
-      break;
-    }
-    default: {
-      assertExhaustive(
-        pattern,
-        `Unexpected pattern kind \`${(pattern as any).kind}\``,
-      );
-    }
-  }
-}
-
 export function mapInstructionLValues(
  instr: Instruction,
  fn: (place: Place) => Place,
@@ -777,7 +732,6 @@ export function mapTerminalSuccessors(
    case 'return': {
      return {
        kind: 'return',
-        returnVariant: terminal.returnVariant,
        loc: terminal.loc,
        value: terminal.value,
        id: makeInstructionId(0),
--- a/compiler/packages/babel-plugin-react-compiler/src/Inference/AliasingEffects.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Inference/AliasingEffects.ts
@@ -5,10 +5,9 @@
 * LICENSE file in the root directory of this source tree.
 */

-import {CompilerDiagnostic} from '../CompilerError';
+import {CompilerErrorDetailOptions} from '../CompilerError';
 import {
  FunctionExpression,
-  GeneratedSource,
  Hole,
  IdentifierId,
  ObjectMethod,
@@ -19,7 +18,6 @@ import {
  ValueReason,
 } from '../HIR';
 import {FunctionSignature} from '../HIR/ObjectShape';
-import {printSourceLocation} from '../HIR/PrintHIR';

 /**
 * `AliasingEffect` describes a set of "effects" that an instruction/terminal has on one or
@@ -50,7 +48,7 @@ export type AliasingEffect =
  /**
   * Mutate the value and any direct aliases (not captures). Errors if the value is not mutable.
   */
-  | {kind: 'Mutate'; value: Place; reason?: MutationReason | null}
+  | {kind: 'Mutate'; value: Place}
  /**
   * Mutate the value and any direct aliases (not captures), but only if the value is known mutable.
   * This should be rare.
@@ -90,23 +88,6 @@ export type AliasingEffect =
   * c could be mutating a.
   */
  | {kind: 'Alias'; from: Place; into: Place}
-
-  /**
-   * Indicates the potential for information flow from `from` to `into`. This is used for a specific
-   * case: functions with unknown signatures. If the compiler sees a call such as `foo(x)`, it has to
-   * consider several possibilities (which may depend on the arguments):
-   * - foo(x) returns a new mutable value that does not capture any information from x.
-   * - foo(x) returns a new mutable value that *does* capture information from x.
-   * - foo(x) returns x itself, ie foo is the identity function
-   *
-   * The same is true of functions that take multiple arguments: `cond(a, b, c)` could conditionally
-   * return b or c depending on the value of a.
-   *
-   * To represent this case, MaybeAlias represents the fact that an aliasing relationship could exist.
-   * Any mutations that flow through this relationship automatically become conditional.
-   */
-  | {kind: 'MaybeAlias'; from: Place; into: Place}
-
  /**
   * Records direct assignment: `into = from`.
   */
@@ -150,19 +131,19 @@ export type AliasingEffect =
  /**
   * Mutation of a value known to be immutable
   */
-  | {kind: 'MutateFrozen'; place: Place; error: CompilerDiagnostic}
+  | {kind: 'MutateFrozen'; place: Place; error: CompilerErrorDetailOptions}
  /**
   * Mutation of a global
   */
  | {
      kind: 'MutateGlobal';
      place: Place;
-      error: CompilerDiagnostic;
+      error: CompilerErrorDetailOptions;
    }
  /**
   * Indicates a side-effect that is not safe during render
   */
-  | {kind: 'Impure'; place: Place; error: CompilerDiagnostic}
+  | {kind: 'Impure'; place: Place; error: CompilerErrorDetailOptions}
  /**
   * Indicates that a given place is accessed during render. Used to distingush
   * hook arguments that are known to be called immediately vs those used for
@@ -174,8 +155,6 @@ export type AliasingEffect =
      place: Place;
    };

-export type MutationReason = {kind: 'AssignCurrentProperty'};
-
 export function hashEffect(effect: AliasingEffect): string {
  switch (effect.kind) {
    case 'Apply': {
@@ -202,8 +181,7 @@ export function hashEffect(effect: AliasingEffect): string {
    case 'ImmutableCapture':
    case 'Assign':
    case 'Alias':
-    case 'Capture':
-    case 'MaybeAlias': {
+    case 'Capture': {
      return [
        effect.kind,
        effect.from.identifier.id,
@@ -222,19 +200,10 @@ export function hashEffect(effect: AliasingEffect): string {
      return [effect.kind, effect.value.identifier.id, effect.reason].join(':');
    }
    case 'Impure':
-    case 'Render': {
-      return [effect.kind, effect.place.identifier.id].join(':');
-    }
+    case 'Render':
    case 'MutateFrozen':
    case 'MutateGlobal': {
-      return [
-        effect.kind,
-        effect.place.identifier.id,
-        effect.error.severity,
-        effect.error.reason,
-        effect.error.description,
-        printSourceLocation(effect.error.primaryLocation() ?? GeneratedSource),
-      ].join(':');
+      return [effect.kind, effect.place.identifier.id].join(':');
    }
    case 'Mutate':
    case 'MutateConditionally':
--- a/compiler/packages/babel-plugin-react-compiler/src/Inference/AnalyseFunctions.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Inference/AnalyseFunctions.ts
@@ -6,12 +6,23 @@
 */

 import {CompilerError} from '../CompilerError';
-import {Effect, HIRFunction, IdentifierId, makeInstructionId} from '../HIR';
+import {
+  Effect,
+  HIRFunction,
+  Identifier,
+  IdentifierId,
+  LoweredFunction,
+  isRefOrRefValue,
+  makeInstructionId,
+} from '../HIR';
 import {deadCodeElimination} from '../Optimization';
 import {inferReactiveScopeVariables} from '../ReactiveScopes';
 import {rewriteInstructionKindsBasedOnReassignment} from '../SSA';
+import {inferMutableRanges} from './InferMutableRanges';
+import inferReferenceEffects from './InferReferenceEffects';
 import {assertExhaustive} from '../Utils/utils';
 import {inferMutationAliasingEffects} from './InferMutationAliasingEffects';
+import {inferMutationAliasingFunctionEffects} from './InferMutationAliasingFunctionEffects';
 import {inferMutationAliasingRanges} from './InferMutationAliasingRanges';

 export default function analyseFunctions(func: HIRFunction): void {
@@ -20,22 +31,19 @@ export default function analyseFunctions(func: HIRFunction): void {
      switch (instr.value.kind) {
        case 'ObjectMethod':
        case 'FunctionExpression': {
-          lowerWithMutationAliasing(instr.value.loweredFunc.func);
+          if (!func.env.config.enableNewMutationAliasingModel) {
+            lower(instr.value.loweredFunc.func);
+            infer(instr.value.loweredFunc);
+          } else {
+            lowerWithMutationAliasing(instr.value.loweredFunc.func);
+          }

          /**
           * Reset mutable range for outer inferReferenceEffects
           */
          for (const operand of instr.value.loweredFunc.func.context) {
-            /**
-             * NOTE: inferReactiveScopeVariables makes identifiers in the scope
-             * point to the *same* mutableRange instance. Resetting start/end
-             * here is insufficient, because a later mutation of the range
-             * for any one identifier could affect the range for other identifiers.
-             */
-            operand.identifier.mutableRange = {
-              start: makeInstructionId(0),
-              end: makeInstructionId(0),
-            };
+            operand.identifier.mutableRange.start = makeInstructionId(0);
+            operand.identifier.mutableRange.end = makeInstructionId(0);
            operand.identifier.scope = null;
          }
          break;
@@ -52,12 +60,19 @@ function lowerWithMutationAliasing(fn: HIRFunction): void {
  analyseFunctions(fn);
  inferMutationAliasingEffects(fn, {isFunctionExpression: true});
  deadCodeElimination(fn);
-  const functionEffects = inferMutationAliasingRanges(fn, {
-    isFunctionExpression: true,
-  }).unwrap();
+  inferMutationAliasingRanges(fn, {isFunctionExpression: true});
  rewriteInstructionKindsBasedOnReassignment(fn);
  inferReactiveScopeVariables(fn);
-  fn.aliasingEffects = functionEffects;
+  const effects = inferMutationAliasingFunctionEffects(fn);
+  fn.env.logger?.debugLogIRs?.({
+    kind: 'hir',
+    name: 'AnalyseFunction (inner)',
+    value: fn,
+  });
+  if (effects != null) {
+    fn.aliasingEffects ??= [];
+    fn.aliasingEffects?.push(...effects);
+  }

  /**
   * Phase 2: populate the Effect of each context variable to use in inferring
@@ -65,13 +80,12 @@ function lowerWithMutationAliasing(fn: HIRFunction): void {
   * effects to decide if the function may be mutable or not.
   */
  const capturedOrMutated = new Set<IdentifierId>();
-  for (const effect of functionEffects) {
+  for (const effect of effects ?? []) {
    switch (effect.kind) {
      case 'Assign':
      case 'Alias':
      case 'Capture':
-      case 'CreateFrom':
-      case 'MaybeAlias': {
+      case 'CreateFrom': {
        capturedOrMutated.add(effect.from.identifier.id);
        break;
      }
@@ -118,10 +132,59 @@ function lowerWithMutationAliasing(fn: HIRFunction): void {
      operand.effect = Effect.Read;
    }
  }
+}

-  fn.env.logger?.debugLogIRs?.({
+function lower(func: HIRFunction): void {
+  analyseFunctions(func);
+  inferReferenceEffects(func, {isFunctionExpression: true});
+  deadCodeElimination(func);
+  inferMutableRanges(func);
+  rewriteInstructionKindsBasedOnReassignment(func);
+  inferReactiveScopeVariables(func);
+  func.env.logger?.debugLogIRs?.({
    kind: 'hir',
    name: 'AnalyseFunction (inner)',
-    value: fn,
+    value: func,
  });
 }
+
+function infer(loweredFunc: LoweredFunction): void {
+  for (const operand of loweredFunc.func.context) {
+    const identifier = operand.identifier;
+    CompilerError.invariant(operand.effect === Effect.Unknown, {
+      reason:
+        '[AnalyseFunctions] Expected Function context effects to not have been set',
+      loc: operand.loc,
+    });
+    if (isRefOrRefValue(identifier)) {
+      /*
+       * TODO: this is a hack to ensure we treat functions which reference refs
+       * as having a capture and therefore being considered mutable. this ensures
+       * the function gets a mutable range which accounts for anywhere that it
+       * could be called, and allows us to help ensure it isn't called during
+       * render
+       */
+      operand.effect = Effect.Capture;
+    } else if (isMutatedOrReassigned(identifier)) {
+      /**
+       * Reflects direct reassignments, PropertyStores, and ConditionallyMutate
+       * (directly or through maybe-aliases)
+       */
+      operand.effect = Effect.Capture;
+    } else {
+      operand.effect = Effect.Read;
+    }
+  }
+}
+
+function isMutatedOrReassigned(id: Identifier): boolean {
+  /*
+   * This check checks for mutation and reassingnment, so the usual check for
+   * mutation (ie, `mutableRange.end - mutableRange.start > 1`) isn't quite
+   * enough.
+   *
+   * We need to track re-assignments in context refs as we need to reflect the
+   * re-assignment back to the captured refs.
+   */
+  return id.mutableRange.end > id.mutableRange.start;
+}
--- a/compiler/packages/babel-plugin-react-compiler/src/Inference/DropManualMemoization.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Inference/DropManualMemoization.ts
@@ -5,13 +5,7 @@
 * LICENSE file in the root directory of this source tree.
 */

-import {
-  CompilerDiagnostic,
-  CompilerError,
-  ErrorSeverity,
-  SourceLocation,
-} from '..';
-import {ErrorCategory} from '../CompilerError';
+import {CompilerError, SourceLocation} from '..';
 import {
  CallExpression,
  Effect,
@@ -36,7 +30,6 @@ import {
  makeInstructionId,
 } from '../HIR';
 import {createTemporaryPlace, markInstructionIds} from '../HIR/HIRBuilder';
-import {Result} from '../Utils/Result';

 type ManualMemoCallee = {
  kind: 'useMemo' | 'useCallback';
@@ -290,45 +283,26 @@ function extractManualMemoizationArgs(
  instr: TInstruction<CallExpression> | TInstruction<MethodCall>,
  kind: 'useCallback' | 'useMemo',
  sidemap: IdentifierSidemap,
-  errors: CompilerError,
 ): {
-  fnPlace: Place | null;
+  fnPlace: Place;
  depsList: Array<ManualMemoDependency> | null;
 } {
  const [fnPlace, depsListPlace] = instr.value.args as Array<
    Place | SpreadPattern | undefined
  >;
  if (fnPlace == null) {
-    errors.pushDiagnostic(
-      CompilerDiagnostic.create({
-        category: ErrorCategory.UseMemo,
-        severity: ErrorSeverity.InvalidReact,
-        reason: `Expected a callback function to be passed to ${kind}`,
-        description: `Expected a callback function to be passed to ${kind}`,
-        suggestions: null,
-      }).withDetail({
-        kind: 'error',
-        loc: instr.value.loc,
-        message: `Expected a callback function to be passed to ${kind}`,
-      }),
-    );
-    return {fnPlace: null, depsList: null};
+    CompilerError.throwInvalidReact({
+      reason: `Expected a callback function to be passed to ${kind}`,
+      loc: instr.value.loc,
+      suggestions: null,
+    });
  }
  if (fnPlace.kind === 'Spread' || depsListPlace?.kind === 'Spread') {
-    errors.pushDiagnostic(
-      CompilerDiagnostic.create({
-        category: ErrorCategory.UseMemo,
-        severity: ErrorSeverity.InvalidReact,
-        reason: `Unexpected spread argument to ${kind}`,
-        description: `Unexpected spread argument to ${kind}`,
-        suggestions: null,
-      }).withDetail({
-        kind: 'error',
-        loc: instr.value.loc,
-        message: `Unexpected spread argument to ${kind}`,
-      }),
-    );
-    return {fnPlace: null, depsList: null};
+    CompilerError.throwInvalidReact({
+      reason: `Unexpected spread argument to ${kind}`,
+      loc: instr.value.loc,
+      suggestions: null,
+    });
  }
  let depsList: Array<ManualMemoDependency> | null = null;
  if (depsListPlace != null) {
@@ -336,42 +310,23 @@ function extractManualMemoizationArgs(
      depsListPlace.identifier.id,
    );
    if (maybeDepsList == null) {
-      errors.pushDiagnostic(
-        CompilerDiagnostic.create({
-          category: ErrorCategory.UseMemo,
-          severity: ErrorSeverity.InvalidReact,
-          reason: `Expected the dependency list for ${kind} to be an array literal`,
-          description: `Expected the dependency list for ${kind} to be an array literal`,
-          suggestions: null,
-        }).withDetail({
-          kind: 'error',
-          loc: depsListPlace.loc,
-          message: `Expected the dependency list for ${kind} to be an array literal`,
-        }),
-      );
-      return {fnPlace, depsList: null};
+      CompilerError.throwInvalidReact({
+        reason: `Expected the dependency list for ${kind} to be an array literal`,
+        suggestions: null,
+        loc: depsListPlace.loc,
+      });
    }
-    depsList = [];
-    for (const dep of maybeDepsList) {
+    depsList = maybeDepsList.map(dep => {
      const maybeDep = sidemap.maybeDeps.get(dep.identifier.id);
      if (maybeDep == null) {
-        errors.pushDiagnostic(
-          CompilerDiagnostic.create({
-            category: ErrorCategory.UseMemo,
-            severity: ErrorSeverity.InvalidReact,
-            reason: `Expected the dependency list to be an array of simple expressions (e.g. \`x\`, \`x.y.z\`, \`x?.y?.z\`)`,
-            description: `Expected the dependency list to be an array of simple expressions (e.g. \`x\`, \`x.y.z\`, \`x?.y?.z\`)`,
-            suggestions: null,
-          }).withDetail({
-            kind: 'error',
-            loc: dep.loc,
-            message: `Expected the dependency list to be an array of simple expressions (e.g. \`x\`, \`x.y.z\`, \`x?.y?.z\`)`,
-          }),
-        );
-      } else {
-        depsList.push(maybeDep);
+        CompilerError.throwInvalidReact({
+          reason: `Expected the dependency list to be an array of simple expressions (e.g. \`x\`, \`x.y.z\`, \`x?.y?.z\`)`,
+          suggestions: null,
+          loc: dep.loc,
+        });
      }
-    }
+      return maybeDep;
+    });
  }
  return {
    fnPlace,
@@ -386,14 +341,8 @@ function extractManualMemoizationArgs(
 * rely on type inference to find useMemo/useCallback invocations, and instead does basic tracking
 * of globals and property loads to find both direct calls as well as usage via the React namespace,
 * eg `React.useMemo()`.
- *
- * This pass also validates that useMemo callbacks return a value (not void), ensuring that useMemo
- * is only used for memoizing values and not for running arbitrary side effects.
 */
-export function dropManualMemoization(
-  func: HIRFunction,
-): Result<void, CompilerError> {
-  const errors = new CompilerError();
+export function dropManualMemoization(func: HIRFunction): void {
  const isValidationEnabled =
    func.env.config.validatePreserveExistingMemoizationGuarantees ||
    func.env.config.validateNoSetStateInRender ||
@@ -440,48 +389,7 @@ export function dropManualMemoization(
            instr as TInstruction<CallExpression> | TInstruction<MethodCall>,
            manualMemo.kind,
            sidemap,
-            errors,
          );
-
-          if (fnPlace == null) {
-            continue;
-          }
-
-          /**
-           * Bailout on void return useMemos. This is an anti-pattern where code might be using
-           * useMemo like useEffect: running arbirtary side-effects synced to changes in specific
-           * values.
-           */
-          if (
-            func.env.config.validateNoVoidUseMemo &&
-            manualMemo.kind === 'useMemo'
-          ) {
-            const funcToCheck = sidemap.functions.get(
-              fnPlace.identifier.id,
-            )?.value;
-            if (funcToCheck !== undefined && funcToCheck.loweredFunc.func) {
-              if (!hasNonVoidReturn(funcToCheck.loweredFunc.func)) {
-                errors.pushDiagnostic(
-                  CompilerDiagnostic.create({
-                    severity: ErrorSeverity.InvalidReact,
-                    category: ErrorCategory.UseMemo,
-                    reason: 'useMemo() callbacks must return a value',
-                    description: `This ${
-                      manualMemo.loadInstr.value.kind === 'PropertyLoad'
-                        ? 'React.useMemo'
-                        : 'useMemo'
-                    } callback doesn't return a value. useMemo is for computing and caching values, not for arbitrary side effects.`,
-                    suggestions: null,
-                  }).withDetail({
-                    kind: 'error',
-                    loc: instr.value.loc,
-                    message: 'useMemo() callbacks must return a value',
-                  }),
-                );
-              }
-            }
-          }
-
          instr.value = getManualMemoizationReplacement(
            fnPlace,
            instr.value.loc,
@@ -502,20 +410,11 @@ export function dropManualMemoization(
             * is rare and likely sketchy.
             */
            if (!sidemap.functions.has(fnPlace.identifier.id)) {
-              errors.pushDiagnostic(
-                CompilerDiagnostic.create({
-                  category: ErrorCategory.UseMemo,
-                  severity: ErrorSeverity.InvalidReact,
-                  reason: `Expected the first argument to be an inline function expression`,
-                  description: `Expected the first argument to be an inline function expression`,
-                  suggestions: [],
-                }).withDetail({
-                  kind: 'error',
-                  loc: fnPlace.loc,
-                  message: `Expected the first argument to be an inline function expression`,
-                }),
-              );
-              continue;
+              CompilerError.throwInvalidReact({
+                reason: `Expected the first argument to be an inline function expression`,
+                suggestions: [],
+                loc: fnPlace.loc,
+              });
            }
            const memoDecl: Place =
              manualMemo.kind === 'useMemo'
@@ -587,8 +486,6 @@ export function dropManualMemoization(
      markInstructionIds(func.body);
    }
  }
-
-  return errors.asResult();
 }

 function findOptionalPlaces(fn: HIRFunction): Set<IdentifierId> {
@@ -633,17 +530,3 @@ function findOptionalPlaces(fn: HIRFunction): Set<IdentifierId> {
  }
  return optionals;
 }
-
-function hasNonVoidReturn(func: HIRFunction): boolean {
-  for (const [, block] of func.body.blocks) {
-    if (block.terminal.kind === 'return') {
-      if (
-        block.terminal.returnVariant === 'Explicit' ||
-        block.terminal.returnVariant === 'Implicit'
-      ) {
-        return true;
-      }
-    }
-  }
-  return false;
-}
--- a/compiler/packages/babel-plugin-react-compiler/src/Inference/InerAliasForUncalledFunctions.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Inference/InerAliasForUncalledFunctions.ts
@@ -0,0 +1,134 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {
+  Effect,
+  HIRFunction,
+  Identifier,
+  isMutableEffect,
+  isRefOrRefLikeMutableType,
+  makeInstructionId,
+} from '../HIR/HIR';
+import {eachInstructionValueOperand} from '../HIR/visitors';
+import {isMutable} from '../ReactiveScopes/InferReactiveScopeVariables';
+import DisjointSet from '../Utils/DisjointSet';
+
+/**
+ * If a function captures a mutable value but never gets called, we don't infer a
+ * mutable range for that function. This means that we also don't alias the function
+ * with its mutable captures.
+ *
+ * This case is tricky, because we don't generally know for sure what is a mutation
+ * and what may just be a normal function call. For example:
+ *
+ * ```
+ * hook useFoo() {
+ *   const x = makeObject();
+ *   return () => {
+ *     return readObject(x); // could be a mutation!
+ *   }
+ * }
+ * ```
+ *
+ * If we pessimistically assume that all such cases are mutations, we'd have to group
+ * lots of memo scopes together unnecessarily. However, if there is definitely a mutation:
+ *
+ * ```
+ * hook useFoo(createEntryForKey) {
+ *   const cache = new WeakMap();
+ *   return (key) => {
+ *     let entry = cache.get(key);
+ *     if (entry == null) {
+ *       entry = createEntryForKey(key);
+ *       cache.set(key, entry); // known mutation!
+ *     }
+ *     return entry;
+ *   }
+ * }
+ * ```
+ *
+ * Then we have to ensure that the function and its mutable captures alias together and
+ * end up in the same scope. However, aliasing together isn't enough if the function
+ * and operands all have empty mutable ranges (end = start + 1).
+ *
+ * This pass finds function expressions and object methods that have an empty mutable range
+ * and known-mutable operands which also don't have a mutable range, and ensures that the
+ * function and those operands are aliased together *and* that their ranges are updated to
+ * end after the function expression. This is sufficient to ensure that a reactive scope is
+ * created for the alias set.
+ */
+export function inferAliasForUncalledFunctions(
+  fn: HIRFunction,
+  aliases: DisjointSet<Identifier>,
+): void {
+  for (const block of fn.body.blocks.values()) {
+    instrs: for (const instr of block.instructions) {
+      const {lvalue, value} = instr;
+      if (
+        value.kind !== 'ObjectMethod' &&
+        value.kind !== 'FunctionExpression'
+      ) {
+        continue;
+      }
+      /*
+       * If the function is known to be mutated, we will have
+       * already aliased any mutable operands with it
+       */
+      const range = lvalue.identifier.mutableRange;
+      if (range.end > range.start + 1) {
+        continue;
+      }
+      /*
+       * If the function already has operands with an active mutable range,
+       * then we don't need to do anything — the function will have already
+       * been visited and included in some mutable alias set. This case can
+       * also occur due to visiting the same function in an earlier iteration
+       * of the outer fixpoint loop.
+       */
+      for (const operand of eachInstructionValueOperand(value)) {
+        if (isMutable(instr, operand)) {
+          continue instrs;
+        }
+      }
+      const operands: Set<Identifier> = new Set();
+      for (const effect of value.loweredFunc.func.effects ?? []) {
+        if (effect.kind !== 'ContextMutation') {
+          continue;
+        }
+        /*
+         * We're looking for known-mutations only, so we look at the effects
+         * rather than function context
+         */
+        if (effect.effect === Effect.Store || effect.effect === Effect.Mutate) {
+          for (const operand of effect.places) {
+            /*
+             * It's possible that function effect analysis thinks there was a context mutation,
+             * but then InferReferenceEffects figures out some operands are globals and therefore
+             * creates a non-mutable effect for those operands.
+             * We should change InferReferenceEffects to swap the ContextMutation for a global
+             * mutation in that case, but for now we just filter them out here
+             */
+            if (
+              isMutableEffect(operand.effect, operand.loc) &&
+              !isRefOrRefLikeMutableType(operand.identifier.type)
+            ) {
+              operands.add(operand.identifier);
+            }
+          }
+        }
+      }
+      if (operands.size !== 0) {
+        operands.add(lvalue.identifier);
+        aliases.union([...operands]);
+        // Update mutable ranges, if the ranges are empty then a reactive scope isn't created
+        for (const operand of operands) {
+          operand.mutableRange.end = makeInstructionId(instr.id + 1);
+        }
+      }
+    }
+  }
+}
--- a/compiler/packages/babel-plugin-react-compiler/src/Inference/InferAlias.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Inference/InferAlias.ts
@@ -0,0 +1,68 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {
+  HIRFunction,
+  Identifier,
+  Instruction,
+  isPrimitiveType,
+  Place,
+} from '../HIR/HIR';
+import DisjointSet from '../Utils/DisjointSet';
+
+export type AliasSet = Set<Identifier>;
+
+export function inferAliases(func: HIRFunction): DisjointSet<Identifier> {
+  const aliases = new DisjointSet<Identifier>();
+  for (const [_, block] of func.body.blocks) {
+    for (const instr of block.instructions) {
+      inferInstr(instr, aliases);
+    }
+  }
+
+  return aliases;
+}
+
+function inferInstr(
+  instr: Instruction,
+  aliases: DisjointSet<Identifier>,
+): void {
+  const {lvalue, value: instrValue} = instr;
+  let alias: Place | null = null;
+  switch (instrValue.kind) {
+    case 'LoadLocal':
+    case 'LoadContext': {
+      if (isPrimitiveType(instrValue.place.identifier)) {
+        return;
+      }
+      alias = instrValue.place;
+      break;
+    }
+    case 'StoreLocal':
+    case 'StoreContext': {
+      alias = instrValue.value;
+      break;
+    }
+    case 'Destructure': {
+      alias = instrValue.value;
+      break;
+    }
+    case 'ComputedLoad':
+    case 'PropertyLoad': {
+      alias = instrValue.object;
+      break;
+    }
+    case 'TypeCastExpression': {
+      alias = instrValue.value;
+      break;
+    }
+    default:
+      return;
+  }
+
+  aliases.union([lvalue.identifier, alias.identifier]);
+}
--- a/compiler/packages/babel-plugin-react-compiler/src/Inference/InferAliasForPhis.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Inference/InferAliasForPhis.ts
@@ -0,0 +1,27 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {HIRFunction, Identifier} from '../HIR/HIR';
+import DisjointSet from '../Utils/DisjointSet';
+
+export function inferAliasForPhis(
+  func: HIRFunction,
+  aliases: DisjointSet<Identifier>,
+): void {
+  for (const [_, block] of func.body.blocks) {
+    for (const phi of block.phis) {
+      const isPhiMutatedAfterCreation: boolean =
+        phi.place.identifier.mutableRange.end >
+        (block.instructions.at(0)?.id ?? block.terminal.id);
+      if (isPhiMutatedAfterCreation) {
+        for (const [, operand] of phi.operands) {
+          aliases.union([phi.place.identifier, operand.identifier]);
+        }
+      }
+    }
+  }
+}
--- a/compiler/packages/babel-plugin-react-compiler/src/Inference/InferAliasForStores.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Inference/InferAliasForStores.ts
@@ -0,0 +1,68 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {
+  Effect,
+  HIRFunction,
+  Identifier,
+  InstructionId,
+  Place,
+} from '../HIR/HIR';
+import {
+  eachInstructionLValue,
+  eachInstructionValueOperand,
+} from '../HIR/visitors';
+import DisjointSet from '../Utils/DisjointSet';
+
+export function inferAliasForStores(
+  func: HIRFunction,
+  aliases: DisjointSet<Identifier>,
+): void {
+  for (const [_, block] of func.body.blocks) {
+    for (const instr of block.instructions) {
+      const {value, lvalue} = instr;
+      const isStore =
+        lvalue.effect === Effect.Store ||
+        /*
+         * Some typed functions annotate callees or arguments
+         * as Effect.Store.
+         */
+        ![...eachInstructionValueOperand(value)].every(
+          operand => operand.effect !== Effect.Store,
+        );
+
+      if (!isStore) {
+        continue;
+      }
+      for (const operand of eachInstructionLValue(instr)) {
+        maybeAlias(aliases, lvalue, operand, instr.id);
+      }
+      for (const operand of eachInstructionValueOperand(value)) {
+        if (
+          operand.effect === Effect.Capture ||
+          operand.effect === Effect.Store
+        ) {
+          maybeAlias(aliases, lvalue, operand, instr.id);
+        }
+      }
+    }
+  }
+}
+
+function maybeAlias(
+  aliases: DisjointSet<Identifier>,
+  lvalue: Place,
+  rvalue: Place,
+  id: InstructionId,
+): void {
+  if (
+    lvalue.identifier.mutableRange.end > id + 1 ||
+    rvalue.identifier.mutableRange.end > id
+  ) {
+    aliases.union([lvalue.identifier, rvalue.identifier]);
+  }
+}
--- a/compiler/packages/babel-plugin-react-compiler/src/Inference/InferEffectDependencies.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Inference/InferEffectDependencies.ts
@@ -57,8 +57,6 @@ import {
 } from '../HIR/visitors';
 import {empty} from '../Utils/Stack';
 import {getOrInsertWith} from '../Utils/utils';
-import {deadCodeElimination} from '../Optimization';
-import {BuiltInAutodepsId} from '../HIR/ObjectShape';

 /**
 * Infers reactive dependencies captured by useEffect lambdas and adds them as
@@ -79,7 +77,7 @@ export function inferEffectDependencies(fn: HIRFunction): void {
    );
    moduleTargets.set(
      effectTarget.function.importSpecifierName,
-      effectTarget.autodepsIndex,
+      effectTarget.numRequiredArgs,
    );
  }
  const autodepFnLoads = new Map<IdentifierId, number>();
@@ -137,6 +135,7 @@ export function inferEffectDependencies(fn: HIRFunction): void {
        }
      } else if (value.kind === 'LoadGlobal') {
        loadGlobals.add(lvalue.identifier.id);
+
        /*
         * TODO: Handle properties on default exports, like
         * import React from 'react';
@@ -170,22 +169,8 @@ export function inferEffectDependencies(fn: HIRFunction): void {
      ) {
        const callee =
          value.kind === 'CallExpression' ? value.callee : value.property;
-
-        const autodepsArgIndex = value.args.findIndex(
-          arg =>
-            arg.kind === 'Identifier' &&
-            arg.identifier.type.kind === 'Object' &&
-            arg.identifier.type.shapeId === BuiltInAutodepsId,
-        );
-        const autodepsArgExpectedIndex = autodepFnLoads.get(
-          callee.identifier.id,
-        );
-
        if (
-          value.args.length > 0 &&
-          autodepsArgExpectedIndex != null &&
-          autodepsArgIndex === autodepsArgExpectedIndex &&
-          autodepFnLoads.has(callee.identifier.id) &&
+          value.args.length === autodepFnLoads.get(callee.identifier.id) &&
          value.args[0].kind === 'Identifier'
        ) {
          // We have a useEffect call with no deps array, so we need to infer the deps
@@ -275,10 +260,7 @@ export function inferEffectDependencies(fn: HIRFunction): void {
                effects: null,
              },
            });
-            value.args[autodepsArgIndex] = {
-              ...depsPlace,
-              effect: Effect.Freeze,
-            };
+            value.args.push({...depsPlace, effect: Effect.Freeze});
            fn.env.inferredEffectLocations.add(callee.loc);
          } else if (loadGlobals.has(value.args[0].identifier.id)) {
            // Global functions have no reactive dependencies, so we can insert an empty array
@@ -293,10 +275,7 @@ export function inferEffectDependencies(fn: HIRFunction): void {
                effects: null,
              },
            });
-            value.args[autodepsArgIndex] = {
-              ...depsPlace,
-              effect: Effect.Freeze,
-            };
+            value.args.push({...depsPlace, effect: Effect.Freeze});
            fn.env.inferredEffectLocations.add(callee.loc);
          }
        } else if (
@@ -344,7 +323,6 @@ export function inferEffectDependencies(fn: HIRFunction): void {
    // Renumber instructions and fix scope ranges
    markInstructionIds(fn.body);
    fixScopeAndIdentifierRanges(fn.body);
-    deadCodeElimination(fn);

    fn.env.hasInferredEffect = true;
  }
@@ -430,7 +408,6 @@ function rewriteSplices(
  rewriteBlocks.push(currBlock);

  let cursor = 0;
-
  for (const rewrite of splices) {
    while (originalInstrs[cursor].id < rewrite.location) {
      CompilerError.invariant(
@@ -452,7 +429,7 @@ function rewriteSplices(

    if (rewrite.kind === 'instr') {
      currBlock.instructions.push(rewrite.value);
-    } else if (rewrite.kind === 'block') {
+    } else {
      const {entry, blocks} = rewrite.value;
      const entryBlock = blocks.get(entry)!;
      // splice in all instructions from the entry block
--- a/compiler/packages/babel-plugin-react-compiler/src/Inference/InferFunctionEffects.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Inference/InferFunctionEffects.ts
@@ -0,0 +1,347 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {
+  CompilerError,
+  CompilerErrorDetailOptions,
+  ErrorSeverity,
+  ValueKind,
+} from '..';
+import {
+  AbstractValue,
+  BasicBlock,
+  Effect,
+  Environment,
+  FunctionEffect,
+  Instruction,
+  InstructionValue,
+  Place,
+  ValueReason,
+  getHookKind,
+  isRefOrRefValue,
+} from '../HIR';
+import {eachInstructionOperand, eachTerminalOperand} from '../HIR/visitors';
+import {assertExhaustive} from '../Utils/utils';
+
+interface State {
+  kind(place: Place): AbstractValue;
+  values(place: Place): Array<InstructionValue>;
+  isDefined(place: Place): boolean;
+}
+
+function inferOperandEffect(state: State, place: Place): null | FunctionEffect {
+  const value = state.kind(place);
+  CompilerError.invariant(value != null, {
+    reason: 'Expected operand to have a kind',
+    loc: null,
+  });
+
+  switch (place.effect) {
+    case Effect.Store:
+    case Effect.Mutate: {
+      if (isRefOrRefValue(place.identifier)) {
+        break;
+      } else if (value.kind === ValueKind.Context) {
+        CompilerError.invariant(value.context.size > 0, {
+          reason:
+            "[InferFunctionEffects] Expected Context-kind value's capture list to be non-empty.",
+          loc: place.loc,
+        });
+        return {
+          kind: 'ContextMutation',
+          loc: place.loc,
+          effect: place.effect,
+          places: value.context,
+        };
+      } else if (
+        value.kind !== ValueKind.Mutable &&
+        // We ignore mutations of primitives since this is not a React-specific problem
+        value.kind !== ValueKind.Primitive
+      ) {
+        let reason = getWriteErrorReason(value);
+        return {
+          kind:
+            value.reason.size === 1 && value.reason.has(ValueReason.Global)
+              ? 'GlobalMutation'
+              : 'ReactMutation',
+          error: {
+            reason,
+            description:
+              place.identifier.name !== null &&
+              place.identifier.name.kind === 'named'
+                ? `Found mutation of \`${place.identifier.name.value}\``
+                : null,
+            loc: place.loc,
+            suggestions: null,
+            severity: ErrorSeverity.InvalidReact,
+          },
+        };
+      }
+      break;
+    }
+  }
+  return null;
+}
+
+function inheritFunctionEffects(
+  state: State,
+  place: Place,
+): Array<FunctionEffect> {
+  const effects = inferFunctionInstrEffects(state, place);
+
+  return effects
+    .flatMap(effect => {
+      if (effect.kind === 'GlobalMutation' || effect.kind === 'ReactMutation') {
+        return [effect];
+      } else {
+        const effects: Array<FunctionEffect | null> = [];
+        CompilerError.invariant(effect.kind === 'ContextMutation', {
+          reason: 'Expected ContextMutation',
+          loc: null,
+        });
+        /**
+         * Contextual effects need to be replayed against the current inference
+         * state, which may know more about the value to which the effect applied.
+         * The main cases are:
+         * 1. The mutated context value is _still_ a context value in the current scope,
+         *    so we have to continue propagating the original context mutation.
+         * 2. The mutated context value is a mutable value in the current scope,
+         *    so the context mutation was fine and we can skip propagating the effect.
+         * 3. The mutated context value  is an immutable value in the current scope,
+         *    resulting in a non-ContextMutation FunctionEffect. We propagate that new,
+         *    more detailed effect to the current function context.
+         */
+        for (const place of effect.places) {
+          if (state.isDefined(place)) {
+            const replayedEffect = inferOperandEffect(state, {
+              ...place,
+              loc: effect.loc,
+              effect: effect.effect,
+            });
+            if (replayedEffect != null) {
+              if (replayedEffect.kind === 'ContextMutation') {
+                // Case 1, still a context value so propagate the original effect
+                effects.push(effect);
+              } else {
+                // Case 3, immutable value so propagate the more precise effect
+                effects.push(replayedEffect);
+              }
+            } // else case 2, local mutable value so this effect was fine
+          }
+        }
+        return effects;
+      }
+    })
+    .filter((effect): effect is FunctionEffect => effect != null);
+}
+
+function inferFunctionInstrEffects(
+  state: State,
+  place: Place,
+): Array<FunctionEffect> {
+  const effects: Array<FunctionEffect> = [];
+  const instrs = state.values(place);
+  CompilerError.invariant(instrs != null, {
+    reason: 'Expected operand to have instructions',
+    loc: null,
+  });
+
+  for (const instr of instrs) {
+    if (
+      (instr.kind === 'FunctionExpression' || instr.kind === 'ObjectMethod') &&
+      instr.loweredFunc.func.effects != null
+    ) {
+      effects.push(...instr.loweredFunc.func.effects);
+    }
+  }
+
+  return effects;
+}
+
+function operandEffects(
+  state: State,
+  place: Place,
+  filterRenderSafe: boolean,
+): Array<FunctionEffect> {
+  const functionEffects: Array<FunctionEffect> = [];
+  const effect = inferOperandEffect(state, place);
+  effect && functionEffects.push(effect);
+  functionEffects.push(...inheritFunctionEffects(state, place));
+  if (filterRenderSafe) {
+    return functionEffects.filter(effect => !isEffectSafeOutsideRender(effect));
+  } else {
+    return functionEffects;
+  }
+}
+
+export function inferInstructionFunctionEffects(
+  env: Environment,
+  state: State,
+  instr: Instruction,
+): Array<FunctionEffect> {
+  const functionEffects: Array<FunctionEffect> = [];
+  switch (instr.value.kind) {
+    case 'JsxExpression': {
+      if (instr.value.tag.kind === 'Identifier') {
+        functionEffects.push(...operandEffects(state, instr.value.tag, false));
+      }
+      instr.value.children?.forEach(child =>
+        functionEffects.push(...operandEffects(state, child, false)),
+      );
+      for (const attr of instr.value.props) {
+        if (attr.kind === 'JsxSpreadAttribute') {
+          functionEffects.push(...operandEffects(state, attr.argument, false));
+        } else {
+          functionEffects.push(...operandEffects(state, attr.place, true));
+        }
+      }
+      break;
+    }
+    case 'ObjectMethod':
+    case 'FunctionExpression': {
+      /**
+       * If this function references other functions, propagate the referenced function's
+       * effects to this function.
+       *
+       * ```
+       * let f = () => global = true;
+       * let g = () => f();
+       * g();
+       * ```
+       *
+       * In this example, because `g` references `f`, we propagate the GlobalMutation from
+       * `f` to `g`. Thus, referencing `g` in `g()` will evaluate the GlobalMutation in the outer
+       * function effect context and report an error. But if instead we do:
+       *
+       * ```
+       * let f = () => global = true;
+       * let g = () => f();
+       * useEffect(() => g(), [g])
+       * ```
+       *
+       * Now `g`'s effects will be discarded since they're in a useEffect.
+       */
+      for (const operand of eachInstructionOperand(instr)) {
+        instr.value.loweredFunc.func.effects ??= [];
+        instr.value.loweredFunc.func.effects.push(
+          ...inferFunctionInstrEffects(state, operand),
+        );
+      }
+      break;
+    }
+    case 'MethodCall':
+    case 'CallExpression': {
+      let callee;
+      if (instr.value.kind === 'MethodCall') {
+        callee = instr.value.property;
+        functionEffects.push(
+          ...operandEffects(state, instr.value.receiver, false),
+        );
+      } else {
+        callee = instr.value.callee;
+      }
+      functionEffects.push(...operandEffects(state, callee, false));
+      let isHook = getHookKind(env, callee.identifier) != null;
+      for (const arg of instr.value.args) {
+        const place = arg.kind === 'Identifier' ? arg : arg.place;
+        /*
+         * Join the effects of the argument with the effects of the enclosing function,
+         * unless the we're detecting a global mutation inside a useEffect hook
+         */
+        functionEffects.push(...operandEffects(state, place, isHook));
+      }
+      break;
+    }
+    case 'StartMemoize':
+    case 'FinishMemoize':
+    case 'LoadLocal':
+    case 'StoreLocal': {
+      break;
+    }
+    case 'StoreGlobal': {
+      functionEffects.push({
+        kind: 'GlobalMutation',
+        error: {
+          reason:
+            'Unexpected reassignment of a variable which was defined outside of the component. Components and hooks should be pure and side-effect free, but variable reassignment is a form of side-effect. If this variable is used in rendering, use useState instead. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#side-effects-must-run-outside-of-render)',
+          loc: instr.loc,
+          suggestions: null,
+          severity: ErrorSeverity.InvalidReact,
+        },
+      });
+      break;
+    }
+    default: {
+      for (const operand of eachInstructionOperand(instr)) {
+        functionEffects.push(...operandEffects(state, operand, false));
+      }
+    }
+  }
+  return functionEffects;
+}
+
+export function inferTerminalFunctionEffects(
+  state: State,
+  block: BasicBlock,
+): Array<FunctionEffect> {
+  const functionEffects: Array<FunctionEffect> = [];
+  for (const operand of eachTerminalOperand(block.terminal)) {
+    functionEffects.push(...operandEffects(state, operand, true));
+  }
+  return functionEffects;
+}
+
+export function transformFunctionEffectErrors(
+  functionEffects: Array<FunctionEffect>,
+): Array<CompilerErrorDetailOptions> {
+  return functionEffects.map(eff => {
+    switch (eff.kind) {
+      case 'ReactMutation':
+      case 'GlobalMutation': {
+        return eff.error;
+      }
+      case 'ContextMutation': {
+        return {
+          severity: ErrorSeverity.Invariant,
+          reason: `Unexpected ContextMutation in top-level function effects`,
+          loc: eff.loc,
+        };
+      }
+      default:
+        assertExhaustive(
+          eff,
+          `Unexpected function effect kind \`${(eff as any).kind}\``,
+        );
+    }
+  });
+}
+
+function isEffectSafeOutsideRender(effect: FunctionEffect): boolean {
+  return effect.kind === 'GlobalMutation';
+}
+
+export function getWriteErrorReason(abstractValue: AbstractValue): string {
+  if (abstractValue.reason.has(ValueReason.Global)) {
+    return 'Writing to a variable defined outside a component or hook is not allowed. Consider using an effect';
+  } else if (abstractValue.reason.has(ValueReason.JsxCaptured)) {
+    return 'Updating a value used previously in JSX is not allowed. Consider moving the mutation before the JSX';
+  } else if (abstractValue.reason.has(ValueReason.Context)) {
+    return `Mutating a value returned from 'useContext()', which should not be mutated`;
+  } else if (abstractValue.reason.has(ValueReason.KnownReturnSignature)) {
+    return 'Mutating a value returned from a function whose return value should not be mutated';
+  } else if (abstractValue.reason.has(ValueReason.ReactiveFunctionArgument)) {
+    return 'Mutating component props or hook arguments is not allowed. Consider using a local variable instead';
+  } else if (abstractValue.reason.has(ValueReason.State)) {
+    return "Mutating a value returned from 'useState()', which should not be mutated. Use the setter function to update instead";
+  } else if (abstractValue.reason.has(ValueReason.ReducerState)) {
+    return "Mutating a value returned from 'useReducer()', which should not be mutated. Use the dispatch function to update instead";
+  } else if (abstractValue.reason.has(ValueReason.Effect)) {
+    return 'Updating a value used previously in an effect function or as an effect dependency is not allowed. Consider moving the mutation before calling useEffect()';
+  } else {
+    return 'This mutates a variable that React considers immutable';
+  }
+}
--- a/compiler/packages/babel-plugin-react-compiler/src/Inference/InferMutableLifetimes.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Inference/InferMutableLifetimes.ts
@@ -0,0 +1,218 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {
+  Effect,
+  HIRFunction,
+  Identifier,
+  InstructionId,
+  InstructionKind,
+  isArrayType,
+  isMapType,
+  isRefOrRefValue,
+  isSetType,
+  makeInstructionId,
+  Place,
+} from '../HIR/HIR';
+import {printPlace} from '../HIR/PrintHIR';
+import {
+  eachInstructionLValue,
+  eachInstructionOperand,
+  eachTerminalOperand,
+} from '../HIR/visitors';
+import {assertExhaustive} from '../Utils/utils';
+
+/*
+ * For each usage of a value in the given function, determines if the usage
+ * may be succeeded by a mutable usage of that same value and if so updates
+ * the usage to be mutable.
+ *
+ * Stated differently, this inference ensures that inferred capabilities of
+ * each reference are as follows:
+ * - freeze: the value is frozen at this point
+ * - readonly: the value is not modified at this point *or any subsequent
+ *    point*
+ * - mutable: the value is modified at this point *or some subsequent point*.
+ *
+ * Note that this refines the capabilities inferered by InferReferenceCapability,
+ * which looks at individual references and not the lifetime of a value's mutability.
+ *
+ * == Algorithm
+ *
+ * TODO:
+ * 1. Forward data-flow analysis to determine aliasing. Unlike InferReferenceCapability
+ *     which only tracks aliasing of top-level variables (`y = x`), this analysis needs
+ *     to know if a value is aliased anywhere (`y.x = x`). The forward data flow tracks
+ *     all possible locations which may have aliased a value. The concrete result is
+ *     a mapping of each Place to the set of possibly-mutable values it may alias.
+ *
+ * ```
+ * const x = []; // {x: v0; v0: mutable []}
+ * const y = {}; // {x: v0, y: v1; v0: mutable [], v1: mutable []}
+ * y.x = x;      // {x: v0, y: v1; v0: mutable [v1], v1: mutable [v0]}
+ * read(x);      // {x: v0, y: v1; v0: mutable [v1], v1: mutable [v0]}
+ * mutate(y);    // can infer that y mutates v0 and v1
+ * ```
+ *
+ * DONE:
+ * 2. Forward data-flow analysis to compute mutability liveness. Walk forwards over
+ *     the CFG and track which values are mutated in a successor.
+ *
+ * ```
+ * mutate(y);    // mutable y => v0, v1 mutated
+ * read(x);      // x maps to v0, v1, those are in the mutated-later set, so x is mutable here
+ * ...
+ * ```
+ */
+
+function infer(place: Place, instrId: InstructionId): void {
+  if (!isRefOrRefValue(place.identifier)) {
+    place.identifier.mutableRange.end = makeInstructionId(instrId + 1);
+  }
+}
+
+function inferPlace(
+  place: Place,
+  instrId: InstructionId,
+  inferMutableRangeForStores: boolean,
+): void {
+  switch (place.effect) {
+    case Effect.Unknown: {
+      throw new Error(`Found an unknown place ${printPlace(place)}}!`);
+    }
+    case Effect.Capture:
+    case Effect.Read:
+    case Effect.Freeze:
+      return;
+    case Effect.Store:
+      if (inferMutableRangeForStores) {
+        infer(place, instrId);
+      }
+      return;
+    case Effect.ConditionallyMutateIterator: {
+      const identifier = place.identifier;
+      if (
+        !isArrayType(identifier) &&
+        !isSetType(identifier) &&
+        !isMapType(identifier)
+      ) {
+        infer(place, instrId);
+      }
+      return;
+    }
+    case Effect.ConditionallyMutate:
+    case Effect.Mutate: {
+      infer(place, instrId);
+      return;
+    }
+    default:
+      assertExhaustive(place.effect, `Unexpected ${printPlace(place)} effect`);
+  }
+}
+
+export function inferMutableLifetimes(
+  func: HIRFunction,
+  inferMutableRangeForStores: boolean,
+): void {
+  /*
+   * Context variables only appear to mutate where they are assigned, but we need
+   * to force their range to start at their declaration. Track the declaring instruction
+   * id so that the ranges can be extended if/when they are reassigned
+   */
+  const contextVariableDeclarationInstructions = new Map<
+    Identifier,
+    InstructionId
+  >();
+  for (const [_, block] of func.body.blocks) {
+    for (const phi of block.phis) {
+      const isPhiMutatedAfterCreation: boolean =
+        phi.place.identifier.mutableRange.end >
+        (block.instructions.at(0)?.id ?? block.terminal.id);
+      if (
+        inferMutableRangeForStores &&
+        isPhiMutatedAfterCreation &&
+        phi.place.identifier.mutableRange.start === 0
+      ) {
+        for (const [, operand] of phi.operands) {
+          if (phi.place.identifier.mutableRange.start === 0) {
+            phi.place.identifier.mutableRange.start =
+              operand.identifier.mutableRange.start;
+          } else {
+            phi.place.identifier.mutableRange.start = makeInstructionId(
+              Math.min(
+                phi.place.identifier.mutableRange.start,
+                operand.identifier.mutableRange.start,
+              ),
+            );
+          }
+        }
+      }
+    }
+
+    for (const instr of block.instructions) {
+      for (const operand of eachInstructionLValue(instr)) {
+        const lvalueId = operand.identifier;
+
+        /*
+         * lvalue start being mutable when they're initially assigned a
+         * value.
+         */
+        lvalueId.mutableRange.start = instr.id;
+
+        /*
+         * Let's be optimistic and assume this lvalue is not mutable by
+         * default.
+         */
+        lvalueId.mutableRange.end = makeInstructionId(instr.id + 1);
+      }
+      for (const operand of eachInstructionOperand(instr)) {
+        inferPlace(operand, instr.id, inferMutableRangeForStores);
+      }
+
+      if (
+        instr.value.kind === 'DeclareContext' ||
+        (instr.value.kind === 'StoreContext' &&
+          instr.value.lvalue.kind !== InstructionKind.Reassign &&
+          !contextVariableDeclarationInstructions.has(
+            instr.value.lvalue.place.identifier,
+          ))
+      ) {
+        /**
+         * Save declarations of context variables if they hasn't already been
+         * declared (due to hoisted declarations).
+         */
+        contextVariableDeclarationInstructions.set(
+          instr.value.lvalue.place.identifier,
+          instr.id,
+        );
+      } else if (instr.value.kind === 'StoreContext') {
+        /*
+         * Else this is a reassignment, extend the range from the declaration (if present).
+         * Note that declarations may not be present for context variables that are reassigned
+         * within a function expression before (or without) a read of the same variable
+         */
+        const declaration = contextVariableDeclarationInstructions.get(
+          instr.value.lvalue.place.identifier,
+        );
+        if (
+          declaration != null &&
+          !isRefOrRefValue(instr.value.lvalue.place.identifier)
+        ) {
+          const range = instr.value.lvalue.place.identifier.mutableRange;
+          if (range.start === 0) {
+            range.start = declaration;
+          } else {
+            range.start = makeInstructionId(Math.min(range.start, declaration));
+          }
+        }
+      }
+    }
+    for (const operand of eachTerminalOperand(block.terminal)) {
+      inferPlace(operand, block.terminal.id, inferMutableRangeForStores);
+    }
+  }
+}
--- a/compiler/packages/babel-plugin-react-compiler/src/Inference/InferMutableRanges.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Inference/InferMutableRanges.ts
@@ -0,0 +1,102 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {HIRFunction, Identifier} from '../HIR/HIR';
+import {inferAliasForUncalledFunctions} from './InerAliasForUncalledFunctions';
+import {inferAliases} from './InferAlias';
+import {inferAliasForPhis} from './InferAliasForPhis';
+import {inferAliasForStores} from './InferAliasForStores';
+import {inferMutableLifetimes} from './InferMutableLifetimes';
+import {inferMutableRangesForAlias} from './InferMutableRangesForAlias';
+import {inferTryCatchAliases} from './InferTryCatchAliases';
+
+export function inferMutableRanges(ir: HIRFunction): void {
+  // Infer mutable ranges for non fields
+  inferMutableLifetimes(ir, false);
+
+  // Calculate aliases
+  const aliases = inferAliases(ir);
+  /*
+   * Calculate aliases for try/catch, where any value created
+   * in the try block could be aliased to the catch param
+   */
+  inferTryCatchAliases(ir, aliases);
+
+  /*
+   * Eagerly canonicalize so that if nothing changes we can bail out
+   * after a single iteration
+   */
+  let prevAliases: Map<Identifier, Identifier> = aliases.canonicalize();
+  while (true) {
+    // Infer mutable ranges for aliases that are not fields
+    inferMutableRangesForAlias(ir, aliases);
+
+    // Update aliasing information of fields
+    inferAliasForStores(ir, aliases);
+
+    // Update aliasing information of phis
+    inferAliasForPhis(ir, aliases);
+
+    const nextAliases = aliases.canonicalize();
+    if (areEqualMaps(prevAliases, nextAliases)) {
+      break;
+    }
+    prevAliases = nextAliases;
+  }
+
+  // Re-infer mutable ranges for all values
+  inferMutableLifetimes(ir, true);
+
+  /**
+   * The second inferMutableLifetimes() call updates mutable ranges
+   * of values to account for Store effects. Now we need to update
+   * all aliases of such values to extend their ranges as well. Note
+   * that the store only mutates the the directly aliased value and
+   * not any of its inner captured references. For example:
+   *
+   * ```
+   * let y;
+   * if (cond) {
+   *   y = [];
+   * } else {
+   *   y = [{}];
+   * }
+   * y.push(z);
+   * ```
+   *
+   * The Store effect from the `y.push` modifies the values that `y`
+   * directly aliases - the two arrays from the if/else branches -
+   * but does not modify values that `y` "contains" such as the
+   * object literal or `z`.
+   */
+  prevAliases = aliases.canonicalize();
+  while (true) {
+    inferMutableRangesForAlias(ir, aliases);
+    inferAliasForPhis(ir, aliases);
+    inferAliasForUncalledFunctions(ir, aliases);
+    const nextAliases = aliases.canonicalize();
+    if (areEqualMaps(prevAliases, nextAliases)) {
+      break;
+    }
+    prevAliases = nextAliases;
+  }
+}
+
+function areEqualMaps<T, U>(a: Map<T, U>, b: Map<T, U>): boolean {
+  if (a.size !== b.size) {
+    return false;
+  }
+  for (const [key, value] of a) {
+    if (!b.has(key)) {
+      return false;
+    }
+    if (b.get(key) !== value) {
+      return false;
+    }
+  }
+  return true;
+}
--- a/compiler/packages/babel-plugin-react-compiler/src/Inference/InferMutableRangesForAlias.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Inference/InferMutableRangesForAlias.ts
@@ -0,0 +1,54 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {
+  HIRFunction,
+  Identifier,
+  InstructionId,
+  isRefOrRefValue,
+} from '../HIR/HIR';
+import DisjointSet from '../Utils/DisjointSet';
+
+export function inferMutableRangesForAlias(
+  _fn: HIRFunction,
+  aliases: DisjointSet<Identifier>,
+): void {
+  const aliasSets = aliases.buildSets();
+  for (const aliasSet of aliasSets) {
+    /*
+     * Update mutableRange.end only if the identifiers have actually been
+     * mutated.
+     */
+    const mutatingIdentifiers = [...aliasSet].filter(
+      id =>
+        id.mutableRange.end - id.mutableRange.start > 1 && !isRefOrRefValue(id),
+    );
+
+    if (mutatingIdentifiers.length > 0) {
+      // Find final instruction which mutates this alias set.
+      let lastMutatingInstructionId = 0;
+      for (const id of mutatingIdentifiers) {
+        if (id.mutableRange.end > lastMutatingInstructionId) {
+          lastMutatingInstructionId = id.mutableRange.end;
+        }
+      }
+
+      /*
+       * Update mutableRange.end for all aliases in this set ending before the
+       * last mutation.
+       */
+      for (const alias of aliasSet) {
+        if (
+          alias.mutableRange.end < lastMutatingInstructionId &&
+          !isRefOrRefValue(alias)
+        ) {
+          alias.mutableRange.end = lastMutatingInstructionId as InstructionId;
+        }
+      }
+    }
+  }
+}
--- a/compiler/packages/babel-plugin-react-compiler/src/Inference/InferMutationAliasingEffects.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Inference/InferMutationAliasingEffects.ts
--- a/compiler/packages/babel-plugin-react-compiler/src/Inference/InferMutationAliasingFunctionEffects.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Inference/InferMutationAliasingFunctionEffects.ts
@@ -0,0 +1,206 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {HIRFunction, IdentifierId, Place, ValueKind, ValueReason} from '../HIR';
+import {getOrInsertDefault} from '../Utils/utils';
+import {AliasingEffect} from './AliasingEffects';
+
+/**
+ * This function tracks data flow within an inner function expression in order to
+ * compute a set of data-flow aliasing effects describing data flow between the function's
+ * params, context variables, and return value.
+ *
+ * For example, consider the following function expression:
+ *
+ * ```
+ * (x) => { return [x, y] }
+ * ```
+ *
+ * This function captures both param `x` and context variable `y` into the return value.
+ * Unlike our previous inference which counted this as a mutation of x and y, we want to
+ * build a signature for the function that describes the data flow. We would infer
+ * `Capture x -> return, Capture y -> return` effects for this function.
+ *
+ * This function *also* propagates more ambient-style effects (MutateFrozen, MutateGlobal, Impure, Render)
+ * from instructions within the function up to the function itself.
+ */
+export function inferMutationAliasingFunctionEffects(
+  fn: HIRFunction,
+): Array<AliasingEffect> | null {
+  const effects: Array<AliasingEffect> = [];
+
+  /**
+   * Map used to identify tracked variables: params, context vars, return value
+   * This is used to detect mutation/capturing/aliasing of params/context vars
+   */
+  const tracked = new Map<IdentifierId, Place>();
+  tracked.set(fn.returns.identifier.id, fn.returns);
+  for (const operand of [...fn.context, ...fn.params]) {
+    const place = operand.kind === 'Identifier' ? operand : operand.place;
+    tracked.set(place.identifier.id, place);
+  }
+
+  /**
+   * Track capturing/aliasing of context vars and params into each other and into the return.
+   * We don't need to track locals and intermediate values, since we're only concerned with effects
+   * as they relate to arguments visible outside the function.
+   *
+   * For each aliased identifier we track capture/alias/createfrom and then merge this with how
+   * the value is used. Eg capturing an alias => capture. See joinEffects() helper.
+   */
+  type AliasedIdentifier = {
+    kind: AliasingKind;
+    place: Place;
+  };
+  const dataFlow = new Map<IdentifierId, Array<AliasedIdentifier>>();
+
+  /*
+   * Check for aliasing of tracked values. Also joins the effects of how the value is
+   * used (@param kind) with the aliasing type of each value
+   */
+  function lookup(
+    place: Place,
+    kind: AliasedIdentifier['kind'],
+  ): Array<AliasedIdentifier> | null {
+    if (tracked.has(place.identifier.id)) {
+      return [{kind, place}];
+    }
+    return (
+      dataFlow.get(place.identifier.id)?.map(aliased => ({
+        kind: joinEffects(aliased.kind, kind),
+        place: aliased.place,
+      })) ?? null
+    );
+  }
+
+  // todo: fixpoint
+  for (const block of fn.body.blocks.values()) {
+    for (const phi of block.phis) {
+      const operands: Array<AliasedIdentifier> = [];
+      for (const operand of phi.operands.values()) {
+        const inputs = lookup(operand, 'Alias');
+        if (inputs != null) {
+          operands.push(...inputs);
+        }
+      }
+      if (operands.length !== 0) {
+        dataFlow.set(phi.place.identifier.id, operands);
+      }
+    }
+    for (const instr of block.instructions) {
+      if (instr.effects == null) continue;
+      for (const effect of instr.effects) {
+        if (
+          effect.kind === 'Assign' ||
+          effect.kind === 'Capture' ||
+          effect.kind === 'Alias' ||
+          effect.kind === 'CreateFrom'
+        ) {
+          const from = lookup(effect.from, effect.kind);
+          if (from == null) {
+            continue;
+          }
+          const into = lookup(effect.into, 'Alias');
+          if (into == null) {
+            getOrInsertDefault(dataFlow, effect.into.identifier.id, []).push(
+              ...from,
+            );
+          } else {
+            for (const aliased of into) {
+              getOrInsertDefault(
+                dataFlow,
+                aliased.place.identifier.id,
+                [],
+              ).push(...from);
+            }
+          }
+        } else if (
+          effect.kind === 'Create' ||
+          effect.kind === 'CreateFunction'
+        ) {
+          getOrInsertDefault(dataFlow, effect.into.identifier.id, [
+            {kind: 'Alias', place: effect.into},
+          ]);
+        } else if (
+          effect.kind === 'MutateFrozen' ||
+          effect.kind === 'MutateGlobal' ||
+          effect.kind === 'Impure' ||
+          effect.kind === 'Render'
+        ) {
+          effects.push(effect);
+        }
+      }
+    }
+    if (block.terminal.kind === 'return') {
+      const from = lookup(block.terminal.value, 'Alias');
+      if (from != null) {
+        getOrInsertDefault(dataFlow, fn.returns.identifier.id, []).push(
+          ...from,
+        );
+      }
+    }
+  }
+
+  // Create aliasing effects based on observed data flow
+  let hasReturn = false;
+  for (const [into, from] of dataFlow) {
+    const input = tracked.get(into);
+    if (input == null) {
+      continue;
+    }
+    for (const aliased of from) {
+      if (
+        aliased.place.identifier.id === input.identifier.id ||
+        !tracked.has(aliased.place.identifier.id)
+      ) {
+        continue;
+      }
+      const effect = {kind: aliased.kind, from: aliased.place, into: input};
+      effects.push(effect);
+      if (
+        into === fn.returns.identifier.id &&
+        (aliased.kind === 'Assign' || aliased.kind === 'CreateFrom')
+      ) {
+        hasReturn = true;
+      }
+    }
+  }
+  // TODO: more precise return effect inference
+  if (!hasReturn) {
+    effects.unshift({
+      kind: 'Create',
+      into: fn.returns,
+      value:
+        fn.returnType.kind === 'Primitive'
+          ? ValueKind.Primitive
+          : ValueKind.Mutable,
+      reason: ValueReason.KnownReturnSignature,
+    });
+  }
+
+  return effects;
+}
+
+export enum MutationKind {
+  None = 0,
+  Conditional = 1,
+  Definite = 2,
+}
+
+type AliasingKind = 'Alias' | 'Capture' | 'CreateFrom' | 'Assign';
+function joinEffects(
+  effect1: AliasingKind,
+  effect2: AliasingKind,
+): AliasingKind {
+  if (effect1 === 'Capture' || effect2 === 'Capture') {
+    return 'Capture';
+  } else if (effect1 === 'Assign' || effect2 === 'Assign') {
+    return 'Assign';
+  } else {
+    return 'Alias';
+  }
+}
--- a/compiler/packages/babel-plugin-react-compiler/src/Inference/InferMutationAliasingRanges.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Inference/InferMutationAliasingRanges.ts
@@ -5,6 +5,7 @@
 * LICENSE file in the root directory of this source tree.
 */

+import prettyFormat from 'pretty-format';
 import {CompilerError, SourceLocation} from '..';
 import {
  BlockId,
@@ -13,12 +14,8 @@ import {
  Identifier,
  IdentifierId,
  InstructionId,
-  isJsxType,
  makeInstructionId,
-  ValueKind,
-  ValueReason,
  Place,
-  isPrimitiveType,
 } from '../HIR/HIR';
 import {
  eachInstructionLValue,
@@ -26,58 +23,43 @@ import {
  eachTerminalOperand,
 } from '../HIR/visitors';
 import {assertExhaustive, getOrInsertWith} from '../Utils/utils';
-import {Err, Ok, Result} from '../Utils/Result';
-import {AliasingEffect, MutationReason} from './AliasingEffects';
+import {printFunction} from '../HIR';
+import {printIdentifier, printPlace} from '../HIR/PrintHIR';
+import {MutationKind} from './InferMutationAliasingFunctionEffects';
+import {Result} from '../Utils/Result';
+
+const DEBUG = false;
+const VERBOSE = false;

 /**
- * This pass builds an abstract model of the heap and interprets the effects of the
- * given function in order to determine the following:
- * - The mutable ranges of all identifiers in the function
- * - The externally-visible effects of the function, such as mutations of params and
- *   context-vars, aliasing between params/context-vars/return-value, and impure side
- *   effects.
- * - The legacy `Effect` to store on each Place.
- *
- * This pass builds a data flow graph using the effects, tracking an abstract notion
- * of "when" each effect occurs relative to the others. It then walks each mutation
- * effect against the graph, updating the range of each node that would be reachable
- * at the "time" that the effect occurred.
+ * Infers mutable ranges for all values in the program, using previously inferred
+ * mutation/aliasing effects. This pass builds a data flow graph using the effects,
+ * tracking an abstract notion of "when" each effect occurs relative to the others.
+ * It then walks each mutation effect against the graph, updating the range of each
+ * node that would be reachable at the "time" that the effect occurred.
 *
 * This pass also validates against invalid effects: any function that is reachable
 * by being called, or via a Render effect, is validated against mutating globals
 * or calling impure code.
 *
 * Note that this function also populates the outer function's aliasing effects with
- * any mutations that apply to its params or context variables.
- *
- * ## Example
- * A function expression such as the following:
+ * any mutations that apply to its params or context variables. For example, a
+ * function expression such as the following:
 *
 * ```
 * (x) => { x.y = true }
 * ```
 *
 * Would populate a `Mutate x` aliasing effect on the outer function.
- *
- * ## Returned Function Effects
- *
- * The function returns (if successful) a list of externally-visible effects.
- * This is determined by simulating a conditional, transitive mutation against
- * each param, context variable, and return value in turn, and seeing which other
- * such values are affected. If they're affected, they must be captured, so we
- * record a Capture.
- *
- * The only tricky bit is the return value, which could _alias_ (or even assign)
- * one or more of the params/context-vars rather than just capturing. So we have
- * to do a bit more tracking for returns.
 */
 export function inferMutationAliasingRanges(
  fn: HIRFunction,
  {isFunctionExpression}: {isFunctionExpression: boolean},
-): Result<Array<AliasingEffect>, CompilerError> {
-  // The set of externally-visible effects
-  const functionEffects: Array<AliasingEffect> = [];
-
+): Result<void, CompilerError> {
+  if (VERBOSE) {
+    console.log();
+    console.log(printFunction(fn));
+  }
  /**
   * Part 1: Infer mutable ranges for values. We build an abstract model of
   * values, the alias/capture edges between them, and the set of mutations.
@@ -101,7 +83,6 @@ export function inferMutationAliasingRanges(
    transitive: boolean;
    kind: MutationKind;
    place: Place;
-    reason: MutationReason | null;
  }> = [];
  const renders: Array<{index: number; place: Place}> = [];

@@ -134,6 +115,20 @@ export function inferMutationAliasingRanges(
    seenBlocks.add(block.id);

    for (const instr of block.instructions) {
+      if (
+        instr.value.kind === 'FunctionExpression' ||
+        instr.value.kind === 'ObjectMethod'
+      ) {
+        state.create(instr.lvalue, {
+          kind: 'Function',
+          function: instr.value.loweredFunc.func,
+        });
+      } else {
+        for (const lvalue of eachInstructionLValue(instr)) {
+          state.create(lvalue, {kind: 'Object'});
+        }
+      }
+
      if (instr.effects == null) continue;
      for (const effect of instr.effects) {
        if (effect.kind === 'Create') {
@@ -141,28 +136,17 @@ export function inferMutationAliasingRanges(
        } else if (effect.kind === 'CreateFunction') {
          state.create(effect.into, {
            kind: 'Function',
-            effect,
+            function: effect.function.loweredFunc.func,
          });
        } else if (effect.kind === 'CreateFrom') {
          state.createFrom(index++, effect.from, effect.into);
        } else if (effect.kind === 'Assign') {
-          /**
-           * TODO: Invariant that the node is not initialized yet
-           *
-           * InferFunctionExpressionAliasingEffectSignatures currently infers
-           * Assign effects in some places that should be Alias, leading to
-           * Assign effects that reinitialize a value. The end result appears to
-           * be fine, but we should fix that inference pass so that we add the
-           * invariant here.
-           */
          if (!state.nodes.has(effect.into.identifier)) {
-            state.create(effect.into, {kind: 'Assign'});
+            state.create(effect.into, {kind: 'Object'});
          }
          state.assign(index++, effect.from, effect.into);
        } else if (effect.kind === 'Alias') {
          state.assign(index++, effect.from, effect.into);
-        } else if (effect.kind === 'MaybeAlias') {
-          state.maybeAlias(index++, effect.from, effect.into);
        } else if (effect.kind === 'Capture') {
          state.capture(index++, effect.from, effect.into);
        } else if (
@@ -177,7 +161,6 @@ export function inferMutationAliasingRanges(
              effect.kind === 'MutateTransitive'
                ? MutationKind.Definite
                : MutationKind.Conditional,
-            reason: null,
            place: effect.value,
          });
        } else if (
@@ -192,7 +175,6 @@ export function inferMutationAliasingRanges(
              effect.kind === 'Mutate'
                ? MutationKind.Definite
                : MutationKind.Conditional,
-            reason: effect.kind === 'Mutate' ? (effect.reason ?? null) : null,
            place: effect.value,
          });
        } else if (
@@ -200,11 +182,9 @@ export function inferMutationAliasingRanges(
          effect.kind === 'MutateGlobal' ||
          effect.kind === 'Impure'
        ) {
-          errors.pushDiagnostic(effect.error);
-          functionEffects.push(effect);
+          errors.push(effect.error);
        } else if (effect.kind === 'Render') {
          renders.push({index: index++, place: effect.place});
-          functionEffects.push(effect);
        }
      }
    }
@@ -236,6 +216,10 @@ export function inferMutationAliasingRanges(
    }
  }

+  if (VERBOSE) {
+    console.log(state.debug());
+    console.log(pretty(mutations));
+  }
  for (const mutation of mutations) {
    state.mutate(
      mutation.index,
@@ -244,16 +228,18 @@ export function inferMutationAliasingRanges(
      mutation.transitive,
      mutation.kind,
      mutation.place.loc,
-      mutation.reason,
      errors,
    );
  }
  for (const render of renders) {
    state.render(render.index, render.place.identifier, errors);
  }
+  if (DEBUG) {
+    console.log(pretty([...state.nodes.keys()]));
+  }
+  fn.aliasingEffects ??= [];
  for (const param of [...fn.context, ...fn.params]) {
    const place = param.kind === 'Identifier' ? param : param.place;
-
    const node = state.nodes.get(place.identifier);
    if (node == null) {
      continue;
@@ -262,29 +248,28 @@ export function inferMutationAliasingRanges(
    if (node.local != null) {
      if (node.local.kind === MutationKind.Conditional) {
        mutated = true;
-        functionEffects.push({
+        fn.aliasingEffects.push({
          kind: 'MutateConditionally',
          value: {...place, loc: node.local.loc},
        });
      } else if (node.local.kind === MutationKind.Definite) {
        mutated = true;
-        functionEffects.push({
+        fn.aliasingEffects.push({
          kind: 'Mutate',
          value: {...place, loc: node.local.loc},
-          reason: node.mutationReason,
        });
      }
    }
    if (node.transitive != null) {
      if (node.transitive.kind === MutationKind.Conditional) {
        mutated = true;
-        functionEffects.push({
+        fn.aliasingEffects.push({
          kind: 'MutateTransitiveConditionally',
          value: {...place, loc: node.transitive.loc},
        });
      } else if (node.transitive.kind === MutationKind.Definite) {
        mutated = true;
-        functionEffects.push({
+        fn.aliasingEffects.push({
          kind: 'MutateTransitive',
          value: {...place, loc: node.transitive.loc},
        });
@@ -354,8 +339,7 @@ export function inferMutationAliasingRanges(
          case 'Assign':
          case 'Alias':
          case 'Capture':
-          case 'CreateFrom':
-          case 'MaybeAlias': {
+          case 'CreateFrom': {
            const isMutatedOrReassigned =
              effect.into.identifier.mutableRange.end > instr.id;
            if (isMutatedOrReassigned) {
@@ -474,160 +458,10 @@ export function inferMutationAliasingRanges(
    }
  }

-  const tracked: Array<Place> = [];
-  for (const param of [...fn.params, ...fn.context, fn.returns]) {
-    const place = param.kind === 'Identifier' ? param : param.place;
-    tracked.push(place);
+  if (VERBOSE) {
+    console.log(printFunction(fn));
  }
-
-  const returned: Set<Node> = new Set();
-  const queue: Array<Node> = [state.nodes.get(fn.returns.identifier)!];
-  const seen: Set<Node> = new Set();
-  while (queue.length !== 0) {
-    const node = queue.pop()!;
-    if (seen.has(node)) {
-      continue;
-    }
-    seen.add(node);
-    for (const id of node.aliases.keys()) {
-      queue.push(state.nodes.get(id)!);
-    }
-    for (const id of node.createdFrom.keys()) {
-      queue.push(state.nodes.get(id)!);
-    }
-    if (node.id.id === fn.returns.identifier.id) {
-      continue;
-    }
-    switch (node.value.kind) {
-      case 'Assign':
-      case 'CreateFrom': {
-        break;
-      }
-      case 'Phi':
-      case 'Object':
-      case 'Function': {
-        returned.add(node);
-        break;
-      }
-      default: {
-        assertExhaustive(
-          node.value,
-          `Unexpected node value kind '${(node.value as any).kind}'`,
-        );
-      }
-    }
-  }
-  const returnedValues = [...returned];
-  if (
-    returnedValues.length === 1 &&
-    returnedValues[0].value.kind === 'Object' &&
-    tracked.some(place => place.identifier.id === returnedValues[0].id.id)
-  ) {
-    const from = tracked.find(
-      place => place.identifier.id === returnedValues[0].id.id,
-    )!;
-    functionEffects.push({
-      kind: 'Assign',
-      from,
-      into: fn.returns,
-    });
-  } else if (
-    returnedValues.length === 1 &&
-    returnedValues[0].value.kind === 'Function'
-  ) {
-    const outerContext = new Set(fn.context.map(p => p.identifier.id));
-    const effect = returnedValues[0].value.effect;
-    functionEffects.push({
-      kind: 'CreateFunction',
-      function: {
-        ...effect.function,
-        loweredFunc: {
-          func: {
-            ...effect.function.loweredFunc.func,
-            context: effect.function.loweredFunc.func.context.filter(p =>
-              outerContext.has(p.identifier.id),
-            ),
-          },
-        },
-      },
-      captures: effect.captures.filter(p => outerContext.has(p.identifier.id)),
-      into: fn.returns,
-    });
-  } else {
-    const returns = fn.returns.identifier;
-    functionEffects.push({
-      kind: 'Create',
-      into: fn.returns,
-      value: isPrimitiveType(returns)
-        ? ValueKind.Primitive
-        : isJsxType(returns.type)
-          ? ValueKind.Frozen
-          : ValueKind.Mutable,
-      reason: ValueReason.KnownReturnSignature,
-    });
-  }
-
-  /**
-   * Part 3
-   * Finish populating the externally visible effects. Above we bubble-up the side effects
-   * (MutateFrozen/MutableGlobal/Impure/Render) as well as mutations of context variables.
-   * Here we populate an effect to create the return value as well as populating alias/capture
-   * effects for how data flows between the params, context vars, and return.
-   */
-  /**
-   * Determine precise data-flow effects by simulating transitive mutations of the params/
-   * captures and seeing what other params/context variables are affected. Anything that
-   * would be transitively mutated needs a capture relationship.
-   */
-  const ignoredErrors = new CompilerError();
-  for (const into of tracked) {
-    const mutationIndex = index++;
-    state.mutate(
-      mutationIndex,
-      into.identifier,
-      null,
-      true,
-      MutationKind.Conditional,
-      into.loc,
-      null,
-      ignoredErrors,
-    );
-    for (const from of tracked) {
-      if (
-        from.identifier.id === into.identifier.id ||
-        from.identifier.id === fn.returns.identifier.id
-      ) {
-        continue;
-      }
-      const fromNode = state.nodes.get(from.identifier);
-      CompilerError.invariant(fromNode != null, {
-        reason: `Expected a node to exist for all parameters and context variables`,
-        loc: into.loc,
-      });
-      if (fromNode.lastMutated === mutationIndex) {
-        if (into.identifier.id === fn.returns.identifier.id) {
-          // The return value could be any of the params/context variables
-          functionEffects.push({
-            kind: 'Alias',
-            from,
-            into,
-          });
-        } else {
-          // Otherwise params/context-vars can only capture each other
-          functionEffects.push({
-            kind: 'Capture',
-            from,
-            into,
-          });
-        }
-      }
-    }
-  }
-
-  if (errors.hasErrors() && !isFunctionExpression) {
-    return Err(errors);
-  }
-  return Ok(functionEffects);
+  return errors.asResult();
 }

 function appendFunctionErrors(errors: CompilerError, fn: HIRFunction): void {
@@ -636,43 +470,25 @@ function appendFunctionErrors(errors: CompilerError, fn: HIRFunction): void {
      case 'Impure':
      case 'MutateFrozen':
      case 'MutateGlobal': {
-        errors.pushDiagnostic(effect.error);
+        errors.push(effect.error);
        break;
      }
    }
  }
 }

-export enum MutationKind {
-  None = 0,
-  Conditional = 1,
-  Definite = 2,
-}
-
 type Node = {
  id: Identifier;
  createdFrom: Map<Identifier, number>;
  captures: Map<Identifier, number>;
  aliases: Map<Identifier, number>;
-  maybeAliases: Map<Identifier, number>;
-  edges: Array<{
-    index: number;
-    node: Identifier;
-    kind: 'capture' | 'alias' | 'maybeAlias';
-  }>;
+  edges: Array<{index: number; node: Identifier; kind: 'capture' | 'alias'}>;
  transitive: {kind: MutationKind; loc: SourceLocation} | null;
  local: {kind: MutationKind; loc: SourceLocation} | null;
-  lastMutated: number;
-  mutationReason: MutationReason | null;
  value:
-    | {kind: 'Assign'}
-    | {kind: 'CreateFrom'}
    | {kind: 'Object'}
    | {kind: 'Phi'}
-    | {
-        kind: 'Function';
-        effect: Extract<AliasingEffect, {kind: 'CreateFunction'}>;
-      };
+    | {kind: 'Function'; function: HIRFunction};
 };
 class AliasingState {
  nodes: Map<Identifier, Node> = new Map();
@@ -683,21 +499,23 @@ class AliasingState {
      createdFrom: new Map(),
      captures: new Map(),
      aliases: new Map(),
-      maybeAliases: new Map(),
      edges: [],
      transitive: null,
      local: null,
-      lastMutated: 0,
-      mutationReason: null,
      value,
    });
  }

  createFrom(index: number, from: Place, into: Place): void {
-    this.create(into, {kind: 'CreateFrom'});
+    this.create(into, {kind: 'Object'});
    const fromNode = this.nodes.get(from.identifier);
    const toNode = this.nodes.get(into.identifier);
    if (fromNode == null || toNode == null) {
+      if (VERBOSE) {
+        console.log(
+          `skip: createFrom ${printPlace(from)}${!!fromNode} -> ${printPlace(into)}${!!toNode}`,
+        );
+      }
      return;
    }
    fromNode.edges.push({index, node: into.identifier, kind: 'alias'});
@@ -710,6 +528,11 @@ class AliasingState {
    const fromNode = this.nodes.get(from.identifier);
    const toNode = this.nodes.get(into.identifier);
    if (fromNode == null || toNode == null) {
+      if (VERBOSE) {
+        console.log(
+          `skip: capture ${printPlace(from)}${!!fromNode} -> ${printPlace(into)}${!!toNode}`,
+        );
+      }
      return;
    }
    fromNode.edges.push({index, node: into.identifier, kind: 'capture'});
@@ -722,6 +545,11 @@ class AliasingState {
    const fromNode = this.nodes.get(from.identifier);
    const toNode = this.nodes.get(into.identifier);
    if (fromNode == null || toNode == null) {
+      if (VERBOSE) {
+        console.log(
+          `skip: assign ${printPlace(from)}${!!fromNode} -> ${printPlace(into)}${!!toNode}`,
+        );
+      }
      return;
    }
    fromNode.edges.push({index, node: into.identifier, kind: 'alias'});
@@ -730,18 +558,6 @@ class AliasingState {
    }
  }

-  maybeAlias(index: number, from: Place, into: Place): void {
-    const fromNode = this.nodes.get(from.identifier);
-    const toNode = this.nodes.get(into.identifier);
-    if (fromNode == null || toNode == null) {
-      return;
-    }
-    fromNode.edges.push({index, node: into.identifier, kind: 'maybeAlias'});
-    if (!toNode.maybeAliases.has(from.identifier)) {
-      toNode.maybeAliases.set(from.identifier, index);
-    }
-  }
-
  render(index: number, start: Identifier, errors: CompilerError): void {
    const seen = new Set<Identifier>();
    const queue: Array<Identifier> = [start];
@@ -756,10 +572,7 @@ class AliasingState {
        continue;
      }
      if (node.value.kind === 'Function') {
-        appendFunctionErrors(
-          errors,
-          node.value.effect.function.loweredFunc.func,
-        );
+        appendFunctionErrors(errors, node.value.function);
      }
      for (const [alias, when] of node.createdFrom) {
        if (when >= index) {
@@ -785,48 +598,52 @@ class AliasingState {
  mutate(
    index: number,
    start: Identifier,
-    // Null is used for simulated mutations
-    end: InstructionId | null,
+    end: InstructionId,
    transitive: boolean,
-    startKind: MutationKind,
+    kind: MutationKind,
    loc: SourceLocation,
-    reason: MutationReason | null,
    errors: CompilerError,
  ): void {
-    const seen = new Map<Identifier, MutationKind>();
+    if (DEBUG) {
+      console.log(
+        `mutate ix=${index} start=$${start.id} end=[${end}]${transitive ? ' transitive' : ''} kind=${kind}`,
+      );
+    }
+    const seen = new Set<Identifier>();
    const queue: Array<{
      place: Identifier;
      transitive: boolean;
      direction: 'backwards' | 'forwards';
-      kind: MutationKind;
-    }> = [{place: start, transitive, direction: 'backwards', kind: startKind}];
+    }> = [{place: start, transitive, direction: 'backwards'}];
    while (queue.length !== 0) {
-      const {place: current, transitive, direction, kind} = queue.pop()!;
-      const previousKind = seen.get(current);
-      if (previousKind != null && previousKind >= kind) {
+      const {place: current, transitive, direction} = queue.pop()!;
+      if (seen.has(current)) {
        continue;
      }
-      seen.set(current, kind);
+      seen.add(current);
      const node = this.nodes.get(current);
      if (node == null) {
+        if (DEBUG) {
+          console.log(
+            `no node! ${printIdentifier(start)} for identifier ${printIdentifier(current)}`,
+          );
+        }
        continue;
      }
-      node.mutationReason ??= reason;
-      node.lastMutated = Math.max(node.lastMutated, index);
-      if (end != null) {
-        node.id.mutableRange.end = makeInstructionId(
-          Math.max(node.id.mutableRange.end, end),
+      if (DEBUG) {
+        console.log(
+          `  mutate $${node.id.id} transitive=${transitive} direction=${direction}`,
        );
      }
+      node.id.mutableRange.end = makeInstructionId(
+        Math.max(node.id.mutableRange.end, end),
+      );
      if (
        node.value.kind === 'Function' &&
        node.transitive == null &&
        node.local == null
      ) {
-        appendFunctionErrors(
-          errors,
-          node.value.effect.function.loweredFunc.func,
-        );
+        appendFunctionErrors(errors, node.value.function);
      }
      if (transitive) {
        if (node.transitive == null || node.transitive.kind < kind) {
@@ -846,18 +663,13 @@ class AliasingState {
        if (edge.index >= index) {
          break;
        }
-        queue.push({place: edge.node, transitive, direction: 'forwards', kind});
+        queue.push({place: edge.node, transitive, direction: 'forwards'});
      }
      for (const [alias, when] of node.createdFrom) {
        if (when >= index) {
          continue;
        }
-        queue.push({
-          place: alias,
-          transitive: true,
-          direction: 'backwards',
-          kind,
-        });
+        queue.push({place: alias, transitive: true, direction: 'backwards'});
      }
      if (direction === 'backwards' || node.value.kind !== 'Phi') {
        /**
@@ -874,25 +686,7 @@ class AliasingState {
          if (when >= index) {
            continue;
          }
-          queue.push({place: alias, transitive, direction: 'backwards', kind});
-        }
-        /**
-         * MaybeAlias indicates potential data flow from unknown function calls,
-         * so we downgrade mutations through these aliases to consider them
-         * conditional. This means we'll consider them for mutation *range*
-         * purposes but not report validation errors for mutations, since
-         * we aren't sure that the `from` value could actually be aliased.
-         */
-        for (const [alias, when] of node.maybeAliases) {
-          if (when >= index) {
-            continue;
-          }
-          queue.push({
-            place: alias,
-            transitive,
-            direction: 'backwards',
-            kind: MutationKind.Conditional,
-          });
+          queue.push({place: alias, transitive, direction: 'backwards'});
        }
      }
      /**
@@ -903,14 +697,41 @@ class AliasingState {
          if (when >= index) {
            continue;
          }
-          queue.push({
-            place: capture,
-            transitive,
-            direction: 'backwards',
-            kind,
-          });
+          queue.push({place: capture, transitive, direction: 'backwards'});
        }
      }
    }
+    if (DEBUG) {
+      const nodes = new Map();
+      for (const id of seen) {
+        const node = this.nodes.get(id);
+        nodes.set(id.id, node);
+      }
+      console.log(pretty(nodes));
+    }
+  }
+
+  debug(): string {
+    return pretty(this.nodes);
  }
 }
+
+export function pretty(v: any): string {
+  return prettyFormat(v, {
+    plugins: [
+      {
+        test: v =>
+          v !== null && typeof v === 'object' && v.kind === 'Identifier',
+        serialize: v => printPlace(v),
+      },
+      {
+        test: v =>
+          v !== null &&
+          typeof v === 'object' &&
+          typeof v.declarationId === 'number',
+        serialize: v =>
+          `${printIdentifier(v)}:${v.mutableRange.start}:${v.mutableRange.end}`,
+      },
+    ],
+  });
+}
--- a/compiler/packages/babel-plugin-react-compiler/src/Inference/InferReactivePlaces.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Inference/InferReactivePlaces.ts
@@ -21,6 +21,7 @@ import {
  isStableType,
  isStableTypeContainer,
  isUseOperator,
+  isUseRefType,
 } from '../HIR';
 import {PostDominator} from '../HIR/Dominator';
 import {
@@ -69,6 +70,13 @@ class StableSidemap {
              isStable: false,
            });
          }
+        } else if (
+          this.env.config.enableTreatRefLikeIdentifiersAsRefs &&
+          isUseRefType(lvalue.identifier)
+        ) {
+          this.map.set(lvalue.identifier.id, {
+            isStable: true,
+          });
        }
        break;
      }
--- a/compiler/packages/babel-plugin-react-compiler/src/Inference/InferReferenceEffects.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Inference/InferReferenceEffects.ts
--- a/compiler/packages/babel-plugin-react-compiler/src/Inference/InferTryCatchAliases.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Inference/InferTryCatchAliases.ts
@@ -0,0 +1,49 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {BlockId, HIRFunction, Identifier} from '../HIR';
+import DisjointSet from '../Utils/DisjointSet';
+
+/*
+ * Any values created within a try/catch block could be aliased to the try handler.
+ * Our lowering ensures that every instruction within a try block will be lowered into a
+ * basic block ending in a maybe-throw terminal that points to its catch block, so we can
+ * iterate such blocks and alias their instruction lvalues to the handler's param (if present).
+ */
+export function inferTryCatchAliases(
+  fn: HIRFunction,
+  aliases: DisjointSet<Identifier>,
+): void {
+  const handlerParams: Map<BlockId, Identifier> = new Map();
+  for (const [_, block] of fn.body.blocks) {
+    if (
+      block.terminal.kind === 'try' &&
+      block.terminal.handlerBinding !== null
+    ) {
+      handlerParams.set(
+        block.terminal.handler,
+        block.terminal.handlerBinding.identifier,
+      );
+    } else if (block.terminal.kind === 'maybe-throw') {
+      const handlerParam = handlerParams.get(block.terminal.handler);
+      if (handlerParam === undefined) {
+        /*
+         * There's no catch clause param, nothing to alias to so
+         * skip this block
+         */
+        continue;
+      }
+      /*
+       * Otherwise alias all values created in this block to the
+       * catch clause param
+       */
+      for (const instr of block.instructions) {
+        aliases.union([handlerParam, instr.lvalue.identifier]);
+      }
+    }
+  }
+}
--- a/compiler/packages/babel-plugin-react-compiler/src/Inference/InlineImmediatelyInvokedFunctionExpressions.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Inference/InlineImmediatelyInvokedFunctionExpressions.ts
@@ -11,7 +11,6 @@ import {
  Environment,
  FunctionExpression,
  GeneratedSource,
-  GotoTerminal,
  GotoVariant,
  HIRFunction,
  IdentifierId,
@@ -20,7 +19,6 @@ import {
  Place,
  isStatementBlockKind,
  makeInstructionId,
-  mergeConsecutiveBlocks,
  promoteTemporary,
  reversePostorderBlocks,
 } from '../HIR';
@@ -75,10 +73,6 @@ import {retainWhere} from '../Utils/utils';
 * - All return statements in the original function expression are replaced with a
 *    StoreLocal to the temporary we allocated before plus a Goto to the fallthrough
 *    block (code following the CallExpression).
- *
- * Note that if the inliined function has only one return, we avoid the labeled block
- * and fully inline the code. The original return is replaced with an assignmen to the
- * IIFE's call expression lvalue.
 */
 export function inlineImmediatelyInvokedFunctionExpressions(
  fn: HIRFunction,
@@ -152,75 +146,37 @@ export function inlineImmediatelyInvokedFunctionExpressions(
             */
            block.instructions.length = ii;

-            if (hasSingleExitReturnTerminal(body.loweredFunc.func)) {
-              block.terminal = {
-                kind: 'goto',
-                block: body.loweredFunc.func.body.entry,
-                id: block.terminal.id,
-                loc: block.terminal.loc,
-                variant: GotoVariant.Break,
-              } as GotoTerminal;
-              for (const block of body.loweredFunc.func.body.blocks.values()) {
-                if (block.terminal.kind === 'return') {
-                  block.instructions.push({
-                    id: makeInstructionId(0),
-                    loc: block.terminal.loc,
-                    lvalue: instr.lvalue,
-                    value: {
-                      kind: 'LoadLocal',
-                      loc: block.terminal.loc,
-                      place: block.terminal.value,
-                    },
-                    effects: null,
-                  });
-                  block.terminal = {
-                    kind: 'goto',
-                    block: continuationBlockId,
-                    id: block.terminal.id,
-                    loc: block.terminal.loc,
-                    variant: GotoVariant.Break,
-                  } as GotoTerminal;
-                }
-              }
-              for (const [id, block] of body.loweredFunc.func.body.blocks) {
-                block.preds.clear();
-                fn.body.blocks.set(id, block);
-              }
-            } else {
-              /*
-               * To account for multiple returns within the lambda, we treat the lambda
-               * as if it were a single labeled statement, and replace all returns with gotos
-               * to the label fallthrough.
-               */
-              const newTerminal: LabelTerminal = {
-                block: body.loweredFunc.func.body.entry,
-                id: makeInstructionId(0),
-                kind: 'label',
-                fallthrough: continuationBlockId,
-                loc: block.terminal.loc,
-              };
-              block.terminal = newTerminal;
+            /*
+             * To account for complex control flow within the lambda, we treat the lambda
+             * as if it were a single labeled statement, and replace all returns with gotos
+             * to the label fallthrough.
+             */
+            const newTerminal: LabelTerminal = {
+              block: body.loweredFunc.func.body.entry,
+              id: makeInstructionId(0),
+              kind: 'label',
+              fallthrough: continuationBlockId,
+              loc: block.terminal.loc,
+            };
+            block.terminal = newTerminal;

-              // We store the result in the IIFE temporary
-              const result = instr.lvalue;
+            // We store the result in the IIFE temporary
+            const result = instr.lvalue;

-              // Declare the IIFE temporary
-              declareTemporary(fn.env, block, result);
+            // Declare the IIFE temporary
+            declareTemporary(fn.env, block, result);

-              // Promote the temporary with a name as we require this to persist
-              if (result.identifier.name == null) {
-                promoteTemporary(result.identifier);
-              }
+            // Promote the temporary with a name as we require this to persist
+            promoteTemporary(result.identifier);

-              /*
-               * Rewrite blocks from the lambda to replace any `return` with a
-               * store to the result and `goto` the continuation block
-               */
-              for (const [id, block] of body.loweredFunc.func.body.blocks) {
-                block.preds.clear();
-                rewriteBlock(fn.env, block, continuationBlockId, result);
-                fn.body.blocks.set(id, block);
-              }
+            /*
+             * Rewrite blocks from the lambda to replace any `return` with a
+             * store to the result and `goto` the continuation block
+             */
+            for (const [id, block] of body.loweredFunc.func.body.blocks) {
+              block.preds.clear();
+              rewriteBlock(fn.env, block, continuationBlockId, result);
+              fn.body.blocks.set(id, block);
            }

            /*
@@ -243,7 +199,7 @@ export function inlineImmediatelyInvokedFunctionExpressions(

  if (inlinedFunctions.size !== 0) {
    // Remove instructions that define lambdas which we inlined
-    for (const block of fn.body.blocks.values()) {
+    for (const [, block] of fn.body.blocks) {
      retainWhere(
        block.instructions,
        instr => !inlinedFunctions.has(instr.lvalue.identifier.id),
@@ -257,25 +213,9 @@ export function inlineImmediatelyInvokedFunctionExpressions(
    reversePostorderBlocks(fn.body);
    markInstructionIds(fn.body);
    markPredecessors(fn.body);
-    mergeConsecutiveBlocks(fn);
  }
 }

-/**
- * Returns true if the function has a single exit terminal (throw/return) which is a return
- */
-function hasSingleExitReturnTerminal(fn: HIRFunction): boolean {
-  let hasReturn = false;
-  let exitCount = 0;
-  for (const [, block] of fn.body.blocks) {
-    if (block.terminal.kind === 'return' || block.terminal.kind === 'throw') {
-      hasReturn ||= block.terminal.kind === 'return';
-      exitCount++;
-    }
-  }
-  return exitCount === 1 && hasReturn;
-}
-
 /*
 * Rewrites the block so that all `return` terminals are replaced:
 * * Add a StoreLocal <returnValue> = <terminal.value>
--- a/compiler/packages/babel-plugin-react-compiler/src/Inference/MUTABILITY_ALIASING_MODEL.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/Inference/MUTABILITY_ALIASING_MODEL.md
@@ -1,559 +0,0 @@
-# The Mutability & Aliasing Model
-
-This document describes the new (as of June 2025) mutability and aliasing model powering React Compiler. The mutability and aliasing system is a conceptual subcomponent whose primary role is to determine minimal sets of values that mutate together, and the range of instructions over which those mutations occur. These minimal sets of values that mutate together, and the corresponding instructions doing those mutations, are ultimately grouped into reactive scopes, which then translate into memoization blocks in the output (after substantial additional processing described in the comments of those passes).
-
-To build an intuition, consider the following example:
-
-```js
-function Component() {
-    // a is created and mutated over the course of these two instructions:
-    const a = {};
-    mutate(a);
-
-    // b and c are created and mutated together — mutate might modify b via c
-    const b = {};
-    const c = {b};
-    mutate(c);
-
-    // does not modify a/b/c
-    return <Foo a={a} c={c} />
-}
-```
-
-The goal of mutability and aliasing inference is to understand the set of instructions that create/modify a, b, and c.
-
-In code, the mutability and aliasing model is compromised of the following phases:
-
-* `InferMutationAliasingEffects`. Infers a set of mutation and aliasing effects for each instruction. The approach is to generate a set of candidate effects based purely on the semantics of each instruction and the types of the operands, then use abstract interpretation to determine the actual effects (or errros) that would apply. For example, an instruction that by default has a Capture effect might downgrade to an ImmutableCapture effect if the value is known to be frozen.
-* `InferMutationAliasingRanges`. Infers a mutable range (start:end instruction ids) for each value in the program, and annotates each Place with its effect type for usage in later passes. This builds a graph of data flow through the program over time in order to understand which mutations effect which values.
-* `InferReactiveScopeVariables`. Given the per-Place effects, determines disjoint sets of values that mutate together and assigns all identifiers in each set to a unique scope, and updates the range to include the ranges of all constituent values.
-
-Finally, `AnalyzeFunctions` needs to understand the mutation and aliasing semantics of nested FunctionExpression and ObjectMethod values. `AnalyzeFunctions` calls `InferFunctionExpressionAliasingEffectsSignature` to determine the publicly observable set of mutation/aliasing effects for nested functions.
-
-## Mutation and Aliasing Effects
-
-The inference model is based on a set of "effects" that describe subtle aspects of mutation, aliasing, and other changes to the state of values over time
-
-### Creation Effects
-
-#### Create
-
-```js
-{
-    kind: 'Create';
-    into: Place;
-    value: ValueKind;
-    reason: ValueReason;
-}
-```
-
-Describes the creation of a new value with the given kind, and reason for having that kind. For example, `x = 10` might have an effect like `Create x = ValueKind.Primitive [ValueReason.Other]`.
-
-#### CreateFunction
-
-```js
-{
-    kind: 'CreateFunction';
-    captures: Array<Place>;
-    function: FunctionExpression | ObjectMethod;
-    into: Place;
-}
-```
-
-Describes the creation of new function value, capturing the given set of mutable values. CreateFunction is used to specifically track function types so that we can precisely model calls to those functions with `Apply`.
-
-#### Apply
-
-```js
-{
-    kind: 'Apply';
-    receiver: Place;
-    function: Place; // same as receiver for function calls
-    mutatesFunction: boolean; // indicates if this is a type that we consdier to mutate the function itself by default
-    args: Array<Place | SpreadPattern | Hole>;
-    into: Place; // where result is stored
-    signature: FunctionSignature | null;
-}
-```
-
-Describes the potential creation of a value by calling a function. This models `new`, function calls, and method calls. The inference algorithm uses the most precise signature it can determine:
-
-* If the function is a locally created function expression, we use a signature inferred from the behavior of that function to interpret the effects of calling it with the given arguments.
-* Else if the function has a known aliasing signature (new style precise effects signature), we apply the arguments to that signature to get a precise set of effects.
-* Else if the function has a legacy style signature (with per-param effects) we convert the legacy per-Place effects into aliasing effects (described in this doc) and apply those.
-* Else fall back to inferring a generic set of effects.
-
-The generic fallback is to assume:
- The return value may alias any of the arguments (Alias param -> return)
- Any arguments *may* be transitively mutated (MutateTransitiveConditionally param)
- Any argument may be captured into any other argument (Capture paramN -> paramM for all N,M where N != M)
-
-### Aliasing Effects
-
-These effects describe data-flow only, separately from mutation or other state-changing semantics.
-
-#### Assign
-
-```js
-{
-    kind: 'Assign';
-    from: Place;
-    into: Place;
-}
-```
-
-Describes an `x = y` assignment, where the receiving (into) value is overwritten with a new (from) value. After this effect, any previous assignments/aliases to the receiving value are dropped. Note that `Alias` initializes the receiving value.
-
-> TODO: InferMutationAliasingRanges may not fully reset aliases on encountering this effect
-
-#### Alias
-
-```js
-{
-    kind: 'Alias';
-    from: Place;
-    into: Place;
-}
-```
-
-Describes that an assignment _may_ occur, but that the possible assignment is non-exclusive. The canonical use-case for `Alias` is a function that may return more than one of its arguments, such as `(x, y, z) => x ? y : z`. Here, the result of this function may be `y` or `z`, but neither one overwrites the other. Note that `Alias` does _not_ initialize the receiving value: it should always be paired with an effect to create the receiving value.
-
-#### Capture
-
-```js
-{
-    kind: 'Capture';
-    from: Place;
-    into: Place;
-}
-```
-
-Describes that a reference to one variable (from) is stored within another value (into). Examples include:
- An array expression captures the items of the array (`array = [capturedValue]`)
- Array.prototype.push captures the pushed values into the array (`array.push(capturedValue)`)
- Property assignment captures the value onto the object (`object.property = capturedValue`)
-
-#### CreateFrom
-
-```js
-{
-    kind: 'CreateFrom';
-    from: Place;
-    into: Place;
-}
-```
-
-This is somewhat the inverse of `Capture`. The `CreateFrom` effect describes that a variable is initialized by extracting _part_ of another value, without taking a direct alias to the full other value. Examples include:
-
- Indexing into an array (`createdFrom = array[0]`)
- Reading an object property (`createdFrom = object.property`)
- Getting a Map key (`createdFrom = map.get(key)`)
-
-#### ImmutableCapture
-
-Describes immutable data flow from one value to another. This is not currently used for anything, but is intended to eventually power a more sophisticated escape analysis.
-
-### MaybeAlias
-
-Describes potential data flow that the compiler knows may occur behind a function call, but cannot be sure about. For example, `foo(x)` _may_ be the identity function and return `x`, or `cond(a, b, c)` may conditionally return `b` or `c` depending on the value of `a`, but those functions could just as easily return new mutable values and not capture any information from their arguments. MaybeAlias represents that we have to consider the potential for data flow when deciding mutable ranges, but should be conservative about reporting errors. For example, `foo(someFrozenValue).property = true` should not error since we don't know for certain that foo returns its input.
-
-### State-Changing Effects
-
-The following effects describe state changes to specific values, not data flow. In many cases, JavaScript semantics will involve a combination of both data-flow effects *and* state-change effects. For example, `object.property = value` has data flow (`Capture object <- value`) and mutation (`Mutate object`).
-
-#### Freeze
-
-```js
-{
-    kind: 'Freeze',
-    // The reference being frozen
-    value: Place;
-    // The reason the value is frozen (passed to a hook, passed to jsx, etc)
-    reason: ValueReason;
-}
-```
-
-Once a reference to a value has been passed to React, that value is generally not safe to mutate further. This is not a strictly required property of React, but is a natural consequence of making components and hooks composable without leaking implementation details. Concretely, once a value has been passed as a JSX prop, passed as argument to a hook, or returned from a hook, it must be assumed that the other "side" — receiver of the prop/argument/return value — will use that value as an input to an effect or memoization unit. Mutating that value (instead of creating a new value) will fail to cause the consuming computation to update:
-
-```js
-// INVALID DO NOT DO THIS
-function Component(props) {
-    const array = useArray(props.value);
-    // OOPS! this value is memoized, the array won't get re-created
-    // when `props.value` changes, so we might just keep pushing new
-    // values to the same array on every render!
-    array.push(props.otherValue);
-}
-
-function useArray(a) {
-    return useMemo(() => [a], [a]);
-}
-```
-
-The **Freeze** effect accepts a variable reference and a reason that the value is being frozen. Note: _freeze only applies to the reference, not the underlying value_. Our inference is conservative, and assumes that there may still be other references to the same underlying value which are mutated later. For example:
-
-```js
-const x = {};
-const y = [];
-x.y = y;
-freeze(y); // y _reference_ is frozen
-x.y.push(props.value); // but y is still considered mutable bc of this
-```
-
-#### Mutate (and MutateConditionally)
-
-```js
-{
-    kind: 'Mutate';
-    value: Place;
-}
-```
-
-Mutate indicates that a value is mutated, without modifying any of the values that it may transitively have captured. Canonical examples include:
-
- Pushing an item onto an array modifies the array, but does not modify any items stored _within_ the array (unless the array has a reference to itself!)
- Assigning a value to an object property modifies the object, but not any values stored in the object's other properties.
-
-This helps explain the distinction between Assign/Alias and Capture: Mutate only affects assign/alias but not captures.
-
-`MutateConditionally` is an alternative in which the mutation _may_ happen depending on the type of the value. The conditional variant is not generally used and included for completeness.
-
-
-
-#### MutateTransitiveConditionally (and MutateTransitive)
-
-`MutateTransitiveConditionally` represents an operation that may mutate _any_ aspect of a value, including reaching arbitrarily deep into nested values to mutate them. This is the default semantic for unknown functions — we have no idea what they do, so we assume that they are idempotent but may mutate any aspect of the mutable values that are passed to them.
-
-There is also `MutateTransitive` for completeness, but this is not generally used.
-
-### Side Effects
-
-Finally, there are a few effects that describe error, or potential error, conditions:
-
- `MutateFrozen` is always an error, because it indicates known mutation of a value that should not be mutated.
- `MutateGlobal` indicates known mutation of a global value, which is not safe during render. This effect is an error if reachable during render, but allowed if only reachable via an event handler or useEffect.
- `Impure` indicates calling some other logic that is impure/side-effecting. This is an error if reachable during render, but allowed if only reachable via an event handler or useEffect.
-  - TODO: we could probably merge this and MutateGlobal
- `Render` indicates a value that is not mutated, but is known to be called during render. It's used for a few particular places like JSX tags and JSX children, which we assume are accessed during render (while other props may be event handlers etc). This helps to detect more MutateGlobal/Impure effects and reject more invalid programs.
-
-
-## Rules
-
-### Mutation of Alias Mutates the Source Value
-
-```
-Alias a <- b
-Mutate a
-=>
-Mutate b
-```
-
-Example:
-
-```js
-const a = maybeIdentity(b); // Alias a <- b
-a.property = value; // a could be b, so this mutates b
-```
-
-### Mutation of Assignment Mutates the Source Value
-
-```
-Assign a <- b
-Mutate a
-=>
-Mutate b
-```
-
-Example:
-
-```js
-const a = b;
-a.property = value // a _is_ b, this mutates b
-```
-
-### Mutation of CreateFrom Mutates the Source Value
-
-```
-CreateFrom a <- b
-Mutate a
-=>
-Mutate b
-```
-
-Example:
-
-```js
-const a = b[index];
-a.property = value // the contents of b are transitively mutated
-```
-
-
-### Mutation of Capture Does *Not* Mutate the Source Value
-
-```
-Capture a <- b
-Mutate a
-!=>
-~Mutate b~
-```
-
-Example:
-
-```js
-const a = {};
-a.b = b;
-a.property = value; // mutates a, not b
-```
-
-### Mutation of Source Affects Alias, Assignment, CreateFrom, and Capture
-
-```
-Alias a <- b OR Assign a <- b OR CreateFrom a <- b OR Capture a <- b
-Mutate b
-=>
-Mutate a
-```
-
-A derived value changes when it's source value is mutated.
-
-Example:
-
-```js
-const x = {};
-const y = [x];
-x.y = true; // this changes the value within `y` ie mutates y
-```
-
-
-### TransitiveMutation of Alias, Assignment, CreateFrom, or Capture Mutates the Source
-
-```
-Alias a <- b OR Assign a <- b OR CreateFrom a <- b OR Capture a <- b
-MutateTransitive a
-=>
-MutateTransitive b
-```
-
-Remember, the intuition for a transitive mutation is that it's something that could traverse arbitrarily deep into an object and mutate whatever it finds. Imagine something that recurses into every nested object/array and sets `.field = value`. Given a function `mutate()` that does this, then:
-
-```js
-const a = b; // assign
-mutate(a); // clearly can transitively mutate b
-
-const a = maybeIdentity(b); // alias
-mutate(a); // clearly can transitively mutate b
-
-const a = b[index]; // createfrom
-mutate(a); // clearly can transitively mutate b
-
-const a = {};
-a.b = b; // capture
-mutate(a); // can transitively mutate b
-```
-
-### MaybeAlias makes mutation conditional
-
-Because we don't know for certain that the aliasing occurs, we consider the mutation conditional against the source.
-
-```
-MaybeAlias a <- b
-Mutate a
-=>
-MutateConditional b
-```
-
-### Freeze Does Not Freeze the Value
-
-Freeze does not freeze the value itself:
-
-```
-Create x
-Assign y <- x OR Alias y <- x OR CreateFrom y <- x OR Capture y <- x
-Freeze y
-!=>
-~Freeze x~
-```
-
-This means that subsequent mutations of the original value are valid:
-
-```
-Create x
-Assign y <- x OR Alias y <- x OR CreateFrom y <- x OR Capture y <- x
-Freeze y
-Mutate x
-=>
-Mutate x (mutation is ok)
-```
-
-As well as mutations through other assignments/aliases/captures/createfroms of the original value:
-
-```
-Create x
-Assign y <- x OR Alias y <- x OR CreateFrom y <- x OR Capture y <- x
-Freeze y
-Alias z <- x OR Capture z <- x OR CreateFrom z <- x OR Assign z <- x
-Mutate z
-=>
-Mutate x (mutation is ok)
-```
-
-### Freeze Freezes The Reference 
-
-Although freeze doesn't freeze the value, it does affect the reference. The reference cannot be used to mutate.
-
-Conditional mutations of the reference are no-ops:
-
-```
-Create x
-Assign y <- x OR Alias y <- x OR CreateFrom y <- x OR Capture y <- x
-Freeze y
-MutateConditional y
-=>
-(no mutation)
-```
-
-And known mutations of the reference are errors:
-
-```
-Create x
-Assign y <- x OR Alias y <- x OR CreateFrom y <- x OR Capture y <- x
-Freeze y
-MutateConditional y
-=>
-MutateFrozen y error=...
-```
-
-### Corollary: Transitivity of Assign/Alias/CreateFrom/Capture
-
-A key part of the inference model is inferring a signature for function expressions. The signature is a minimal set of effects that describes the publicly observable behavior of the function. This can include "global" effects like side effects (MutateGlobal/Impure) as well as mutations/aliasing of parameters and free variables.
-
-In order to determine the aliasing of params and free variables into each other and/or the return value, we may encounter chains of assign, alias, createfrom, and capture effects. For example:
-
-```js
-const f = (x) => {
-    const y = [x];  // capture y <- x
-    const z = y[0]; // createfrom z <- y
-    return z;     // assign return <- z
-}
-// <Effect> return <- x
-```
-
-In this example we can see that there should be some effect on `f` that tracks the flow of data from `x` into the return value. The key constraint is preserving the semantics around how local/transitive mutations of the destination would affect the source.
-
-#### Each of the effects is transitive with itself
-
-```
-Assign b <- a
-Assign c <- b
-=>
-Assign c <- a
-```
-
-```
-Alias b <- a
-Alias c <- b
-=>
-Alias c <- a
-```
-
-```
-CreateFrom b <- a
-CreateFrom c <- b
-=>
-CreateFrom c <- a
-```
-
-```
-Capture b <- a
-Capture c <- b
-=>
-Capture c <- a
-```
-
-#### Alias > Assign
-
-```
-Assign b <- a
-Alias c <- b
-=>
-Alias c <- a
-```
-
-```
-Alias b <- a
-Assign c <- b
-=>
-Alias c <- a
-```
-
-### CreateFrom > Assign/Alias
-
-Intuition: 
-
-```
-CreateFrom b <- a
-Alias c <- b OR Assign c <- b
-=>
-CreateFrom c <- a
-```
-
-```
-Alias b <- a OR Assign b <- a
-CreateFrom c <- b
-=>
-CreateFrom c <- a
-```
-
-### Capture > Assign/Alias
-
-Intuition: capturing means that a local mutation of the destination will not affect the source, so we preserve the capture.
-
-```
-Capture b <- a
-Alias c <- b OR Assign c <- b
-=>
-Capture c <- a
-```
-
-```
-Alias b <- a OR Assign b <- a
-Capture c <- b
-=>
-Capture c <- a
-```
-
-### Capture And CreateFrom
-
-Intuition: these effects are inverses of each other (capturing into an object, extracting from an object). The result is based on the order of operations:
-
-Capture then CreatFrom is equivalent to Alias: we have to assume that the result _is_ the original value and that a local mutation of the result could mutate the original.
-
-```js
-const b = [a]; // capture
-const c = b[0]; // createfrom
-mutate(c); // this clearly can mutate a, so the result must be one of Assign/Alias/CreateFrom 
-```
-
-We use Alias as the return type because the mutability kind of the result is not derived from the source value (there's a fresh object in between due to the capture), so the full set of effects in practice would be a Create+Alias.
-
-```
-Capture b <- a
-CreateFrom c <- b
-=>
-Alias c <- a
-```
-
-Meanwhile the opposite direction preserves the capture, because the result is not the same as the source:
-
-```js
-const b = a[0]; // createfrom
-const c = [b]; // capture
-mutate(c); // does not mutate a, so the result must be Capture
-```
-
-```
-CreateFrom b <- a
-Capture c <- b
-=>
-Capture c <- a
-```
--- a/compiler/packages/babel-plugin-react-compiler/src/Inference/index.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Inference/index.ts
@@ -7,6 +7,8 @@

 export {default as analyseFunctions} from './AnalyseFunctions';
 export {dropManualMemoization} from './DropManualMemoization';
+export {inferMutableRanges} from './InferMutableRanges';
 export {inferReactivePlaces} from './InferReactivePlaces';
+export {default as inferReferenceEffects} from './InferReferenceEffects';
 export {inlineImmediatelyInvokedFunctionExpressions} from './InlineImmediatelyInvokedFunctionExpressions';
 export {inferEffectDependencies} from './InferEffectDependencies';
--- a/compiler/packages/babel-plugin-react-compiler/src/Optimization/InlineJsxTransform.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Optimization/InlineJsxTransform.ts
@@ -42,7 +42,6 @@ import {
  mapInstructionValueOperands,
  mapTerminalOperands,
 } from '../HIR/visitors';
-import {ErrorCategory} from '../CompilerError';

 type InlinedJsxDeclarationMap = Map<
  DeclarationId,
@@ -84,7 +83,6 @@ export function inlineJsxTransform(
          kind: 'CompileDiagnostic',
          fnLoc: null,
          detail: {
-            category: ErrorCategory.Todo,
            reason: 'JSX Inlining is not supported on value blocks',
            loc: instr.loc,
          },
--- a/compiler/packages/babel-plugin-react-compiler/src/Optimization/LowerContextAccess.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Optimization/LowerContextAccess.ts
@@ -25,6 +25,7 @@ import {
  makeBlockId,
  makeInstructionId,
  makePropertyLiteral,
+  makeType,
  markInstructionIds,
  promoteTemporary,
  reversePostorderBlocks,
@@ -237,7 +238,6 @@ function emitSelectorFn(env: Environment, keys: Array<string>): Instruction {
    terminal: {
      id: makeInstructionId(0),
      kind: 'return',
-      returnVariant: 'Explicit',
      loc: GeneratedSource,
      value: arrayInstr.lvalue,
      effects: null,
@@ -253,8 +253,10 @@ function emitSelectorFn(env: Environment, keys: Array<string>): Instruction {
    env,
    params: [obj],
    returnTypeAnnotation: null,
+    returnType: makeType(),
    returns: createTemporaryPlace(env, GeneratedSource),
    context: [],
+    effects: null,
    body: {
      entry: block.id,
      blocks: new Map([[block.id, block]]),
@@ -262,7 +264,6 @@ function emitSelectorFn(env: Environment, keys: Array<string>): Instruction {
    generator: false,
    async: false,
    directives: [],
-    aliasingEffects: [],
  };

  reversePostorderBlocks(fn.body);
--- a/compiler/packages/babel-plugin-react-compiler/src/Optimization/OutlineJsx.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Optimization/OutlineJsx.ts
@@ -21,6 +21,7 @@ import {
  makeBlockId,
  makeIdentifierName,
  makeInstructionId,
+  makeType,
  ObjectProperty,
  Place,
  promoteTemporary,
@@ -352,7 +353,6 @@ function emitOutlinedFn(
    terminal: {
      id: makeInstructionId(0),
      kind: 'return',
-      returnVariant: 'Explicit',
      loc: GeneratedSource,
      value: instructions.at(-1)!.lvalue,
      effects: null,
@@ -368,8 +368,10 @@ function emitOutlinedFn(
    env,
    params: [propsObj],
    returnTypeAnnotation: null,
+    returnType: makeType(),
    returns: createTemporaryPlace(env, GeneratedSource),
    context: [],
+    effects: null,
    body: {
      entry: block.id,
      blocks: new Map([[block.id, block]]),
@@ -377,7 +379,6 @@ function emitOutlinedFn(
    generator: false,
    async: false,
    directives: [],
-    aliasingEffects: [],
  };
  return fn;
 }
--- a/compiler/packages/babel-plugin-react-compiler/src/ReactiveScopes/CodegenReactiveFunction.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/ReactiveScopes/CodegenReactiveFunction.ts
@@ -13,7 +13,7 @@ import {
  pruneUnusedLabels,
  renameVariables,
 } from '.';
-import {CompilerError, ErrorCategory, ErrorSeverity} from '../CompilerError';
+import {CompilerError, ErrorSeverity} from '../CompilerError';
 import {Environment, ExternalFunction} from '../HIR';
 import {
  ArrayPattern,
@@ -349,9 +349,11 @@ function codegenReactiveFunction(
  fn: ReactiveFunction,
 ): Result<CodegenFunction, CompilerError> {
  for (const param of fn.params) {
-    const place = param.kind === 'Identifier' ? param : param.place;
-    cx.temp.set(place.identifier.declarationId, null);
-    cx.declare(place.identifier);
+    if (param.kind === 'Identifier') {
+      cx.temp.set(param.identifier.declarationId, null);
+    } else {
+      cx.temp.set(param.place.identifier.declarationId, null);
+    }
  }

  const params = fn.params.map(param => convertParameter(param));
@@ -1181,7 +1183,7 @@ function codegenTerminal(
              ? codegenPlaceToExpression(cx, case_.test)
              : null;
          const block = codegenBlock(cx, case_.block!);
-          return t.switchCase(test, block.body.length === 0 ? [] : [block]);
+          return t.switchCase(test, [block]);
        }),
      );
    }
@@ -2185,7 +2187,6 @@ function codegenInstructionValue(
                (declarator.id as t.Identifier).name
              }'`,
              severity: ErrorSeverity.Todo,
-              category: ErrorCategory.Todo,
              loc: declarator.loc ?? null,
              suggestions: null,
            });
@@ -2194,7 +2195,6 @@ function codegenInstructionValue(
            cx.errors.push({
              reason: `(CodegenReactiveFunction::codegenInstructionValue) Handle conversion of ${stmt.type} to expression`,
              severity: ErrorSeverity.Todo,
-              category: ErrorCategory.Todo,
              loc: stmt.loc ?? null,
              suggestions: null,
            });
--- a/compiler/packages/babel-plugin-react-compiler/src/ReactiveScopes/ExtractScopeDeclarationsFromDestructuring.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/ReactiveScopes/ExtractScopeDeclarationsFromDestructuring.ts
@@ -79,10 +79,6 @@ export function extractScopeDeclarationsFromDestructuring(
  fn: ReactiveFunction,
 ): void {
  const state = new State(fn.env);
-  for (const param of fn.params) {
-    const place = param.kind === 'Identifier' ? param : param.place;
-    state.declared.add(place.identifier.declarationId);
-  }
  visitReactiveFunction(fn, new Visitor(), state);
 }

--- a/compiler/packages/babel-plugin-react-compiler/src/ReactiveScopes/MergeReactiveScopesThatInvalidateTogether.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/ReactiveScopes/MergeReactiveScopesThatInvalidateTogether.ts
@@ -119,7 +119,6 @@ class FindLastUsageVisitor extends ReactiveFunctionVisitor<void> {

 class Transform extends ReactiveFunctionTransform<ReactiveScopeDependencies | null> {
  lastUsage: Map<DeclarationId, InstructionId>;
-  temporaries: Map<DeclarationId, DeclarationId> = new Map();

  constructor(lastUsage: Map<DeclarationId, InstructionId>) {
    super();
@@ -216,12 +215,6 @@ class Transform extends ReactiveFunctionTransform<ReactiveScopeDependencies | nu
                current.lvalues.add(
                  instr.instruction.lvalue.identifier.declarationId,
                );
-                if (instr.instruction.value.kind === 'LoadLocal') {
-                  this.temporaries.set(
-                    instr.instruction.lvalue.identifier.declarationId,
-                    instr.instruction.value.place.identifier.declarationId,
-                  );
-                }
              }
              break;
            }
@@ -243,13 +236,6 @@ class Transform extends ReactiveFunctionTransform<ReactiveScopeDependencies | nu
                  )) {
                    current.lvalues.add(lvalue.identifier.declarationId);
                  }
-                  this.temporaries.set(
-                    instr.instruction.value.lvalue.place.identifier
-                      .declarationId,
-                    this.temporaries.get(
-                      instr.instruction.value.value.identifier.declarationId,
-                    ) ?? instr.instruction.value.value.identifier.declarationId,
-                  );
                } else {
                  log(
                    `Reset scope @${current.block.scope.id} from StoreLocal in [${instr.instruction.id}]`,
@@ -274,7 +260,7 @@ class Transform extends ReactiveFunctionTransform<ReactiveScopeDependencies | nu
        case 'scope': {
          if (
            current !== null &&
-            canMergeScopes(current.block, instr, this.temporaries) &&
+            canMergeScopes(current.block, instr) &&
            areLValuesLastUsedByScope(
              instr.scope,
              current.lvalues,
@@ -440,7 +426,6 @@ function areLValuesLastUsedByScope(
 function canMergeScopes(
  current: ReactiveScopeBlock,
  next: ReactiveScopeBlock,
-  temporaries: Map<DeclarationId, DeclarationId>,
 ): boolean {
  // Don't merge scopes with reassignments
  if (
@@ -480,14 +465,11 @@ function canMergeScopes(
    (next.scope.dependencies.size !== 0 &&
      [...next.scope.dependencies].every(
        dep =>
-          dep.path.length === 0 &&
          isAlwaysInvalidatingType(dep.identifier.type) &&
          Iterable_some(
            current.scope.declarations.values(),
            decl =>
-              decl.identifier.declarationId === dep.identifier.declarationId ||
-              decl.identifier.declarationId ===
-                temporaries.get(dep.identifier.declarationId),
+              decl.identifier.declarationId === dep.identifier.declarationId,
          ),
      ))
  ) {
@@ -495,16 +477,12 @@ function canMergeScopes(
    return true;
  }
  log(`  cannot merge scopes:`);
-  log(
-    `  ${printReactiveScopeSummary(current.scope)} ${[...current.scope.declarations.values()].map(decl => decl.identifier.declarationId)}`,
-  );
-  log(
-    `  ${printReactiveScopeSummary(next.scope)} ${[...next.scope.dependencies].map(dep => `${dep.identifier.declarationId} ${temporaries.get(dep.identifier.declarationId) ?? dep.identifier.declarationId}`)}`,
-  );
+  log(`  ${printReactiveScopeSummary(current.scope)}`);
+  log(`  ${printReactiveScopeSummary(next.scope)}`);
  return false;
 }

-export function isAlwaysInvalidatingType(type: Type): boolean {
+function isAlwaysInvalidatingType(type: Type): boolean {
  switch (type.kind) {
    case 'Object': {
      switch (type.shapeId) {
--- a/compiler/packages/babel-plugin-react-compiler/src/ReactiveScopes/PruneNonEscapingScopes.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/ReactiveScopes/PruneNonEscapingScopes.ts
@@ -24,6 +24,7 @@ import {
  getHookKind,
  isMutableEffect,
 } from '../HIR';
+import {getFunctionCallSignature} from '../Inference/InferReferenceEffects';
 import {assertExhaustive, getOrInsertDefault} from '../Utils/utils';
 import {getPlaceScope, ReactiveScope} from '../HIR/HIR';
 import {
@@ -34,7 +35,6 @@ import {
  visitReactiveFunction,
 } from './visitors';
 import {printPlace} from '../HIR/PrintHIR';
-import {getFunctionCallSignature} from '../Inference/InferMutationAliasingEffects';

 /*
 * This pass prunes reactive scopes that are not necessary to bound downstream computation.
@@ -829,14 +829,12 @@ class CollectDependenciesVisitor extends ReactiveFunctionVisitor<
        };
      }
      case 'UnsupportedNode': {
-        const lvalues = [];
-        if (lvalue !== null) {
-          lvalues.push({place: lvalue, level: MemoizationLevel.Never});
-        }
-        return {
-          lvalues,
-          rvalues: [],
-        };
+        CompilerError.invariant(false, {
+          reason: `Unexpected unsupported node`,
+          description: null,
+          loc: value.loc,
+          suggestions: null,
+        });
      }
      default: {
        assertExhaustive(
@@ -1066,29 +1064,12 @@ class PruneScopesTransform extends ReactiveFunctionTransform<

    const value = instruction.value;
    if (value.kind === 'StoreLocal' && value.lvalue.kind === 'Reassign') {
-      // Complex cases of useMemo inlining result in a temporary that is reassigned
      const ids = getOrInsertDefault(
        this.reassignments,
        value.lvalue.place.identifier.declarationId,
        new Set(),
      );
      ids.add(value.value.identifier);
-    } else if (
-      value.kind === 'LoadLocal' &&
-      value.place.identifier.scope != null &&
-      instruction.lvalue != null &&
-      instruction.lvalue.identifier.scope == null
-    ) {
-      /*
-       * Simpler cases result in a direct assignment to the original lvalue, with a
-       * LoadLocal
-       */
-      const ids = getOrInsertDefault(
-        this.reassignments,
-        instruction.lvalue.identifier.declarationId,
-        new Set(),
-      );
-      ids.add(value.place.identifier);
    } else if (value.kind === 'FinishMemoize') {
      let decls;
      if (value.decl.identifier.scope == null) {
--- a/compiler/packages/babel-plugin-react-compiler/src/Transform/TransformFire.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Transform/TransformFire.ts
@@ -42,7 +42,6 @@ import {
 import {eachInstructionOperand} from '../HIR/visitors';
 import {printSourceLocationLine} from '../HIR/PrintHIR';
 import {USE_FIRE_FUNCTION_NAME} from '../HIR/Environment';
-import {ErrorCategory} from '../CompilerError';

 /*
 * TODO(jmbrown):
@@ -134,7 +133,6 @@ function replaceFireFunctions(fn: HIRFunction, context: Context): void {
                  loc: value.loc,
                  description: null,
                  severity: ErrorSeverity.Invariant,
-                  category: ErrorCategory.Invariant,
                  reason: '[InsertFire] No LoadGlobal found for useEffect call',
                  suggestions: null,
                });
@@ -181,7 +179,6 @@ function replaceFireFunctions(fn: HIRFunction, context: Context): void {
                description:
                  'You must use an array literal for an effect dependency array when that effect uses `fire()`',
                severity: ErrorSeverity.Invariant,
-                category: ErrorCategory.Fire,
                reason: CANNOT_COMPILE_FIRE,
                suggestions: null,
              });
@@ -192,7 +189,6 @@ function replaceFireFunctions(fn: HIRFunction, context: Context): void {
              description:
                'You must use an array literal for an effect dependency array when that effect uses `fire()`',
              severity: ErrorSeverity.Invariant,
-              category: ErrorCategory.Fire,
              reason: CANNOT_COMPILE_FIRE,
              suggestions: null,
            });
@@ -227,7 +223,6 @@ function replaceFireFunctions(fn: HIRFunction, context: Context): void {
                loc: value.loc,
                description: null,
                severity: ErrorSeverity.Invariant,
-                category: ErrorCategory.Invariant,
                reason:
                  '[InsertFire] No loadLocal found for fire call argument',
                suggestions: null,
@@ -251,7 +246,6 @@ function replaceFireFunctions(fn: HIRFunction, context: Context): void {
              description:
                '`fire()` can only receive a function call such as `fire(fn(a,b)). Method calls and other expressions are not allowed',
              severity: ErrorSeverity.InvalidReact,
-              category: ErrorCategory.Fire,
              reason: CANNOT_COMPILE_FIRE,
              suggestions: null,
            });
@@ -270,7 +264,6 @@ function replaceFireFunctions(fn: HIRFunction, context: Context): void {
            loc: value.loc,
            description,
            severity: ErrorSeverity.InvalidReact,
-            category: ErrorCategory.Fire,
            reason: CANNOT_COMPILE_FIRE,
            suggestions: null,
          });
@@ -402,7 +395,6 @@ function ensureNoRemainingCalleeCaptures(
 this effect or not used with a fire() call at all. ${calleeName} was used with fire() on line \
 ${printSourceLocationLine(calleeInfo.fireLoc)} in this effect`,
        severity: ErrorSeverity.InvalidReact,
-        category: ErrorCategory.Fire,
        reason: CANNOT_COMPILE_FIRE,
        suggestions: null,
      });
@@ -419,7 +411,6 @@ function ensureNoMoreFireUses(fn: HIRFunction, context: Context): void {
      context.pushError({
        loc: place.identifier.loc,
        description: 'Cannot use `fire` outside of a useEffect function',
-        category: ErrorCategory.Fire,
        severity: ErrorSeverity.Invariant,
        reason: CANNOT_COMPILE_FIRE,
        suggestions: null,
--- a/compiler/packages/babel-plugin-react-compiler/src/TypeInference/InferTypes.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/TypeInference/InferTypes.ts
@@ -14,7 +14,6 @@ import {
  Identifier,
  IdentifierId,
  Instruction,
-  InstructionKind,
  makePropertyLiteral,
  makeType,
  PropType,
@@ -91,8 +90,7 @@ function apply(func: HIRFunction, unifier: Unifier): void {
      }
    }
  }
-  const returns = func.returns.identifier;
-  returns.type = unifier.get(returns.type);
+  func.returnType = unifier.get(func.returnType);
 }

 type TypeEquation = {
@@ -145,12 +143,12 @@ function* generate(
    }
  }
  if (returnTypes.length > 1) {
-    yield equation(func.returns.identifier.type, {
+    yield equation(func.returnType, {
      kind: 'Phi',
      operands: returnTypes,
    });
  } else if (returnTypes.length === 1) {
-    yield equation(func.returns.identifier.type, returnTypes[0]!);
+    yield equation(func.returnType, returnTypes[0]!);
  }
 }

@@ -195,29 +193,12 @@ function* generateInstructionTypes(
      break;
    }

-    // We intentionally do not infer types for most context variables
+    // We intentionally do not infer types for context variables
    case 'DeclareContext':
+    case 'StoreContext':
    case 'LoadContext': {
      break;
    }
-    case 'StoreContext': {
-      /**
-       * The caveat is StoreContext const, where we know the value is
-       * assigned once such that everywhere the value is accessed, it
-       * must have the same type from the rvalue.
-       *
-       * A concrete example where this is useful is `const ref = useRef()`
-       * where the ref is referenced before its declaration in a function
-       * expression, causing it to be converted to a const context variable.
-       */
-      if (value.lvalue.kind === InstructionKind.Const) {
-        yield equation(
-          value.lvalue.place.identifier.type,
-          value.value.identifier.type,
-        );
-      }
-      break;
-    }

    case 'StoreLocal': {
      if (env.config.enableUseTypeAnnotations) {
@@ -378,12 +359,6 @@ function* generateInstructionTypes(
                value: makePropertyLiteral(propertyName),
              },
            });
-          } else if (item.kind === 'Spread') {
-            // Array pattern spread always creates an array
-            yield equation(item.place.identifier.type, {
-              kind: 'Object',
-              shapeId: BuiltInArrayId,
-            });
          } else {
            break;
          }
@@ -432,7 +407,7 @@ function* generateInstructionTypes(
      yield equation(left, {
        kind: 'Function',
        shapeId: BuiltInFunctionId,
-        return: value.loweredFunc.func.returns.identifier.type,
+        return: value.loweredFunc.func.returnType,
        isConstructor: false,
      });
      break;
@@ -451,18 +426,6 @@ function* generateInstructionTypes(

    case 'JsxExpression':
    case 'JsxFragment': {
-      if (env.config.enableTreatRefLikeIdentifiersAsRefs) {
-        if (value.kind === 'JsxExpression') {
-          for (const prop of value.props) {
-            if (prop.kind === 'JsxAttribute' && prop.name === 'ref') {
-              yield equation(prop.place.identifier.type, {
-                kind: 'Object',
-                shapeId: BuiltInUseRefId,
-              });
-            }
-          }
-        }
-      }
      yield equation(left, {kind: 'Object', shapeId: BuiltInJsxId});
      break;
    }
@@ -478,36 +441,7 @@ function* generateInstructionTypes(
      yield equation(left, returnType);
      break;
    }
-    case 'PropertyStore': {
-      /**
-       * Infer types based on assignments to known object properties
-       * This is important for refs, where assignment to `<maybeRef>.current`
-       * can help us infer that an object itself is a ref
-       */
-      yield equation(
-        /**
-         * Our property type declarations are best-effort and we haven't tested
-         * using them to drive inference of rvalues from lvalues. We want to emit
-         * a Property type in order to infer refs from `.current` accesses, but
-         * stay conservative by not otherwise inferring anything about rvalues.
-         * So we use a dummy type here.
-         *
-         * TODO: consider using the rvalue type here
-         */
-        makeType(),
-        // unify() only handles properties in the second position
-        {
-          kind: 'Property',
-          objectType: value.object.identifier.type,
-          objectName: getName(names, value.object.identifier.id),
-          propertyName: {
-            kind: 'literal',
-            value: value.property,
-          },
-        },
-      );
-      break;
-    }
+    case 'PropertyStore':
    case 'DeclareLocal':
    case 'RegExpLiteral':
    case 'MetaProperty':
@@ -777,15 +711,6 @@ class Unifier {
      return {kind: 'Phi', operands: type.operands.map(o => this.get(o))};
    }

-    if (type.kind === 'Function') {
-      return {
-        kind: 'Function',
-        isConstructor: type.isConstructor,
-        shapeId: type.shapeId,
-        return: this.get(type.return),
-      };
-    }
-
    return type;
  }
 }
--- a/compiler/packages/babel-plugin-react-compiler/src/TypeInference/PropagatePhiTypes.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/TypeInference/PropagatePhiTypes.ts
@@ -0,0 +1,110 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {HIRFunction, IdentifierId, Type, typeEquals} from '../HIR';
+
+/**
+ * Temporary workaround for InferTypes not propagating the types of phis.
+ * Previously, LeaveSSA would replace all the identifiers for each phi (operands and
+ * the phi itself) with a single "canonical" identifier, generally chosen as the first
+ * operand to flow into the phi. In case of a phi whose operand was a phi, this could
+ * sometimes be an operand from the earlier phi.
+ *
+ * As a result, even though InferTypes did not propagate types for phis, LeaveSSA
+ * could end up replacing the phi Identifier with another identifer from an operand,
+ * which _did_ have a type inferred.
+ *
+ * This didn't affect the initial construction of mutable ranges because InferMutableRanges
+ * runs before LeaveSSA - thus, the types propagated by LeaveSSA only affected later optimizations,
+ * notably MergeScopesThatInvalidateTogether which uses type to determine if a scope's output
+ * will always invalidate with its input.
+ *
+ * The long-term correct approach is to update InferTypes to infer the types of phis,
+ * but this is complicated because InferMutableRanges inadvertently depends on phis
+ * never having a known type, such that a Store effect cannot occur on a phi value.
+ * Once we fix InferTypes to infer phi types, then we'll also have to update InferMutableRanges
+ * to handle this case.
+ *
+ * As a temporary workaround, this pass propagates the type of phis and can be called
+ * safely *after* InferMutableRanges. Unlike LeaveSSA, this pass only propagates the
+ * type if all operands have the same type, it's its more correct.
+ */
+export function propagatePhiTypes(fn: HIRFunction): void {
+  /**
+   * We track which SSA ids have had their types propagated to handle nested ternaries,
+   * see the StoreLocal handling below
+   */
+  const propagated = new Set<IdentifierId>();
+  for (const [, block] of fn.body.blocks) {
+    for (const phi of block.phis) {
+      /*
+       * We replicate the previous LeaveSSA behavior and only propagate types for
+       * unnamed variables. LeaveSSA would have chosen one of the operands as the
+       * canonical id and taken its type as the type of all identifiers. We're
+       * more conservative and only propagate if the types are the same and the
+       * phi didn't have a type inferred.
+       *
+       * Note that this can change output slightly in cases such as
+       * `cond ? <div /> : null`.
+       *
+       * Previously the first operand's type (BuiltInJsx) would have been propagated,
+       * and this expression may have been merged with subsequent reactive scopes
+       * since it appears (based on that type) to always invalidate.
+       *
+       * But the correct type is `BuiltInJsx | null`, which we can't express and
+       * so leave as a generic `Type`, which does not always invalidate and therefore
+       * does not merge with subsequent scopes.
+       *
+       * We also don't propagate scopes for named variables, to preserve compatibility
+       * with previous LeaveSSA behavior.
+       */
+      if (
+        phi.place.identifier.type.kind !== 'Type' ||
+        phi.place.identifier.name !== null
+      ) {
+        continue;
+      }
+      let type: Type | null = null;
+      for (const [, operand] of phi.operands) {
+        if (type === null) {
+          type = operand.identifier.type;
+        } else if (!typeEquals(type, operand.identifier.type)) {
+          type = null;
+          break;
+        }
+      }
+      if (type !== null) {
+        phi.place.identifier.type = type;
+        propagated.add(phi.place.identifier.id);
+      }
+    }
+    for (const instr of block.instructions) {
+      const {value} = instr;
+      switch (value.kind) {
+        case 'StoreLocal': {
+          /**
+           * Nested ternaries can lower to a form with an intermediate StoreLocal where
+           * the value.lvalue is the temporary of the outer ternary, and the value.value
+           * is the result of the inner ternary.
+           *
+           * This is a common pattern in practice and easy enough to support. Again, the
+           * long-term approach is to update InferTypes and InferMutableRanges.
+           */
+          const lvalue = value.lvalue.place;
+          if (
+            propagated.has(value.value.identifier.id) &&
+            lvalue.identifier.type.kind === 'Type' &&
+            lvalue.identifier.name === null
+          ) {
+            lvalue.identifier.type = value.value.identifier.type;
+            propagated.add(lvalue.identifier.id);
+          }
+        }
+      }
+    }
+  }
+}
--- a/compiler/packages/babel-plugin-react-compiler/src/Utils/DisjointSet.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Utils/DisjointSet.ts
@@ -78,10 +78,6 @@ export default class DisjointSet<T> {
    return root;
  }

-  has(item: T): boolean {
-    return this.#entries.has(item);
-  }
-
  /*
   * Forces the set into canonical form, ie with all items pointing directly to
   * their root, and returns a Map representing the mapping of items to their roots.
--- a/compiler/packages/babel-plugin-react-compiler/src/Utils/Keyword.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Utils/Keyword.ts
@@ -1,87 +0,0 @@
-/**
- * Copyright (c) Meta Platforms, Inc. and affiliates.
- *
- * This source code is licensed under the MIT license found in the
- * LICENSE file in the root directory of this source tree.
- */
-
-/**
- * https://tc39.es/ecma262/multipage/ecmascript-language-lexical-grammar.html#sec-keywords-and-reserved-words
- */
-
-/**
- * Note: `await` and `yield` are contextually allowed as identifiers.
- *   await: reserved inside async functions and modules
- *   yield: reserved inside generator functions
- *
- * Note: `async` is not reserved.
- */
-const RESERVED_WORDS = new Set([
-  'break',
-  'case',
-  'catch',
-  'class',
-  'const',
-  'continue',
-  'debugger',
-  'default',
-  'delete',
-  'do',
-  'else',
-  'enum',
-  'export',
-  'extends',
-  'false',
-  'finally',
-  'for',
-  'function',
-  'if',
-  'import',
-  'in',
-  'instanceof',
-  'new',
-  'null',
-  'return',
-  'super',
-  'switch',
-  'this',
-  'throw',
-  'true',
-  'try',
-  'typeof',
-  'var',
-  'void',
-  'while',
-  'with',
-]);
-
-/**
- * Reserved when a module has a 'use strict' directive.
- */
-const STRICT_MODE_RESERVED_WORDS = new Set([
-  'let',
-  'static',
-  'implements',
-  'interface',
-  'package',
-  'private',
-  'protected',
-  'public',
-]);
-/**
- * The names arguments and eval are not keywords, but they are subject to some restrictions in
- * strict mode code.
- */
-const STRICT_MODE_RESTRICTED_WORDS = new Set(['eval', 'arguments']);
-
-/**
- * Conservative check for whether an identifer name is reserved or not. We assume that code is
- * written with strict mode.
- */
-export function isReservedWord(identifierName: string): boolean {
-  return (
-    RESERVED_WORDS.has(identifierName) ||
-    STRICT_MODE_RESERVED_WORDS.has(identifierName) ||
-    STRICT_MODE_RESTRICTED_WORDS.has(identifierName)
-  );
-}
--- a/compiler/packages/babel-plugin-react-compiler/src/Utils/Result.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Utils/Result.ts
@@ -90,13 +90,10 @@ export function Ok<T>(val: T): OkImpl<T> {
 }

 class OkImpl<T> implements Result<T, never> {
-  #val: T;
-  constructor(val: T) {
-    this.#val = val;
-  }
+  constructor(private val: T) {}

  map<U>(fn: (val: T) => U): Result<U, never> {
-    return new OkImpl(fn(this.#val));
+    return new OkImpl(fn(this.val));
  }

  mapErr<F>(_fn: (val: never) => F): Result<T, F> {
@@ -104,15 +101,15 @@ class OkImpl<T> implements Result<T, never> {
  }

  mapOr<U>(_fallback: U, fn: (val: T) => U): U {
-    return fn(this.#val);
+    return fn(this.val);
  }

  mapOrElse<U>(_fallback: () => U, fn: (val: T) => U): U {
-    return fn(this.#val);
+    return fn(this.val);
  }

  andThen<U>(fn: (val: T) => Result<U, never>): Result<U, never> {
-    return fn(this.#val);
+    return fn(this.val);
  }

  and<U>(res: Result<U, never>): Result<U, never> {
@@ -136,30 +133,30 @@ class OkImpl<T> implements Result<T, never> {
  }

  expect(_msg: string): T {
-    return this.#val;
+    return this.val;
  }

  expectErr(msg: string): never {
-    throw new Error(`${msg}: ${this.#val}`);
+    throw new Error(`${msg}: ${this.val}`);
  }

  unwrap(): T {
-    return this.#val;
+    return this.val;
  }

  unwrapOr(_fallback: T): T {
-    return this.#val;
+    return this.val;
  }

  unwrapOrElse(_fallback: (val: never) => T): T {
-    return this.#val;
+    return this.val;
  }

  unwrapErr(): never {
-    if (this.#val instanceof Error) {
-      throw this.#val;
+    if (this.val instanceof Error) {
+      throw this.val;
    }
-    throw new Error(`Can't unwrap \`Ok\` to \`Err\`: ${this.#val}`);
+    throw new Error(`Can't unwrap \`Ok\` to \`Err\`: ${this.val}`);
  }
 }

@@ -168,17 +165,14 @@ export function Err<E>(val: E): ErrImpl<E> {
 }

 class ErrImpl<E> implements Result<never, E> {
-  #val: E;
-  constructor(val: E) {
-    this.#val = val;
-  }
+  constructor(private val: E) {}

  map<U>(_fn: (val: never) => U): Result<U, E> {
    return this;
  }

  mapErr<F>(fn: (val: E) => F): Result<never, F> {
-    return new ErrImpl(fn(this.#val));
+    return new ErrImpl(fn(this.val));
  }

  mapOr<U>(fallback: U, _fn: (val: never) => U): U {
@@ -202,7 +196,7 @@ class ErrImpl<E> implements Result<never, E> {
  }

  orElse<F>(fn: (val: E) => ErrImpl<F>): Result<never, F> {
-    return fn(this.#val);
+    return fn(this.val);
  }

  isOk(): this is OkImpl<never> {
@@ -214,18 +208,18 @@ class ErrImpl<E> implements Result<never, E> {
  }

  expect(msg: string): never {
-    throw new Error(`${msg}: ${this.#val}`);
+    throw new Error(`${msg}: ${this.val}`);
  }

  expectErr(_msg: string): E {
-    return this.#val;
+    return this.val;
  }

  unwrap(): never {
-    if (this.#val instanceof Error) {
-      throw this.#val;
+    if (this.val instanceof Error) {
+      throw this.val;
    }
-    throw new Error(`Can't unwrap \`Err\` to \`Ok\`: ${this.#val}`);
+    throw new Error(`Can't unwrap \`Err\` to \`Ok\`: ${this.val}`);
  }

  unwrapOr<T>(fallback: T): T {
@@ -233,10 +227,10 @@ class ErrImpl<E> implements Result<never, E> {
  }

  unwrapOrElse<T>(fallback: (val: E) => T): T {
-    return fallback(this.#val);
+    return fallback(this.val);
  }

  unwrapErr(): E {
-    return this.#val;
+    return this.val;
  }
 }
--- a/compiler/packages/babel-plugin-react-compiler/src/Utils/TestUtils.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Utils/TestUtils.ts
@@ -75,21 +75,21 @@ const testComplexConfigDefaults: PartialEnvironmentConfig = {
        source: 'react',
        importSpecifierName: 'useEffect',
      },
-      autodepsIndex: 1,
+      numRequiredArgs: 1,
    },
    {
      function: {
        source: 'shared-runtime',
        importSpecifierName: 'useSpecialEffect',
      },
-      autodepsIndex: 2,
+      numRequiredArgs: 2,
    },
    {
      function: {
        source: 'useEffectWrapper',
        importSpecifierName: 'default',
      },
-      autodepsIndex: 1,
+      numRequiredArgs: 1,
    },
  ],
 };
@@ -113,13 +113,8 @@ function* splitPragma(
 */
 function parseConfigPragmaEnvironmentForTest(
  pragma: string,
-  defaultConfig: PartialEnvironmentConfig,
 ): EnvironmentConfig {
-  // throw early if the defaults are invalid
-  EnvironmentConfigSchema.parse(defaultConfig);
-
-  const maybeConfig: Partial<Record<keyof EnvironmentConfig, unknown>> =
-    defaultConfig;
+  const maybeConfig: Partial<Record<keyof EnvironmentConfig, unknown>> = {};

  for (const {key, value: val} of splitPragma(pragma)) {
    if (!hasOwnProperty(EnvironmentConfigSchema.shape, key)) {
@@ -179,18 +174,9 @@ export function parseConfigPragmaForTests(
  pragma: string,
  defaults: {
    compilationMode: CompilationMode;
-    environment?: PartialEnvironmentConfig;
  },
 ): PluginOptions {
-  const overridePragma = parseConfigPragmaAsString(pragma);
-  if (overridePragma !== '') {
-    return parseConfigStringAsJS(overridePragma, defaults);
-  }
-
-  const environment = parseConfigPragmaEnvironmentForTest(
-    pragma,
-    defaults.environment ?? {},
-  );
+  const environment = parseConfigPragmaEnvironmentForTest(pragma);
  const options: Record<keyof PluginOptions, unknown> = {
    ...defaultOptions,
    panicThreshold: 'all_errors',
@@ -222,104 +208,3 @@ export function parseConfigPragmaForTests(
  }
  return parsePluginOptions(options);
 }
-
-export function parseConfigPragmaAsString(pragma: string): string {
-  // Check if it's in JS override format
-  for (const {key, value: val} of splitPragma(pragma)) {
-    if (key === 'OVERRIDE' && val != null) {
-      return val;
-    }
-  }
-  return '';
-}
-
-function parseConfigStringAsJS(
-  configString: string,
-  defaults: {
-    compilationMode: CompilationMode;
-    environment?: PartialEnvironmentConfig;
-  },
-): PluginOptions {
-  let parsedConfig: any;
-  try {
-    // Parse the JavaScript object literal
-    parsedConfig = new Function(`return ${configString}`)();
-  } catch (error) {
-    CompilerError.invariant(false, {
-      reason: 'Failed to parse config pragma as JavaScript object',
-      description: `Could not parse: ${configString}. Error: ${error}`,
-      loc: null,
-      suggestions: null,
-    });
-  }
-
-  console.log('OVERRIDE:', parsedConfig);
-
-  const options: Record<keyof PluginOptions, unknown> = {
-    ...defaultOptions,
-    panicThreshold: 'all_errors',
-    compilationMode: defaults.compilationMode,
-    environment: defaults.environment ?? defaultOptions.environment,
-  };
-
-  // Apply parsed config, merging environment if it exists
-  if (parsedConfig.environment) {
-    const mergedEnvironment = {
-      ...(options.environment as Record<string, unknown>),
-      ...parsedConfig.environment,
-    };
-
-    // Apply complex defaults for environment flags that are set to true
-    const environmentConfig: Partial<Record<keyof EnvironmentConfig, unknown>> =
-      {};
-    for (const [key, value] of Object.entries(mergedEnvironment)) {
-      if (hasOwnProperty(EnvironmentConfigSchema.shape, key)) {
-        if (value === true && key in testComplexConfigDefaults) {
-          environmentConfig[key] = testComplexConfigDefaults[key];
-        } else {
-          environmentConfig[key] = value;
-        }
-      }
-    }
-
-    // Validate environment config
-    const validatedEnvironment =
-      EnvironmentConfigSchema.safeParse(environmentConfig);
-    if (!validatedEnvironment.success) {
-      CompilerError.invariant(false, {
-        reason: 'Invalid environment configuration in config pragma',
-        description: `${fromZodError(validatedEnvironment.error)}`,
-        loc: null,
-        suggestions: null,
-      });
-    }
-
-    if (validatedEnvironment.data.enableResetCacheOnSourceFileChanges == null) {
-      validatedEnvironment.data.enableResetCacheOnSourceFileChanges = false;
-    }
-
-    options.environment = validatedEnvironment.data;
-  }
-
-  // Apply other config options
-  for (const [key, value] of Object.entries(parsedConfig)) {
-    if (key === 'environment') {
-      continue;
-    }
-
-    if (hasOwnProperty(defaultOptions, key)) {
-      if (value === true && key in testComplexPluginOptionDefaults) {
-        options[key] = testComplexPluginOptionDefaults[key];
-      } else if (key === 'target' && value === 'donotuse_meta_internal') {
-        options[key] = {
-          kind: value,
-          runtimeModule: 'react',
-        };
-      } else {
-        options[key] = value;
-      }
-    }
-  }
-
-  return parsePluginOptions(options);
-}
--- a/compiler/packages/babel-plugin-react-compiler/src/Utils/utils.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Utils/utils.ts
@@ -33,12 +33,12 @@ export function assertExhaustive(_: never, errorMsg: string): never {
 // Modifies @param array in place, retaining only the items where the predicate returns true.
 export function retainWhere<T>(
  array: Array<T>,
-  predicate: (item: T, index: number) => boolean,
+  predicate: (item: T) => boolean,
 ): void {
  let writeIndex = 0;
  for (let readIndex = 0; readIndex < array.length; readIndex++) {
    const item = array[readIndex];
-    if (predicate(item, readIndex) === true) {
+    if (predicate(item) === true) {
      array[writeIndex++] = item;
    }
  }
--- a/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateHooksUsage.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateHooksUsage.ts
@@ -9,7 +9,6 @@ import * as t from '@babel/types';
 import {
  CompilerError,
  CompilerErrorDetail,
-  ErrorCategory,
  ErrorSeverity,
 } from '../CompilerError';
 import {computeUnconditionalBlocks} from '../HIR/ComputeUnconditionalBlocks';
@@ -125,7 +124,6 @@ export function validateHooksUsage(
      recordError(
        place.loc,
        new CompilerErrorDetail({
-          category: ErrorCategory.Hooks,
          description: null,
          reason,
          loc: place.loc,
@@ -142,7 +140,6 @@ export function validateHooksUsage(
      recordError(
        place.loc,
        new CompilerErrorDetail({
-          category: ErrorCategory.Hooks,
          description: null,
          reason:
            'Hooks may not be referenced as normal values, they must be called. See https://react.dev/reference/rules/react-calls-components-and-hooks#never-pass-around-hooks-as-regular-values',
@@ -160,7 +157,6 @@ export function validateHooksUsage(
      recordError(
        place.loc,
        new CompilerErrorDetail({
-          category: ErrorCategory.Hooks,
          description: null,
          reason:
            'Hooks must be the same function on every render, but this value may change over time to a different function. See https://react.dev/reference/rules/react-calls-components-and-hooks#dont-dynamically-use-hooks',
@@ -428,7 +424,7 @@ export function validateHooksUsage(
  }

  for (const [, error] of errorsByPlace) {
-    errors.pushErrorDetail(error);
+    errors.push(error);
  }
  return errors.asResult();
 }
@@ -452,7 +448,6 @@ function visitFunctionExpression(errors: CompilerError, fn: HIRFunction): void {
          if (hookKind != null) {
            errors.pushErrorDetail(
              new CompilerErrorDetail({
-                category: ErrorCategory.Hooks,
                severity: ErrorSeverity.InvalidReact,
                reason:
                  'Hooks must be called at the top level in the body of a function component or custom hook, and may not be called within function expressions. See the Rules of Hooks (https://react.dev/warnings/invalid-hook-call-warning)',
--- a/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateLocalsNotReassignedAfterRender.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateLocalsNotReassignedAfterRender.ts
@@ -5,15 +5,14 @@
 * LICENSE file in the root directory of this source tree.
 */

-import {CompilerDiagnostic, CompilerError, Effect, ErrorSeverity} from '..';
-import {ErrorCategory} from '../CompilerError';
+import {CompilerError, Effect} from '..';
 import {HIRFunction, IdentifierId, Place} from '../HIR';
 import {
  eachInstructionLValue,
  eachInstructionValueOperand,
  eachTerminalOperand,
 } from '../HIR/visitors';
-import {getFunctionCallSignature} from '../Inference/InferMutationAliasingEffects';
+import {getFunctionCallSignature} from '../Inference/InferReferenceEffects';

 /**
 * Validates that local variables cannot be reassigned after render.
@@ -29,25 +28,16 @@ export function validateLocalsNotReassignedAfterRender(fn: HIRFunction): void {
    false,
  );
  if (reassignment !== null) {
-    const errors = new CompilerError();
-    const variable =
-      reassignment.identifier.name != null &&
-      reassignment.identifier.name.kind === 'named'
-        ? `\`${reassignment.identifier.name.value}\``
-        : 'variable';
-    errors.pushDiagnostic(
-      CompilerDiagnostic.create({
-        category: ErrorCategory.Immutability,
-        severity: ErrorSeverity.InvalidReact,
-        reason: 'Cannot reassign variable after render completes',
-        description: `Reassigning ${variable} after render has completed can cause inconsistent behavior on subsequent renders. Consider using state instead.`,
-      }).withDetail({
-        kind: 'error',
-        loc: reassignment.loc,
-        message: `Cannot reassign ${variable} after render completes`,
-      }),
-    );
-    throw errors;
+    CompilerError.throwInvalidReact({
+      reason:
+        'Reassigning a variable after render has completed can cause inconsistent behavior on subsequent renders. Consider using state instead',
+      description:
+        reassignment.identifier.name !== null &&
+        reassignment.identifier.name.kind === 'named'
+          ? `Variable \`${reassignment.identifier.name.value}\` cannot be reassigned after render`
+          : '',
+      loc: reassignment.loc,
+    });
  }
 }

@@ -85,26 +75,16 @@ function getContextReassignment(
          // if the function or its depends reassign, propagate that fact on the lvalue
          if (reassignment !== null) {
            if (isAsync || value.loweredFunc.func.async) {
-              const errors = new CompilerError();
-              const variable =
-                reassignment.identifier.name !== null &&
-                reassignment.identifier.name.kind === 'named'
-                  ? `\`${reassignment.identifier.name.value}\``
-                  : 'variable';
-              errors.pushDiagnostic(
-                CompilerDiagnostic.create({
-                  category: ErrorCategory.Immutability,
-                  severity: ErrorSeverity.InvalidReact,
-                  reason: 'Cannot reassign variable in async function',
-                  description:
-                    'Reassigning a variable in an async function can cause inconsistent behavior on subsequent renders. Consider using state instead',
-                }).withDetail({
-                  kind: 'error',
-                  loc: reassignment.loc,
-                  message: `Cannot reassign ${variable}`,
-                }),
-              );
-              throw errors;
+              CompilerError.throwInvalidReact({
+                reason:
+                  'Reassigning a variable in an async function can cause inconsistent behavior on subsequent renders. Consider using state instead',
+                description:
+                  reassignment.identifier.name !== null &&
+                  reassignment.identifier.name.kind === 'named'
+                    ? `Variable \`${reassignment.identifier.name.value}\` cannot be reassigned after render`
+                    : '',
+                loc: reassignment.loc,
+              });
            }
            reassigningFunctions.set(lvalue.identifier.id, reassignment);
          }
--- a/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateMemoizedEffectDependencies.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateMemoizedEffectDependencies.ts
@@ -6,7 +6,6 @@
 */

 import {CompilerError, ErrorSeverity} from '..';
-import {ErrorCategory} from '../CompilerError';
 import {
  Identifier,
  Instruction,
@@ -109,7 +108,6 @@ class Visitor extends ReactiveFunctionVisitor<CompilerError> {
          isUnmemoized(deps.identifier, this.scopes))
      ) {
        state.push({
-          category: ErrorCategory.EffectDependencies,
          reason:
            'React Compiler has skipped optimizing this component because the effect dependencies could not be memoized. Unmemoized effect dependencies can trigger an infinite loop or other unexpected behavior',
          description: null,
--- a/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoCapitalizedCalls.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoCapitalizedCalls.ts
@@ -6,7 +6,6 @@
 */

 import {CompilerError, EnvironmentConfig, ErrorSeverity} from '..';
-import {ErrorCategory} from '../CompilerError';
 import {HIRFunction, IdentifierId} from '../HIR';
 import {DEFAULT_GLOBALS} from '../HIR/Globals';
 import {Result} from '../Utils/Result';
@@ -57,7 +56,6 @@ export function validateNoCapitalizedCalls(
          const calleeName = capitalLoadGlobals.get(calleeIdentifier);
          if (calleeName != null) {
            CompilerError.throwInvalidReact({
-              category: ErrorCategory.CapitalizedCalls,
              reason,
              description: `${calleeName} may be a component.`,
              loc: value.loc,
@@ -81,7 +79,6 @@ export function validateNoCapitalizedCalls(
          const propertyName = capitalizedProperties.get(propertyIdentifier);
          if (propertyName != null) {
            errors.push({
-              category: ErrorCategory.CapitalizedCalls,
              severity: ErrorSeverity.InvalidReact,
              reason,
              description: `${propertyName} may be a component.`,
--- a/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoDerivedComputationsInEffects.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoDerivedComputationsInEffects.ts
@@ -1,232 +0,0 @@
-/**
- * Copyright (c) Meta Platforms, Inc. and affiliates.
- *
- * This source code is licensed under the MIT license found in the
- * LICENSE file in the root directory of this source tree.
- */
-
-import {CompilerError, ErrorSeverity, SourceLocation} from '..';
-import {ErrorCategory} from '../CompilerError';
-import {
-  ArrayExpression,
-  BlockId,
-  FunctionExpression,
-  HIRFunction,
-  IdentifierId,
-  isSetStateType,
-  isUseEffectHookType,
-} from '../HIR';
-import {
-  eachInstructionValueOperand,
-  eachTerminalOperand,
-} from '../HIR/visitors';
-
-/**
- * Validates that useEffect is not used for derived computations which could/should
- * be performed in render.
- *
- * See https://react.dev/learn/you-might-not-need-an-effect#updating-state-based-on-props-or-state
- *
- * Example:
- *
- * ```
- * // 🔴 Avoid: redundant state and unnecessary Effect
- * const [fullName, setFullName] = useState('');
- * useEffect(() => {
- *   setFullName(firstName + ' ' + lastName);
- * }, [firstName, lastName]);
- * ```
- *
- * Instead use:
- *
- * ```
- * // ✅ Good: calculated during rendering
- * const fullName = firstName + ' ' + lastName;
- * ```
- */
-export function validateNoDerivedComputationsInEffects(fn: HIRFunction): void {
-  const candidateDependencies: Map<IdentifierId, ArrayExpression> = new Map();
-  const functions: Map<IdentifierId, FunctionExpression> = new Map();
-  const locals: Map<IdentifierId, IdentifierId> = new Map();
-
-  const errors = new CompilerError();
-
-  for (const block of fn.body.blocks.values()) {
-    for (const instr of block.instructions) {
-      const {lvalue, value} = instr;
-      if (value.kind === 'LoadLocal') {
-        locals.set(lvalue.identifier.id, value.place.identifier.id);
-      } else if (value.kind === 'ArrayExpression') {
-        candidateDependencies.set(lvalue.identifier.id, value);
-      } else if (value.kind === 'FunctionExpression') {
-        functions.set(lvalue.identifier.id, value);
-      } else if (
-        value.kind === 'CallExpression' ||
-        value.kind === 'MethodCall'
-      ) {
-        const callee =
-          value.kind === 'CallExpression' ? value.callee : value.property;
-        if (
-          isUseEffectHookType(callee.identifier) &&
-          value.args.length === 2 &&
-          value.args[0].kind === 'Identifier' &&
-          value.args[1].kind === 'Identifier'
-        ) {
-          const effectFunction = functions.get(value.args[0].identifier.id);
-          const deps = candidateDependencies.get(value.args[1].identifier.id);
-          if (
-            effectFunction != null &&
-            deps != null &&
-            deps.elements.length !== 0 &&
-            deps.elements.every(element => element.kind === 'Identifier')
-          ) {
-            const dependencies: Array<IdentifierId> = deps.elements.map(dep => {
-              CompilerError.invariant(dep.kind === 'Identifier', {
-                reason: `Dependency is checked as a place above`,
-                loc: value.loc,
-              });
-              return locals.get(dep.identifier.id) ?? dep.identifier.id;
-            });
-            validateEffect(
-              effectFunction.loweredFunc.func,
-              dependencies,
-              errors,
-            );
-          }
-        }
-      }
-    }
-  }
-  if (errors.hasErrors()) {
-    throw errors;
-  }
-}
-
-function validateEffect(
-  effectFunction: HIRFunction,
-  effectDeps: Array<IdentifierId>,
-  errors: CompilerError,
-): void {
-  for (const operand of effectFunction.context) {
-    if (isSetStateType(operand.identifier)) {
-      continue;
-    } else if (effectDeps.find(dep => dep === operand.identifier.id) != null) {
-      continue;
-    } else {
-      // Captured something other than the effect dep or setState
-      return;
-    }
-  }
-  for (const dep of effectDeps) {
-    if (
-      effectFunction.context.find(operand => operand.identifier.id === dep) ==
-      null
-    ) {
-      // effect dep wasn't actually used in the function
-      return;
-    }
-  }
-
-  const seenBlocks: Set<BlockId> = new Set();
-  const values: Map<IdentifierId, Array<IdentifierId>> = new Map();
-  for (const dep of effectDeps) {
-    values.set(dep, [dep]);
-  }
-
-  const setStateLocations: Array<SourceLocation> = [];
-  for (const block of effectFunction.body.blocks.values()) {
-    for (const pred of block.preds) {
-      if (!seenBlocks.has(pred)) {
-        // skip if block has a back edge
-        return;
-      }
-    }
-    for (const phi of block.phis) {
-      const aggregateDeps: Set<IdentifierId> = new Set();
-      for (const operand of phi.operands.values()) {
-        const deps = values.get(operand.identifier.id);
-        if (deps != null) {
-          for (const dep of deps) {
-            aggregateDeps.add(dep);
-          }
-        }
-      }
-      if (aggregateDeps.size !== 0) {
-        values.set(phi.place.identifier.id, Array.from(aggregateDeps));
-      }
-    }
-    for (const instr of block.instructions) {
-      switch (instr.value.kind) {
-        case 'Primitive':
-        case 'JSXText':
-        case 'LoadGlobal': {
-          break;
-        }
-        case 'LoadLocal': {
-          const deps = values.get(instr.value.place.identifier.id);
-          if (deps != null) {
-            values.set(instr.lvalue.identifier.id, deps);
-          }
-          break;
-        }
-        case 'ComputedLoad':
-        case 'PropertyLoad':
-        case 'BinaryExpression':
-        case 'TemplateLiteral':
-        case 'CallExpression':
-        case 'MethodCall': {
-          const aggregateDeps: Set<IdentifierId> = new Set();
-          for (const operand of eachInstructionValueOperand(instr.value)) {
-            const deps = values.get(operand.identifier.id);
-            if (deps != null) {
-              for (const dep of deps) {
-                aggregateDeps.add(dep);
-              }
-            }
-          }
-          if (aggregateDeps.size !== 0) {
-            values.set(instr.lvalue.identifier.id, Array.from(aggregateDeps));
-          }
-
-          if (
-            instr.value.kind === 'CallExpression' &&
-            isSetStateType(instr.value.callee.identifier) &&
-            instr.value.args.length === 1 &&
-            instr.value.args[0].kind === 'Identifier'
-          ) {
-            const deps = values.get(instr.value.args[0].identifier.id);
-            if (deps != null && new Set(deps).size === effectDeps.length) {
-              setStateLocations.push(instr.value.callee.loc);
-            } else {
-              // doesn't depend on any deps
-              return;
-            }
-          }
-          break;
-        }
-        default: {
-          return;
-        }
-      }
-    }
-    for (const operand of eachTerminalOperand(block.terminal)) {
-      if (values.has(operand.identifier.id)) {
-        //
-        return;
-      }
-    }
-    seenBlocks.add(block.id);
-  }
-
-  for (const loc of setStateLocations) {
-    errors.push({
-      category: ErrorCategory.EffectDerivationsOfState,
-      reason:
-        'Values derived from props and state should be calculated during render, not in an effect. (https://react.dev/learn/you-might-not-need-an-effect#updating-state-based-on-props-or-state)',
-      description: null,
-      severity: ErrorSeverity.InvalidReact,
-      loc,
-      suggestions: null,
-    });
-  }
-}
--- a/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoFreezingKnownMutableFunctions.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoFreezingKnownMutableFunctions.ts
@@ -5,11 +5,12 @@
 * LICENSE file in the root directory of this source tree.
 */

-import {CompilerDiagnostic, CompilerError, Effect, ErrorSeverity} from '..';
-import {ErrorCategory} from '../CompilerError';
+import {CompilerError, Effect, ErrorSeverity} from '..';
 import {
+  FunctionEffect,
  HIRFunction,
  IdentifierId,
+  isMutableEffect,
  isRefOrRefLikeMutableType,
  Place,
 } from '../HIR';
@@ -17,8 +18,8 @@ import {
  eachInstructionValueOperand,
  eachTerminalOperand,
 } from '../HIR/visitors';
-import {AliasingEffect} from '../Inference/AliasingEffects';
 import {Result} from '../Utils/Result';
+import {Iterable_some} from '../Utils/utils';

 /**
 * Validates that functions with known mutations (ie due to types) cannot be passed
@@ -49,38 +50,23 @@ export function validateNoFreezingKnownMutableFunctions(
  const errors = new CompilerError();
  const contextMutationEffects: Map<
    IdentifierId,
-    Extract<AliasingEffect, {kind: 'Mutate'} | {kind: 'MutateTransitive'}>
+    Extract<FunctionEffect, {kind: 'ContextMutation'}>
  > = new Map();

  function visitOperand(operand: Place): void {
    if (operand.effect === Effect.Freeze) {
      const effect = contextMutationEffects.get(operand.identifier.id);
      if (effect != null) {
-        const place = effect.value;
-        const variable =
-          place != null &&
-          place.identifier.name != null &&
-          place.identifier.name.kind === 'named'
-            ? `\`${place.identifier.name.value}\``
-            : 'a local variable';
-        errors.pushDiagnostic(
-          CompilerDiagnostic.create({
-            category: ErrorCategory.Immutability,
-            severity: ErrorSeverity.InvalidReact,
-            reason: 'Cannot modify local variables after render completes',
-            description: `This argument is a function which may reassign or mutate ${variable} after render, which can cause inconsistent behavior on subsequent renders. Consider using state instead.`,
-          })
-            .withDetail({
-              kind: 'error',
-              loc: operand.loc,
-              message: `This function may (indirectly) reassign or modify ${variable} after render`,
-            })
-            .withDetail({
-              kind: 'error',
-              loc: effect.value.loc,
-              message: `This modifies ${variable}`,
-            }),
-        );
+        errors.push({
+          reason: `This argument is a function which may reassign or mutate local variables after render, which can cause inconsistent behavior on subsequent renders. Consider using state instead`,
+          loc: operand.loc,
+          severity: ErrorSeverity.InvalidReact,
+        });
+        errors.push({
+          reason: `The function modifies a local variable here`,
+          loc: effect.loc,
+          severity: ErrorSeverity.InvalidReact,
+        });
      }
    }
  }
@@ -108,7 +94,27 @@ export function validateNoFreezingKnownMutableFunctions(
          break;
        }
        case 'FunctionExpression': {
-          if (value.loweredFunc.func.aliasingEffects != null) {
+          const knownMutation = (value.loweredFunc.func.effects ?? []).find(
+            effect => {
+              return (
+                effect.kind === 'ContextMutation' &&
+                (effect.effect === Effect.Store ||
+                  effect.effect === Effect.Mutate) &&
+                Iterable_some(effect.places, place => {
+                  return (
+                    isMutableEffect(place.effect, place.loc) &&
+                    !isRefOrRefLikeMutableType(place.identifier.type)
+                  );
+                })
+              );
+            },
+          );
+          if (knownMutation && knownMutation.kind === 'ContextMutation') {
+            contextMutationEffects.set(lvalue.identifier.id, knownMutation);
+          } else if (
+            fn.env.config.enableNewMutationAliasingModel &&
+            value.loweredFunc.func.aliasingEffects != null
+          ) {
            const context = new Set(
              value.loweredFunc.func.context.map(p => p.identifier.id),
            );
@@ -129,7 +135,12 @@ export function validateNoFreezingKnownMutableFunctions(
                    context.has(effect.value.identifier.id) &&
                    !isRefOrRefLikeMutableType(effect.value.identifier.type)
                  ) {
-                    contextMutationEffects.set(lvalue.identifier.id, effect);
+                    contextMutationEffects.set(lvalue.identifier.id, {
+                      kind: 'ContextMutation',
+                      effect: Effect.Mutate,
+                      loc: effect.value.loc,
+                      places: new Set([effect.value]),
+                    });
                    break effects;
                  }
                  break;
--- a/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoImpureFunctionsInRender.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoImpureFunctionsInRender.ts
@@ -5,10 +5,9 @@
 * LICENSE file in the root directory of this source tree.
 */

-import {CompilerDiagnostic, CompilerError, ErrorSeverity} from '..';
-import {ErrorCategory} from '../CompilerError';
+import {CompilerError, ErrorSeverity} from '..';
 import {HIRFunction} from '../HIR';
-import {getFunctionCallSignature} from '../Inference/InferMutationAliasingEffects';
+import {getFunctionCallSignature} from '../Inference/InferReferenceEffects';
 import {Result} from '../Utils/Result';

 /**
@@ -35,23 +34,17 @@ export function validateNoImpureFunctionsInRender(
          callee.identifier.type,
        );
        if (signature != null && signature.impure === true) {
-          errors.pushDiagnostic(
-            CompilerDiagnostic.create({
-              category: ErrorCategory.Purity,
-              reason: 'Cannot call impure function during render',
-              description:
-                (signature.canonicalName != null
-                  ? `\`${signature.canonicalName}\` is an impure function. `
-                  : '') +
-                'Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent)',
-              severity: ErrorSeverity.InvalidReact,
-              suggestions: null,
-            }).withDetail({
-              kind: 'error',
-              loc: callee.loc,
-              message: 'Cannot call impure function',
-            }),
-          );
+          errors.push({
+            reason:
+              'Calling an impure function can produce unstable results. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent)',
+            description:
+              signature.canonicalName != null
+                ? `\`${signature.canonicalName}\` is an impure function whose results may change on every call`
+                : null,
+            severity: ErrorSeverity.InvalidReact,
+            loc: callee.loc,
+            suggestions: null,
+          });
        }
      }
    }
--- a/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoJSXInTryStatement.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoJSXInTryStatement.ts
@@ -5,8 +5,7 @@
 * LICENSE file in the root directory of this source tree.
 */

-import {CompilerDiagnostic, CompilerError, ErrorSeverity} from '..';
-import {ErrorCategory} from '../CompilerError';
+import {CompilerError, ErrorSeverity} from '..';
 import {BlockId, HIRFunction} from '../HIR';
 import {Result} from '../Utils/Result';
 import {retainWhere} from '../Utils/utils';
@@ -35,18 +34,11 @@ export function validateNoJSXInTryStatement(
        switch (value.kind) {
          case 'JsxExpression':
          case 'JsxFragment': {
-            errors.pushDiagnostic(
-              CompilerDiagnostic.create({
-                category: ErrorCategory.ErrorBoundaries,
-                severity: ErrorSeverity.InvalidReact,
-                reason: 'Avoid constructing JSX within try/catch',
-                description: `React does not immediately render components when JSX is rendered, so any errors from this component will not be caught by the try/catch. To catch errors in rendering a given component, wrap that component in an error boundary. (https://react.dev/reference/react/Component#catching-rendering-errors-with-an-error-boundary)`,
-              }).withDetail({
-                kind: 'error',
-                loc: value.loc,
-                message: 'Avoid constructing JSX within try/catch',
-              }),
-            );
+            errors.push({
+              severity: ErrorSeverity.InvalidReact,
+              reason: `Unexpected JSX element within a try statement. To catch errors in rendering a given component, wrap that component in an error boundary. (https://react.dev/reference/react/Component#catching-rendering-errors-with-an-error-boundary)`,
+              loc: value.loc,
+            });
            break;
          }
        }
--- a/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoRefAccessInRender.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoRefAccessInRender.ts
@@ -5,12 +5,7 @@
 * LICENSE file in the root directory of this source tree.
 */

-import {
-  CompilerDiagnostic,
-  CompilerError,
-  ErrorCategory,
-  ErrorSeverity,
-} from '../CompilerError';
+import {CompilerError, ErrorSeverity} from '../CompilerError';
 import {
  BlockId,
  HIRFunction,
@@ -28,7 +23,6 @@ import {
  eachTerminalOperand,
 } from '../HIR/visitors';
 import {Err, Ok, Result} from '../Utils/Result';
-import {retainWhere} from '../Utils/utils';

 /**
 * Validates that a function does not access a ref value during render. This includes a partial check
@@ -81,18 +75,8 @@ type RefAccessRefType =

 type RefFnType = {readRefEffect: boolean; returnType: RefAccessType};

-class Env {
+class Env extends Map<IdentifierId, RefAccessType> {
  #changed = false;
-  #data: Map<IdentifierId, RefAccessType> = new Map();
-  #temporaries: Map<IdentifierId, Place> = new Map();
-
-  lookup(place: Place): Place {
-    return this.#temporaries.get(place.identifier.id) ?? place;
-  }
-
-  define(place: Place, value: Place): void {
-    this.#temporaries.set(place.identifier.id, value);
-  }

  resetChanged(): void {
    this.#changed = false;
@@ -102,14 +86,8 @@ class Env {
    return this.#changed;
  }

-  get(key: IdentifierId): RefAccessType | undefined {
-    const operandId = this.#temporaries.get(key)?.identifier.id ?? key;
-    return this.#data.get(operandId);
-  }
-
-  set(key: IdentifierId, value: RefAccessType): this {
-    const operandId = this.#temporaries.get(key)?.identifier.id ?? key;
-    const cur = this.#data.get(operandId);
+  override set(key: IdentifierId, value: RefAccessType): this {
+    const cur = this.get(key);
    const widenedValue = joinRefAccessTypes(value, cur ?? {kind: 'None'});
    if (
      !(cur == null && widenedValue.kind === 'None') &&
@@ -117,8 +95,7 @@ class Env {
    ) {
      this.#changed = true;
    }
-    this.#data.set(operandId, widenedValue);
-    return this;
+    return super.set(key, widenedValue);
  }
 }

@@ -126,48 +103,9 @@ export function validateNoRefAccessInRender(
  fn: HIRFunction,
 ): Result<void, CompilerError> {
  const env = new Env();
-  collectTemporariesSidemap(fn, env);
  return validateNoRefAccessInRenderImpl(fn, env).map(_ => undefined);
 }

-function collectTemporariesSidemap(fn: HIRFunction, env: Env): void {
-  for (const block of fn.body.blocks.values()) {
-    for (const instr of block.instructions) {
-      const {lvalue, value} = instr;
-      switch (value.kind) {
-        case 'LoadLocal': {
-          const temp = env.lookup(value.place);
-          if (temp != null) {
-            env.define(lvalue, temp);
-          }
-          break;
-        }
-        case 'StoreLocal': {
-          const temp = env.lookup(value.value);
-          if (temp != null) {
-            env.define(lvalue, temp);
-            env.define(value.lvalue.place, temp);
-          }
-          break;
-        }
-        case 'PropertyLoad': {
-          if (
-            isUseRefType(value.object.identifier) &&
-            value.property === 'current'
-          ) {
-            continue;
-          }
-          const temp = env.lookup(value.object);
-          if (temp != null) {
-            env.define(lvalue, temp);
-          }
-          break;
-        }
-      }
-    }
-  }
-}
-
 function refTypeOfType(place: Place): RefAccessType {
  if (isRefValueType(place.identifier)) {
    return {kind: 'RefValue'};
@@ -320,27 +258,12 @@ function validateNoRefAccessInRenderImpl(
    env.set(place.identifier.id, type);
  }

-  const interpolatedAsJsx = new Set<IdentifierId>();
-  for (const block of fn.body.blocks.values()) {
-    for (const instr of block.instructions) {
-      const {value} = instr;
-      if (value.kind === 'JsxExpression' || value.kind === 'JsxFragment') {
-        if (value.children != null) {
-          for (const child of value.children) {
-            interpolatedAsJsx.add(child.identifier.id);
-          }
-        }
-      }
-    }
-  }
-
  for (let i = 0; (i == 0 || env.hasChanged()) && i < 10; i++) {
    env.resetChanged();
    returnValues = [];
-    const safeBlocks: Array<{block: BlockId; ref: RefId}> = [];
+    const safeBlocks = new Map<BlockId, RefId>();
    const errors = new CompilerError();
    for (const [, block] of fn.body.blocks) {
-      retainWhere(safeBlocks, entry => entry.block !== block.id);
      for (const phi of block.phis) {
        env.set(
          phi.place.identifier.id,
@@ -462,80 +385,28 @@ function validateNoRefAccessInRenderImpl(
            const hookKind = getHookKindForType(fn.env, callee.identifier.type);
            let returnType: RefAccessType = {kind: 'None'};
            const fnType = env.get(callee.identifier.id);
-            let didError = false;
            if (fnType?.kind === 'Structure' && fnType.fn !== null) {
              returnType = fnType.fn.returnType;
              if (fnType.fn.readRefEffect) {
-                didError = true;
-                errors.pushDiagnostic(
-                  CompilerDiagnostic.create({
-                    category: ErrorCategory.Refs,
-                    severity: ErrorSeverity.InvalidReact,
-                    reason: 'Cannot access refs during render',
-                    description: ERROR_DESCRIPTION,
-                  }).withDetail({
-                    kind: 'error',
-                    loc: callee.loc,
-                    message: `This function accesses a ref value`,
-                  }),
-                );
+                errors.push({
+                  severity: ErrorSeverity.InvalidReact,
+                  reason:
+                    'This function accesses a ref value (the `current` property), which may not be accessed during render. (https://react.dev/reference/react/useRef)',
+                  loc: callee.loc,
+                  description:
+                    callee.identifier.name !== null &&
+                    callee.identifier.name.kind === 'named'
+                      ? `Function \`${callee.identifier.name.value}\` accesses a ref`
+                      : null,
+                  suggestions: null,
+                });
              }
            }
-            /*
-             * If we already reported an error on this instruction, don't report
-             * duplicate errors
-             */
-            if (!didError) {
-              const isRefLValue = isUseRefType(instr.lvalue.identifier);
-              for (const operand of eachInstructionValueOperand(instr.value)) {
-                /**
-                 * By default we check that function call operands are not refs,
-                 * ref values, or functions that can access refs.
-                 */
-                if (
-                  isRefLValue ||
-                  (hookKind != null &&
-                    hookKind !== 'useState' &&
-                    hookKind !== 'useReducer')
-                ) {
-                  /**
-                   * Special cases:
-                   *
-                   * 1. the lvalue is a ref
-                   * In general passing a ref to a function may access that ref
-                   * value during render, so we disallow it.
-                   *
-                   * The main exception is the "mergeRefs" pattern, ie a function
-                   * that accepts multiple refs as arguments (or an array of refs)
-                   * and returns a new, aggregated ref. If the lvalue is a ref,
-                   * we assume that the user is doing this pattern and allow passing
-                   * refs.
-                   *
-                   * Eg `const mergedRef = mergeRefs(ref1, ref2)`
-                   *
-                   * 2. calling hooks
-                   *
-                   * Hooks are independently checked to ensure they don't access refs
-                   * during render.
-                   */
-                  validateNoDirectRefValueAccess(errors, operand, env);
-                } else if (interpolatedAsJsx.has(instr.lvalue.identifier.id)) {
-                  /**
-                   * Special case: the lvalue is passed as a jsx child
-                   *
-                   * For example `<Foo>{renderHelper(ref)}</Foo>`. Here we have more
-                   * context and infer that the ref is being passed to a component-like
-                   * render function which attempts to obey the rules.
-                   */
-                  validateNoRefValueAccess(errors, env, operand);
-                } else {
-                  validateNoRefPassedToFunction(
-                    errors,
-                    env,
-                    operand,
-                    operand.loc,
-                  );
-                }
+            for (const operand of eachInstructionValueOperand(instr.value)) {
+              if (hookKind != null) {
+                validateNoDirectRefValueAccess(errors, operand, env);
+              } else {
+                validateNoRefAccess(errors, env, operand, operand.loc);
              }
            }
            env.set(instr.lvalue.identifier.id, returnType);
@@ -568,39 +439,23 @@ function validateNoRefAccessInRenderImpl(
          case 'PropertyStore':
          case 'ComputedDelete':
          case 'ComputedStore': {
+            const safe = safeBlocks.get(block.id);
            const target = env.get(instr.value.object.identifier.id);
-            let safe: (typeof safeBlocks)['0'] | null | undefined = null;
            if (
              instr.value.kind === 'PropertyStore' &&
-              target != null &&
-              target.kind === 'Ref'
+              safe != null &&
+              target?.kind === 'Ref' &&
+              target.refId === safe
            ) {
-              safe = safeBlocks.find(entry => entry.ref === target.refId);
-            }
-            if (safe != null) {
-              retainWhere(safeBlocks, entry => entry !== safe);
+              safeBlocks.delete(block.id);
            } else {
-              validateNoRefUpdate(errors, env, instr.value.object, instr.loc);
+              validateNoRefAccess(errors, env, instr.value.object, instr.loc);
            }
-            if (
-              instr.value.kind === 'ComputedDelete' ||
-              instr.value.kind === 'ComputedStore'
-            ) {
-              validateNoRefValueAccess(errors, env, instr.value.property);
-            }
-            if (
-              instr.value.kind === 'ComputedStore' ||
-              instr.value.kind === 'PropertyStore'
-            ) {
-              validateNoDirectRefValueAccess(errors, instr.value.value, env);
-              const type = env.get(instr.value.value.identifier.id);
-              if (type != null && type.kind === 'Structure') {
-                let objectType: RefAccessType = type;
-                if (target != null) {
-                  objectType = joinRefAccessTypes(objectType, target);
-                }
-                env.set(instr.value.object.identifier.id, objectType);
+            for (const operand of eachInstructionValueOperand(instr.value)) {
+              if (operand === instr.value.object) {
+                continue;
              }
+              validateNoRefValueAccess(errors, env, operand);
            }
            break;
          }
@@ -680,11 +535,8 @@ function validateNoRefAccessInRenderImpl(

      if (block.terminal.kind === 'if') {
        const test = env.get(block.terminal.test.identifier.id);
-        if (
-          test?.kind === 'Guard' &&
-          safeBlocks.find(entry => entry.ref === test.refId) == null
-        ) {
-          safeBlocks.push({block: block.terminal.fallthrough, ref: test.refId});
+        if (test?.kind === 'Guard') {
+          safeBlocks.set(block.terminal.consequent, test.refId);
        }
      }

@@ -731,18 +583,18 @@ function destructure(

 function guardCheck(errors: CompilerError, operand: Place, env: Env): void {
  if (env.get(operand.identifier.id)?.kind === 'Guard') {
-    errors.pushDiagnostic(
-      CompilerDiagnostic.create({
-        category: ErrorCategory.Refs,
-        severity: ErrorSeverity.InvalidReact,
-        reason: 'Cannot access refs during render',
-        description: ERROR_DESCRIPTION,
-      }).withDetail({
-        kind: 'error',
-        loc: operand.loc,
-        message: `Cannot access ref value during render`,
-      }),
-    );
+    errors.push({
+      severity: ErrorSeverity.InvalidReact,
+      reason:
+        'Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)',
+      loc: operand.loc,
+      description:
+        operand.identifier.name !== null &&
+        operand.identifier.name.kind === 'named'
+          ? `Cannot access ref value \`${operand.identifier.name.value}\``
+          : null,
+      suggestions: null,
+    });
  }
 }

@@ -756,22 +608,22 @@ function validateNoRefValueAccess(
    type?.kind === 'RefValue' ||
    (type?.kind === 'Structure' && type.fn?.readRefEffect)
  ) {
-    errors.pushDiagnostic(
-      CompilerDiagnostic.create({
-        category: ErrorCategory.Refs,
-        severity: ErrorSeverity.InvalidReact,
-        reason: 'Cannot access refs during render',
-        description: ERROR_DESCRIPTION,
-      }).withDetail({
-        kind: 'error',
-        loc: (type.kind === 'RefValue' && type.loc) || operand.loc,
-        message: `Cannot access ref value during render`,
-      }),
-    );
+    errors.push({
+      severity: ErrorSeverity.InvalidReact,
+      reason:
+        'Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)',
+      loc: (type.kind === 'RefValue' && type.loc) || operand.loc,
+      description:
+        operand.identifier.name !== null &&
+        operand.identifier.name.kind === 'named'
+          ? `Cannot access ref value \`${operand.identifier.name.value}\``
+          : null,
+      suggestions: null,
+    });
  }
 }

-function validateNoRefPassedToFunction(
+function validateNoRefAccess(
  errors: CompilerError,
  env: Env,
  operand: Place,
@@ -783,41 +635,18 @@ function validateNoRefPassedToFunction(
    type?.kind === 'RefValue' ||
    (type?.kind === 'Structure' && type.fn?.readRefEffect)
  ) {
-    errors.pushDiagnostic(
-      CompilerDiagnostic.create({
-        category: ErrorCategory.Refs,
-        severity: ErrorSeverity.InvalidReact,
-        reason: 'Cannot access refs during render',
-        description: ERROR_DESCRIPTION,
-      }).withDetail({
-        kind: 'error',
-        loc: (type.kind === 'RefValue' && type.loc) || loc,
-        message: `Passing a ref to a function may read its value during render`,
-      }),
-    );
-  }
-}
-
-function validateNoRefUpdate(
-  errors: CompilerError,
-  env: Env,
-  operand: Place,
-  loc: SourceLocation,
-): void {
-  const type = destructure(env.get(operand.identifier.id));
-  if (type?.kind === 'Ref' || type?.kind === 'RefValue') {
-    errors.pushDiagnostic(
-      CompilerDiagnostic.create({
-        category: ErrorCategory.Refs,
-        severity: ErrorSeverity.InvalidReact,
-        reason: 'Cannot access refs during render',
-        description: ERROR_DESCRIPTION,
-      }).withDetail({
-        kind: 'error',
-        loc: (type.kind === 'RefValue' && type.loc) || loc,
-        message: `Cannot update ref during render`,
-      }),
-    );
+    errors.push({
+      severity: ErrorSeverity.InvalidReact,
+      reason:
+        'Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)',
+      loc: (type.kind === 'RefValue' && type.loc) || loc,
+      description:
+        operand.identifier.name !== null &&
+        operand.identifier.name.kind === 'named'
+          ? `Cannot access ref value \`${operand.identifier.name.value}\``
+          : null,
+      suggestions: null,
+    });
  }
 }

@@ -828,23 +657,17 @@ function validateNoDirectRefValueAccess(
 ): void {
  const type = destructure(env.get(operand.identifier.id));
  if (type?.kind === 'RefValue') {
-    errors.pushDiagnostic(
-      CompilerDiagnostic.create({
-        category: ErrorCategory.Refs,
-        severity: ErrorSeverity.InvalidReact,
-        reason: 'Cannot access refs during render',
-        description: ERROR_DESCRIPTION,
-      }).withDetail({
-        kind: 'error',
-        loc: type.loc ?? operand.loc,
-        message: `Cannot access ref value during render`,
-      }),
-    );
+    errors.push({
+      severity: ErrorSeverity.InvalidReact,
+      reason:
+        'Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)',
+      loc: type.loc ?? operand.loc,
+      description:
+        operand.identifier.name !== null &&
+        operand.identifier.name.kind === 'named'
+          ? `Cannot access ref value \`${operand.identifier.name.value}\``
+          : null,
+      suggestions: null,
+    });
  }
 }
-
-const ERROR_DESCRIPTION =
-  'React refs are values that are not needed for rendering. Refs should only be accessed ' +
-  'outside of render, such as in event handlers or effects. ' +
-  'Accessing a ref value (the `current` property) during render can cause your component ' +
-  'not to update as expected (https://react.dev/reference/react/useRef)';
--- a/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoSetStateInPassiveEffects.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoSetStateInPassiveEffects.ts
@@ -5,33 +5,26 @@
 * LICENSE file in the root directory of this source tree.
 */

-import {
-  CompilerDiagnostic,
-  CompilerError,
-  ErrorCategory,
-  ErrorSeverity,
-} from '../CompilerError';
+import {CompilerError, ErrorSeverity} from '../CompilerError';
 import {
  HIRFunction,
  IdentifierId,
  isSetStateType,
  isUseEffectHookType,
-  isUseInsertionEffectHookType,
-  isUseLayoutEffectHookType,
  Place,
 } from '../HIR';
 import {eachInstructionValueOperand} from '../HIR/visitors';
 import {Result} from '../Utils/Result';

 /**
- * Validates against calling setState in the body of an effect (useEffect and friends),
+ * Validates against calling setState in the body of a *passive* effect (useEffect),
 * while allowing calling setState in callbacks scheduled by the effect.
 *
 * Calling setState during execution of a useEffect triggers a re-render, which is
 * often bad for performance and frequently has more efficient and straightforward
 * alternatives. See https://react.dev/learn/you-might-not-need-an-effect for examples.
 */
-export function validateNoSetStateInEffects(
+export function validateNoSetStateInPassiveEffects(
  fn: HIRFunction,
 ): Result<void, CompilerError> {
  const setStateFunctions: Map<IdentifierId, Place> = new Map();
@@ -86,36 +79,19 @@ export function validateNoSetStateInEffects(
            instr.value.kind === 'MethodCall'
              ? instr.value.receiver
              : instr.value.callee;
-          if (
-            isUseEffectHookType(callee.identifier) ||
-            isUseLayoutEffectHookType(callee.identifier) ||
-            isUseInsertionEffectHookType(callee.identifier)
-          ) {
+          if (isUseEffectHookType(callee.identifier)) {
            const arg = instr.value.args[0];
            if (arg !== undefined && arg.kind === 'Identifier') {
              const setState = setStateFunctions.get(arg.identifier.id);
              if (setState !== undefined) {
-                errors.pushDiagnostic(
-                  CompilerDiagnostic.create({
-                    category: ErrorCategory.EffectSetState,
-                    reason:
-                      'Calling setState synchronously within an effect can trigger cascading renders',
-                    description:
-                      'Effects are intended to synchronize state between React and external systems such as manually updating the DOM, state management libraries, or other platform APIs. ' +
-                      'In general, the body of an effect should do one or both of the following:\n' +
-                      '* Update external systems with the latest state from React.\n' +
-                      '* Subscribe for updates from some external system, calling setState in a callback function when external state changes.\n\n' +
-                      'Calling setState synchronously within an effect body causes cascading renders that can hurt performance, and is not recommended. ' +
-                      '(https://react.dev/learn/you-might-not-need-an-effect)',
-                    severity: ErrorSeverity.InvalidReact,
-                    suggestions: null,
-                  }).withDetail({
-                    kind: 'error',
-                    loc: setState.loc,
-                    message:
-                      'Avoid calling setState() directly within an effect',
-                  }),
-                );
+                errors.push({
+                  reason:
+                    'Calling setState directly within a useEffect causes cascading renders and is not recommended. Consider alternatives to useEffect. (https://react.dev/learn/you-might-not-need-an-effect)',
+                  description: null,
+                  severity: ErrorSeverity.InvalidReact,
+                  loc: setState.loc,
+                  suggestions: null,
+                });
              }
            }
          }
--- a/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoSetStateInRender.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoSetStateInRender.ts
@@ -5,12 +5,7 @@
 * LICENSE file in the root directory of this source tree.
 */

-import {
-  CompilerDiagnostic,
-  CompilerError,
-  ErrorCategory,
-  ErrorSeverity,
-} from '../CompilerError';
+import {CompilerError, ErrorSeverity} from '../CompilerError';
 import {HIRFunction, IdentifierId, isSetStateType} from '../HIR';
 import {computeUnconditionalBlocks} from '../HIR/ComputeUnconditionalBlocks';
 import {eachInstructionValueOperand} from '../HIR/visitors';
@@ -127,37 +122,23 @@ function validateNoSetStateInRenderImpl(
            unconditionalSetStateFunctions.has(callee.identifier.id)
          ) {
            if (activeManualMemoId !== null) {
-              errors.pushDiagnostic(
-                CompilerDiagnostic.create({
-                  category: ErrorCategory.RenderSetState,
-                  reason:
-                    'Calling setState from useMemo may trigger an infinite loop',
-                  description:
-                    'Each time the memo callback is evaluated it will change state. This can cause a memoization dependency to change, running the memo function again and causing an infinite loop. Instead of setting state in useMemo(), prefer deriving the value during render. (https://react.dev/reference/react/useState)',
-                  severity: ErrorSeverity.InvalidReact,
-                  suggestions: null,
-                }).withDetail({
-                  kind: 'error',
-                  loc: callee.loc,
-                  message: 'Found setState() within useMemo()',
-                }),
-              );
+              errors.push({
+                reason:
+                  'Calling setState from useMemo may trigger an infinite loop. (https://react.dev/reference/react/useState)',
+                description: null,
+                severity: ErrorSeverity.InvalidReact,
+                loc: callee.loc,
+                suggestions: null,
+              });
            } else if (unconditionalBlocks.has(block.id)) {
-              errors.pushDiagnostic(
-                CompilerDiagnostic.create({
-                  category: ErrorCategory.RenderSetState,
-                  reason:
-                    'Calling setState during render may trigger an infinite loop',
-                  description:
-                    'Calling setState during render will trigger another render, and can lead to infinite loops. (https://react.dev/reference/react/useState)',
-                  severity: ErrorSeverity.InvalidReact,
-                  suggestions: null,
-                }).withDetail({
-                  kind: 'error',
-                  loc: callee.loc,
-                  message: 'Found setState() in render',
-                }),
-              );
+              errors.push({
+                reason:
+                  'This is an unconditional set state during render, which will trigger an infinite loop. (https://react.dev/reference/react/useState)',
+                description: null,
+                severity: ErrorSeverity.InvalidReact,
+                loc: callee.loc,
+                suggestions: null,
+              });
            }
          }
          break;
--- a/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidatePreservedManualMemoization.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidatePreservedManualMemoization.ts
@@ -5,12 +5,7 @@
 * LICENSE file in the root directory of this source tree.
 */

-import {
-  CompilerDiagnostic,
-  CompilerError,
-  ErrorCategory,
-  ErrorSeverity,
-} from '../CompilerError';
+import {CompilerError, ErrorSeverity} from '../CompilerError';
 import {
  DeclarationId,
  Effect,
@@ -280,38 +275,27 @@ function validateInferredDep(
      errorDiagnostic = merge(errorDiagnostic ?? compareResult, compareResult);
    }
  }
-  errorState.pushDiagnostic(
-    CompilerDiagnostic.create({
-      category: ErrorCategory.PreserveManualMemo,
-      severity: ErrorSeverity.CannotPreserveMemoization,
-      reason:
-        'Compilation skipped because existing memoization could not be preserved',
-      description: [
-        'React Compiler has skipped optimizing this component because the existing manual memoization could not be preserved. ',
-        'The inferred dependencies did not match the manually specified dependencies, which could cause the value to change more or less frequently than expected. ',
-        DEBUG ||
-        // If the dependency is a named variable then we can report it. Otherwise only print in debug mode
-        (dep.identifier.name != null && dep.identifier.name.kind === 'named')
-          ? `The inferred dependency was \`${prettyPrintScopeDependency(
-              dep,
-            )}\`, but the source dependencies were [${validDepsInMemoBlock
-              .map(dep => printManualMemoDependency(dep, true))
-              .join(', ')}]. ${
-              errorDiagnostic
-                ? getCompareDependencyResultDescription(errorDiagnostic)
-                : 'Inferred dependency not present in source'
-            }.`
-          : '',
-      ]
-        .join('')
-        .trim(),
-      suggestions: null,
-    }).withDetail({
-      kind: 'error',
-      loc: memoLocation,
-      message: 'Could not preserve existing manual memoization',
-    }),
-  );
+  errorState.push({
+    severity: ErrorSeverity.CannotPreserveMemoization,
+    reason:
+      'React Compiler has skipped optimizing this component because the existing manual memoization could not be preserved. The inferred dependencies did not match the manually specified dependencies, which could cause the value to change more or less frequently than expected',
+    description:
+      DEBUG ||
+      // If the dependency is a named variable then we can report it. Otherwise only print in debug mode
+      (dep.identifier.name != null && dep.identifier.name.kind === 'named')
+        ? `The inferred dependency was \`${prettyPrintScopeDependency(
+            dep,
+          )}\`, but the source dependencies were [${validDepsInMemoBlock
+            .map(dep => printManualMemoDependency(dep, true))
+            .join(', ')}]. ${
+            errorDiagnostic
+              ? getCompareDependencyResultDescription(errorDiagnostic)
+              : 'Inferred dependency not present in source'
+          }`
+        : null,
+    loc: memoLocation,
+    suggestions: null,
+  });
 }

 class Visitor extends ReactiveFunctionVisitor<VisitorState> {
@@ -461,13 +445,11 @@ class Visitor extends ReactiveFunctionVisitor<VisitorState> {
     */
    this.recordTemporaries(instruction, state);
    const value = instruction.value;
-    // Track reassignments from inlining of manual memo
    if (
      value.kind === 'StoreLocal' &&
      value.lvalue.kind === 'Reassign' &&
      state.manualMemoState != null
    ) {
-      // Complex cases of inlining end up with a temporary that is reassigned
      const ids = getOrInsertDefault(
        state.manualMemoState.reassignments,
        value.lvalue.place.identifier.declarationId,
@@ -475,21 +457,6 @@ class Visitor extends ReactiveFunctionVisitor<VisitorState> {
      );
      ids.add(value.value.identifier);
    }
-    if (
-      value.kind === 'LoadLocal' &&
-      value.place.identifier.scope != null &&
-      instruction.lvalue != null &&
-      instruction.lvalue.identifier.scope == null &&
-      state.manualMemoState != null
-    ) {
-      // Simpler cases of inlining assign to the original IIFE lvalue
-      const ids = getOrInsertDefault(
-        state.manualMemoState.reassignments,
-        instruction.lvalue.identifier.declarationId,
-        new Set(),
-      );
-      ids.add(value.place.identifier);
-    }
    if (value.kind === 'StartMemoize') {
      let depsFromSource: Array<ManualMemoDependency> | null = null;
      if (value.deps != null) {
@@ -535,22 +502,14 @@ class Visitor extends ReactiveFunctionVisitor<VisitorState> {
          !this.scopes.has(identifier.scope.id) &&
          !this.prunedScopes.has(identifier.scope.id)
        ) {
-          state.errors.pushDiagnostic(
-            CompilerDiagnostic.create({
-              category: ErrorCategory.PreserveManualMemo,
-              severity: ErrorSeverity.CannotPreserveMemoization,
-              reason:
-                'Compilation skipped because existing memoization could not be preserved',
-              description: [
-                'React Compiler has skipped optimizing this component because the existing manual memoization could not be preserved. ',
-                'This dependency may be mutated later, which could cause the value to change unexpectedly.',
-              ].join(''),
-            }).withDetail({
-              kind: 'error',
-              loc,
-              message: 'This dependency may be modified later',
-            }),
-          );
+          state.errors.push({
+            reason:
+              'React Compiler has skipped optimizing this component because the existing manual memoization could not be preserved. This dependency may be mutated later, which could cause the value to change unexpectedly',
+            description: null,
+            severity: ErrorSeverity.CannotPreserveMemoization,
+            loc,
+            suggestions: null,
+          });
        }
      }
    }
@@ -584,26 +543,16 @@ class Visitor extends ReactiveFunctionVisitor<VisitorState> {

          for (const identifier of decls) {
            if (isUnmemoized(identifier, this.scopes)) {
-              state.errors.pushDiagnostic(
-                CompilerDiagnostic.create({
-                  category: ErrorCategory.PreserveManualMemo,
-                  severity: ErrorSeverity.CannotPreserveMemoization,
-                  reason:
-                    'Compilation skipped because existing memoization could not be preserved',
-                  description: [
-                    'React Compiler has skipped optimizing this component because the existing manual memoization could not be preserved. This value was memoized in source but not in compilation output. ',
-                    DEBUG
-                      ? `${printIdentifier(identifier)} was not memoized.`
-                      : '',
-                  ]
-                    .join('')
-                    .trim(),
-                }).withDetail({
-                  kind: 'error',
-                  loc,
-                  message: 'Could not preserve existing memoization',
-                }),
-              );
+              state.errors.push({
+                reason:
+                  'React Compiler has skipped optimizing this component because the existing manual memoization could not be preserved. This value was memoized in source but not in compilation output.',
+                description: DEBUG
+                  ? `${printIdentifier(identifier)} was not memoized`
+                  : null,
+                severity: ErrorSeverity.CannotPreserveMemoization,
+                loc,
+                suggestions: null,
+              });
            }
          }
        }
--- a/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateStaticComponents.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateStaticComponents.ts
@@ -5,12 +5,7 @@
 * LICENSE file in the root directory of this source tree.
 */

-import {
-  CompilerDiagnostic,
-  CompilerError,
-  ErrorCategory,
-  ErrorSeverity,
-} from '../CompilerError';
+import {CompilerError, ErrorSeverity} from '../CompilerError';
 import {HIRFunction, IdentifierId, SourceLocation} from '../HIR';
 import {Result} from '../Utils/Result';

@@ -64,24 +59,20 @@ export function validateStaticComponents(
              value.tag.identifier.id,
            );
            if (location != null) {
-              error.pushDiagnostic(
-                CompilerDiagnostic.create({
-                  category: ErrorCategory.StaticComponents,
-                  severity: ErrorSeverity.InvalidReact,
-                  reason: 'Cannot create components during render',
-                  description: `Components created during render will reset their state each time they are created. Declare components outside of render. `,
-                })
-                  .withDetail({
-                    kind: 'error',
-                    loc: value.tag.loc,
-                    message: 'This component is created during render',
-                  })
-                  .withDetail({
-                    kind: 'error',
-                    loc: location,
-                    message: 'The component is created during render here',
-                  }),
-              );
+              error.push({
+                reason: `Components created during render will reset their state each time they are created. Declare components outside of render. `,
+                severity: ErrorSeverity.InvalidReact,
+                loc: value.tag.loc,
+                description: null,
+                suggestions: null,
+              });
+              error.push({
+                reason: `The component may be created during render`,
+                severity: ErrorSeverity.InvalidReact,
+                loc: location,
+                description: null,
+                suggestions: null,
+              });
            }
          }
        }
--- a/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateUseMemo.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateUseMemo.ts
@@ -5,12 +5,7 @@
 * LICENSE file in the root directory of this source tree.
 */

-import {
-  CompilerDiagnostic,
-  CompilerError,
-  ErrorCategory,
-  ErrorSeverity,
-} from '../CompilerError';
+import {CompilerError, ErrorSeverity} from '..';
 import {FunctionExpression, HIRFunction, IdentifierId} from '../HIR';
 import {Result} from '../Utils/Result';

@@ -68,43 +63,24 @@ export function validateUseMemo(fn: HIRFunction): Result<void, CompilerError> {
          }

          if (body.loweredFunc.func.params.length > 0) {
-            const firstParam = body.loweredFunc.func.params[0];
-            const loc =
-              firstParam.kind === 'Identifier'
-                ? firstParam.loc
-                : firstParam.place.loc;
-            errors.pushDiagnostic(
-              CompilerDiagnostic.create({
-                category: ErrorCategory.UseMemo,
-                severity: ErrorSeverity.InvalidReact,
-                reason: 'useMemo() callbacks may not accept parameters',
-                description:
-                  'useMemo() callbacks are called by React to cache calculations across re-renders. They should not take parameters. Instead, directly reference the props, state, or local variables needed for the computation.',
-                suggestions: null,
-              }).withDetail({
-                kind: 'error',
-                loc,
-                message: 'Callbacks with parameters are not supported',
-              }),
-            );
+            errors.push({
+              severity: ErrorSeverity.InvalidReact,
+              reason: 'useMemo callbacks may not accept any arguments',
+              description: null,
+              loc: body.loc,
+              suggestions: null,
+            });
          }

          if (body.loweredFunc.func.async || body.loweredFunc.func.generator) {
-            errors.pushDiagnostic(
-              CompilerDiagnostic.create({
-                category: ErrorCategory.UseMemo,
-                severity: ErrorSeverity.InvalidReact,
-                reason:
-                  'useMemo() callbacks may not be async or generator functions',
-                description:
-                  'useMemo() callbacks are called once and must synchronously return a value.',
-                suggestions: null,
-              }).withDetail({
-                kind: 'error',
-                loc: body.loc,
-                message: 'Async and generator functions are not supported',
-              }),
-            );
+            errors.push({
+              severity: ErrorSeverity.InvalidReact,
+              reason:
+                'useMemo callbacks may not be async or generator functions',
+              description: null,
+              loc: body.loc,
+              suggestions: null,
+            });
          }

          break;
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/Logger-test.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/Logger-test.ts
@@ -58,8 +58,7 @@ it('logs failed compilation', () => {

  expect(event.detail.severity).toEqual('InvalidReact');
  //@ts-ignore
-  const {start, end, identifierName} =
-    event.detail.primaryLocation() as t.SourceLocation;
+  const {start, end, identifierName} = event.detail.loc as t.SourceLocation;
  expect(start).toEqual({column: 28, index: 28, line: 1});
  expect(end).toEqual({column: 33, index: 33, line: 1});
  expect(identifierName).toEqual('props');
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/envConfig-test.ts
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/envConfig-test.ts
@@ -20,7 +20,7 @@ describe('parseConfigPragma()', () => {
        validateHooksUsage: 1,
      } as any);
    }).toThrowErrorMatchingInlineSnapshot(
-      `"Error: Could not validate environment config. Update React Compiler config to fix the error. Validation error: Expected boolean, received number at "validateHooksUsage"."`,
+      `"InvalidConfig: Could not validate environment config. Update React Compiler config to fix the error. Validation error: Expected boolean, received number at "validateHooksUsage""`,
    );
  });

@@ -33,12 +33,12 @@ describe('parseConfigPragma()', () => {
              source: 'react',
              importSpecifierName: 'useEffect',
            },
-            autodepsIndex: 0,
+            numRequiredArgs: 0,
          },
        ],
      } as any);
    }).toThrowErrorMatchingInlineSnapshot(
-      `"Error: Could not validate environment config. Update React Compiler config to fix the error. Validation error: autodepsIndex must be > 0 at "inferEffectDependencies[0].autodepsIndex"."`,
+      `"InvalidConfig: Could not validate environment config. Update React Compiler config to fix the error. Validation error: numRequiredArgs must be > 0 at "inferEffectDependencies[0].numRequiredArgs""`,
    );
  });

--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/aliased-nested-scope-truncated-dep.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/aliased-nested-scope-truncated-dep.expect.md
@@ -175,14 +175,21 @@ import {
 * and mutability.
 */
 function Component(t0) {
-  const $ = _c(2);
+  const $ = _c(4);
  const { prop } = t0;
  let t1;
  if ($[0] !== prop) {
    const obj = shallowCopy(prop);
    const aliasedObj = identity(obj);
-
-    const id = [obj.id];
+    let t2;
+    if ($[2] !== obj) {
+      t2 = [obj.id];
+      $[2] = obj;
+      $[3] = t2;
+    } else {
+      t2 = $[3];
+    }
+    const id = t2;

    mutate(aliasedObj);
    setPropertyByKey(aliasedObj, "id", prop.id + 1);
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/align-scopes-iife-return-modified-later-logical.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/align-scopes-iife-return-modified-later-logical.expect.md
@@ -26,16 +26,20 @@ import { c as _c } from "react/compiler-runtime";
 import { getNull } from "shared-runtime";

 function Component(props) {
-  const $ = _c(2);
+  const $ = _c(3);
+  let t0;
  let items;
  if ($[0] !== props.a) {
-    items = getNull() ?? [];
+    t0 = getNull() ?? [];
+    items = t0;

    items.push(props.a);
    $[0] = props.a;
    $[1] = items;
+    $[2] = t0;
  } else {
    items = $[1];
+    t0 = $[2];
  }
  return items;
 }
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/allow-assigning-ref-accessing-function-to-object-property-if-not-mutated.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/allow-assigning-ref-accessing-function-to-object-property-if-not-mutated.expect.md
@@ -1,52 +0,0 @@
-
-## Input
-
-```javascript
-import {useRef} from 'react';
-import {Stringify} from 'shared-runtime';
-
-function Component(props) {
-  const ref = useRef(props.value);
-  const object = {};
-  object.foo = () => ref.current;
-  return <Stringify object={object} shouldInvokeFns={true} />;
-}
-
-export const FIXTURE_ENTRYPOINT = {
-  fn: Component,
-  params: [{value: 42}],
-};
-
-```
-
-## Code
-
-```javascript
-import { c as _c } from "react/compiler-runtime";
-import { useRef } from "react";
-import { Stringify } from "shared-runtime";
-
-function Component(props) {
-  const $ = _c(1);
-  const ref = useRef(props.value);
-  let t0;
-  if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
-    const object = {};
-    object.foo = () => ref.current;
-    t0 = <Stringify object={object} shouldInvokeFns={true} />;
-    $[0] = t0;
-  } else {
-    t0 = $[0];
-  }
-  return t0;
-}
-
-export const FIXTURE_ENTRYPOINT = {
-  fn: Component,
-  params: [{ value: 42 }],
-};
-
-```
-      
-### Eval output
-(kind: ok) <div>{"object":{"foo":{"kind":"Function","result":42}},"shouldInvokeFns":true}</div>
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/allow-assigning-ref-accessing-function-to-object-property-if-not-mutated.js
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/allow-assigning-ref-accessing-function-to-object-property-if-not-mutated.js
@@ -1,14 +0,0 @@
-import {useRef} from 'react';
-import {Stringify} from 'shared-runtime';
-
-function Component(props) {
-  const ref = useRef(props.value);
-  const object = {};
-  object.foo = () => ref.current;
-  return <Stringify object={object} shouldInvokeFns={true} />;
-}
-
-export const FIXTURE_ENTRYPOINT = {
-  fn: Component,
-  params: [{value: 42}],
-};
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/allow-assigning-to-global-in-function-spread-as-jsx.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/allow-assigning-to-global-in-function-spread-as-jsx.expect.md
@@ -1,39 +0,0 @@
-
-## Input
-
-```javascript
-// @enableNewMutationAliasingModel:false
-function Component() {
-  const foo = () => {
-    someGlobal = true;
-  };
-  // spreading a function is weird, but it doesn't call the function so this is allowed
-  return <div {...foo} />;
-}
-
-```
-
-## Code
-
-```javascript
-import { c as _c } from "react/compiler-runtime"; // @enableNewMutationAliasingModel:false
-function Component() {
-  const $ = _c(1);
-  const foo = _temp;
-  let t0;
-  if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
-    t0 = <div {...foo} />;
-    $[0] = t0;
-  } else {
-    t0 = $[0];
-  }
-  return t0;
-}
-function _temp() {
-  someGlobal = true;
-}
-
-```
-      
-### Eval output
-(kind: exception) Fixture not implemented
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/allow-merge-refs-pattern.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/allow-merge-refs-pattern.expect.md
@@ -1,44 +0,0 @@
-
-## Input
-
-```javascript
-// @enableTreatRefLikeIdentifiersAsRefs @validateRefAccessDuringRender
-
-import {useRef} from 'react';
-
-function Component() {
-  const ref = useRef(null);
-  const ref2 = useRef(null);
-  const mergedRef = mergeRefs([ref], ref2);
-
-  return <Stringify ref={mergedRef} />;
-}
-
-```
-
-## Code
-
-```javascript
-import { c as _c } from "react/compiler-runtime"; // @enableTreatRefLikeIdentifiersAsRefs @validateRefAccessDuringRender
-
-import { useRef } from "react";
-
-function Component() {
-  const $ = _c(1);
-  const ref = useRef(null);
-  const ref2 = useRef(null);
-  const mergedRef = mergeRefs([ref], ref2);
-  let t0;
-  if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
-    t0 = <Stringify ref={mergedRef} />;
-    $[0] = t0;
-  } else {
-    t0 = $[0];
-  }
-  return t0;
-}
-
-```
-      
-### Eval output
-(kind: exception) Fixture not implemented
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/allow-merge-refs-pattern.js
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/allow-merge-refs-pattern.js
@@ -1,11 +0,0 @@
-// @enableTreatRefLikeIdentifiersAsRefs @validateRefAccessDuringRender
-
-import {useRef} from 'react';
-
-function Component() {
-  const ref = useRef(null);
-  const ref2 = useRef(null);
-  const mergedRef = mergeRefs([ref], ref2);
-
-  return <Stringify ref={mergedRef} />;
-}
--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/allow-modify-global-in-callback-jsx.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/allow-modify-global-in-callback-jsx.expect.md
@@ -52,13 +52,15 @@ function Component(t0) {
  }
  const onClick = t1;
  let t2;
+  let t3;
  if ($[2] !== onClick) {
-    t2 = <div onClick={onClick}>{someGlobal.value}</div>;
+    t3 = <div onClick={onClick}>{someGlobal.value}</div>;
    $[2] = onClick;
-    $[3] = t2;
+    $[3] = t3;
  } else {
-    t2 = $[3];
+    t3 = $[3];
  }
+  t2 = t3;
  return t2;
 }

--- a/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/allow-passing-ref-to-render-helper-props-object.expect.md
+++ b/compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/allow-passing-ref-to-render-helper-props-object.expect.md
@@ -1,45 +0,0 @@
-
-## Input
-
-```javascript
-// @enableTreatRefLikeIdentifiersAsRefs @validateRefAccessDuringRender
-
-import {useRef} from 'react';
-
-function Component(props) {
-  const ref = useRef(null);
-
-  return <Foo>{props.render({ref})}</Foo>;
-}
-
-```
-
-## Code
-
-```javascript
-import { c as _c } from "react/compiler-runtime"; // @enableTreatRefLikeIdentifiersAsRefs @validateRefAccessDuringRender
-
-import { useRef } from "react";
-
-function Component(props) {
-  const $ = _c(3);
-  const ref = useRef(null);
-
-  const T0 = Foo;
-  const t0 = props.render({ ref });
-  let t1;
-  if ($[0] !== T0 || $[1] !== t0) {
-    t1 = <T0>{t0}</T0>;
-    $[0] = T0;
-    $[1] = t0;
-    $[2] = t1;
-  } else {
-    t1 = $[2];
-  }
-  return t1;
-}
-
-```
-      
-### Eval output
-(kind: exception) Fixture not implemented
--- a/Show More
+++ b/Show More