[compiler] Improve ref validation error message

Improves the error message for ValidateNoRefAccessInRender, using the new diagnostic type as well as providing a longer but succinct summary of what refs are for and why they're unsafe to access in render.

.eslintrc.js

@@ -474,7 +474,7 @@ module.exports = {
     {
       files: ['packages/react-server-dom-turbopack/**/*.js'],
       globals: {
-        __turbopack_load__: 'readonly',
+        __turbopack_load_by_url__: 'readonly',
         __turbopack_require__: 'readonly',
       },
     },
@@ -496,6 +496,7 @@ module.exports = {
         'packages/react-devtools-shared/src/devtools/views/**/*.js',
         'packages/react-devtools-shared/src/hook.js',
         'packages/react-devtools-shared/src/backend/console.js',
+        'packages/react-devtools-shared/src/backend/fiber/renderer.js',
         'packages/react-devtools-shared/src/backend/shared/DevToolsComponentStackFrame.js',
         'packages/react-devtools-shared/src/frontend/utils/withPermissionsCheck.js',
       ],
@@ -504,6 +505,7 @@ module.exports = {
         __IS_FIREFOX__: 'readonly',
         __IS_EDGE__: 'readonly',
         __IS_NATIVE__: 'readonly',
+        __IS_INTERNAL_MCP_BUILD__: 'readonly',
         __IS_INTERNAL_VERSION__: 'readonly',
         chrome: 'readonly',
       },
@@ -559,6 +561,7 @@ module.exports = {
     ConsoleTask: 'readonly', // TOOD: Figure out what the official name of this will be.
     ReturnType: 'readonly',
     AnimationFrameID: 'readonly',
+    WeakRef: 'readonly',
     // For Flow type annotation. Only `BigInt` is valid at runtime.
     bigint: 'readonly',
     BigInt: 'readonly',
@@ -605,10 +608,12 @@ module.exports = {
     symbol: 'readonly',
     SyntheticEvent: 'readonly',
     SyntheticMouseEvent: 'readonly',
+    SyntheticPointerEvent: 'readonly',
     Thenable: 'readonly',
     TimeoutID: 'readonly',
     WheelEventHandler: 'readonly',
     FinalizationRegistry: 'readonly',
+    Exclude: 'readonly',
     Omit: 'readonly',
     Keyframe: 'readonly',
     PropertyIndexedKeyframes: 'readonly',
@@ -618,6 +623,7 @@ module.exports = {
     ScrollTimeline: 'readonly',
     EventListenerOptionsOrUseCapture: 'readonly',
     FocusOptions: 'readonly',
+    OptionalEffectTiming: 'readonly',
 
     spyOnDev: 'readonly',
     spyOnDevAndProd: 'readonly',

.github/workflows/compiler_discord_notify.yml

@@ -11,6 +11,7 @@ permissions: {}
 
 jobs:
   check_access:
+    if: ${{ github.event.pull_request.draft == false }}
     runs-on: ubuntu-latest
     outputs:
       is_member_or_collaborator: ${{ steps.check_is_member_or_collaborator.outputs.is_member_or_collaborator }}

.github/workflows/runtime_build_and_test.yml

@@ -6,6 +6,12 @@ on:
   pull_request:
     paths-ignore:
       - compiler/**
+  workflow_dispatch:
+    inputs:
+      commit_sha:
+        required: false
+        type: string
+        default: ''
 
 permissions: {}
 
@@ -28,7 +34,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
         with:
-          ref: ${{ github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
       - name: Check cache hit
         uses: actions/cache/restore@v4
         id: node_modules
@@ -69,7 +75,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
         with:
-          ref: ${{ github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
       - name: Check cache hit
         uses: actions/cache/restore@v4
         id: node_modules
@@ -117,7 +123,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
         with:
-          ref: ${{ github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
       - uses: actions/github-script@v7
         id: set-matrix
         with:
@@ -136,7 +142,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
         with:
-          ref: ${{ github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
       - uses: actions/setup-node@v4
         with:
           node-version-file: '.nvmrc'
@@ -166,7 +172,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
         with:
-          ref: ${{ github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
       - uses: actions/setup-node@v4
         with:
           node-version-file: '.nvmrc'
@@ -198,7 +204,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
         with:
-          ref: ${{ github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
       - uses: actions/setup-node@v4
         with:
           node-version-file: '.nvmrc'
@@ -254,7 +260,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
         with:
-          ref: ${{ github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
       - uses: actions/setup-node@v4
         with:
           node-version-file: '.nvmrc'
@@ -280,6 +286,37 @@ jobs:
         if: steps.node_modules.outputs.cache-hit != 'true'
       - run: yarn test ${{ matrix.params }} --ci --shard=${{ matrix.shard }}
 
+  # Hardcoded to improve parallelism
+  test-linter:
+    name: Test eslint-plugin-react-hooks
+    needs: [runtime_compiler_node_modules_cache]
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version-file: '.nvmrc'
+          cache: yarn
+          cache-dependency-path:  |
+            yarn.lock
+            compiler/yarn.lock
+      - name: Restore cached node_modules
+        uses: actions/cache@v4
+        id: node_modules
+        with:
+          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
+        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
@@ -294,7 +331,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
         with:
-          ref: ${{ github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
       - uses: actions/setup-node@v4
         with:
           node-version-file: '.nvmrc'
@@ -389,7 +426,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
         with:
-          ref: ${{ github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
       - uses: actions/setup-node@v4
         with:
           node-version-file: '.nvmrc'
@@ -434,7 +471,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
         with:
-          ref: ${{ github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
       - uses: actions/setup-node@v4
         with:
           node-version-file: '.nvmrc'
@@ -462,7 +499,7 @@ jobs:
           merge-multiple: true
       - name: Display structure of build
         run: ls -R build
-      - run: echo ${{ github.event.pull_request.head.sha || github.sha }} >> build/COMMIT_SHA
+      - run: echo ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }} >> build/COMMIT_SHA
       - name: Scrape warning messages
         run: |
           mkdir -p ./build/__test_utils__
@@ -499,7 +536,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
         with:
-          ref: ${{ github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
       - uses: actions/setup-node@v4
         with:
           node-version-file: '.nvmrc'
@@ -539,7 +576,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
         with:
-          ref: ${{ github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
       - uses: actions/setup-node@v4
         with:
           node-version-file: '.nvmrc'
@@ -576,7 +613,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
         with:
-          ref: ${{ github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
       - uses: actions/setup-node@v4
         with:
           node-version-file: '.nvmrc'
@@ -617,7 +654,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
         with:
-          ref: ${{ github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
       - uses: actions/setup-node@v4
         with:
           node-version-file: '.nvmrc'
@@ -691,7 +728,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
         with:
-          ref: ${{ github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
       - uses: actions/setup-node@v4
         with:
           node-version-file: '.nvmrc'
@@ -748,7 +785,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
         with:
-          ref: ${{ github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
       - uses: actions/setup-node@v4
         with:
           node-version-file: '.nvmrc'
@@ -793,7 +830,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
         with:
-          ref: ${{ github.event.pull_request.head.sha || github.sha }}
+          ref: ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || github.event.pull_request.head.sha || github.sha }}
       - uses: actions/setup-node@v4
         with:
           node-version-file: '.nvmrc'
@@ -842,7 +879,7 @@ 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.pull_request.head.sha || github.sha }} >> build/COMMIT_SHA
+      - run: echo ${{ github.event.inputs.commit_sha != '' && github.event.inputs.commit_sha || 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

.github/workflows/runtime_discord_notify.yml

@@ -11,6 +11,7 @@ permissions: {}
 
 jobs:
   check_access:
+    if: ${{ github.event.pull_request.draft == false }}
     runs-on: ubuntu-latest
     outputs:
       is_member_or_collaborator: ${{ steps.check_is_member_or_collaborator.outputs.is_member_or_collaborator }}

.github/workflows/runtime_prereleases.yml

@@ -17,6 +17,17 @@ on:
         description: 'Whether to notify the team on Discord when the release fails. Useful if this workflow is called from an automation.'
         required: false
         type: boolean
+      only_packages:
+        description: Packages to publish (space separated)
+        type: string
+      skip_packages:
+        description: Packages to NOT publish (space separated)
+        type: string
+      dry:
+        required: true
+        description: Dry run instead of publish?
+        type: boolean
+        default: true
     secrets:
       DISCORD_WEBHOOK_URL:
         description: 'Discord webhook URL to notify on failure. Only required if enableFailureNotification is true.'
@@ -61,15 +72,41 @@ jobs:
         if: steps.node_modules.outputs.cache-hit != 'true'
       - run: yarn --cwd scripts/release install --frozen-lockfile
         if: steps.node_modules.outputs.cache-hit != 'true'
+      - run: cp ./scripts/release/ci-npmrc ~/.npmrc
       - run: |
           GH_TOKEN=${{ secrets.GH_TOKEN }} scripts/release/prepare-release-from-ci.js --skipTests -r ${{ inputs.release_channel }} --commit=${{ inputs.commit_sha }}
-          cp ./scripts/release/ci-npmrc ~/.npmrc
-          scripts/release/publish.js --ci --tags ${{ inputs.dist_tag }}
+      - name: Check prepared files
+        run: ls -R build/node_modules
+      - if: '${{ inputs.only_packages }}'
+        name: 'Publish ${{ inputs.only_packages }}'
+        run: |
+          scripts/release/publish.js \
+            --ci \
+            --skipTests \
+            --tags=${{ inputs.dist_tag }} \
+            --onlyPackages=${{ inputs.only_packages }} ${{ (inputs.dry && '') || '\'}}
+            ${{ inputs.dry && '--dry' || '' }}
+      - if: '${{ inputs.skip_packages }}'
+        name: 'Publish all packages EXCEPT ${{ inputs.skip_packages }}'
+        run: |
+          scripts/release/publish.js \
+            --ci \
+            --skipTests \
+            --tags=${{ inputs.dist_tag }} \
+            --skipPackages=${{ inputs.skip_packages }} ${{ (inputs.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' || '' }}
       - 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: 'Publish of $${{ inputs.release_channel }} release failed'
+          embed-title: '[Runtime] Publish of ${{ inputs.release_channel }}@${{ inputs.dist_tag}} release failed'
           embed-url: ${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}/attempts/${{ github.run_attempt }}

.github/workflows/runtime_prereleases_manual.yml

@@ -5,6 +5,25 @@ on:
     inputs:
       prerelease_commit_sha:
         required: true
+      only_packages:
+        description: Packages to publish (space separated)
+        type: string
+      skip_packages:
+        description: Packages to NOT publish (space separated)
+        type: string
+      dry:
+        required: true
+        description: Dry run instead of publish?
+        type: boolean
+        default: true
+      experimental_only:
+        type: boolean
+        description: Only publish to the experimental tag
+        default: false
+      force_notify:
+        description: Force a Discord notification?
+        type: boolean
+        default: false
 
 permissions: {}
 
@@ -12,8 +31,26 @@ env:
   TZ: /usr/share/zoneinfo/America/Los_Angeles
 
 jobs:
+  notify:
+    if: ${{ inputs.force_notify || inputs.dry == false || inputs.dry == 'false' }}
+    runs-on: ubuntu-latest
+    steps:
+      - name: Discord Webhook Action
+        uses: tsickert/discord-webhook@86dc739f3f165f16dadc5666051c367efa1692f4
+        with:
+          webhook-url: ${{ secrets.DISCORD_WEBHOOK_URL }}
+          embed-author-name: ${{ github.event.sender.login }}
+          embed-author-url: ${{ github.event.sender.html_url }}
+          embed-author-icon-url: ${{ github.event.sender.avatar_url }}
+          embed-title: "⚠️ Publishing ${{ inputs.experimental_only && 'EXPERIMENTAL' || 'CANARY & EXPERIMENTAL' }} release ${{ (inputs.dry && ' (dry run)') || '' }}"
+          embed-description: |
+            ```json
+            ${{ toJson(inputs) }}
+            ```
+          embed-url: https://github.com/facebook/react/actions/runs/${{ github.run_id }}
 
   publish_prerelease_canary:
+    if: ${{ !inputs.experimental_only }}
     name: Publish to Canary channel
     uses: facebook/react/.github/workflows/runtime_prereleases.yml@main
     permissions:
@@ -33,6 +70,9 @@ jobs:
       # downstream consumers might still expect that tag. We can remove this
       # after some time has elapsed and the change has been communicated.
       dist_tag: canary,next
+      only_packages: ${{ inputs.only_packages }}
+      skip_packages: ${{ inputs.skip_packages }}
+      dry: ${{ inputs.dry }}
     secrets:
       NPM_TOKEN: ${{ secrets.NPM_TOKEN }}
       GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
@@ -48,10 +88,15 @@ jobs:
     # different versions of the same package, even if they use different
     # dist tags.
     needs: publish_prerelease_canary
+    # Ensures the job runs even if canary is skipped
+    if: always()
     with:
       commit_sha: ${{ inputs.prerelease_commit_sha }}
       release_channel: experimental
       dist_tag: experimental
+      only_packages: ${{ inputs.only_packages }}
+      skip_packages: ${{ inputs.skip_packages }}
+      dry: ${{ inputs.dry }}
     secrets:
       NPM_TOKEN: ${{ secrets.NPM_TOKEN }}
       GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}

.github/workflows/runtime_prereleases_nightly.yml

@@ -22,6 +22,7 @@ jobs:
       release_channel: stable
       dist_tag: canary,next
       enableFailureNotification: true
+      dry: false
     secrets:
       DISCORD_WEBHOOK_URL: ${{ secrets.DISCORD_WEBHOOK_URL }}
       NPM_TOKEN: ${{ secrets.NPM_TOKEN }}
@@ -43,6 +44,7 @@ jobs:
       release_channel: experimental
       dist_tag: experimental
       enableFailureNotification: true
+      dry: false
     secrets:
       DISCORD_WEBHOOK_URL: ${{ secrets.DISCORD_WEBHOOK_URL }}
       NPM_TOKEN: ${{ secrets.NPM_TOKEN }}

.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:

.github/workflows/shared_stale.yml

@@ -6,7 +6,10 @@ on:
     - cron: '0 * * * *'
   workflow_dispatch:
 
-permissions: {}
+permissions:
+  # https://github.com/actions/stale/tree/v9/?tab=readme-ov-file#recommended-permissions
+  issues: write
+  pull-requests: write
 
 env:
   TZ: /usr/share/zoneinfo/America/Los_Angeles

.prettierrc.js

@@ -3,13 +3,12 @@
 const {esNextPaths} = require('./scripts/shared/pathsByLanguageVersion');
 
 module.exports = {
-  plugins: ['prettier-plugin-hermes-parser'],
   bracketSpacing: false,
   singleQuote: true,
   bracketSameLine: true,
   trailingComma: 'es5',
   printWidth: 80,
-  parser: 'hermes',
+  parser: 'flow',
   arrowParens: 'avoid',
   overrides: [
     {

CHANGELOG.md

@@ -1,3 +1,8 @@
+## 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
@@ -19,11 +24,11 @@ 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 Complier and bindings [#31808](https://github.com/facebook/react/pull/31808)
+* Improved consistency across prod and dev to improve compatibility with Google Closure Compiler 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 [#32479](https://github.com/facebook/react/pull/32479)
+* Added support for beforetoggle and toggle events on the dialog element. [#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)

compiler/.gitignore

@@ -1,28 +1,14 @@
 .DS_Store
 .spr.yml
 
-# Generated by Cargo
-# will have compiled files and executables
-debug/
-target/
-
-# These are backup files generated by rustfmt
-**/*.rs.bk
-
-# MSVC Windows builds of rustc generate these, which store debugging information
-*.pdb
-
 node_modules
 .watchmanconfig
 .watchman-cookie-*
 dist
 .vscode
 !packages/playground/.vscode
-.spr.yml
 testfilter.txt
 
-bundle-oss.sh
-
 # forgive
 *.vsix
 .vscode-test

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;

compiler/apps/playground/components/Editor/EditorImpl.tsx

@@ -11,6 +11,7 @@ import * as t from '@babel/types';
 import BabelPluginReactCompiler, {
   CompilerError,
   CompilerErrorDetail,
+  CompilerDiagnostic,
   Effect,
   ErrorSeverity,
   parseConfigPragmaForTests,
@@ -44,6 +45,7 @@ import {
   PrintedCompilerPipelineValue,
 } from './Output';
 import {transformFromAstSync} from '@babel/core';
+import {LoggerEvent} from 'babel-plugin-react-compiler/dist/Entrypoint';
 
 function parseInput(
   input: string,
@@ -140,9 +142,13 @@ const COMMON_HOOKS: Array<[string, Hook]> = [
   ],
 ];
 
-function compile(source: string): [CompilerOutput, 'flow' | 'typescript'] {
+function compile(
+  source: string,
+  mode: 'compiler' | 'linter',
+): [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)) {
@@ -201,6 +207,23 @@ function compile(source: string): [CompilerOutput, 'flow' | 'typescript'] {
     };
     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,
@@ -210,7 +233,11 @@ function compile(source: string): [CompilerOutput, 'flow' | 'typescript'] {
       },
       logger: {
         debugLogIRs: logIR,
-        logEvent: () => {},
+        logEvent: (_filename: string | null, event: LoggerEvent) => {
+          if (event.kind === 'CompileError') {
+            otherErrors.push(event.detail);
+          }
+        },
       },
     });
     transformOutput = invokeCompiler(source, language, opts);
@@ -220,7 +247,7 @@ function compile(source: string): [CompilerOutput, 'flow' | 'typescript'] {
      * (i.e. object shape that is not CompilerError)
      */
     if (err instanceof CompilerError && err.details.length > 0) {
-      error.details.push(...err.details);
+      error.merge(err);
     } else {
       /**
        * Handle unexpected failures by logging (to get a stack trace)
@@ -237,10 +264,17 @@ function compile(source: string): [CompilerOutput, 'flow' | 'typescript'] {
       );
     }
   }
-  if (error.hasErrors()) {
-    return [{kind: 'err', results, error: error}, language];
+  // Only include logger errors if there weren't other errors
+  if (!error.hasErrors() && otherErrors.length !== 0) {
+    otherErrors.forEach(e => error.details.push(e));
   }
-  return [{kind: 'ok', results, transformOutput}, language];
+  if (error.hasErrors()) {
+    return [{kind: 'err', results, error}, language];
+  }
+  return [
+    {kind: 'ok', results, transformOutput, errors: error.details},
+    language,
+  ];
 }
 
 export default function Editor(): JSX.Element {
@@ -249,7 +283,11 @@ export default function Editor(): JSX.Element {
   const dispatchStore = useStoreDispatch();
   const {enqueueSnackbar} = useSnackbar();
   const [compilerOutput, language] = useMemo(
-    () => compile(deferredStore.source),
+    () => compile(deferredStore.source, 'compiler'),
+    [deferredStore.source],
+  );
+  const [linterOutput] = useMemo(
+    () => compile(deferredStore.source, 'linter'),
     [deferredStore.source],
   );
 
@@ -275,19 +313,26 @@ 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">
         <div className={clsx('relative sm:basis-1/4')}>
-          <Input
-            language={language}
-            errors={
-              compilerOutput.kind === 'err' ? compilerOutput.error.details : []
-            }
-          />
+          <Input language={language} errors={errors} />
         </div>
         <div className={clsx('flex sm:flex flex-wrap')}>
-          <Output store={deferredStore} compilerOutput={compilerOutput} />
+          <Output store={deferredStore} compilerOutput={mergedOutput} />
         </div>
       </div>
     </>

compiler/apps/playground/components/Editor/Input.tsx

@@ -36,13 +36,18 @@ 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});
+    renderReactCompilerMarkers({
+      monaco,
+      model,
+      details: errors,
+      source: store.source,
+    });
     /**
      * 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]);
+  }, [monaco, errors, store.source]);
 
   useEffect(() => {
     /**

compiler/apps/playground/components/Editor/Output.tsx

@@ -11,7 +11,11 @@ import {
   InformationCircleIcon,
 } from '@heroicons/react/outline';
 import MonacoEditor, {DiffEditor} from '@monaco-editor/react';
-import {type CompilerError} from 'babel-plugin-react-compiler';
+import {
+  CompilerErrorDetail,
+  CompilerDiagnostic,
+  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';
@@ -44,6 +48,7 @@ export type CompilerOutput =
       kind: 'ok';
       transformOutput: CompilerTransformOutput;
       results: Map<string, Array<PrintedCompilerPipelineValue>>;
+      errors: Array<CompilerErrorDetail | CompilerDiagnostic>;
     }
   | {
       kind: 'err';
@@ -123,10 +128,36 @@ 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(
-      'JS',
+      'Output',
       <TextTabContent
-        output={code}
+        output={output}
+        language={language}
         diff={null}
         showInfoPanel={false}></TextTabContent>,
     );
@@ -142,6 +173,18 @@ async function tabify(
         </>,
       );
     }
+  } 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);
@@ -162,17 +205,32 @@ function getSourceMapUrl(code: string, map: string): string | null {
 }
 
 function Output({store, compilerOutput}: Props): JSX.Element {
-  const [tabsOpen, setTabsOpen] = useState<Set<string>>(() => new Set(['JS']));
+  const [tabsOpen, setTabsOpen] = useState<Set<string>>(
+    () => new Set(['Output']),
+  );
   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(['JS', 'HIR']); // Initial and final passes should always be bold
+  const changedPasses: Set<string> = new Set(['Output', 'HIR']); // Initial and final passes should always be bold
   let lastResult: string = '';
   for (const [passName, results] of compilerOutput.results) {
     for (const result of results) {
@@ -196,20 +254,6 @@ 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}
     </>
   );
 }
@@ -218,10 +262,12 @@ function TextTabContent({
   output,
   diff,
   showInfoPanel,
+  language,
 }: {
   output: string;
   diff: string | null;
   showInfoPanel: boolean;
+  language: string;
 }): JSX.Element {
   const [diffMode, setDiffMode] = useState(false);
   return (
@@ -272,7 +318,7 @@ function TextTabContent({
         />
       ) : (
         <MonacoEditor
-          defaultLanguage="javascript"
+          language={language ?? 'javascript'}
           value={output}
           options={{
             ...monacoOptions,

compiler/apps/playground/components/Editor/monacoOptions.ts

@@ -28,5 +28,5 @@ export const monacoOptions: Partial<EditorProps['options']> = {
 
   automaticLayout: true,
   wordWrap: 'on',
-  wrappingIndent: 'deepIndent',
+  wrappingIndent: 'same',
 };

compiler/apps/playground/lib/reactCompilerMonacoDiagnostics.ts

@@ -6,7 +6,11 @@
  */
 
 import {Monaco} from '@monaco-editor/react';
-import {CompilerErrorDetail, ErrorSeverity} from 'babel-plugin-react-compiler';
+import {
+  CompilerDiagnostic,
+  CompilerErrorDetail,
+  ErrorSeverity,
+} from 'babel-plugin-react-compiler';
 import {MarkerSeverity, type editor} from 'monaco-editor';
 
 function mapReactCompilerSeverityToMonaco(
@@ -22,38 +26,46 @@ function mapReactCompilerSeverityToMonaco(
 }
 
 function mapReactCompilerDiagnosticToMonacoMarker(
-  detail: CompilerErrorDetail,
+  detail: CompilerErrorDetail | CompilerDiagnostic,
   monaco: Monaco,
+  source: string,
 ): editor.IMarkerData | null {
-  if (detail.loc == null || typeof detail.loc === 'symbol') {
+  const loc = detail.primaryLocation();
+  if (loc == null || typeof loc === 'symbol') {
     return null;
   }
   const severity = mapReactCompilerSeverityToMonaco(detail.severity, monaco);
-  let message = detail.printErrorMessage();
+  let message = detail.printErrorMessage(source, {eslint: true});
   return {
     severity,
     message,
-    startLineNumber: detail.loc.start.line,
-    startColumn: detail.loc.start.column + 1,
-    endLineNumber: detail.loc.end.line,
-    endColumn: detail.loc.end.column + 1,
+    startLineNumber: loc.start.line,
+    startColumn: loc.start.column + 1,
+    endLineNumber: loc.end.line,
+    endColumn: loc.end.column + 1,
   };
 }
 
 type ReactCompilerMarkerConfig = {
   monaco: Monaco;
   model: editor.ITextModel;
-  details: Array<CompilerErrorDetail>;
+  details: Array<CompilerErrorDetail | CompilerDiagnostic>;
+  source: string;
 };
 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);
+    const marker = mapReactCompilerDiagnosticToMonacoMarker(
+      detail,
+      monaco,
+      source,
+    );
     if (marker == null) {
       continue;
     }

compiler/apps/playground/scripts/link-compiler.sh

@@ -8,8 +8,8 @@ set -eo pipefail
 
 HERE=$(pwd)
 
-cd ../../packages/react-compiler-runtime && yarn --silent link && cd $HERE
-cd ../../packages/babel-plugin-react-compiler && yarn --silent link && cd $HERE
+cd ../../packages/react-compiler-runtime && yarn --silent link && cd "$HERE"
+cd ../../packages/babel-plugin-react-compiler && yarn --silent link && cd "$HERE"
 
 yarn --silent link babel-plugin-react-compiler
 yarn --silent link react-compiler-runtime

compiler/packages/babel-plugin-react-compiler/src/Babel/BabelPlugin.ts

@@ -12,6 +12,7 @@ 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';
@@ -34,51 +35,58 @@ export default function BabelPluginReactCompiler(
        */
       Program: {
         enter(prog, pass): void {
-          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',
+          try {
+            const filename = pass.filename ?? 'unknown';
+            if (ENABLE_REACT_COMPILER_TIMINGS === true) {
+              performance.mark(`${filename}:start`, {
+                detail: 'BabelPlugin:Program:start',
+              });
+            }
+            let opts = parsePluginOptions(pass.opts);
+            const isDev =
+              (typeof __DEV__ !== 'undefined' && __DEV__ === true) ||
+              process.env['NODE_ENV'] === 'development';
+            if (
+              opts.enableReanimatedCheck === true &&
+              pipelineUsesReanimatedPlugin(pass.file.opts.plugins)
+            ) {
+              opts = injectReanimatedFlag(opts);
+            }
+            if (
+              opts.environment.enableResetCacheOnSourceFileChanges !== false &&
+              isDev
+            ) {
+              opts = {
+                ...opts,
+                environment: {
+                  ...opts.environment,
+                  enableResetCacheOnSourceFileChanges: true,
+                },
+              };
+            }
+            const result = compileProgram(prog, {
+              opts,
+              filename: pass.filename ?? null,
+              comments: pass.file.ast.comments ?? [],
+              code: pass.file.code,
             });
+            validateNoUntransformedReferences(
+              prog,
+              pass.filename ?? null,
+              opts.logger,
+              opts.environment,
+              result,
+            );
+            if (ENABLE_REACT_COMPILER_TIMINGS === true) {
+              performance.mark(`${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 {

compiler/packages/babel-plugin-react-compiler/src/CompilerError.ts

@@ -5,6 +5,8 @@
  * 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 {Err, Ok, Result} from './Utils/Result';
 import {assertExhaustive} from './Utils/utils';
@@ -15,6 +17,11 @@ 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.
    */
@@ -39,6 +46,24 @@ export enum ErrorSeverity {
   Invariant = 'Invariant',
 }
 
+export type CompilerDiagnosticOptions = {
+  severity: ErrorSeverity;
+  category: 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;
+  };
+
 export enum CompilerSuggestionOperation {
   InsertBefore,
   InsertAfter,
@@ -69,6 +94,103 @@ export type CompilerErrorDetailOptions = {
   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 category(): CompilerDiagnosticOptions['category'] {
+    return this.options.category;
+  }
+  get description(): CompilerDiagnosticOptions['description'] {
+    return this.options.description;
+  }
+  get severity(): CompilerDiagnosticOptions['severity'] {
+    return this.options.severity;
+  }
+  get suggestions(): CompilerDiagnosticOptions['suggestions'] {
+    return this.options.suggestions;
+  }
+
+  withDetail(detail: CompilerDiagnosticDetail): CompilerDiagnostic {
+    this.options.details.push(detail);
+    return this;
+  }
+
+  primaryLocation(): SourceLocation | null {
+    return this.options.details.filter(d => d.kind === 'error')[0]?.loc ?? null;
+  }
+
+  printErrorMessage(source: string, options: PrintErrorMessageOptions): string {
+    const buffer = [
+      printErrorSummary(this.severity, this.category),
+      '\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;
+        }
+        default: {
+          assertExhaustive(
+            detail.kind,
+            `Unexpected detail kind ${(detail as any).kind}`,
+          );
+        }
+      }
+    }
+    return buffer.join('');
+  }
+
+  toString(): string {
+    const buffer = [printErrorSummary(this.severity, this.category)];
+    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.
@@ -96,24 +218,51 @@ export class CompilerErrorDetail {
     return this.options.suggestions;
   }
 
-  printErrorMessage(): string {
-    const buffer = [`${this.severity}: ${this.reason}`];
+  primaryLocation(): SourceLocation | null {
+    return this.loc;
+  }
+
+  printErrorMessage(source: string, options: PrintErrorMessageOptions): string {
+    const buffer = [printErrorSummary(this.severity, this.reason)];
     if (this.description != null) {
-      buffer.push(`. ${this.description}`);
+      buffer.push(`\n\n${this.description}.`);
     }
-    if (this.loc != null && typeof this.loc !== 'symbol') {
-      buffer.push(` (${this.loc.start.line}:${this.loc.end.line})`);
+    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');
     }
     return buffer.join('');
   }
 
   toString(): string {
-    return this.printErrorMessage();
+    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('');
   }
 }
 
 export class CompilerError extends Error {
-  details: Array<CompilerErrorDetail> = [];
+  details: Array<CompilerErrorDetail | CompilerDiagnostic> = [];
+  printedMessage: string | null = null;
 
   static invariant(
     condition: unknown,
@@ -131,6 +280,12 @@ 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'>,
   ): never {
@@ -193,18 +348,49 @@ export class CompilerError extends Error {
   }
 
   override get message(): string {
-    return this.toString();
+    return this.printedMessage ?? 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({
       reason: options.reason,
@@ -241,13 +427,69 @@ 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}`;
+}

compiler/packages/babel-plugin-react-compiler/src/Entrypoint/Options.ts

@@ -7,7 +7,12 @@
 
 import * as t from '@babel/types';
 import {z} from 'zod';
-import {CompilerError, CompilerErrorDetailOptions} from '../CompilerError';
+import {
+  CompilerDiagnostic,
+  CompilerError,
+  CompilerErrorDetail,
+  CompilerErrorDetailOptions,
+} from '../CompilerError';
 import {
   EnvironmentConfig,
   ExternalFunction,
@@ -37,6 +42,14 @@ const PanicThresholdOptionsSchema = z.enum([
 ]);
 
 export type PanicThresholdOptions = z.infer<typeof PanicThresholdOptionsSchema>;
+const DynamicGatingOptionsSchema = z.object({
+  source: z.string(),
+});
+export type DynamicGatingOptions = z.infer<typeof DynamicGatingOptionsSchema>;
+const CustomOptOutDirectiveSchema = z
+  .nullable(z.array(z.string()))
+  .default(null);
+type CustomOptOutDirective = z.infer<typeof CustomOptOutDirectiveSchema>;
 
 export type PluginOptions = {
   environment: EnvironmentConfig;
@@ -65,6 +78,28 @@ export type PluginOptions = {
    */
   gating: ExternalFunction | null;
 
+  /**
+   * If specified, this enables dynamic gating which matches `use memo if(...)`
+   * directives.
+   *
+   * Example usage:
+   * ```js
+   * // @dynamicGating:{"source":"myModule"}
+   * export function MyComponent() {
+   *   'use memo if(isEnabled)';
+   *    return <div>...</div>;
+   * }
+   * ```
+   * This will emit:
+   * ```js
+   * import {isEnabled} from 'myModule';
+   * export const MyComponent = isEnabled()
+   *   ? <optimized version>
+   *   : <original version>;
+   * ```
+   */
+  dynamicGating: DynamicGatingOptions | null;
+
   panicThreshold: PanicThresholdOptions;
 
   /*
@@ -106,6 +141,11 @@ export type PluginOptions = {
    */
   ignoreUseNoForget: boolean;
 
+  /**
+   * Unstable / do not use
+   */
+  customOptOutDirectives: CustomOptOutDirective;
+
   sources: Array<string> | ((filename: string) => boolean) | null;
 
   /**
@@ -189,7 +229,7 @@ export type LoggerEvent =
 export type CompileErrorEvent = {
   kind: 'CompileError';
   fnLoc: t.SourceLocation | null;
-  detail: CompilerErrorDetailOptions;
+  detail: CompilerErrorDetail | CompilerDiagnostic;
 };
 export type CompileDiagnosticEvent = {
   kind: 'CompileDiagnostic';
@@ -244,6 +284,7 @@ export const defaultOptions: PluginOptions = {
   logger: null,
   gating: null,
   noEmit: false,
+  dynamicGating: null,
   eslintSuppressionRules: null,
   flowSuppressions: true,
   ignoreUseNoForget: false,
@@ -251,6 +292,7 @@ export const defaultOptions: PluginOptions = {
     return filename.indexOf('node_modules') === -1;
   },
   enableReanimatedCheck: true,
+  customOptOutDirectives: null,
   target: '19',
 } as const;
 
@@ -292,6 +334,40 @@ export function parsePluginOptions(obj: unknown): PluginOptions {
           }
           break;
         }
+        case 'dynamicGating': {
+          if (value == null) {
+            parsedOptions[key] = null;
+          } else {
+            const result = DynamicGatingOptionsSchema.safeParse(value);
+            if (result.success) {
+              parsedOptions[key] = result.data;
+            } else {
+              CompilerError.throwInvalidConfig({
+                reason:
+                  'Could not parse dynamic gating. Update React Compiler config to fix the error',
+                description: `${fromZodError(result.error)}`,
+                loc: null,
+                suggestions: null,
+              });
+            }
+          }
+          break;
+        }
+        case 'customOptOutDirectives': {
+          const result = CustomOptOutDirectiveSchema.safeParse(value);
+          if (result.success) {
+            parsedOptions[key] = result.data;
+          } else {
+            CompilerError.throwInvalidConfig({
+              reason:
+                'Could not parse custom opt out directives. Update React Compiler config to fix the error',
+              description: `${fromZodError(result.error)}`,
+              loc: null,
+              suggestions: null,
+            });
+          }
+          break;
+        }
         default: {
           parsedOptions[key] = value;
         }

compiler/packages/babel-plugin-react-compiler/src/Entrypoint/Pipeline.ts

@@ -94,7 +94,7 @@ import {validateLocalsNotReassignedAfterRender} from '../Validation/ValidateLoca
 import {outlineFunctions} from '../Optimization/OutlineFunctions';
 import {propagatePhiTypes} from '../TypeInference/PropagatePhiTypes';
 import {lowerContextAccess} from '../Optimization/LowerContextAccess';
-import {validateNoSetStateInPassiveEffects} from '../Validation/ValidateNoSetStateInPassiveEffects';
+import {validateNoSetStateInEffects} from '../Validation/ValidateNoSetStateInEffects';
 import {validateNoJSXInTryStatement} from '../Validation/ValidateNoJSXInTryStatement';
 import {propagateScopeDependenciesHIR} from '../HIR/PropagateScopeDependenciesHIR';
 import {outlineJSX} from '../Optimization/OutlineJsx';
@@ -104,6 +104,8 @@ import {validateNoImpureFunctionsInRender} from '../Validation/ValidateNoImpureF
 import {CompilerError} from '..';
 import {validateStaticComponents} from '../Validation/ValidateStaticComponents';
 import {validateNoFreezingKnownMutableFunctions} from '../Validation/ValidateNoFreezingKnownMutableFunctions';
+import {inferMutationAliasingEffects} from '../Inference/InferMutationAliasingEffects';
+import {inferMutationAliasingRanges} from '../Inference/InferMutationAliasingRanges';
 
 export type CompilerPipelineValue =
   | {kind: 'ast'; name: string; value: CodegenFunction}
@@ -130,6 +132,7 @@ function run(
     mode,
     config,
     contextIdentifiers,
+    func,
     logger,
     filename,
     code,
@@ -171,7 +174,7 @@ function runWithEnvironment(
     !env.config.disableMemoizationForDebugging &&
     !env.config.enableChangeDetectionForDebugging
   ) {
-    dropManualMemoization(hir);
+    dropManualMemoization(hir).unwrap();
     log({kind: 'hir', name: 'DropManualMemoization', value: hir});
   }
 
@@ -226,15 +229,27 @@ function runWithEnvironment(
   analyseFunctions(hir);
   log({kind: 'hir', name: 'AnalyseFunctions', value: hir});
 
-  const fnEffectErrors = inferReferenceEffects(hir);
-  if (env.isInferredMemoEnabled) {
-    if (fnEffectErrors.length > 0) {
-      CompilerError.throw(fnEffectErrors[0]);
+  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();
+      }
     }
   }
-  log({kind: 'hir', name: 'InferReferenceEffects', value: hir});
 
-  validateLocalsNotReassignedAfterRender(hir);
+  if (!env.config.enableNewMutationAliasingModel) {
+    validateLocalsNotReassignedAfterRender(hir);
+  }
 
   // Note: Has to come after infer reference effects because "dead" code may still affect inference
   deadCodeElimination(hir);
@@ -248,8 +263,21 @@ function runWithEnvironment(
   pruneMaybeThrows(hir);
   log({kind: 'hir', name: 'PruneMaybeThrows', value: hir});
 
-  inferMutableRanges(hir);
-  log({kind: 'hir', name: 'InferMutableRanges', value: hir});
+  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);
+    }
+  }
 
   if (env.isInferredMemoEnabled) {
     if (env.config.assertValidMutableRanges) {
@@ -264,8 +292,8 @@ function runWithEnvironment(
       validateNoSetStateInRender(hir).unwrap();
     }
 
-    if (env.config.validateNoSetStateInPassiveEffects) {
-      env.logErrors(validateNoSetStateInPassiveEffects(hir));
+    if (env.config.validateNoSetStateInEffects) {
+      env.logErrors(validateNoSetStateInEffects(hir));
     }
 
     if (env.config.validateNoJSXInTryStatements) {
@@ -276,7 +304,10 @@ function runWithEnvironment(
       validateNoImpureFunctionsInRender(hir).unwrap();
     }
 
-    if (env.config.validateNoFreezingKnownMutableFunctions) {
+    if (
+      env.config.validateNoFreezingKnownMutableFunctions ||
+      env.config.enableNewMutationAliasingModel
+    ) {
       validateNoFreezingKnownMutableFunctions(hir).unwrap();
     }
   }

compiler/packages/babel-plugin-react-compiler/src/Entrypoint/Program.ts

@@ -12,7 +12,7 @@ import {
   CompilerErrorDetail,
   ErrorSeverity,
 } from '../CompilerError';
-import {ReactFunctionType} from '../HIR/Environment';
+import {ExternalFunction, ReactFunctionType} from '../HIR/Environment';
 import {CodegenFunction} from '../ReactiveScopes';
 import {isComponentDeclaration} from '../Utils/ComponentDeclaration';
 import {isHookDeclaration} from '../Utils/HookDeclaration';
@@ -31,6 +31,7 @@ import {
   suppressionsToCompilerError,
 } from './Suppression';
 import {GeneratedSource} from '../HIR';
+import {Err, Ok, Result} from '../Utils/Result';
 
 export type CompilerPass = {
   opts: PluginOptions;
@@ -40,26 +41,102 @@ export type CompilerPass = {
 };
 export const OPT_IN_DIRECTIVES = new Set(['use forget', 'use memo']);
 export const OPT_OUT_DIRECTIVES = new Set(['use no forget', 'use no memo']);
+const DYNAMIC_GATING_DIRECTIVE = new RegExp('^use memo if\\(([^\\)]*)\\)$');
 
-export function findDirectiveEnablingMemoization(
+export function tryFindDirectiveEnablingMemoization(
   directives: Array<t.Directive>,
-): t.Directive | null {
-  return (
-    directives.find(directive =>
-      OPT_IN_DIRECTIVES.has(directive.value.value),
-    ) ?? null
+  opts: PluginOptions,
+): Result<t.Directive | null, CompilerError> {
+  const optIn = directives.find(directive =>
+    OPT_IN_DIRECTIVES.has(directive.value.value),
   );
+  if (optIn != null) {
+    return Ok(optIn);
+  }
+  const dynamicGating = findDirectivesDynamicGating(directives, opts);
+  if (dynamicGating.isOk()) {
+    return Ok(dynamicGating.unwrap()?.directive ?? null);
+  } else {
+    return Err(dynamicGating.unwrapErr());
+  }
 }
 
 export function findDirectiveDisablingMemoization(
   directives: Array<t.Directive>,
+  {customOptOutDirectives}: PluginOptions,
 ): t.Directive | null {
+  if (customOptOutDirectives != null) {
+    return (
+      directives.find(
+        directive =>
+          customOptOutDirectives.indexOf(directive.value.value) !== -1,
+      ) ?? null
+    );
+  }
   return (
     directives.find(directive =>
       OPT_OUT_DIRECTIVES.has(directive.value.value),
     ) ?? null
   );
 }
+function findDirectivesDynamicGating(
+  directives: Array<t.Directive>,
+  opts: PluginOptions,
+): Result<
+  {
+    gating: ExternalFunction;
+    directive: t.Directive;
+  } | null,
+  CompilerError
+> {
+  if (opts.dynamicGating === null) {
+    return Ok(null);
+  }
+  const errors = new CompilerError();
+  const result: Array<{directive: t.Directive; match: string}> = [];
+
+  for (const directive of directives) {
+    const maybeMatch = DYNAMIC_GATING_DIRECTIVE.exec(directive.value.value);
+    if (maybeMatch != null && maybeMatch[1] != null) {
+      if (t.isValidIdentifier(maybeMatch[1])) {
+        result.push({directive, match: maybeMatch[1]});
+      } else {
+        errors.push({
+          reason: `Dynamic gating directive is not a valid JavaScript identifier`,
+          description: `Found '${directive.value.value}'`,
+          severity: ErrorSeverity.InvalidReact,
+          loc: directive.loc ?? null,
+          suggestions: null,
+        });
+      }
+    }
+  }
+  if (errors.hasErrors()) {
+    return Err(errors);
+  } else if (result.length > 1) {
+    const error = new CompilerError();
+    error.push({
+      reason: `Multiple dynamic gating directives found`,
+      description: `Expected a single directive but found [${result
+        .map(r => r.directive.value.value)
+        .join(', ')}]`,
+      severity: ErrorSeverity.InvalidReact,
+      loc: result[0].directive.loc ?? null,
+      suggestions: null,
+    });
+    return Err(error);
+  } else if (result.length === 1) {
+    return Ok({
+      gating: {
+        source: opts.dynamicGating.source,
+        importSpecifierName: result[0].match,
+      },
+      directive: result[0].directive,
+    });
+  } else {
+    return Ok(null);
+  }
+}
 
 function isCriticalError(err: unknown): boolean {
   return !(err instanceof CompilerError) || err.isCritical();
@@ -104,7 +181,7 @@ function logError(
         context.opts.logger.logEvent(context.filename, {
           kind: 'CompileError',
           fnLoc,
-          detail: detail.options,
+          detail,
         });
       }
     } else {
@@ -326,7 +403,8 @@ export function compileProgram(
     code: pass.code,
     suppressions,
     hasModuleScopeOptOut:
-      findDirectiveDisablingMemoization(program.node.directives) != null,
+      findDirectiveDisablingMemoization(program.node.directives, pass.opts) !=
+      null,
   });
 
   const queue: Array<CompileSource> = findFunctionsToCompile(
@@ -477,13 +555,36 @@ function processFn(
   fnType: ReactFunctionType,
   programContext: ProgramContext,
 ): null | CodegenFunction {
-  let directives;
+  let directives: {
+    optIn: t.Directive | null;
+    optOut: t.Directive | null;
+  };
   if (fn.node.body.type !== 'BlockStatement') {
-    directives = {optIn: null, optOut: null};
-  } else {
     directives = {
-      optIn: findDirectiveEnablingMemoization(fn.node.body.directives),
-      optOut: findDirectiveDisablingMemoization(fn.node.body.directives),
+      optIn: null,
+      optOut: null,
+    };
+  } else {
+    const optIn = tryFindDirectiveEnablingMemoization(
+      fn.node.body.directives,
+      programContext.opts,
+    );
+    if (optIn.isErr()) {
+      /**
+       * If parsing opt-in directive fails, it's most likely that React Compiler
+       * was not tested or rolled out on this function. In that case, we handle
+       * the error and fall back to the safest option which is to not optimize
+       * the function.
+       */
+      handleError(optIn.unwrapErr(), programContext, fn.node.loc ?? null);
+      return null;
+    }
+    directives = {
+      optIn: optIn.unwrapOr(null),
+      optOut: findDirectiveDisablingMemoization(
+        fn.node.body.directives,
+        programContext.opts,
+      ),
     };
   }
 
@@ -659,25 +760,31 @@ function applyCompiledFunctions(
   pass: CompilerPass,
   programContext: ProgramContext,
 ): void {
-  const referencedBeforeDeclared =
-    pass.opts.gating != null
-      ? getFunctionReferencedBeforeDeclarationAtTopLevel(program, compiledFns)
-      : null;
+  let referencedBeforeDeclared = null;
   for (const result of compiledFns) {
     const {kind, originalFn, compiledFn} = result;
     const transformedFn = createNewFunctionNode(originalFn, compiledFn);
     programContext.alreadyCompiled.add(transformedFn);
 
-    if (referencedBeforeDeclared != null && kind === 'original') {
-      CompilerError.invariant(pass.opts.gating != null, {
-        reason: "Expected 'gating' import to be present",
-        loc: null,
-      });
+    let dynamicGating: ExternalFunction | null = null;
+    if (originalFn.node.body.type === 'BlockStatement') {
+      const result = findDirectivesDynamicGating(
+        originalFn.node.body.directives,
+        pass.opts,
+      );
+      if (result.isOk()) {
+        dynamicGating = result.unwrap()?.gating ?? null;
+      }
+    }
+    const functionGating = dynamicGating ?? pass.opts.gating;
+    if (kind === 'original' && functionGating != null) {
+      referencedBeforeDeclared ??=
+        getFunctionReferencedBeforeDeclarationAtTopLevel(program, compiledFns);
       insertGatedFunctionDeclaration(
         originalFn,
         transformedFn,
         programContext,
-        pass.opts.gating,
+        functionGating,
         referencedBeforeDeclared.has(result),
       );
     } else {
@@ -733,8 +840,13 @@ function getReactFunctionType(
 ): ReactFunctionType | null {
   const hookPattern = pass.opts.environment.hookPattern;
   if (fn.node.body.type === 'BlockStatement') {
-    if (findDirectiveEnablingMemoization(fn.node.body.directives) != null)
+    const optInDirectives = tryFindDirectiveEnablingMemoization(
+      fn.node.body.directives,
+      pass.opts,
+    );
+    if (optInDirectives.unwrapOr(null) != null) {
       return getComponentOrHookLike(fn, hookPattern) ?? 'Other';
+    }
   }
 
   // Component and hook declarations are known components/hooks

compiler/packages/babel-plugin-react-compiler/src/Entrypoint/Suppression.ts

@@ -8,8 +8,8 @@
 import {NodePath} from '@babel/core';
 import * as t from '@babel/types';
 import {
+  CompilerDiagnostic,
   CompilerError,
-  CompilerErrorDetail,
   CompilerSuggestionOperation,
   ErrorSeverity,
 } from '../CompilerError';
@@ -181,12 +181,11 @@ export function suppressionsToCompilerError(
           'Unhandled suppression source',
         );
     }
-    error.pushErrorDetail(
-      new CompilerErrorDetail({
-        reason: `${reason}. React Compiler only works when your components follow all the rules of React, disabling them may result in unexpected or incorrect behavior`,
-        description: suppressionRange.disableComment.value.trim(),
+    error.pushDiagnostic(
+      CompilerDiagnostic.create({
+        category: reason,
+        description: `React Compiler only works when your components follow all the rules of React, disabling them may result in unexpected or incorrect behavior. Found suppression \`${suppressionRange.disableComment.value.trim()}\``,
         severity: ErrorSeverity.InvalidReact,
-        loc: suppressionRange.disableComment.loc ?? null,
         suggestions: [
           {
             description: suggestion,
@@ -197,6 +196,10 @@ export function suppressionsToCompilerError(
             op: CompilerSuggestionOperation.Remove,
           },
         ],
+      }).withDetail({
+        kind: 'error',
+        loc: suppressionRange.disableComment.loc ?? null,
+        message: 'Found React rule suppression',
       }),
     );
   }

compiler/packages/babel-plugin-react-compiler/src/Entrypoint/ValidateNoUntransformedReferences.ts

@@ -8,35 +8,63 @@
 import {NodePath} from '@babel/core';
 import * as t from '@babel/types';
 
-import {
-  CompilerError,
-  CompilerErrorDetailOptions,
-  EnvironmentConfig,
-  ErrorSeverity,
-  Logger,
-} from '..';
+import {CompilerError, EnvironmentConfig, ErrorSeverity, Logger} from '..';
 import {getOrInsertWith} from '../Utils/utils';
-import {Environment} from '../HIR';
+import {Environment, GeneratedSource} from '../HIR';
 import {DEFAULT_EXPORT} from '../HIR/Environment';
 import {CompileProgramMetadata} from './Program';
+import {CompilerDiagnostic, CompilerDiagnosticOptions} from '../CompilerError';
 
 function throwInvalidReact(
-  options: Omit<CompilerErrorDetailOptions, 'severity'>,
+  options: Omit<CompilerDiagnosticOptions, 'severity'>,
   {logger, filename}: TraversalState,
 ): never {
-  const detail: CompilerErrorDetailOptions = {
-    ...options,
+  const detail: CompilerDiagnosticOptions = {
     severity: ErrorSeverity.InvalidReact,
+    ...options,
   };
   logger?.logEvent(filename, {
     kind: 'CompileError',
     fnLoc: null,
-    detail,
+    detail: new CompilerDiagnostic(detail),
   });
-  CompilerError.throw(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;
 }
 function assertValidEffectImportReference(
-  numArgs: number,
+  autodepsIndex: number,
   paths: Array<NodePath<t.Node>>,
   context: TraversalState,
 ): void {
@@ -49,11 +77,10 @@ function assertValidEffectImportReference(
         maybeCalleeLoc != null &&
         context.inferredEffectLocations.has(maybeCalleeLoc);
       /**
-       * 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?
+       * Error on effect calls that still have AUTODEPS in their args
        */
-      if (args.length === numArgs && !hasInferredEffect) {
+      const hasAutodepsArg = args.some(isAutodepsSigil);
+      if (hasAutodepsArg && !hasInferredEffect) {
         const maybeErrorDiagnostic = matchCompilerDiagnostic(
           path,
           context.transformErrors,
@@ -65,14 +92,18 @@ function assertValidEffectImportReference(
          */
         throwInvalidReact(
           {
-            reason:
-              '[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,
+            category:
+              '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,
+              },
+            ],
           },
           context,
         );
@@ -92,13 +123,20 @@ function assertValidFireImportReference(
     );
     throwInvalidReact(
       {
-        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,
+        category:
+          '[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,
+          },
+        ],
       },
       context,
     );
@@ -128,12 +166,12 @@ export default function validateNoUntransformedReferences(
   if (env.inferEffectDependencies) {
     for (const {
       function: {source, importSpecifierName},
-      numRequiredArgs,
+      autodepsIndex,
     } of env.inferEffectDependencies) {
       const module = getOrInsertWith(moduleLoadChecks, source, () => new Map());
       module.set(
         importSpecifierName,
-        assertValidEffectImportReference.bind(null, numRequiredArgs),
+        assertValidEffectImportReference.bind(null, autodepsIndex),
       );
     }
   }

compiler/packages/babel-plugin-react-compiler/src/HIR/AssertValidMutableRanges.ts

@@ -5,13 +5,14 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import invariant from 'invariant';
-import {HIRFunction, Identifier, MutableRange} from './HIR';
+import {HIRFunction, MutableRange, Place} from './HIR';
 import {
   eachInstructionLValue,
   eachInstructionOperand,
   eachTerminalOperand,
 } from './visitors';
+import {CompilerError} from '..';
+import {printPlace} from './PrintHIR';
 
 /*
  * Checks that all mutable ranges in the function are well-formed, with
@@ -20,38 +21,43 @@ import {
 export function assertValidMutableRanges(fn: HIRFunction): void {
   for (const [, block] of fn.body.blocks) {
     for (const phi of block.phis) {
-      visitIdentifier(phi.place.identifier);
-      for (const [, operand] of phi.operands) {
-        visitIdentifier(operand.identifier);
+      visit(phi.place, `phi for block bb${block.id}`);
+      for (const [pred, operand] of phi.operands) {
+        visit(operand, `phi predecessor bb${pred} for block bb${block.id}`);
       }
     }
     for (const instr of block.instructions) {
       for (const operand of eachInstructionLValue(instr)) {
-        visitIdentifier(operand.identifier);
+        visit(operand, `instruction [${instr.id}]`);
       }
       for (const operand of eachInstructionOperand(instr)) {
-        visitIdentifier(operand.identifier);
+        visit(operand, `instruction [${instr.id}]`);
       }
     }
     for (const operand of eachTerminalOperand(block.terminal)) {
-      visitIdentifier(operand.identifier);
+      visit(operand, `terminal [${block.terminal.id}]`);
     }
   }
 }
 
-function visitIdentifier(identifier: Identifier): void {
-  validateMutableRange(identifier.mutableRange);
-  if (identifier.scope !== null) {
-    validateMutableRange(identifier.scope.range);
+function visit(place: Place, description: string): void {
+  validateMutableRange(place, place.identifier.mutableRange, description);
+  if (place.identifier.scope !== null) {
+    validateMutableRange(place, place.identifier.scope.range, description);
   }
 }
 
-function validateMutableRange(mutableRange: MutableRange): void {
-  invariant(
-    (mutableRange.start === 0 && mutableRange.end === 0) ||
-      mutableRange.end > mutableRange.start,
-    'Identifier scope mutableRange was invalid: [%s:%s]',
-    mutableRange.start,
-    mutableRange.end,
+function validateMutableRange(
+  place: Place,
+  range: MutableRange,
+  description: string,
+): void {
+  CompilerError.invariant(
+    (range.start === 0 && range.end === 0) || range.end > range.start,
+    {
+      reason: `Invalid mutable range: [${range.start}:${range.end}]`,
+      description: `${printPlace(place)} in ${description}`,
+      loc: place.loc,
+    },
   );
 }

compiler/packages/babel-plugin-react-compiler/src/HIR/BuildHIR.ts

@@ -9,6 +9,7 @@ import {NodePath, Scope} from '@babel/traverse';
 import * as t from '@babel/types';
 import invariant from 'invariant';
 import {
+  CompilerDiagnostic,
   CompilerError,
   CompilerSuggestionOperation,
   ErrorSeverity,
@@ -47,7 +48,7 @@ import {
   makeType,
   promoteTemporary,
 } from './HIR';
-import HIRBuilder, {Bindings} from './HIRBuilder';
+import HIRBuilder, {Bindings, createTemporaryPlace} from './HIRBuilder';
 import {BuiltInArrayId} from './ObjectShape';
 
 /*
@@ -70,21 +71,23 @@ import {BuiltInArrayId} from './ObjectShape';
 export function lower(
   func: NodePath<t.Function>,
   env: Environment,
+  // Bindings captured from the outer function, in case lower() is called recursively (for lambdas)
   bindings: Bindings | null = null,
-  capturedRefs: Array<t.Identifier> = [],
-  // the outermost function being compiled, in case lower() is called recursively (for lambdas)
-  parent: NodePath<t.Function> | null = null,
+  capturedRefs: Map<t.Identifier, SourceLocation> = new Map(),
 ): Result<HIRFunction, CompilerError> {
-  const builder = new HIRBuilder(env, parent ?? func, bindings, capturedRefs);
+  const builder = new HIRBuilder(env, {
+    bindings,
+    context: capturedRefs,
+  });
   const context: HIRFunction['context'] = [];
 
-  for (const ref of capturedRefs ?? []) {
+  for (const [ref, loc] of capturedRefs ?? []) {
     context.push({
       kind: 'Identifier',
       identifier: builder.resolveBinding(ref),
       effect: Effect.Unknown,
       reactive: false,
-      loc: ref.loc ?? GeneratedSource,
+      loc,
     });
   }
 
@@ -102,12 +105,17 @@ export function lower(
     if (param.isIdentifier()) {
       const binding = builder.resolveIdentifier(param);
       if (binding.kind !== 'Identifier') {
-        builder.errors.push({
-          reason: `(BuildHIR::lower) Could not find binding for param \`${param.node.name}\``,
-          severity: ErrorSeverity.Invariant,
-          loc: param.node.loc ?? null,
-          suggestions: null,
-        });
+        builder.errors.pushDiagnostic(
+          CompilerDiagnostic.create({
+            severity: ErrorSeverity.Invariant,
+            category: 'Could not find binding',
+            description: `[BuildHIR] Could not find binding for param \`${param.node.name}\`.`,
+          }).withDetail({
+            kind: 'error',
+            loc: param.node.loc ?? null,
+            message: 'Could not find binding',
+          }),
+        );
         return;
       }
       const place: Place = {
@@ -161,12 +169,17 @@ export function lower(
         'Assignment',
       );
     } else {
-      builder.errors.push({
-        reason: `(BuildHIR::lower) Handle ${param.node.type} params`,
-        severity: ErrorSeverity.Todo,
-        loc: param.node.loc ?? null,
-        suggestions: null,
-      });
+      builder.errors.pushDiagnostic(
+        CompilerDiagnostic.create({
+          severity: ErrorSeverity.Todo,
+          category: `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',
+        }),
+      );
     }
   });
 
@@ -176,22 +189,28 @@ export function lower(
     const fallthrough = builder.reserve('block');
     const terminal: ReturnTerminal = {
       kind: 'return',
+      returnVariant: 'Implicit',
       loc: GeneratedSource,
       value: lowerExpressionToTemporary(builder, body),
       id: makeInstructionId(0),
+      effects: null,
     };
     builder.terminateWithContinuation(terminal, fallthrough);
   } else if (body.isBlockStatement()) {
     lowerStatement(builder, body);
     directives = body.get('directives').map(d => d.node.value.value);
   } else {
-    builder.errors.push({
-      severity: ErrorSeverity.InvalidJS,
-      reason: `Unexpected function body kind`,
-      description: `Expected function body to be an expression or a block statement, got \`${body.type}\``,
-      loc: body.node.loc ?? null,
-      suggestions: null,
-    });
+    builder.errors.pushDiagnostic(
+      CompilerDiagnostic.create({
+        severity: ErrorSeverity.InvalidJS,
+        category: `Unexpected function body kind`,
+        description: `Expected function body to be an expression or a block statement, got \`${body.type}\`.`,
+      }).withDetail({
+        kind: 'error',
+        loc: body.node.loc ?? null,
+        message: 'Expected a block statement or expression',
+      }),
+    );
   }
 
   if (builder.errors.hasErrors()) {
@@ -201,6 +220,7 @@ export function lower(
   builder.terminate(
     {
       kind: 'return',
+      returnVariant: 'Void',
       loc: GeneratedSource,
       value: lowerValueToTemporary(builder, {
         kind: 'Primitive',
@@ -208,6 +228,7 @@ export function lower(
         loc: GeneratedSource,
       }),
       id: makeInstructionId(0),
+      effects: null,
     },
     null,
   );
@@ -215,9 +236,9 @@ export function lower(
   return Ok({
     id,
     params,
-    fnType: parent == null ? env.fnType : 'Other',
+    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,
     generator: func.node.generator === true,
@@ -225,6 +246,7 @@ export function lower(
     loc: func.node.loc ?? GeneratedSource,
     env,
     effects: null,
+    aliasingEffects: null,
     directives,
   });
 }
@@ -282,9 +304,11 @@ function lowerStatement(
       }
       const terminal: ReturnTerminal = {
         kind: 'return',
+        returnVariant: 'Explicit',
         loc: stmt.node.loc ?? GeneratedSource,
         value,
         id: makeInstructionId(0),
+        effects: null,
       };
       builder.terminate(terminal, 'block');
       return;
@@ -1235,6 +1259,7 @@ function lowerStatement(
           kind: 'Debugger',
           loc,
         },
+        effects: null,
         loc,
       });
       return;
@@ -1348,13 +1373,85 @@ function lowerStatement(
 
       return;
     }
-    case 'TypeAlias':
-    case 'TSInterfaceDeclaration':
-    case 'TSTypeAliasDeclaration': {
-      // We do not preserve type annotations/syntax through transformation
+    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,
+        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,
+        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,
+        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,
+        loc: stmtPath.node.loc ?? null,
+        suggestions: null,
+      });
+      lowerValueToTemporary(builder, {
+        kind: 'UnsupportedNode',
+        loc: stmtPath.node.loc ?? GeneratedSource,
+        node: stmtPath.node,
+      });
       return;
     }
-    case 'ClassDeclaration':
     case 'DeclareClass':
     case 'DeclareExportAllDeclaration':
     case 'DeclareExportDeclaration':
@@ -1365,31 +1462,14 @@ 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 'TSEnumDeclaration':
-    case 'TSExportAssignment':
-    case 'TSImportEqualsDeclaration':
+    case 'TSInterfaceDeclaration':
     case 'TSModuleDeclaration':
-    case 'TSNamespaceExportDeclaration':
-    case 'WithStatement': {
-      builder.errors.push({
-        reason: `(BuildHIR::lowerStatement) Handle ${stmtPath.type} statements`,
-        severity: ErrorSeverity.Todo,
-        loc: stmtPath.node.loc ?? null,
-        suggestions: null,
-      });
-      lowerValueToTemporary(builder, {
-        kind: 'UnsupportedNode',
-        loc: stmtPath.node.loc ?? GeneratedSource,
-        node: stmtPath.node,
-      });
+    case 'TSTypeAliasDeclaration':
+    case 'TypeAlias': {
+      // We do not preserve type annotations/syntax through transformation
       return;
     }
     default: {
@@ -1892,6 +1972,7 @@ function lowerExpression(
           place: leftValue,
           loc: exprLoc,
         },
+        effects: null,
         loc: exprLoc,
       });
       builder.terminateWithContinuation(
@@ -2208,11 +2289,17 @@ function lowerExpression(
         });
         for (const [name, locations] of Object.entries(fbtLocations)) {
           if (locations.length > 1) {
-            CompilerError.throwTodo({
-              reason: `Support <${tagName}> tags with multiple <${tagName}:${name}> values`,
-              loc: locations.at(-1) ?? GeneratedSource,
-              description: null,
-              suggestions: null,
+            CompilerError.throwDiagnostic({
+              severity: ErrorSeverity.Todo,
+              category: '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,
+                };
+              }),
             });
           }
         }
@@ -2827,6 +2914,7 @@ function lowerOptionalCallExpression(
           args,
           loc,
         },
+        effects: null,
         loc,
       });
     } else {
@@ -2840,6 +2928,7 @@ function lowerOptionalCallExpression(
           args,
           loc,
         },
+        effects: null,
         loc,
       });
     }
@@ -2936,6 +3025,8 @@ function isReorderableExpression(
         }
       }
     }
+    case 'TSAsExpression':
+    case 'TSNonNullExpression':
     case 'TypeCastExpression': {
       return isReorderableExpression(
         builder,
@@ -3417,7 +3508,7 @@ function lowerFunction(
     | t.ObjectMethod
   >,
 ): LoweredFunction | null {
-  const componentScope: Scope = builder.parentFunction.scope;
+  const componentScope: Scope = builder.environment.parentFunction.scope;
   const capturedContext = gatherCapturedContext(expr, componentScope);
 
   /*
@@ -3432,14 +3523,12 @@ function lowerFunction(
     expr,
     builder.environment,
     builder.bindings,
-    [...builder.context, ...capturedContext],
-    builder.parentFunction,
+    new Map([...builder.context, ...capturedContext]),
   );
   let loweredFunc: HIRFunction;
   if (lowering.isErr()) {
-    lowering
-      .unwrapErr()
-      .details.forEach(detail => builder.errors.pushErrorDetail(detail));
+    const functionErrors = lowering.unwrapErr();
+    builder.errors.merge(functionErrors);
     return null;
   }
   loweredFunc = lowering.unwrap();
@@ -3456,7 +3545,7 @@ function lowerExpressionToTemporary(
   return lowerValueToTemporary(builder, value);
 }
 
-function lowerValueToTemporary(
+export function lowerValueToTemporary(
   builder: HIRBuilder,
   value: InstructionValue,
 ): Place {
@@ -3466,9 +3555,10 @@ function lowerValueToTemporary(
   const place: Place = buildTemporaryPlace(builder, value.loc);
   builder.push({
     id: makeInstructionId(0),
-    value: value,
-    loc: value.loc,
     lvalue: {...place},
+    value: value,
+    effects: null,
+    loc: value.loc,
   });
   return place;
 }
@@ -3492,6 +3582,16 @@ 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,
+          loc: exprPath.node.loc ?? null,
+          suggestions: null,
+        });
+      }
       return lowerValueToTemporary(builder, {
         kind: 'LoadGlobal',
         binding,
@@ -4151,6 +4251,11 @@ 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
@@ -4159,8 +4264,8 @@ function gatherCapturedContext(
     | t.ObjectMethod
   >,
   componentScope: Scope,
-): Array<t.Identifier> {
-  const capturedIds = new Set<t.Identifier>();
+): Map<t.Identifier, SourceLocation> {
+  const capturedIds = new Map<t.Identifier, SourceLocation>();
 
   /*
    * Capture all the scopes from the parent of this function up to and including
@@ -4203,8 +4308,15 @@ 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.add(binding.identifier);
+    if (
+      binding !== undefined &&
+      pureScopes.has(binding.scope) &&
+      !capturedIds.has(binding.identifier)
+    ) {
+      capturedIds.set(
+        binding.identifier,
+        path.node.loc ?? binding.identifier.loc ?? GeneratedSource,
+      );
     }
   }
 
@@ -4241,7 +4353,7 @@ function gatherCapturedContext(
     },
   });
 
-  return [...capturedIds.keys()];
+  return capturedIds;
 }
 
 function notNull<T>(value: T | null): value is T {

compiler/packages/babel-plugin-react-compiler/src/HIR/CollectHoistablePropertyLoads.ts

@@ -241,7 +241,10 @@ type PropertyPathNode =
 class PropertyPathRegistry {
   roots: Map<IdentifierId, RootNode> = new Map();
 
-  getOrCreateIdentifier(identifier: Identifier): PropertyPathNode {
+  getOrCreateIdentifier(
+    identifier: Identifier,
+    reactive: boolean,
+  ): PropertyPathNode {
     /**
      * Reads from a statically scoped variable are always safe in JS,
      * with the exception of TDZ (not addressed by this pass).
@@ -255,12 +258,19 @@ class PropertyPathRegistry {
         optionalProperties: new Map(),
         fullPath: {
           identifier,
+          reactive,
           path: [],
         },
         hasOptional: false,
         parent: null,
       };
       this.roots.set(identifier.id, rootNode);
+    } else {
+      CompilerError.invariant(reactive === rootNode.fullPath.reactive, {
+        reason:
+          '[HoistablePropertyLoads] Found inconsistencies in `reactive` flag when deduping identifier reads within the same scope',
+        loc: identifier.loc,
+      });
     }
     return rootNode;
   }
@@ -278,6 +288,7 @@ class PropertyPathRegistry {
         parent: parent,
         fullPath: {
           identifier: parent.fullPath.identifier,
+          reactive: parent.fullPath.reactive,
           path: parent.fullPath.path.concat(entry),
         },
         hasOptional: parent.hasOptional || entry.optional,
@@ -293,7 +304,7 @@ class PropertyPathRegistry {
      * so all subpaths of a PropertyLoad should already exist
      * (e.g. a.b is added before a.b.c),
      */
-    let currNode = this.getOrCreateIdentifier(n.identifier);
+    let currNode = this.getOrCreateIdentifier(n.identifier, n.reactive);
     if (n.path.length === 0) {
       return currNode;
     }
@@ -315,10 +326,11 @@ function getMaybeNonNullInInstruction(
   instr: InstructionValue,
   context: CollectHoistablePropertyLoadsContext,
 ): PropertyPathNode | null {
-  let path = null;
+  let path: ReactiveScopeDependency | null = null;
   if (instr.kind === 'PropertyLoad') {
     path = context.temporaries.get(instr.object.identifier.id) ?? {
       identifier: instr.object.identifier,
+      reactive: instr.object.reactive,
       path: [],
     };
   } else if (instr.kind === 'Destructure') {
@@ -381,7 +393,7 @@ function collectNonNullsInBlocks(
   ) {
     const identifier = fn.params[0].identifier;
     knownNonNullIdentifiers.add(
-      context.registry.getOrCreateIdentifier(identifier),
+      context.registry.getOrCreateIdentifier(identifier, true),
     );
   }
   const nodes = new Map<
@@ -616,9 +628,11 @@ function reduceMaybeOptionalChains(
     changed = false;
 
     for (const original of optionalChainNodes) {
-      let {identifier, path: origPath} = original.fullPath;
-      let currNode: PropertyPathNode =
-        registry.getOrCreateIdentifier(identifier);
+      let {identifier, path: origPath, reactive} = original.fullPath;
+      let currNode: PropertyPathNode = registry.getOrCreateIdentifier(
+        identifier,
+        reactive,
+      );
       for (let i = 0; i < origPath.length; i++) {
         const entry = origPath[i];
         // If the base is known to be non-null, replace with a non-optional load

compiler/packages/babel-plugin-react-compiler/src/HIR/CollectOptionalChainDependencies.ts

@@ -290,6 +290,7 @@ function traverseOptionalBlock(
     );
     baseObject = {
       identifier: maybeTest.instructions[0].value.place.identifier,
+      reactive: maybeTest.instructions[0].value.place.reactive,
       path,
     };
     test = maybeTest.terminal;
@@ -391,6 +392,7 @@ function traverseOptionalBlock(
   );
   const load = {
     identifier: baseObject.identifier,
+    reactive: baseObject.reactive,
     path: [
       ...baseObject.path,
       {

compiler/packages/babel-plugin-react-compiler/src/HIR/DeriveMinimalDependenciesHIR.ts

@@ -25,8 +25,9 @@ export class ReactiveScopeDependencyTreeHIR {
    * `identifier.path`, or `identifier?.path` is in this map, it is safe to
    * evaluate (non-optional) PropertyLoads from.
    */
-  #hoistableObjects: Map<Identifier, HoistableNode> = new Map();
-  #deps: Map<Identifier, DependencyNode> = new Map();
+  #hoistableObjects: Map<Identifier, HoistableNode & {reactive: boolean}> =
+    new Map();
+  #deps: Map<Identifier, DependencyNode & {reactive: boolean}> = new Map();
 
   /**
    * @param hoistableObjects a set of paths from which we can safely evaluate
@@ -35,9 +36,10 @@ export class ReactiveScopeDependencyTreeHIR {
    * duplicates when traversing the CFG.
    */
   constructor(hoistableObjects: Iterable<ReactiveScopeDependency>) {
-    for (const {path, identifier} of hoistableObjects) {
+    for (const {path, identifier, reactive} of hoistableObjects) {
       let currNode = ReactiveScopeDependencyTreeHIR.#getOrCreateRoot(
         identifier,
+        reactive,
         this.#hoistableObjects,
         path.length > 0 && path[0].optional ? 'Optional' : 'NonNull',
       );
@@ -70,7 +72,8 @@ export class ReactiveScopeDependencyTreeHIR {
 
   static #getOrCreateRoot<T extends string>(
     identifier: Identifier,
-    roots: Map<Identifier, TreeNode<T>>,
+    reactive: boolean,
+    roots: Map<Identifier, TreeNode<T> & {reactive: boolean}>,
     defaultAccessType: T,
   ): TreeNode<T> {
     // roots can always be accessed unconditionally in JS
@@ -79,9 +82,16 @@ export class ReactiveScopeDependencyTreeHIR {
     if (rootNode === undefined) {
       rootNode = {
         properties: new Map(),
+        reactive,
         accessType: defaultAccessType,
       };
       roots.set(identifier, rootNode);
+    } else {
+      CompilerError.invariant(reactive === rootNode.reactive, {
+        reason: '[DeriveMinimalDependenciesHIR] Conflicting reactive root flag',
+        description: `Identifier ${printIdentifier(identifier)}`,
+        loc: GeneratedSource,
+      });
     }
     return rootNode;
   }
@@ -92,9 +102,10 @@ export class ReactiveScopeDependencyTreeHIR {
    * safe-to-evaluate subpath
    */
   addDependency(dep: ReactiveScopeDependency): void {
-    const {identifier, path} = dep;
+    const {identifier, reactive, path} = dep;
     let depCursor = ReactiveScopeDependencyTreeHIR.#getOrCreateRoot(
       identifier,
+      reactive,
       this.#deps,
       PropertyAccessType.UnconditionalAccess,
     );
@@ -172,7 +183,13 @@ export class ReactiveScopeDependencyTreeHIR {
   deriveMinimalDependencies(): Set<ReactiveScopeDependency> {
     const results = new Set<ReactiveScopeDependency>();
     for (const [rootId, rootNode] of this.#deps.entries()) {
-      collectMinimalDependenciesInSubtree(rootNode, rootId, [], results);
+      collectMinimalDependenciesInSubtree(
+        rootNode,
+        rootNode.reactive,
+        rootId,
+        [],
+        results,
+      );
     }
 
     return results;
@@ -294,25 +311,24 @@ type HoistableNode = TreeNode<'Optional' | 'NonNull'>;
 type DependencyNode = TreeNode<PropertyAccessType>;
 
 /**
- * TODO: this is directly pasted from DeriveMinimalDependencies. Since we no
- * longer have conditionally accessed nodes, we can simplify
- *
  * Recursively calculates minimal dependencies in a subtree.
  * @param node DependencyNode representing a dependency subtree.
  * @returns a minimal list of dependencies in this subtree.
  */
 function collectMinimalDependenciesInSubtree(
   node: DependencyNode,
+  reactive: boolean,
   rootIdentifier: Identifier,
   path: Array<DependencyPathEntry>,
   results: Set<ReactiveScopeDependency>,
 ): void {
   if (isDependency(node.accessType)) {
-    results.add({identifier: rootIdentifier, path});
+    results.add({identifier: rootIdentifier, reactive, path});
   } else {
     for (const [childName, childNode] of node.properties) {
       collectMinimalDependenciesInSubtree(
         childNode,
+        reactive,
         rootIdentifier,
         [
           ...path,

compiler/packages/babel-plugin-react-compiler/src/HIR/Environment.ts

@@ -47,7 +47,7 @@ import {
   ShapeRegistry,
   addHook,
 } from './ObjectShape';
-import {Scope as BabelScope} from '@babel/traverse';
+import {Scope as BabelScope, NodePath} from '@babel/traverse';
 import {TypeSchema} from './TypeSchema';
 
 export const ReactElementSymbolSchema = z.object({
@@ -243,6 +243,11 @@ export const EnvironmentConfigSchema = z.object({
    */
   enableUseTypeAnnotations: z.boolean().default(false),
 
+  /**
+   * Enable a new model for mutability and aliasing inference
+   */
+  enableNewMutationAliasingModel: z.boolean().default(true),
+
   /**
    * Enables inference of optional dependency chains. Without this flag
    * a property chain such as `props?.items?.foo` will infer as a dep on
@@ -260,21 +265,19 @@ export const EnvironmentConfigSchema = z.object({
    *   {
    *     module: 'react',
    *     imported: 'useEffect',
-   *     numRequiredArgs: 1,
+   *     autodepsIndex: 1,
    *   },{
    *     module: 'MyExperimentalEffectHooks',
    *     imported: 'useExperimentalEffect',
-   *     numRequiredArgs: 2,
+   *     autodepsIndex: 2,
    *   },
    * ]
    * would insert dependencies for calls of `useEffect` imported from `react` and calls of
    * useExperimentalEffect` from `MyExperimentalEffectHooks`.
    *
-   * `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
+   * `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.
    *
    * Still experimental.
    */
@@ -283,7 +286,7 @@ export const EnvironmentConfigSchema = z.object({
       z.array(
         z.object({
           function: ExternalFunctionSchema,
-          numRequiredArgs: z.number().min(1, 'numRequiredArgs must be > 0'),
+          autodepsIndex: z.number().min(1, 'autodepsIndex must be > 0'),
         }),
       ),
     )
@@ -315,10 +318,10 @@ export const EnvironmentConfigSchema = z.object({
   validateNoSetStateInRender: z.boolean().default(true),
 
   /**
-   * Validates that setState is not called directly within a passive effect (useEffect).
+   * Validates that setState is not called synchronously within an effect (useEffect and friends).
    * Scheduling a setState (with an event listener, subscription, etc) is valid.
    */
-  validateNoSetStateInPassiveEffects: z.boolean().default(false),
+  validateNoSetStateInEffects: z.boolean().default(false),
 
   /**
    * Validates against creating JSX within a try block and recommends using an error boundary
@@ -628,6 +631,17 @@ 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),
 });
 
 export type EnvironmentConfig = z.infer<typeof EnvironmentConfigSchema>;
@@ -675,6 +689,7 @@ export class Environment {
 
   #contextIdentifiers: Set<t.Identifier>;
   #hoistedIdentifiers: Set<t.Identifier>;
+  parentFunction: NodePath<t.Function>;
 
   constructor(
     scope: BabelScope,
@@ -682,6 +697,7 @@ export class Environment {
     compilerMode: CompilerMode,
     config: EnvironmentConfig,
     contextIdentifiers: Set<t.Identifier>,
+    parentFunction: NodePath<t.Function>, // the outermost function being compiled
     logger: Logger | null,
     filename: string | null,
     code: string | null,
@@ -740,6 +756,7 @@ export class Environment {
       this.#moduleTypes.set(REANIMATED_MODULE_NAME, reanimatedModuleType);
     }
 
+    this.parentFunction = parentFunction;
     this.#contextIdentifiers = contextIdentifiers;
     this.#hoistedIdentifiers = new Set();
   }

compiler/packages/babel-plugin-react-compiler/src/HIR/Globals.ts

@@ -9,6 +9,7 @@ import {Effect, ValueKind, ValueReason} from './HIR';
 import {
   BUILTIN_SHAPES,
   BuiltInArrayId,
+  BuiltInAutodepsId,
   BuiltInFireFunctionId,
   BuiltInFireId,
   BuiltInMapId,
@@ -17,6 +18,7 @@ import {
   BuiltInSetId,
   BuiltInUseActionStateId,
   BuiltInUseContextHookId,
+  BuiltInUseEffectEventId,
   BuiltInUseEffectHookId,
   BuiltInUseInsertionEffectHookId,
   BuiltInUseLayoutEffectHookId,
@@ -27,6 +29,7 @@ import {
   BuiltInUseTransitionId,
   BuiltInWeakMapId,
   BuiltInWeakSetId,
+  BuiltinEffectEventId,
   ReanimatedSharedValueId,
   ShapeRegistry,
   addFunction,
@@ -642,6 +645,41 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
         calleeEffect: Effect.Read,
         hookKind: 'useEffect',
         returnValueKind: ValueKind.Frozen,
+        aliasing: {
+          receiver: '@receiver',
+          params: [],
+          rest: '@rest',
+          returns: '@returns',
+          temporaries: ['@effect'],
+          effects: [
+            // Freezes the function and deps
+            {
+              kind: 'Freeze',
+              value: '@rest',
+              reason: ValueReason.Effect,
+            },
+            // Internally creates an effect object that captures the function and deps
+            {
+              kind: 'Create',
+              into: '@effect',
+              value: ValueKind.Frozen,
+              reason: ValueReason.KnownReturnSignature,
+            },
+            // The effect stores the function and dependencies
+            {
+              kind: 'Capture',
+              from: '@rest',
+              into: '@effect',
+            },
+            // Returns undefined
+            {
+              kind: 'Create',
+              into: '@returns',
+              value: ValueKind.Primitive,
+              reason: ValueReason.KnownReturnSignature,
+            },
+          ],
+        },
       },
       BuiltInUseEffectHookId,
     ),
@@ -722,6 +760,28 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
       BuiltInFireId,
     ),
   ],
+  [
+    'useEffectEvent',
+    addHook(
+      DEFAULT_SHAPES,
+      {
+        positionalParams: [],
+        restParam: Effect.Freeze,
+        returnType: {
+          kind: 'Function',
+          return: {kind: 'Poly'},
+          shapeId: BuiltinEffectEventId,
+          isConstructor: false,
+        },
+        calleeEffect: Effect.Read,
+        hookKind: 'useEffectEvent',
+        // Frozen because it should not mutate any locally-bound values
+        returnValueKind: ValueKind.Frozen,
+      },
+      BuiltInUseEffectEventId,
+    ),
+  ],
+  ['AUTODEPS', addObject(DEFAULT_SHAPES, BuiltInAutodepsId, [])],
 ];
 
 TYPED_GLOBALS.push(
@@ -847,6 +907,7 @@ export function installTypeConfig(
         noAlias: typeConfig.noAlias === true,
         mutableOnlyIfOperandsAreMutable:
           typeConfig.mutableOnlyIfOperandsAreMutable === true,
+        aliasing: typeConfig.aliasing,
       });
     }
     case 'hook': {
@@ -864,6 +925,7 @@ export function installTypeConfig(
         ),
         returnValueKind: typeConfig.returnValueKind ?? ValueKind.Frozen,
         noAlias: typeConfig.noAlias === true,
+        aliasing: typeConfig.aliasing,
       });
     }
     case 'object': {

compiler/packages/babel-plugin-react-compiler/src/HIR/HIR.ts

@@ -13,6 +13,7 @@ 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';
 
 /*
  * *******************************************************************************************
@@ -100,6 +101,7 @@ export type ReactiveInstruction = {
   id: InstructionId;
   lvalue: Place | null;
   value: ReactiveValue;
+  effects?: Array<AliasingEffect> | null; // TODO make non-optional
   loc: SourceLocation;
 };
 
@@ -277,13 +279,14 @@ 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;
 };
 
 export type FunctionEffect =
@@ -443,12 +446,25 @@ 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;
   fallthrough?: never;
+  effects: Array<AliasingEffect> | null;
 };
 
 export type GotoTerminal = {
@@ -609,6 +625,7 @@ export type MaybeThrowTerminal = {
   id: InstructionId;
   loc: SourceLocation;
   fallthrough?: never;
+  effects: Array<AliasingEffect> | null;
 };
 
 export type ReactiveScopeTerminal = {
@@ -645,12 +662,14 @@ export type Instruction = {
   lvalue: Place;
   value: InstructionValue;
   loc: SourceLocation;
+  effects: Array<AliasingEffect> | null;
 };
 
 export type TInstruction<T extends InstructionValue> = {
   id: InstructionId;
   lvalue: Place;
   value: T;
+  effects: Array<AliasingEffect> | null;
   loc: SourceLocation;
 };
 
@@ -1380,6 +1399,21 @@ 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
+   */
+  Effect = 'effect',
+
   /**
    * Return value of a function with known frozen return value, e.g. `useState`.
    */
@@ -1430,6 +1464,20 @@ 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
@@ -1568,6 +1616,18 @@ export type DependencyPathEntry = {
 export type DependencyPath = Array<DependencyPathEntry>;
 export type ReactiveScopeDependency = {
   identifier: Identifier;
+  /**
+   * Reflects whether the base identifier is reactive. Note that some reactive
+   * objects may have non-reactive properties, but we do not currently track
+   * this.
+   *
+   * ```js
+   * // Technically, result[0] is reactive and result[1] is not.
+   * // Currently, both dependencies would be marked as reactive.
+   * const result = useState();
+   * ```
+   */
+  reactive: boolean;
   path: DependencyPath;
 };
 
@@ -1721,6 +1781,10 @@ 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);
 }
@@ -1773,6 +1837,13 @@ export function isFireFunctionType(id: Identifier): boolean {
   );
 }
 
+export function isEffectEventFunctionType(id: Identifier): boolean {
+  return (
+    id.type.kind === 'Function' &&
+    id.type.shapeId === 'BuiltInEffectEventFunction'
+  );
+}
+
 export function isStableType(id: Identifier): boolean {
   return (
     isSetStateType(id) ||

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} from '../CompilerError';
+import {CompilerError, ErrorSeverity} from '../CompilerError';
 import {Environment} from './Environment';
 import {
   BasicBlock,
@@ -106,11 +106,10 @@ export default class HIRBuilder {
   #current: WipBlock;
   #entry: BlockId;
   #scopes: Array<Scope> = [];
-  #context: Array<t.Identifier>;
+  #context: Map<t.Identifier, SourceLocation>;
   #bindings: Bindings;
   #env: Environment;
   #exceptionHandlerStack: Array<BlockId> = [];
-  parentFunction: NodePath<t.Function>;
   errors: CompilerError = new CompilerError();
   /**
    * Traversal context: counts the number of `fbt` tag parents
@@ -122,7 +121,7 @@ export default class HIRBuilder {
     return this.#env.nextIdentifierId;
   }
 
-  get context(): Array<t.Identifier> {
+  get context(): Map<t.Identifier, SourceLocation> {
     return this.#context;
   }
 
@@ -136,16 +135,17 @@ export default class HIRBuilder {
 
   constructor(
     env: Environment,
-    parentFunction: NodePath<t.Function>, // the outermost function being compiled
-    bindings: Bindings | null = null,
-    context: Array<t.Identifier> | null = null,
+    options?: {
+      bindings?: Bindings | null;
+      context?: Map<t.Identifier, SourceLocation>;
+      entryBlockKind?: BlockKind;
+    },
   ) {
     this.#env = env;
-    this.#bindings = bindings ?? new Map();
-    this.parentFunction = parentFunction;
-    this.#context = context ?? [];
+    this.#bindings = options?.bindings ?? new Map();
+    this.#context = options?.context ?? new Map();
     this.#entry = makeBlockId(env.nextBlockId);
-    this.#current = newBlock(this.#entry, 'block');
+    this.#current = newBlock(this.#entry, options?.entryBlockKind ?? 'block');
   }
 
   currentBlockKind(): BlockKind {
@@ -165,6 +165,7 @@ export default class HIRBuilder {
           handler: exceptionHandler,
           id: makeInstructionId(0),
           loc: instruction.loc,
+          effects: null,
         },
         continuationBlock,
       );
@@ -239,7 +240,7 @@ export default class HIRBuilder {
 
     // Check if the binding is from module scope
     const outerBinding =
-      this.parentFunction.scope.parent.getBinding(originalName);
+      this.#env.parentFunction.scope.parent.getBinding(originalName);
     if (babelBinding === outerBinding) {
       const path = babelBinding.path;
       if (path.isImportDefaultSpecifier()) {
@@ -293,7 +294,7 @@ export default class HIRBuilder {
     const binding = this.#resolveBabelBinding(path);
     if (binding) {
       // Check if the binding is from module scope, if so return null
-      const outerBinding = this.parentFunction.scope.parent.getBinding(
+      const outerBinding = this.#env.parentFunction.scope.parent.getBinding(
         path.node.name,
       );
       if (binding === outerBinding) {
@@ -307,9 +308,18 @@ export default class HIRBuilder {
 
   resolveBinding(node: t.Identifier): Identifier {
     if (node.name === 'fbt') {
-      CompilerError.throwTodo({
-        reason: 'Support local variables named "fbt"',
-        loc: node.loc ?? null,
+      CompilerError.throwDiagnostic({
+        severity: ErrorSeverity.Todo,
+        category: '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,
+          },
+        ],
       });
     }
     const originalName = node.name;
@@ -376,7 +386,7 @@ export default class HIRBuilder {
   }
 
   // Terminate the current block w the given terminal, and start a new block
-  terminate(terminal: Terminal, nextBlockKind: BlockKind | null): void {
+  terminate(terminal: Terminal, nextBlockKind: BlockKind | null): BlockId {
     const {id: blockId, kind, instructions} = this.#current;
     this.#completed.set(blockId, {
       kind,
@@ -390,6 +400,7 @@ export default class HIRBuilder {
       const nextId = this.#env.nextBlockId;
       this.#current = newBlock(nextId, nextBlockKind);
     }
+    return blockId;
   }
 
   /*
@@ -746,6 +757,11 @@ function getReversePostorderedBlocks(func: HIR): HIR['blocks'] {
      * (eg bb2 then bb1), we ensure that they get reversed back to the correct order.
      */
     const block = func.blocks.get(blockId)!;
+    CompilerError.invariant(block != null, {
+      reason: '[HIRBuilder] Unexpected null block',
+      description: `expected block ${blockId} to exist`,
+      loc: GeneratedSource,
+    });
     const successors = [...eachTerminalSuccessor(block.terminal)].reverse();
     const fallthrough = terminalFallthrough(block.terminal);
 

compiler/packages/babel-plugin-react-compiler/src/HIR/MergeConsecutiveBlocks.ts

@@ -12,6 +12,7 @@ import {
   GeneratedSource,
   HIRFunction,
   Instruction,
+  Place,
 } from './HIR';
 import {markPredecessors} from './HIRBuilder';
 import {terminalFallthrough, terminalHasFallthrough} from './visitors';
@@ -80,20 +81,22 @@ export function mergeConsecutiveBlocks(fn: HIRFunction): void {
         suggestions: null,
       });
       const operand = Array.from(phi.operands.values())[0]!;
+      const lvalue: Place = {
+        kind: 'Identifier',
+        identifier: phi.place.identifier,
+        effect: Effect.ConditionallyMutate,
+        reactive: false,
+        loc: GeneratedSource,
+      };
       const instr: Instruction = {
         id: predecessor.terminal.id,
-        lvalue: {
-          kind: 'Identifier',
-          identifier: phi.place.identifier,
-          effect: Effect.ConditionallyMutate,
-          reactive: false,
-          loc: GeneratedSource,
-        },
+        lvalue: {...lvalue},
         value: {
           kind: 'LoadLocal',
           place: {...operand},
           loc: GeneratedSource,
         },
+        effects: [{kind: 'Alias', from: {...operand}, into: {...lvalue}}],
         loc: GeneratedSource,
       };
       predecessor.instructions.push(instr);
@@ -104,6 +107,17 @@ 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)) {

compiler/packages/babel-plugin-react-compiler/src/HIR/ObjectShape.ts

@@ -6,14 +6,30 @@
  */
 
 import {CompilerError} from '../CompilerError';
-import {Effect, ValueKind, ValueReason} from './HIR';
+import {AliasingEffect, AliasingSignature} from '../Inference/AliasingEffects';
+import {assertExhaustive} from '../Utils/utils';
+import {
+  Effect,
+  GeneratedSource,
+  Hole,
+  makeDeclarationId,
+  makeIdentifierId,
+  makeInstructionId,
+  Place,
+  SourceLocation,
+  SpreadPattern,
+  ValueKind,
+  ValueReason,
+} from './HIR';
 import {
   BuiltInType,
   FunctionType,
+  makeType,
   ObjectType,
   PolyType,
   PrimitiveType,
 } from './Types';
+import {AliasingEffectConfig, AliasingSignatureConfig} from './TypeSchema';
 
 /*
  * This file exports types and defaults for JavaScript object shapes. These are
@@ -42,13 +58,20 @@ function createAnonId(): string {
 export function addFunction(
   registry: ShapeRegistry,
   properties: Iterable<[string, BuiltInType | PolyType]>,
-  fn: Omit<FunctionSignature, 'hookKind'>,
+  fn: Omit<FunctionSignature, 'hookKind' | 'aliasing'> & {
+    aliasing?: AliasingSignatureConfig | null | undefined;
+  },
   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 {
@@ -66,11 +89,18 @@ export function addFunction(
  */
 export function addHook(
   registry: ShapeRegistry,
-  fn: FunctionSignature & {hookKind: HookKind},
+  fn: Omit<FunctionSignature, 'aliasing'> & {
+    hookKind: HookKind;
+    aliasing?: AliasingSignatureConfig | null | undefined;
+  },
   id: string | null = null,
 ): FunctionType {
   const shapeId = id ?? createAnonId();
-  addShape(registry, shapeId, [], fn);
+  const aliasing =
+    fn.aliasing != null
+      ? parseAliasingSignatureConfig(fn.aliasing, '<builtin>', GeneratedSource)
+      : null;
+  addShape(registry, shapeId, [], {...fn, aliasing});
   return {
     kind: 'Function',
     return: fn.returnType,
@@ -79,6 +109,129 @@ 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 '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.
  *
@@ -131,6 +284,7 @@ export type HookKind =
   | 'useCallback'
   | 'useTransition'
   | 'useImperativeHandle'
+  | 'useEffectEvent'
   | 'Custom';
 
 /*
@@ -179,6 +333,8 @@ export type FunctionSignature = {
   impure?: boolean;
 
   canonicalName?: string;
+
+  aliasing?: AliasingSignature | null | undefined;
 };
 
 /*
@@ -226,6 +382,9 @@ export const BuiltInUseTransitionId = 'BuiltInUseTransition';
 export const BuiltInStartTransitionId = 'BuiltInStartTransition';
 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';
@@ -302,6 +461,30 @@ addObject(BUILTIN_SHAPES, BuiltInArrayId, [
       returnType: PRIMITIVE_TYPE,
       calleeEffect: Effect.Store,
       returnValueKind: ValueKind.Primitive,
+      aliasing: {
+        receiver: '@receiver',
+        params: [],
+        rest: '@rest',
+        returns: '@returns',
+        temporaries: [],
+        effects: [
+          // Push directly mutates the array itself
+          {kind: 'Mutate', value: '@receiver'},
+          // The arguments are captured into the array
+          {
+            kind: 'Capture',
+            from: '@rest',
+            into: '@receiver',
+          },
+          // Returns the new length, a primitive
+          {
+            kind: 'Create',
+            into: '@returns',
+            value: ValueKind.Primitive,
+            reason: ValueReason.KnownReturnSignature,
+          },
+        ],
+      },
     }),
   ],
   [
@@ -332,6 +515,60 @@ addObject(BUILTIN_SHAPES, BuiltInArrayId, [
       returnValueKind: ValueKind.Mutable,
       noAlias: true,
       mutableOnlyIfOperandsAreMutable: true,
+      aliasing: {
+        receiver: '@receiver',
+        params: ['@callback'],
+        rest: null,
+        returns: '@returns',
+        temporaries: [
+          // Temporary representing captured items of the receiver
+          '@item',
+          // Temporary representing the result of the callback
+          '@callbackReturn',
+          /*
+           * Undefined `this` arg to the callback. Note the signature does not
+           * support passing an explicit thisArg second param
+           */
+          '@thisArg',
+        ],
+        effects: [
+          // Map creates a new mutable array
+          {
+            kind: 'Create',
+            into: '@returns',
+            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',
+          },
+          // The undefined this for the callback
+          {
+            kind: 'Create',
+            into: '@thisArg',
+            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',
+            mutatesFunction: false,
+          },
+          // captures the result of the callback into the return array
+          {
+            kind: 'Capture',
+            from: '@callbackReturn',
+            into: '@returns',
+          },
+        ],
+      },
     }),
   ],
   [
@@ -479,6 +716,32 @@ addObject(BUILTIN_SHAPES, BuiltInSetId, [
       calleeEffect: Effect.Store,
       // returnValueKind is technically dependent on the ValueKind of the set itself
       returnValueKind: ValueKind.Mutable,
+      aliasing: {
+        receiver: '@receiver',
+        params: [],
+        rest: '@rest',
+        returns: '@returns',
+        temporaries: [],
+        effects: [
+          // Set.add returns the receiver Set
+          {
+            kind: 'Assign',
+            from: '@receiver',
+            into: '@returns',
+          },
+          // Set.add mutates the set itself
+          {
+            kind: 'Mutate',
+            value: '@receiver',
+          },
+          // Captures the rest params into the set
+          {
+            kind: 'Capture',
+            from: '@rest',
+            into: '@receiver',
+          },
+        ],
+      },
     }),
   ],
   [
@@ -948,6 +1211,21 @@ addObject(BUILTIN_SHAPES, BuiltInRefValueId, [
   ['*', {kind: 'Object', shapeId: BuiltInRefValueId}],
 ]);
 
+addObject(BUILTIN_SHAPES, ReanimatedSharedValueId, []);
+
+addFunction(
+  BUILTIN_SHAPES,
+  [],
+  {
+    positionalParams: [],
+    restParam: Effect.ConditionallyMutate,
+    returnType: {kind: 'Poly'},
+    calleeEffect: Effect.ConditionallyMutate,
+    returnValueKind: ValueKind.Mutable,
+  },
+  BuiltinEffectEventId,
+);
+
 /**
  * MixedReadOnly =
  *   | primitive
@@ -1166,6 +1444,53 @@ 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',
 );
+
+export function signatureArgument(id: number): Place {
+  const place: Place = {
+    kind: 'Identifier',
+    effect: Effect.Unknown,
+    loc: GeneratedSource,
+    reactive: false,
+    identifier: {
+      declarationId: makeDeclarationId(id),
+      id: makeIdentifierId(id),
+      loc: GeneratedSource,
+      mutableRange: {start: makeInstructionId(0), end: makeInstructionId(0)},
+      name: null,
+      scope: null,
+      type: makeType(),
+    },
+  };
+  return place;
+}

compiler/packages/babel-plugin-react-compiler/src/HIR/PrintHIR.ts

@@ -5,7 +5,6 @@
  * 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';
@@ -35,6 +34,7 @@ import type {
   Type,
 } from './HIR';
 import {GotoVariant, InstructionKind} from './HIR';
+import {AliasingEffect, AliasingSignature} from '../Inference/AliasingEffects';
 
 export type Options = {
   indent: number;
@@ -53,6 +53,8 @@ export function printFunction(fn: HIRFunction): string {
   let definition = '';
   if (fn.id !== null) {
     definition += fn.id;
+  } else {
+    definition += '<<anonymous>>';
   }
   if (fn.params.length !== 0) {
     definition +=
@@ -67,13 +69,13 @@ export function printFunction(fn: HIRFunction): string {
         })
         .join(', ') +
       ')';
+  } else {
+    definition += '()';
   }
-  if (definition.length !== 0) {
-    output.push(definition);
-  }
-  output.push(printType(fn.returnType));
-  output.push(printHIR(fn.body));
+  definition += `: ${printPlace(fn.returns)}`;
+  output.push(definition);
   output.push(...fn.directives);
+  output.push(printHIR(fn.body));
   return output.join('\n');
 }
 
@@ -151,7 +153,10 @@ export function printMixedHIR(
 
 export function printInstruction(instr: ReactiveInstruction): string {
   const id = `[${instr.id}]`;
-  const value = printInstructionValue(instr.value);
+  let value = printInstructionValue(instr.value);
+  if (instr.effects != null) {
+    value += `\n    ${instr.effects.map(printAliasingEffect).join('\n    ')}`;
+  }
 
   if (instr.lvalue !== null) {
     return `${id} ${printPlace(instr.lvalue)} = ${value}`;
@@ -210,9 +215,12 @@ export function printTerminal(terminal: Terminal): Array<string> | string {
       break;
     }
     case 'return': {
-      value = `[${terminal.id}] Return${
+      value = `[${terminal.id}] Return ${terminal.returnVariant}${
         terminal.value != null ? ' ' + printPlace(terminal.value) : ''
       }`;
+      if (terminal.effects != null) {
+        value += `\n    ${terminal.effects.map(printAliasingEffect).join('\n    ')}`;
+      }
       break;
     }
     case 'goto': {
@@ -281,6 +289,9 @@ export function printTerminal(terminal: Terminal): Array<string> | string {
     }
     case 'maybe-throw': {
       value = `[${terminal.id}] MaybeThrow continuation=bb${terminal.continuation} handler=bb${terminal.handler}`;
+      if (terminal.effects != null) {
+        value += `\n    ${terminal.effects.map(printAliasingEffect).join('\n    ')}`;
+      }
       break;
     }
     case 'scope': {
@@ -454,7 +465,7 @@ export function printInstructionValue(instrValue: ReactiveValue): string {
       break;
     }
     case 'UnsupportedNode': {
-      value = `UnsupportedNode(${generate(instrValue.node).code})`;
+      value = `UnsupportedNode ${instrValue.node.type}`;
       break;
     }
     case 'LoadLocal': {
@@ -555,8 +566,11 @@ export function printInstructionValue(instrValue: ReactiveValue): string {
             }
           })
           .join(', ') ?? '';
-      const type = printType(instrValue.loweredFunc.func.returnType).trim();
-      value = `${kind} ${name} @context[${context}] @effects[${effects}]${type !== '' ? ` return${type}` : ''}:\n${fn}`;
+      const aliasingEffects =
+        instrValue.loweredFunc.func.aliasingEffects
+          ?.map(printAliasingEffect)
+          ?.join(', ') ?? '';
+      value = `${kind} ${name} @context[${context}] @effects[${effects}] @aliasingEffects=[${aliasingEffects}]\n${fn}`;
       break;
     }
     case 'TaggedTemplateExpression': {
@@ -700,7 +714,7 @@ export function printInstructionValue(instrValue: ReactiveValue): string {
       break;
     }
     case 'FinishMemoize': {
-      value = `FinishMemoize decl=${printPlace(instrValue.decl)}`;
+      value = `FinishMemoize decl=${printPlace(instrValue.decl)}${instrValue.pruned ? ' pruned' : ''}`;
       break;
     }
     default: {
@@ -922,3 +936,110 @@ function getFunctionName(
       return defaultValue;
   }
 }
+
+export function printAliasingEffect(effect: AliasingEffect): string {
+  switch (effect.kind) {
+    case 'Assign': {
+      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)}`;
+    }
+    case 'Capture': {
+      return `Capture ${printPlaceForAliasEffect(effect.into)} <- ${printPlaceForAliasEffect(effect.from)}`;
+    }
+    case 'ImmutableCapture': {
+      return `ImmutableCapture ${printPlaceForAliasEffect(effect.into)} <- ${printPlaceForAliasEffect(effect.from)}`;
+    }
+    case 'Create': {
+      return `Create ${printPlaceForAliasEffect(effect.into)} = ${effect.value}`;
+    }
+    case 'CreateFrom': {
+      return `Create ${printPlaceForAliasEffect(effect.into)} = kindOf(${printPlaceForAliasEffect(effect.from)})`;
+    }
+    case 'CreateFunction': {
+      return `Function ${printPlaceForAliasEffect(effect.into)} = Function captures=[${effect.captures.map(printPlaceForAliasEffect).join(', ')}]`;
+    }
+    case 'Apply': {
+      const receiverCallee =
+        effect.receiver.identifier.id === effect.function.identifier.id
+          ? printPlaceForAliasEffect(effect.receiver)
+          : `${printPlaceForAliasEffect(effect.receiver)}.${printPlaceForAliasEffect(effect.function)}`;
+      const args = effect.args
+        .map(arg => {
+          if (arg.kind === 'Identifier') {
+            return printPlaceForAliasEffect(arg);
+          } else if (arg.kind === 'Hole') {
+            return ' ';
+          }
+          return `...${printPlaceForAliasEffect(arg.place)}`;
+        })
+        .join(', ');
+      let signature = '';
+      if (effect.signature != null) {
+        if (effect.signature.aliasing != null) {
+          signature = printAliasingSignature(effect.signature.aliasing);
+        } else {
+          signature = JSON.stringify(effect.signature, null, 2);
+        }
+      }
+      return `Apply ${printPlaceForAliasEffect(effect.into)} = ${receiverCallee}(${args})${signature != '' ? '\n     ' : ''}${signature}`;
+    }
+    case 'Freeze': {
+      return `Freeze ${printPlaceForAliasEffect(effect.value)} ${effect.reason}`;
+    }
+    case 'Mutate':
+    case 'MutateConditionally':
+    case 'MutateTransitive':
+    case 'MutateTransitiveConditionally': {
+      return `${effect.kind} ${printPlaceForAliasEffect(effect.value)}`;
+    }
+    case 'MutateFrozen': {
+      return `MutateFrozen ${printPlaceForAliasEffect(effect.place)} reason=${JSON.stringify(effect.error.category)}`;
+    }
+    case 'MutateGlobal': {
+      return `MutateGlobal ${printPlaceForAliasEffect(effect.place)} reason=${JSON.stringify(effect.error.category)}`;
+    }
+    case 'Impure': {
+      return `Impure ${printPlaceForAliasEffect(effect.place)} reason=${JSON.stringify(effect.error.category)}`;
+    }
+    case 'Render': {
+      return `Render ${printPlaceForAliasEffect(effect.place)}`;
+    }
+    default: {
+      assertExhaustive(effect, `Unexpected kind '${(effect as any).kind}'`);
+    }
+  }
+}
+
+function printPlaceForAliasEffect(place: Place): string {
+  return printIdentifier(place.identifier);
+}
+
+export function printAliasingSignature(signature: AliasingSignature): string {
+  const tokens: Array<string> = ['function '];
+  if (signature.temporaries.length !== 0) {
+    tokens.push('<');
+    tokens.push(
+      signature.temporaries.map(temp => `$${temp.identifier.id}`).join(', '),
+    );
+    tokens.push('>');
+  }
+  tokens.push('(');
+  tokens.push('this=$' + String(signature.receiver));
+  for (const param of signature.params) {
+    tokens.push(', $' + String(param));
+  }
+  if (signature.rest != null) {
+    tokens.push(`, ...$${String(signature.rest)}`);
+  }
+  tokens.push('): ');
+  tokens.push('$' + String(signature.returns) + ':');
+  for (const effect of signature.effects) {
+    tokens.push('\n  ' + printAliasingEffect(effect));
+  }
+  return tokens.join('');
+}

compiler/packages/babel-plugin-react-compiler/src/HIR/PropagateScopeDependenciesHIR.ts

@@ -316,6 +316,7 @@ function collectTemporariesSidemapImpl(
         ) {
           temporaries.set(lvalue.identifier.id, {
             identifier: value.place.identifier,
+            reactive: value.place.reactive,
             path: [],
           });
         }
@@ -369,11 +370,13 @@ function getProperty(
   if (resolvedDependency == null) {
     property = {
       identifier: object.identifier,
+      reactive: object.reactive,
       path: [{property: propertyName, optional}],
     };
   } else {
     property = {
       identifier: resolvedDependency.identifier,
+      reactive: resolvedDependency.reactive,
       path: [...resolvedDependency.path, {property: propertyName, optional}],
     };
   }
@@ -532,6 +535,7 @@ export class DependencyCollectionContext {
     this.visitDependency(
       this.#temporaries.get(place.identifier.id) ?? {
         identifier: place.identifier,
+        reactive: place.reactive,
         path: [],
       },
     );
@@ -596,6 +600,7 @@ export class DependencyCollectionContext {
     ) {
       maybeDependency = {
         identifier: maybeDependency.identifier,
+        reactive: maybeDependency.reactive,
         path: [],
       };
     }
@@ -617,7 +622,11 @@ export class DependencyCollectionContext {
         identifier =>
           identifier.declarationId === place.identifier.declarationId,
       ) &&
-      this.#checkValidDependency({identifier: place.identifier, path: []})
+      this.#checkValidDependency({
+        identifier: place.identifier,
+        reactive: place.reactive,
+        path: [],
+      })
     ) {
       currentScope.reassignments.add(place.identifier);
     }

compiler/packages/babel-plugin-react-compiler/src/HIR/ScopeDependencyUtils.ts

@@ -0,0 +1,285 @@
+import {
+  Place,
+  ReactiveScopeDependency,
+  Identifier,
+  makeInstructionId,
+  InstructionKind,
+  GeneratedSource,
+  BlockId,
+  makeTemporaryIdentifier,
+  Effect,
+  GotoVariant,
+  HIR,
+} from './HIR';
+import {CompilerError} from '../CompilerError';
+import {Environment} from './Environment';
+import HIRBuilder from './HIRBuilder';
+import {lowerValueToTemporary} from './BuildHIR';
+
+type DependencyInstructions = {
+  place: Place;
+  value: HIR;
+  exitBlockId: BlockId;
+};
+
+export function buildDependencyInstructions(
+  dep: ReactiveScopeDependency,
+  env: Environment,
+): DependencyInstructions {
+  const builder = new HIRBuilder(env, {
+    entryBlockKind: 'value',
+  });
+  let dependencyValue: Identifier;
+  if (dep.path.every(path => !path.optional)) {
+    dependencyValue = writeNonOptionalDependency(dep, env, builder);
+  } else {
+    dependencyValue = writeOptionalDependency(dep, builder, null);
+  }
+
+  const exitBlockId = builder.terminate(
+    {
+      kind: 'unsupported',
+      loc: GeneratedSource,
+      id: makeInstructionId(0),
+    },
+    null,
+  );
+  return {
+    place: {
+      kind: 'Identifier',
+      identifier: dependencyValue,
+      effect: Effect.Freeze,
+      reactive: dep.reactive,
+      loc: GeneratedSource,
+    },
+    value: builder.build(),
+    exitBlockId,
+  };
+}
+
+/**
+ * Write instructions for a simple dependency (without optional chains)
+ */
+function writeNonOptionalDependency(
+  dep: ReactiveScopeDependency,
+  env: Environment,
+  builder: HIRBuilder,
+): Identifier {
+  const loc = dep.identifier.loc;
+  let curr: Identifier = makeTemporaryIdentifier(env.nextIdentifierId, loc);
+  builder.push({
+    lvalue: {
+      identifier: curr,
+      kind: 'Identifier',
+      effect: Effect.Mutate,
+      reactive: dep.reactive,
+      loc,
+    },
+    value: {
+      kind: 'LoadLocal',
+      place: {
+        identifier: dep.identifier,
+        kind: 'Identifier',
+        effect: Effect.Freeze,
+        reactive: dep.reactive,
+        loc,
+      },
+      loc,
+    },
+    id: makeInstructionId(1),
+    loc: loc,
+    effects: null,
+  });
+
+  /**
+   * Iteratively build up dependency instructions by reading from the last written
+   * instruction.
+   */
+  for (const path of dep.path) {
+    const next = makeTemporaryIdentifier(env.nextIdentifierId, loc);
+    builder.push({
+      lvalue: {
+        identifier: next,
+        kind: 'Identifier',
+        effect: Effect.Mutate,
+        reactive: dep.reactive,
+        loc,
+      },
+      value: {
+        kind: 'PropertyLoad',
+        object: {
+          identifier: curr,
+          kind: 'Identifier',
+          effect: Effect.Freeze,
+          reactive: dep.reactive,
+          loc,
+        },
+        property: path.property,
+        loc,
+      },
+      id: makeInstructionId(1),
+      loc: loc,
+      effects: null,
+    });
+    curr = next;
+  }
+  return curr;
+}
+
+/**
+ * Write a dependency into optional blocks.
+ *
+ * e.g. `a.b?.c.d` is written to an optional block that tests `a.b` and
+ * conditionally evaluates `c.d`.
+ */
+function writeOptionalDependency(
+  dep: ReactiveScopeDependency,
+  builder: HIRBuilder,
+  parentAlternate: BlockId | null,
+): Identifier {
+  const env = builder.environment;
+  /**
+   * Reserve an identifier which will be used to store the result of this
+   * dependency.
+   */
+  const dependencyValue: Place = {
+    kind: 'Identifier',
+    identifier: makeTemporaryIdentifier(env.nextIdentifierId, GeneratedSource),
+    effect: Effect.Mutate,
+    reactive: dep.reactive,
+    loc: GeneratedSource,
+  };
+
+  /**
+   * Reserve a block which is the fallthrough (and transitive successor) of this
+   * optional chain.
+   */
+  const continuationBlock = builder.reserve(builder.currentBlockKind());
+  let alternate;
+  if (parentAlternate != null) {
+    alternate = parentAlternate;
+  } else {
+    /**
+     * If an outermost alternate block has not been reserved, write one
+     *
+     * $N = Primitive undefined
+     * $M = StoreLocal $OptionalResult = $N
+     * goto fallthrough
+     */
+    alternate = builder.enter('value', () => {
+      const temp = lowerValueToTemporary(builder, {
+        kind: 'Primitive',
+        value: undefined,
+        loc: GeneratedSource,
+      });
+      lowerValueToTemporary(builder, {
+        kind: 'StoreLocal',
+        lvalue: {kind: InstructionKind.Const, place: {...dependencyValue}},
+        value: {...temp},
+        type: null,
+        loc: GeneratedSource,
+      });
+      return {
+        kind: 'goto',
+        variant: GotoVariant.Break,
+        block: continuationBlock.id,
+        id: makeInstructionId(0),
+        loc: GeneratedSource,
+      };
+    });
+  }
+
+  // Reserve the consequent block, which is the successor of the test block
+  const consequent = builder.reserve('value');
+
+  let testIdentifier: Identifier | null = null;
+  const testBlock = builder.enter('value', () => {
+    const testDependency = {
+      ...dep,
+      path: dep.path.slice(0, dep.path.length - 1),
+    };
+    const firstOptional = dep.path.findIndex(path => path.optional);
+    CompilerError.invariant(firstOptional !== -1, {
+      reason:
+        '[ScopeDependencyUtils] Internal invariant broken: expected optional path',
+      loc: dep.identifier.loc,
+      description: null,
+      suggestions: null,
+    });
+    if (firstOptional === dep.path.length - 1) {
+      // Base case: the test block is simple
+      testIdentifier = writeNonOptionalDependency(testDependency, env, builder);
+    } else {
+      // Otherwise, the test block is a nested optional chain
+      testIdentifier = writeOptionalDependency(
+        testDependency,
+        builder,
+        alternate,
+      );
+    }
+
+    return {
+      kind: 'branch',
+      test: {
+        identifier: testIdentifier,
+        effect: Effect.Freeze,
+        kind: 'Identifier',
+        loc: GeneratedSource,
+        reactive: dep.reactive,
+      },
+      consequent: consequent.id,
+      alternate,
+      id: makeInstructionId(0),
+      loc: GeneratedSource,
+      fallthrough: continuationBlock.id,
+    };
+  });
+
+  builder.enterReserved(consequent, () => {
+    CompilerError.invariant(testIdentifier !== null, {
+      reason: 'Satisfy type checker',
+      description: null,
+      loc: null,
+      suggestions: null,
+    });
+
+    lowerValueToTemporary(builder, {
+      kind: 'StoreLocal',
+      lvalue: {kind: InstructionKind.Const, place: {...dependencyValue}},
+      value: lowerValueToTemporary(builder, {
+        kind: 'PropertyLoad',
+        object: {
+          identifier: testIdentifier,
+          kind: 'Identifier',
+          effect: Effect.Freeze,
+          reactive: dep.reactive,
+          loc: GeneratedSource,
+        },
+        property: dep.path.at(-1)!.property,
+        loc: GeneratedSource,
+      }),
+      type: null,
+      loc: GeneratedSource,
+    });
+    return {
+      kind: 'goto',
+      variant: GotoVariant.Break,
+      block: continuationBlock.id,
+      id: makeInstructionId(0),
+      loc: GeneratedSource,
+    };
+  });
+  builder.terminateWithContinuation(
+    {
+      kind: 'optional',
+      optional: dep.path.at(-1)!.optional,
+      test: testBlock,
+      fallthrough: continuationBlock.id,
+      id: makeInstructionId(0),
+      loc: GeneratedSource,
+    },
+    continuationBlock,
+  );
+
+  return dependencyValue.identifier;
+}

compiler/packages/babel-plugin-react-compiler/src/HIR/TypeSchema.ts

@@ -8,7 +8,12 @@
 import {isValidIdentifier} from '@babel/types';
 import {z} from 'zod';
 import {Effect, ValueKind} from '..';
-import {EffectSchema, ValueKindSchema} from './HIR';
+import {
+  EffectSchema,
+  ValueKindSchema,
+  ValueReason,
+  ValueReasonSchema,
+} from './HIR';
 
 export type ObjectPropertiesConfig = {[key: string]: TypeConfig};
 export const ObjectPropertiesSchema: z.ZodType<ObjectPropertiesConfig> = z
@@ -31,6 +36,194 @@ 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 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
+  | ImpureEffectConfig
+  | MutateEffectConfig
+  | MutateTransitiveConditionallyConfig
+  | ApplyEffectConfig;
+
+export const AliasingEffectSchema: z.ZodType<AliasingEffectConfig> = z.union([
+  FreezeEffectSchema,
+  CreateEffectSchema,
+  CreateFromEffectSchema,
+  AssignEffectSchema,
+  AliasEffectSchema,
+  CaptureEffectSchema,
+  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>;
@@ -42,6 +235,7 @@ 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'),
@@ -54,6 +248,7 @@ 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 = {
@@ -63,6 +258,7 @@ 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'),
@@ -71,6 +267,7 @@ 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 =

compiler/packages/babel-plugin-react-compiler/src/HIR/visitors.ts

@@ -345,6 +345,51 @@ 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,
@@ -732,9 +777,11 @@ export function mapTerminalSuccessors(
     case 'return': {
       return {
         kind: 'return',
+        returnVariant: terminal.returnVariant,
         loc: terminal.loc,
         value: terminal.value,
         id: makeInstructionId(0),
+        effects: terminal.effects,
       };
     }
     case 'throw': {
@@ -842,6 +889,7 @@ export function mapTerminalSuccessors(
         handler,
         id: makeInstructionId(0),
         loc: terminal.loc,
+        effects: terminal.effects,
       };
     }
     case 'try': {

compiler/packages/babel-plugin-react-compiler/src/Inference/AliasingEffects.ts

@@ -0,0 +1,262 @@
+/**
+ * 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 {CompilerDiagnostic} from '../CompilerError';
+import {
+  FunctionExpression,
+  GeneratedSource,
+  Hole,
+  IdentifierId,
+  ObjectMethod,
+  Place,
+  SourceLocation,
+  SpreadPattern,
+  ValueKind,
+  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
+ * more values in a program. These effects include mutation of values, freezing values,
+ * tracking data flow between values, and other specialized cases.
+ */
+export type AliasingEffect =
+  /**
+   * Marks the given value and its direct aliases as frozen.
+   *
+   * Captured values are *not* considered frozen, because we cannot be sure that a previously
+   * captured value will still be captured at the point of the freeze.
+   *
+   * For example:
+   * const x = {};
+   * const y = [x];
+   * y.pop(); // y dosn't contain x anymore!
+   * freeze(y);
+   * mutate(x); // safe to mutate!
+   *
+   * The exception to this is FunctionExpressions - since it is impossible to change which
+   * value a function closes over[1] we can transitively freeze functions and their captures.
+   *
+   * [1] Except for `let` values that are reassigned and closed over by a function, but we
+   * handle this explicitly with StoreContext/LoadContext.
+   */
+  | {kind: 'Freeze'; value: Place; reason: ValueReason}
+  /**
+   * Mutate the value and any direct aliases (not captures). Errors if the value is not mutable.
+   */
+  | {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.
+   *
+   * TODO: this is only used for IteratorNext, but even then MutateTransitiveConditionally is more
+   * correct for iterators of unknown types.
+   */
+  | {kind: 'MutateConditionally'; value: Place}
+  /**
+   * Mutate the value, any direct aliases, and any transitive captures. Errors if the value is not mutable.
+   */
+  | {kind: 'MutateTransitive'; value: Place}
+  /**
+   * Mutates any of the value, its direct aliases, and its transitive captures that are mutable.
+   */
+  | {kind: 'MutateTransitiveConditionally'; value: Place}
+  /**
+   * Records information flow from `from` to `into` in cases where local mutation of the destination
+   * will *not* mutate the source:
+   *
+   * - Capture a -> b and Mutate(b) X=> (does not imply) Mutate(a)
+   * - Capture a -> b and MutateTransitive(b) => (does imply) Mutate(a)
+   *
+   * Example: `array.push(item)`. Information from item is captured into array, but there is not a
+   * direct aliasing, and local mutations of array will not modify item.
+   */
+  | {kind: 'Capture'; from: Place; into: Place}
+  /**
+   * Records information flow from `from` to `into` in cases where local mutation of the destination
+   * *will* mutate the source:
+   *
+   * - Alias a -> b and Mutate(b) => (does imply) Mutate(a)
+   * - Alias a -> b and MutateTransitive(b) => (does imply) Mutate(a)
+   *
+   * Example: `c = identity(a)`. We don't know what `identity()` returns so we can't use Assign.
+   * But we have to assume that it _could_ be returning its input, such that a local mutation of
+   * 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`.
+   */
+  | {kind: 'Assign'; from: Place; into: Place}
+  /**
+   * Creates a value of the given type at the given place
+   */
+  | {kind: 'Create'; into: Place; value: ValueKind; reason: ValueReason}
+  /**
+   * Creates a new value with the same kind as the starting value.
+   */
+  | {kind: 'CreateFrom'; from: Place; into: Place}
+  /**
+   * Immutable data flow, used for escape analysis. Does not influence mutable range analysis:
+   */
+  | {kind: 'ImmutableCapture'; from: Place; into: Place}
+  /**
+   * Calls the function at the given place with the given arguments either captured or aliased,
+   * and captures/aliases the result into the given place.
+   */
+  | {
+      kind: 'Apply';
+      receiver: Place;
+      function: Place;
+      mutatesFunction: boolean;
+      args: Array<Place | SpreadPattern | Hole>;
+      into: Place;
+      signature: FunctionSignature | null;
+      loc: SourceLocation;
+    }
+  /**
+   * Constructs a function value with the given captures. The mutability of the function
+   * will be determined by the mutability of the capture values when evaluated.
+   */
+  | {
+      kind: 'CreateFunction';
+      captures: Array<Place>;
+      function: FunctionExpression | ObjectMethod;
+      into: Place;
+    }
+  /**
+   * Mutation of a value known to be immutable
+   */
+  | {kind: 'MutateFrozen'; place: Place; error: CompilerDiagnostic}
+  /**
+   * Mutation of a global
+   */
+  | {
+      kind: 'MutateGlobal';
+      place: Place;
+      error: CompilerDiagnostic;
+    }
+  /**
+   * Indicates a side-effect that is not safe during render
+   */
+  | {kind: 'Impure'; place: Place; error: CompilerDiagnostic}
+  /**
+   * 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
+   * event handlers/effects, and for JSX values known to be called during render
+   * (tags, children) vs those that may be events/effect (other props).
+   */
+  | {
+      kind: 'Render';
+      place: Place;
+    };
+
+export function hashEffect(effect: AliasingEffect): string {
+  switch (effect.kind) {
+    case 'Apply': {
+      return [
+        effect.kind,
+        effect.receiver.identifier.id,
+        effect.function.identifier.id,
+        effect.mutatesFunction,
+        effect.args
+          .map(a => {
+            if (a.kind === 'Hole') {
+              return '';
+            } else if (a.kind === 'Identifier') {
+              return a.identifier.id;
+            } else {
+              return `...${a.place.identifier.id}`;
+            }
+          })
+          .join(','),
+        effect.into.identifier.id,
+      ].join(':');
+    }
+    case 'CreateFrom':
+    case 'ImmutableCapture':
+    case 'Assign':
+    case 'Alias':
+    case 'Capture':
+    case 'MaybeAlias': {
+      return [
+        effect.kind,
+        effect.from.identifier.id,
+        effect.into.identifier.id,
+      ].join(':');
+    }
+    case 'Create': {
+      return [
+        effect.kind,
+        effect.into.identifier.id,
+        effect.value,
+        effect.reason,
+      ].join(':');
+    }
+    case 'Freeze': {
+      return [effect.kind, effect.value.identifier.id, effect.reason].join(':');
+    }
+    case 'Impure':
+    case 'Render': {
+      return [effect.kind, effect.place.identifier.id].join(':');
+    }
+    case 'MutateFrozen':
+    case 'MutateGlobal': {
+      return [
+        effect.kind,
+        effect.place.identifier.id,
+        effect.error.severity,
+        effect.error.category,
+        effect.error.description,
+        printSourceLocation(effect.error.primaryLocation() ?? GeneratedSource),
+      ].join(':');
+    }
+    case 'Mutate':
+    case 'MutateConditionally':
+    case 'MutateTransitive':
+    case 'MutateTransitiveConditionally': {
+      return [effect.kind, effect.value.identifier.id].join(':');
+    }
+    case 'CreateFunction': {
+      return [
+        effect.kind,
+        effect.into.identifier.id,
+        // return places are a unique way to identify functions themselves
+        effect.function.loweredFunc.func.returns.identifier.id,
+        effect.captures.map(p => p.identifier.id).join(','),
+      ].join(':');
+    }
+  }
+}
+
+export type AliasingSignature = {
+  receiver: IdentifierId;
+  params: Array<IdentifierId>;
+  rest: IdentifierId | null;
+  returns: IdentifierId;
+  effects: Array<AliasingEffect>;
+  temporaries: Array<Place>;
+};

compiler/packages/babel-plugin-react-compiler/src/Inference/AnalyseFunctions.ts

@@ -10,6 +10,7 @@ import {
   Effect,
   HIRFunction,
   Identifier,
+  IdentifierId,
   LoweredFunction,
   isRefOrRefValue,
   makeInstructionId,
@@ -19,6 +20,9 @@ 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 {inferMutationAliasingRanges} from './InferMutationAliasingRanges';
 
 export default function analyseFunctions(func: HIRFunction): void {
   for (const [_, block] of func.body.blocks) {
@@ -26,15 +30,27 @@ export default function analyseFunctions(func: HIRFunction): void {
       switch (instr.value.kind) {
         case 'ObjectMethod':
         case 'FunctionExpression': {
-          lower(instr.value.loweredFunc.func);
-          infer(instr.value.loweredFunc);
+          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) {
-            operand.identifier.mutableRange.start = makeInstructionId(0);
-            operand.identifier.mutableRange.end = makeInstructionId(0);
+            /**
+             * 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.scope = null;
           }
           break;
@@ -44,6 +60,87 @@ export default function analyseFunctions(func: HIRFunction): void {
   }
 }
 
+function lowerWithMutationAliasing(fn: HIRFunction): void {
+  /**
+   * Phase 1: similar to lower(), but using the new mutation/aliasing inference
+   */
+  analyseFunctions(fn);
+  inferMutationAliasingEffects(fn, {isFunctionExpression: true});
+  deadCodeElimination(fn);
+  const functionEffects = inferMutationAliasingRanges(fn, {
+    isFunctionExpression: true,
+  }).unwrap();
+  rewriteInstructionKindsBasedOnReassignment(fn);
+  inferReactiveScopeVariables(fn);
+  fn.aliasingEffects = functionEffects;
+
+  /**
+   * Phase 2: populate the Effect of each context variable to use in inferring
+   * the outer function. For example, InferMutationAliasingEffects uses context variable
+   * effects to decide if the function may be mutable or not.
+   */
+  const capturedOrMutated = new Set<IdentifierId>();
+  for (const effect of functionEffects) {
+    switch (effect.kind) {
+      case 'Assign':
+      case 'Alias':
+      case 'Capture':
+      case 'CreateFrom':
+      case 'MaybeAlias': {
+        capturedOrMutated.add(effect.from.identifier.id);
+        break;
+      }
+      case 'Apply': {
+        CompilerError.invariant(false, {
+          reason: `[AnalyzeFunctions] Expected Apply effects to be replaced with more precise effects`,
+          loc: effect.function.loc,
+        });
+      }
+      case 'Mutate':
+      case 'MutateConditionally':
+      case 'MutateTransitive':
+      case 'MutateTransitiveConditionally': {
+        capturedOrMutated.add(effect.value.identifier.id);
+        break;
+      }
+      case 'Impure':
+      case 'Render':
+      case 'MutateFrozen':
+      case 'MutateGlobal':
+      case 'CreateFunction':
+      case 'Create':
+      case 'Freeze':
+      case 'ImmutableCapture': {
+        // no-op
+        break;
+      }
+      default: {
+        assertExhaustive(
+          effect,
+          `Unexpected effect kind ${(effect as any).kind}`,
+        );
+      }
+    }
+  }
+
+  for (const operand of fn.context) {
+    if (
+      capturedOrMutated.has(operand.identifier.id) ||
+      operand.effect === Effect.Capture
+    ) {
+      operand.effect = Effect.Capture;
+    } else {
+      operand.effect = Effect.Read;
+    }
+  }
+
+  fn.env.logger?.debugLogIRs?.({
+    kind: 'hir',
+    name: 'AnalyseFunction (inner)',
+    value: fn,
+  });
+}
+
 function lower(func: HIRFunction): void {
   analyseFunctions(func);
   inferReferenceEffects(func, {isFunctionExpression: true});

compiler/packages/babel-plugin-react-compiler/src/Inference/DropManualMemoization.ts

@@ -5,7 +5,12 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {CompilerError, SourceLocation} from '..';
+import {
+  CompilerDiagnostic,
+  CompilerError,
+  ErrorSeverity,
+  SourceLocation,
+} from '..';
 import {
   CallExpression,
   Effect,
@@ -30,6 +35,7 @@ import {
   makeInstructionId,
 } from '../HIR';
 import {createTemporaryPlace, markInstructionIds} from '../HIR/HIRBuilder';
+import {Result} from '../Utils/Result';
 
 type ManualMemoCallee = {
   kind: 'useMemo' | 'useCallback';
@@ -197,6 +203,7 @@ function makeManualMemoizationMarkers(
         deps: depsList,
         loc: fnExpr.loc,
       },
+      effects: null,
       loc: fnExpr.loc,
     },
     {
@@ -208,6 +215,7 @@ function makeManualMemoizationMarkers(
         decl: {...memoDecl},
         loc: fnExpr.loc,
       },
+      effects: null,
       loc: fnExpr.loc,
     },
   ];
@@ -281,26 +289,43 @@ function extractManualMemoizationArgs(
   instr: TInstruction<CallExpression> | TInstruction<MethodCall>,
   kind: 'useCallback' | 'useMemo',
   sidemap: IdentifierSidemap,
+  errors: CompilerError,
 ): {
-  fnPlace: Place;
+  fnPlace: Place | null;
   depsList: Array<ManualMemoDependency> | null;
 } {
   const [fnPlace, depsListPlace] = instr.value.args as Array<
     Place | SpreadPattern | undefined
   >;
   if (fnPlace == null) {
-    CompilerError.throwInvalidReact({
-      reason: `Expected a callback function to be passed to ${kind}`,
-      loc: instr.value.loc,
-      suggestions: null,
-    });
+    errors.pushDiagnostic(
+      CompilerDiagnostic.create({
+        severity: ErrorSeverity.InvalidReact,
+        category: `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};
   }
   if (fnPlace.kind === 'Spread' || depsListPlace?.kind === 'Spread') {
-    CompilerError.throwInvalidReact({
-      reason: `Unexpected spread argument to ${kind}`,
-      loc: instr.value.loc,
-      suggestions: null,
-    });
+    errors.pushDiagnostic(
+      CompilerDiagnostic.create({
+        severity: ErrorSeverity.InvalidReact,
+        category: `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};
   }
   let depsList: Array<ManualMemoDependency> | null = null;
   if (depsListPlace != null) {
@@ -308,23 +333,40 @@ function extractManualMemoizationArgs(
       depsListPlace.identifier.id,
     );
     if (maybeDepsList == null) {
-      CompilerError.throwInvalidReact({
-        reason: `Expected the dependency list for ${kind} to be an array literal`,
-        suggestions: null,
-        loc: depsListPlace.loc,
-      });
+      errors.pushDiagnostic(
+        CompilerDiagnostic.create({
+          severity: ErrorSeverity.InvalidReact,
+          category: `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};
     }
-    depsList = maybeDepsList.map(dep => {
+    depsList = [];
+    for (const dep of maybeDepsList) {
       const maybeDep = sidemap.maybeDeps.get(dep.identifier.id);
       if (maybeDep == null) {
-        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,
-        });
+        errors.pushDiagnostic(
+          CompilerDiagnostic.create({
+            severity: ErrorSeverity.InvalidReact,
+            category: `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);
       }
-      return maybeDep;
-    });
+    }
   }
   return {
     fnPlace,
@@ -339,8 +381,14 @@ 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): void {
+export function dropManualMemoization(
+  func: HIRFunction,
+): Result<void, CompilerError> {
+  const errors = new CompilerError();
   const isValidationEnabled =
     func.env.config.validatePreserveExistingMemoizationGuarantees ||
     func.env.config.validateNoSetStateInRender ||
@@ -387,7 +435,47 @@ export function dropManualMemoization(func: HIRFunction): void {
             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: '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,
@@ -408,11 +496,19 @@ export function dropManualMemoization(func: HIRFunction): void {
              * is rare and likely sketchy.
              */
             if (!sidemap.functions.has(fnPlace.identifier.id)) {
-              CompilerError.throwInvalidReact({
-                reason: `Expected the first argument to be an inline function expression`,
-                suggestions: [],
-                loc: fnPlace.loc,
-              });
+              errors.pushDiagnostic(
+                CompilerDiagnostic.create({
+                  severity: ErrorSeverity.InvalidReact,
+                  category: `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;
             }
             const memoDecl: Place =
               manualMemo.kind === 'useMemo'
@@ -484,6 +580,8 @@ export function dropManualMemoization(func: HIRFunction): void {
       markInstructionIds(func.body);
     }
   }
+
+  return errors.asResult();
 }
 
 function findOptionalPlaces(fn: HIRFunction): Set<IdentifierId> {
@@ -528,3 +626,17 @@ 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;
+}

compiler/packages/babel-plugin-react-compiler/src/Inference/InferEffectDependencies.ts

@@ -10,7 +10,6 @@ import {CompilerError, SourceLocation} from '..';
 import {
   ArrayExpression,
   Effect,
-  Environment,
   FunctionExpression,
   GeneratedSource,
   HIRFunction,
@@ -29,6 +28,10 @@ import {
   isSetStateType,
   isFireFunctionType,
   makeScopeId,
+  HIR,
+  BasicBlock,
+  BlockId,
+  isEffectEventFunctionType,
 } from '../HIR';
 import {collectHoistablePropertyLoadsInInnerFn} from '../HIR/CollectHoistablePropertyLoads';
 import {collectOptionalChainSidemap} from '../HIR/CollectOptionalChainDependencies';
@@ -38,22 +41,30 @@ import {
   createTemporaryPlace,
   fixScopeAndIdentifierRanges,
   markInstructionIds,
+  markPredecessors,
+  reversePostorderBlocks,
 } from '../HIR/HIRBuilder';
 import {
   collectTemporariesSidemap,
   DependencyCollectionContext,
   handleInstruction,
 } from '../HIR/PropagateScopeDependenciesHIR';
-import {eachInstructionOperand, eachTerminalOperand} from '../HIR/visitors';
+import {buildDependencyInstructions} from '../HIR/ScopeDependencyUtils';
+import {
+  eachInstructionOperand,
+  eachTerminalOperand,
+  terminalFallthrough,
+} 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
  * a second argument to the useEffect call if no dependency array is provided.
  */
 export function inferEffectDependencies(fn: HIRFunction): void {
-  let hasRewrite = false;
   const fnExpressions = new Map<
     IdentifierId,
     TInstruction<FunctionExpression>
@@ -68,7 +79,7 @@ export function inferEffectDependencies(fn: HIRFunction): void {
     );
     moduleTargets.set(
       effectTarget.function.importSpecifierName,
-      effectTarget.numRequiredArgs,
+      effectTarget.autodepsIndex,
     );
   }
   const autodepFnLoads = new Map<IdentifierId, number>();
@@ -86,6 +97,7 @@ export function inferEffectDependencies(fn: HIRFunction): void {
    * reactive(Identifier i) = Union_{reference of i}(reactive(reference))
    */
   const reactiveIds = inferReactiveIdentifiers(fn);
+  const rewriteBlocks: Array<BasicBlock> = [];
 
   for (const [, block] of fn.body.blocks) {
     if (block.terminal.kind === 'scope') {
@@ -101,7 +113,7 @@ export function inferEffectDependencies(fn: HIRFunction): void {
         );
       }
     }
-    const rewriteInstrs = new Map<InstructionId, Array<Instruction>>();
+    const rewriteInstrs: Array<SpliceInfo> = [];
     for (const instr of block.instructions) {
       const {value, lvalue} = instr;
       if (value.kind === 'FunctionExpression') {
@@ -125,7 +137,6 @@ 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';
@@ -159,13 +170,26 @@ 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 === autodepFnLoads.get(callee.identifier.id) &&
+          value.args.length > 0 &&
+          autodepsArgExpectedIndex != null &&
+          autodepsArgIndex === autodepsArgExpectedIndex &&
+          autodepFnLoads.has(callee.identifier.id) &&
           value.args[0].kind === 'Identifier'
         ) {
           // We have a useEffect call with no deps array, so we need to infer the deps
           const effectDeps: Array<Place> = [];
-          const newInstructions: Array<Instruction> = [];
           const deps: ArrayExpression = {
             kind: 'ArrayExpression',
             elements: effectDeps,
@@ -196,24 +220,29 @@ export function inferEffectDependencies(fn: HIRFunction): void {
              */
 
             const usedDeps = [];
-            for (const dep of minimalDeps) {
+            for (const maybeDep of minimalDeps) {
               if (
-                ((isUseRefType(dep.identifier) ||
-                  isSetStateType(dep.identifier)) &&
-                  !reactiveIds.has(dep.identifier.id)) ||
-                isFireFunctionType(dep.identifier)
+                ((isUseRefType(maybeDep.identifier) ||
+                  isSetStateType(maybeDep.identifier)) &&
+                  !reactiveIds.has(maybeDep.identifier.id)) ||
+                isFireFunctionType(maybeDep.identifier) ||
+                isEffectEventFunctionType(maybeDep.identifier)
               ) {
                 // exclude non-reactive hook results, which will never be in a memo block
                 continue;
               }
 
-              const {place, instructions} = writeDependencyToInstructions(
+              const dep = truncateDepAtCurrent(maybeDep);
+              const {place, value, exitBlockId} = buildDependencyInstructions(
                 dep,
-                reactiveIds.has(dep.identifier.id),
                 fn.env,
-                fnExpr.loc,
               );
-              newInstructions.push(...instructions);
+              rewriteInstrs.push({
+                kind: 'block',
+                location: instr.id,
+                value,
+                exitBlockId: exitBlockId,
+              });
               effectDeps.push(place);
               usedDeps.push(dep);
             }
@@ -234,27 +263,40 @@ export function inferEffectDependencies(fn: HIRFunction): void {
               });
             }
 
-            newInstructions.push({
-              id: makeInstructionId(0),
-              loc: GeneratedSource,
-              lvalue: {...depsPlace, effect: Effect.Mutate},
-              value: deps,
-            });
-
             // Step 2: push the inferred deps array as an argument of the useEffect
-            value.args.push({...depsPlace, effect: Effect.Freeze});
-            rewriteInstrs.set(instr.id, newInstructions);
+            rewriteInstrs.push({
+              kind: 'instr',
+              location: instr.id,
+              value: {
+                id: makeInstructionId(0),
+                loc: GeneratedSource,
+                lvalue: {...depsPlace, effect: Effect.Mutate},
+                value: deps,
+                effects: null,
+              },
+            });
+            value.args[autodepsArgIndex] = {
+              ...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
-            newInstructions.push({
-              id: makeInstructionId(0),
-              loc: GeneratedSource,
-              lvalue: {...depsPlace, effect: Effect.Mutate},
-              value: deps,
+            rewriteInstrs.push({
+              kind: 'instr',
+              location: instr.id,
+              value: {
+                id: makeInstructionId(0),
+                loc: GeneratedSource,
+                lvalue: {...depsPlace, effect: Effect.Mutate},
+                value: deps,
+                effects: null,
+              },
             });
-            value.args.push({...depsPlace, effect: Effect.Freeze});
-            rewriteInstrs.set(instr.id, newInstructions);
+            value.args[autodepsArgIndex] = {
+              ...depsPlace,
+              effect: Effect.Freeze,
+            };
             fn.env.inferredEffectLocations.add(callee.loc);
           }
         } else if (
@@ -285,85 +327,166 @@ export function inferEffectDependencies(fn: HIRFunction): void {
         }
       }
     }
-    if (rewriteInstrs.size > 0) {
-      hasRewrite = true;
-      const newInstrs = [];
-      for (const instr of block.instructions) {
-        const newInstr = rewriteInstrs.get(instr.id);
-        if (newInstr != null) {
-          newInstrs.push(...newInstr, instr);
-        } else {
-          newInstrs.push(instr);
-        }
-      }
-      block.instructions = newInstrs;
-    }
+    rewriteSplices(block, rewriteInstrs, rewriteBlocks);
   }
-  if (hasRewrite) {
+
+  if (rewriteBlocks.length > 0) {
+    for (const block of rewriteBlocks) {
+      fn.body.blocks.set(block.id, block);
+    }
+
+    /**
+     * Fixup the HIR to restore RPO, ensure correct predecessors, and renumber
+     * instructions.
+     */
+    reversePostorderBlocks(fn.body);
+    markPredecessors(fn.body);
     // Renumber instructions and fix scope ranges
     markInstructionIds(fn.body);
     fixScopeAndIdentifierRanges(fn.body);
+    deadCodeElimination(fn);
+
     fn.env.hasInferredEffect = true;
   }
 }
 
-function writeDependencyToInstructions(
+function truncateDepAtCurrent(
   dep: ReactiveScopeDependency,
-  reactive: boolean,
-  env: Environment,
-  loc: SourceLocation,
-): {place: Place; instructions: Array<Instruction>} {
-  const instructions: Array<Instruction> = [];
-  let currValue = createTemporaryPlace(env, GeneratedSource);
-  currValue.reactive = reactive;
-  instructions.push({
-    id: makeInstructionId(0),
-    loc: GeneratedSource,
-    lvalue: {...currValue, effect: Effect.Mutate},
-    value: {
-      kind: 'LoadLocal',
-      place: {
-        kind: 'Identifier',
-        identifier: dep.identifier,
-        effect: Effect.Capture,
-        reactive,
-        loc: loc,
-      },
-      loc: loc,
-    },
-  });
-  for (const path of dep.path) {
-    if (path.optional) {
-      /**
-       * TODO: instead of truncating optional paths, reuse
-       * instructions from hoisted dependencies block(s)
-       */
-      break;
-    }
-    if (path.property === 'current') {
-      /*
-       * Prune ref.current accesses. This may over-capture for non-ref values with
-       * a current property, but that's fine.
-       */
-      break;
-    }
-    const nextValue = createTemporaryPlace(env, GeneratedSource);
-    nextValue.reactive = reactive;
-    instructions.push({
-      id: makeInstructionId(0),
-      loc: GeneratedSource,
-      lvalue: {...nextValue, effect: Effect.Mutate},
-      value: {
-        kind: 'PropertyLoad',
-        object: {...currValue, effect: Effect.Capture},
-        property: path.property,
-        loc: loc,
-      },
-    });
-    currValue = nextValue;
+): ReactiveScopeDependency {
+  const idx = dep.path.findIndex(path => path.property === 'current');
+  if (idx === -1) {
+    return dep;
+  } else {
+    return {...dep, path: dep.path.slice(0, idx)};
   }
-  currValue.effect = Effect.Freeze;
-  return {place: currValue, instructions};
+}
+
+type SpliceInfo =
+  | {kind: 'instr'; location: InstructionId; value: Instruction}
+  | {
+      kind: 'block';
+      location: InstructionId;
+      value: HIR;
+      exitBlockId: BlockId;
+    };
+
+function rewriteSplices(
+  originalBlock: BasicBlock,
+  splices: Array<SpliceInfo>,
+  rewriteBlocks: Array<BasicBlock>,
+): void {
+  if (splices.length === 0) {
+    return;
+  }
+  /**
+   * Splice instructions or value blocks into the original block.
+   * --- original block ---
+   * bb_original
+   *   instr1
+   *   ...
+   *   instr2 <-- splice location
+   *   instr3
+   *   ...
+   *   <original terminal>
+   *
+   * If there is more than one block in the splice, this means that we're
+   * splicing in a set of value-blocks of the following structure:
+   * --- blocks we're splicing in ---
+   * bb_entry:
+   *   instrEntry
+   *   ...
+   *   <splice terminal> fallthrough=bb_exit
+   *
+   * bb1(value):
+   *   ...
+   *
+   * bb_exit:
+   *   instrExit
+   *   ...
+   *   <synthetic terminal>
+   *
+   *
+   * --- rewritten blocks ---
+   * bb_original
+   *   instr1
+   *   ... (original instructions)
+   *   instr2
+   *   instrEntry
+   *   ... (spliced instructions)
+   *   <splice terminal> fallthrough=bb_exit
+   *
+   * bb1(value):
+   *   ...
+   *
+   * bb_exit:
+   *   instrExit
+   *   ... (spliced instructions)
+   *   instr3
+   *   ... (original instructions)
+   *   <original terminal>
+   */
+  const originalInstrs = originalBlock.instructions;
+  let currBlock: BasicBlock = {...originalBlock, instructions: []};
+  rewriteBlocks.push(currBlock);
+
+  let cursor = 0;
+
+  for (const rewrite of splices) {
+    while (originalInstrs[cursor].id < rewrite.location) {
+      CompilerError.invariant(
+        originalInstrs[cursor].id < originalInstrs[cursor + 1].id,
+        {
+          reason:
+            '[InferEffectDependencies] Internal invariant broken: expected block instructions to be sorted',
+          loc: originalInstrs[cursor].loc,
+        },
+      );
+      currBlock.instructions.push(originalInstrs[cursor]);
+      cursor++;
+    }
+    CompilerError.invariant(originalInstrs[cursor].id === rewrite.location, {
+      reason:
+        '[InferEffectDependencies] Internal invariant broken: splice location not found',
+      loc: originalInstrs[cursor].loc,
+    });
+
+    if (rewrite.kind === 'instr') {
+      currBlock.instructions.push(rewrite.value);
+    } else if (rewrite.kind === 'block') {
+      const {entry, blocks} = rewrite.value;
+      const entryBlock = blocks.get(entry)!;
+      // splice in all instructions from the entry block
+      currBlock.instructions.push(...entryBlock.instructions);
+      if (blocks.size > 1) {
+        /**
+         * We're splicing in a set of value-blocks, which means we need
+         * to push new blocks and update terminals.
+         */
+        CompilerError.invariant(
+          terminalFallthrough(entryBlock.terminal) === rewrite.exitBlockId,
+          {
+            reason:
+              '[InferEffectDependencies] Internal invariant broken: expected entry block to have a fallthrough',
+            loc: entryBlock.terminal.loc,
+          },
+        );
+        const originalTerminal = currBlock.terminal;
+        currBlock.terminal = entryBlock.terminal;
+
+        for (const [id, block] of blocks) {
+          if (id === entry) {
+            continue;
+          }
+          if (id === rewrite.exitBlockId) {
+            block.terminal = originalTerminal;
+            currBlock = block;
+          }
+          rewriteBlocks.push(block);
+        }
+      }
+    }
+  }
+  currBlock.instructions.push(...originalInstrs.slice(cursor));
 }
 
 function inferReactiveIdentifiers(fn: HIRFunction): Set<IdentifierId> {

compiler/packages/babel-plugin-react-compiler/src/Inference/InferFunctionEffects.ts

@@ -324,22 +324,28 @@ function isEffectSafeOutsideRender(effect: FunctionEffect): boolean {
   return effect.kind === 'GlobalMutation';
 }
 
-function getWriteErrorReason(abstractValue: AbstractValue): string {
+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';
+    return 'Modifying 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';
+    return 'Modifying a value used previously in JSX is not allowed. Consider moving the modification before the JSX';
   } else if (abstractValue.reason.has(ValueReason.Context)) {
-    return `Mutating a value returned from 'useContext()', which should not be mutated`;
+    return `Modifying a value returned from 'useContext()' is not allowed.`;
   } else if (abstractValue.reason.has(ValueReason.KnownReturnSignature)) {
-    return 'Mutating a value returned from a function whose return value should not be mutated';
+    return 'Modifying 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';
+    return 'Modifying 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";
+    return "Modifying a value returned from 'useState()', which should not be modified directly. 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";
+    return "Modifying a value returned from 'useReducer()', which should not be modified directly. Use the dispatch function to update instead";
+  } else if (abstractValue.reason.has(ValueReason.Effect)) {
+    return 'Modifying a value used previously in an effect function or as an effect dependency is not allowed. Consider moving the modification before calling useEffect()';
+  } else if (abstractValue.reason.has(ValueReason.HookCaptured)) {
+    return 'Modifying a value previously passed as an argument to a hook is not allowed. Consider moving the modification before calling the hook';
+  } else if (abstractValue.reason.has(ValueReason.HookReturn)) {
+    return 'Modifying a value returned from a hook is not allowed. Consider moving the modification into the hook where the value is constructed';
   } else {
-    return 'This mutates a variable that React considers immutable';
+    return 'This modifies a variable that React considers immutable';
   }
 }

compiler/packages/babel-plugin-react-compiler/src/Inference/InferMutableRanges.ts

@@ -86,7 +86,7 @@ export function inferMutableRanges(ir: HIRFunction): void {
   }
 }
 
-function areEqualMaps<T>(a: Map<T, T>, b: Map<T, T>): boolean {
+function areEqualMaps<T, U>(a: Map<T, U>, b: Map<T, U>): boolean {
   if (a.size !== b.size) {
     return false;
   }

compiler/packages/babel-plugin-react-compiler/src/Inference/InferMutationAliasingRanges.ts

@@ -0,0 +1,818 @@
+/**
+ * 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, SourceLocation} from '..';
+import {
+  BlockId,
+  Effect,
+  HIRFunction,
+  Identifier,
+  IdentifierId,
+  InstructionId,
+  isJsxType,
+  makeInstructionId,
+  ValueKind,
+  ValueReason,
+  Place,
+  isPrimitiveType,
+} from '../HIR/HIR';
+import {
+  eachInstructionLValue,
+  eachInstructionValueOperand,
+  eachTerminalOperand,
+} from '../HIR/visitors';
+import {assertExhaustive, getOrInsertWith} from '../Utils/utils';
+import {Err, Ok, Result} from '../Utils/Result';
+import {AliasingEffect} from './AliasingEffects';
+
+/**
+ * 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.
+ *
+ * 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:
+ *
+ * ```
+ * (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> = [];
+
+  /**
+   * 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.
+   * Edges and mutations are ordered, with mutations processed against the
+   * abstract model only after it is fully constructed by visiting all blocks
+   * _and_ connecting phis. Phis are considered ordered at the time of the
+   * phi node.
+   *
+   * This should (may?) mean that mutations are able to see the full state
+   * of the graph and mark all the appropriate identifiers as mutated at
+   * the correct point, accounting for both backward and forward edges.
+   * Ie a mutation of x accounts for both values that flowed into x,
+   * and values that x flowed into.
+   */
+  const state = new AliasingState();
+  type PendingPhiOperand = {from: Place; into: Place; index: number};
+  const pendingPhis = new Map<BlockId, Array<PendingPhiOperand>>();
+  const mutations: Array<{
+    index: number;
+    id: InstructionId;
+    transitive: boolean;
+    kind: MutationKind;
+    place: Place;
+  }> = [];
+  const renders: Array<{index: number; place: Place}> = [];
+
+  let index = 0;
+
+  const errors = new CompilerError();
+
+  for (const param of [...fn.params, ...fn.context, fn.returns]) {
+    const place = param.kind === 'Identifier' ? param : param.place;
+    state.create(place, {kind: 'Object'});
+  }
+  const seenBlocks = new Set<BlockId>();
+  for (const block of fn.body.blocks.values()) {
+    for (const phi of block.phis) {
+      state.create(phi.place, {kind: 'Phi'});
+      for (const [pred, operand] of phi.operands) {
+        if (!seenBlocks.has(pred)) {
+          // NOTE: annotation required to actually typecheck and not silently infer `any`
+          const blockPhis = getOrInsertWith<BlockId, Array<PendingPhiOperand>>(
+            pendingPhis,
+            pred,
+            () => [],
+          );
+          blockPhis.push({from: operand, into: phi.place, index: index++});
+        } else {
+          state.assign(index++, operand, phi.place);
+        }
+      }
+    }
+    seenBlocks.add(block.id);
+
+    for (const instr of block.instructions) {
+      if (instr.effects == null) continue;
+      for (const effect of instr.effects) {
+        if (effect.kind === 'Create') {
+          state.create(effect.into, {kind: 'Object'});
+        } else if (effect.kind === 'CreateFunction') {
+          state.create(effect.into, {
+            kind: 'Function',
+            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: '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 (
+          effect.kind === 'MutateTransitive' ||
+          effect.kind === 'MutateTransitiveConditionally'
+        ) {
+          mutations.push({
+            index: index++,
+            id: instr.id,
+            transitive: true,
+            kind:
+              effect.kind === 'MutateTransitive'
+                ? MutationKind.Definite
+                : MutationKind.Conditional,
+            place: effect.value,
+          });
+        } else if (
+          effect.kind === 'Mutate' ||
+          effect.kind === 'MutateConditionally'
+        ) {
+          mutations.push({
+            index: index++,
+            id: instr.id,
+            transitive: false,
+            kind:
+              effect.kind === 'Mutate'
+                ? MutationKind.Definite
+                : MutationKind.Conditional,
+            place: effect.value,
+          });
+        } else if (
+          effect.kind === 'MutateFrozen' ||
+          effect.kind === 'MutateGlobal' ||
+          effect.kind === 'Impure'
+        ) {
+          errors.pushDiagnostic(effect.error);
+          functionEffects.push(effect);
+        } else if (effect.kind === 'Render') {
+          renders.push({index: index++, place: effect.place});
+          functionEffects.push(effect);
+        }
+      }
+    }
+    const blockPhis = pendingPhis.get(block.id);
+    if (blockPhis != null) {
+      for (const {from, into, index} of blockPhis) {
+        state.assign(index, from, into);
+      }
+    }
+    if (block.terminal.kind === 'return') {
+      state.assign(index++, block.terminal.value, fn.returns);
+    }
+
+    if (
+      (block.terminal.kind === 'maybe-throw' ||
+        block.terminal.kind === 'return') &&
+      block.terminal.effects != null
+    ) {
+      for (const effect of block.terminal.effects) {
+        if (effect.kind === 'Alias') {
+          state.assign(index++, effect.from, effect.into);
+        } else {
+          CompilerError.invariant(effect.kind === 'Freeze', {
+            reason: `Unexpected '${effect.kind}' effect for MaybeThrow terminal`,
+            loc: block.terminal.loc,
+          });
+        }
+      }
+    }
+  }
+
+  for (const mutation of mutations) {
+    state.mutate(
+      mutation.index,
+      mutation.place.identifier,
+      makeInstructionId(mutation.id + 1),
+      mutation.transitive,
+      mutation.kind,
+      mutation.place.loc,
+      errors,
+    );
+  }
+  for (const render of renders) {
+    state.render(render.index, render.place.identifier, errors);
+  }
+  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;
+    }
+    let mutated = false;
+    if (node.local != null) {
+      if (node.local.kind === MutationKind.Conditional) {
+        mutated = true;
+        functionEffects.push({
+          kind: 'MutateConditionally',
+          value: {...place, loc: node.local.loc},
+        });
+      } else if (node.local.kind === MutationKind.Definite) {
+        mutated = true;
+        functionEffects.push({
+          kind: 'Mutate',
+          value: {...place, loc: node.local.loc},
+        });
+      }
+    }
+    if (node.transitive != null) {
+      if (node.transitive.kind === MutationKind.Conditional) {
+        mutated = true;
+        functionEffects.push({
+          kind: 'MutateTransitiveConditionally',
+          value: {...place, loc: node.transitive.loc},
+        });
+      } else if (node.transitive.kind === MutationKind.Definite) {
+        mutated = true;
+        functionEffects.push({
+          kind: 'MutateTransitive',
+          value: {...place, loc: node.transitive.loc},
+        });
+      }
+    }
+    if (mutated) {
+      place.effect = Effect.Capture;
+    }
+  }
+
+  /**
+   * Part 2
+   * Add legacy operand-specific effects based on instruction effects and mutable ranges.
+   * Also fixes up operand mutable ranges, making sure that start is non-zero if the value
+   * is mutated (depended on by later passes like InferReactiveScopeVariables which uses this
+   * to filter spurious mutations of globals, which we now guard against more precisely)
+   */
+  for (const block of fn.body.blocks.values()) {
+    for (const phi of block.phis) {
+      // TODO: we don't actually set these effects today!
+      phi.place.effect = Effect.Store;
+      const isPhiMutatedAfterCreation: boolean =
+        phi.place.identifier.mutableRange.end >
+        (block.instructions.at(0)?.id ?? block.terminal.id);
+      for (const operand of phi.operands.values()) {
+        operand.effect = isPhiMutatedAfterCreation
+          ? Effect.Capture
+          : Effect.Read;
+      }
+      if (
+        isPhiMutatedAfterCreation &&
+        phi.place.identifier.mutableRange.start === 0
+      ) {
+        /*
+         * TODO: ideally we'd construct a precise start range, but what really
+         * matters is that the phi's range appears mutable (end > start + 1)
+         * so we just set the start to the previous instruction before this block
+         */
+        const firstInstructionIdOfBlock =
+          block.instructions.at(0)?.id ?? block.terminal.id;
+        phi.place.identifier.mutableRange.start = makeInstructionId(
+          firstInstructionIdOfBlock - 1,
+        );
+      }
+    }
+    for (const instr of block.instructions) {
+      for (const lvalue of eachInstructionLValue(instr)) {
+        lvalue.effect = Effect.ConditionallyMutate;
+        if (lvalue.identifier.mutableRange.start === 0) {
+          lvalue.identifier.mutableRange.start = instr.id;
+        }
+        if (lvalue.identifier.mutableRange.end === 0) {
+          lvalue.identifier.mutableRange.end = makeInstructionId(
+            Math.max(instr.id + 1, lvalue.identifier.mutableRange.end),
+          );
+        }
+      }
+      for (const operand of eachInstructionValueOperand(instr.value)) {
+        operand.effect = Effect.Read;
+      }
+      if (instr.effects == null) {
+        continue;
+      }
+      const operandEffects = new Map<IdentifierId, Effect>();
+      for (const effect of instr.effects) {
+        switch (effect.kind) {
+          case 'Assign':
+          case 'Alias':
+          case 'Capture':
+          case 'CreateFrom':
+          case 'MaybeAlias': {
+            const isMutatedOrReassigned =
+              effect.into.identifier.mutableRange.end > instr.id;
+            if (isMutatedOrReassigned) {
+              operandEffects.set(effect.from.identifier.id, Effect.Capture);
+              operandEffects.set(effect.into.identifier.id, Effect.Store);
+            } else {
+              operandEffects.set(effect.from.identifier.id, Effect.Read);
+              operandEffects.set(effect.into.identifier.id, Effect.Store);
+            }
+            break;
+          }
+          case 'CreateFunction':
+          case 'Create': {
+            break;
+          }
+          case 'Mutate': {
+            operandEffects.set(effect.value.identifier.id, Effect.Store);
+            break;
+          }
+          case 'Apply': {
+            CompilerError.invariant(false, {
+              reason: `[AnalyzeFunctions] Expected Apply effects to be replaced with more precise effects`,
+              loc: effect.function.loc,
+            });
+          }
+          case 'MutateTransitive':
+          case 'MutateConditionally':
+          case 'MutateTransitiveConditionally': {
+            operandEffects.set(
+              effect.value.identifier.id,
+              Effect.ConditionallyMutate,
+            );
+            break;
+          }
+          case 'Freeze': {
+            operandEffects.set(effect.value.identifier.id, Effect.Freeze);
+            break;
+          }
+          case 'ImmutableCapture': {
+            // no-op, Read is the default
+            break;
+          }
+          case 'Impure':
+          case 'Render':
+          case 'MutateFrozen':
+          case 'MutateGlobal': {
+            // no-op
+            break;
+          }
+          default: {
+            assertExhaustive(
+              effect,
+              `Unexpected effect kind ${(effect as any).kind}`,
+            );
+          }
+        }
+      }
+      for (const lvalue of eachInstructionLValue(instr)) {
+        const effect =
+          operandEffects.get(lvalue.identifier.id) ??
+          Effect.ConditionallyMutate;
+        lvalue.effect = effect;
+      }
+      for (const operand of eachInstructionValueOperand(instr.value)) {
+        if (
+          operand.identifier.mutableRange.end > instr.id &&
+          operand.identifier.mutableRange.start === 0
+        ) {
+          operand.identifier.mutableRange.start = instr.id;
+        }
+        const effect = operandEffects.get(operand.identifier.id) ?? Effect.Read;
+        operand.effect = effect;
+      }
+
+      /**
+       * This case is targeted at hoisted functions like:
+       *
+       * ```
+       * x();
+       * function x() { ... }
+       * ```
+       *
+       * Which turns into:
+       *
+       * t0 = DeclareContext HoistedFunction x
+       * t1 = LoadContext x
+       * t2 = CallExpression t1 ( )
+       * t3 = FunctionExpression ...
+       * t4 = StoreContext Function x = t3
+       *
+       * If the function had captured mutable values, it would already have its
+       * range extended to include the StoreContext. But if the function doesn't
+       * capture any mutable values its range won't have been extended yet. We
+       * want to ensure that the value is memoized along with the context variable,
+       * not independently of it (bc of the way we do codegen for hoisted functions).
+       * So here we check for StoreContext rvalues and if they haven't already had
+       * their range extended to at least this instruction, we extend it.
+       */
+      if (
+        instr.value.kind === 'StoreContext' &&
+        instr.value.value.identifier.mutableRange.end <= instr.id
+      ) {
+        instr.value.value.identifier.mutableRange.end = makeInstructionId(
+          instr.id + 1,
+        );
+      }
+    }
+    if (block.terminal.kind === 'return') {
+      block.terminal.value.effect = isFunctionExpression
+        ? Effect.Read
+        : Effect.Freeze;
+    } else {
+      for (const operand of eachTerminalOperand(block.terminal)) {
+        operand.effect = Effect.Read;
+      }
+    }
+  }
+
+  /**
+   * 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.
+   */
+  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,
+  });
+  /**
+   * 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 tracked: Array<Place> = [];
+  const ignoredErrors = new CompilerError();
+  for (const param of [...fn.params, ...fn.context, fn.returns]) {
+    const place = param.kind === 'Identifier' ? param : param.place;
+    tracked.push(place);
+  }
+  for (const into of tracked) {
+    const mutationIndex = index++;
+    state.mutate(
+      mutationIndex,
+      into.identifier,
+      null,
+      true,
+      MutationKind.Conditional,
+      into.loc,
+      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);
+}
+
+function appendFunctionErrors(errors: CompilerError, fn: HIRFunction): void {
+  for (const effect of fn.aliasingEffects ?? []) {
+    switch (effect.kind) {
+      case 'Impure':
+      case 'MutateFrozen':
+      case 'MutateGlobal': {
+        errors.pushDiagnostic(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';
+  }>;
+  transitive: {kind: MutationKind; loc: SourceLocation} | null;
+  local: {kind: MutationKind; loc: SourceLocation} | null;
+  lastMutated: number;
+  value:
+    | {kind: 'Object'}
+    | {kind: 'Phi'}
+    | {kind: 'Function'; function: HIRFunction};
+};
+class AliasingState {
+  nodes: Map<Identifier, Node> = new Map();
+
+  create(place: Place, value: Node['value']): void {
+    this.nodes.set(place.identifier, {
+      id: place.identifier,
+      createdFrom: new Map(),
+      captures: new Map(),
+      aliases: new Map(),
+      maybeAliases: new Map(),
+      edges: [],
+      transitive: null,
+      local: null,
+      lastMutated: 0,
+      value,
+    });
+  }
+
+  createFrom(index: number, from: Place, into: Place): void {
+    this.create(into, {kind: 'Object'});
+    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: 'alias'});
+    if (!toNode.createdFrom.has(from.identifier)) {
+      toNode.createdFrom.set(from.identifier, index);
+    }
+  }
+
+  capture(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: 'capture'});
+    if (!toNode.captures.has(from.identifier)) {
+      toNode.captures.set(from.identifier, index);
+    }
+  }
+
+  assign(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: 'alias'});
+    if (!toNode.aliases.has(from.identifier)) {
+      toNode.aliases.set(from.identifier, index);
+    }
+  }
+
+  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];
+    while (queue.length !== 0) {
+      const current = queue.pop()!;
+      if (seen.has(current)) {
+        continue;
+      }
+      seen.add(current);
+      const node = this.nodes.get(current);
+      if (node == null || node.transitive != null || node.local != null) {
+        continue;
+      }
+      if (node.value.kind === 'Function') {
+        appendFunctionErrors(errors, node.value.function);
+      }
+      for (const [alias, when] of node.createdFrom) {
+        if (when >= index) {
+          continue;
+        }
+        queue.push(alias);
+      }
+      for (const [alias, when] of node.aliases) {
+        if (when >= index) {
+          continue;
+        }
+        queue.push(alias);
+      }
+      for (const [capture, when] of node.captures) {
+        if (when >= index) {
+          continue;
+        }
+        queue.push(capture);
+      }
+    }
+  }
+
+  mutate(
+    index: number,
+    start: Identifier,
+    // Null is used for simulated mutations
+    end: InstructionId | null,
+    transitive: boolean,
+    startKind: MutationKind,
+    loc: SourceLocation,
+    errors: CompilerError,
+  ): void {
+    const seen = new Map<Identifier, MutationKind>();
+    const queue: Array<{
+      place: Identifier;
+      transitive: boolean;
+      direction: 'backwards' | 'forwards';
+      kind: MutationKind;
+    }> = [{place: start, transitive, direction: 'backwards', kind: startKind}];
+    while (queue.length !== 0) {
+      const {place: current, transitive, direction, kind} = queue.pop()!;
+      const previousKind = seen.get(current);
+      if (previousKind != null && previousKind >= kind) {
+        continue;
+      }
+      seen.set(current, kind);
+      const node = this.nodes.get(current);
+      if (node == null) {
+        continue;
+      }
+      node.lastMutated = Math.max(node.lastMutated, index);
+      if (end != null) {
+        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.function);
+      }
+      if (transitive) {
+        if (node.transitive == null || node.transitive.kind < kind) {
+          node.transitive = {kind, loc};
+        }
+      } else {
+        if (node.local == null || node.local.kind < kind) {
+          node.local = {kind, loc};
+        }
+      }
+      /**
+       * all mutations affect "forward" edges by the rules:
+       * - Capture a -> b, mutate(a) => mutate(b)
+       * - Alias a -> b, mutate(a) => mutate(b)
+       */
+      for (const edge of node.edges) {
+        if (edge.index >= index) {
+          break;
+        }
+        queue.push({place: edge.node, transitive, direction: 'forwards', kind});
+      }
+      for (const [alias, when] of node.createdFrom) {
+        if (when >= index) {
+          continue;
+        }
+        queue.push({
+          place: alias,
+          transitive: true,
+          direction: 'backwards',
+          kind,
+        });
+      }
+      if (direction === 'backwards' || node.value.kind !== 'Phi') {
+        /**
+         * all mutations affect backward alias edges by the rules:
+         * - Alias a -> b, mutate(b) => mutate(a)
+         * - Alias a -> b, mutateTransitive(b) => mutate(a)
+         *
+         * However, if we reached a phi because one of its inputs was mutated
+         * (and we're advancing "forwards" through that node's edges), then
+         * we know we've already processed the mutation at its source. The
+         * phi's other inputs can't be affected.
+         */
+        for (const [alias, when] of node.aliases) {
+          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,
+          });
+        }
+      }
+      /**
+       * but only transitive mutations affect captures
+       */
+      if (transitive) {
+        for (const [capture, when] of node.captures) {
+          if (when >= index) {
+            continue;
+          }
+          queue.push({
+            place: capture,
+            transitive,
+            direction: 'backwards',
+            kind,
+          });
+        }
+      }
+    }
+  }
+}

compiler/packages/babel-plugin-react-compiler/src/Inference/InferReactivePlaces.ts

@@ -21,11 +21,11 @@ import {
   isStableType,
   isStableTypeContainer,
   isUseOperator,
-  isUseRefType,
 } from '../HIR';
 import {PostDominator} from '../HIR/Dominator';
 import {
   eachInstructionLValue,
+  eachInstructionOperand,
   eachInstructionValueOperand,
   eachTerminalOperand,
 } from '../HIR/visitors';
@@ -69,13 +69,6 @@ class StableSidemap {
               isStable: false,
             });
           }
-        } else if (
-          this.env.config.enableTreatRefLikeIdentifiersAsRefs &&
-          isUseRefType(lvalue.identifier)
-        ) {
-          this.map.set(lvalue.identifier.id, {
-            isStable: true,
-          });
         }
         break;
       }
@@ -292,7 +285,7 @@ export function inferReactivePlaces(fn: HIRFunction): void {
         let hasReactiveInput = false;
         /*
          * NOTE: we want to mark all operands as reactive or not, so we
-         * avoid short-circuting here
+         * avoid short-circuiting here
          */
         for (const operand of eachInstructionValueOperand(value)) {
           const reactive = reactiveIdentifiers.isReactive(operand);
@@ -375,6 +368,41 @@ export function inferReactivePlaces(fn: HIRFunction): void {
       }
     }
   } while (reactiveIdentifiers.snapshot());
+
+  function propagateReactivityToInnerFunctions(
+    fn: HIRFunction,
+    isOutermost: boolean,
+  ): void {
+    for (const [, block] of fn.body.blocks) {
+      for (const instr of block.instructions) {
+        if (!isOutermost) {
+          for (const operand of eachInstructionOperand(instr)) {
+            reactiveIdentifiers.isReactive(operand);
+          }
+        }
+        if (
+          instr.value.kind === 'ObjectMethod' ||
+          instr.value.kind === 'FunctionExpression'
+        ) {
+          propagateReactivityToInnerFunctions(
+            instr.value.loweredFunc.func,
+            false,
+          );
+        }
+      }
+      if (!isOutermost) {
+        for (const operand of eachTerminalOperand(block.terminal)) {
+          reactiveIdentifiers.isReactive(operand);
+        }
+      }
+    }
+  }
+
+  /**
+   * Propagate reactivity for inner functions, as we eventually hoist and dedupe
+   * dependency instructions for scopes.
+   */
+  propagateReactivityToInnerFunctions(fn, true);
 }
 
 /*

compiler/packages/babel-plugin-react-compiler/src/Inference/InferReferenceEffects.ts

@@ -48,7 +48,7 @@ import {
   eachTerminalOperand,
   eachTerminalSuccessor,
 } from '../HIR/visitors';
-import {assertExhaustive} from '../Utils/utils';
+import {assertExhaustive, Set_isSuperset} from '../Utils/utils';
 import {
   inferTerminalFunctionEffects,
   inferInstructionFunctionEffects,
@@ -779,7 +779,7 @@ function inferParam(
  * │         Mutable          │───┘
  * └──────────────────────────┘
  */
-function mergeValues(a: ValueKind, b: ValueKind): ValueKind {
+export function mergeValueKinds(a: ValueKind, b: ValueKind): ValueKind {
   if (a === b) {
     return a;
   } else if (a === ValueKind.MaybeFrozen || b === ValueKind.MaybeFrozen) {
@@ -821,28 +821,16 @@ function mergeValues(a: ValueKind, b: ValueKind): ValueKind {
   }
 }
 
-/**
- * @returns `true` if `a` is a superset of `b`.
- */
-function isSuperset<T>(a: ReadonlySet<T>, b: ReadonlySet<T>): boolean {
-  for (const v of b) {
-    if (!a.has(v)) {
-      return false;
-    }
-  }
-  return true;
-}
-
 function mergeAbstractValues(
   a: AbstractValue,
   b: AbstractValue,
 ): AbstractValue {
-  const kind = mergeValues(a.kind, b.kind);
+  const kind = mergeValueKinds(a.kind, b.kind);
   if (
     kind === a.kind &&
     kind === b.kind &&
-    isSuperset(a.reason, b.reason) &&
-    isSuperset(a.context, b.context)
+    Set_isSuperset(a.reason, b.reason) &&
+    Set_isSuperset(a.context, b.context)
   ) {
     return a;
   }
@@ -1989,7 +1977,7 @@ function areArgumentsImmutableAndNonMutating(
   return true;
 }
 
-function getArgumentEffect(
+export function getArgumentEffect(
   signatureEffect: Effect | null,
   arg: Place | SpreadPattern,
 ): Effect {

compiler/packages/babel-plugin-react-compiler/src/Inference/InlineImmediatelyInvokedFunctionExpressions.ts

@@ -11,13 +11,16 @@ import {
   Environment,
   FunctionExpression,
   GeneratedSource,
+  GotoTerminal,
   GotoVariant,
   HIRFunction,
   IdentifierId,
   InstructionKind,
   LabelTerminal,
   Place,
+  isStatementBlockKind,
   makeInstructionId,
+  mergeConsecutiveBlocks,
   promoteTemporary,
   reversePostorderBlocks,
 } from '../HIR';
@@ -72,6 +75,10 @@ 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,
@@ -90,100 +97,144 @@ export function inlineImmediatelyInvokedFunctionExpressions(
    */
   const queue = Array.from(fn.body.blocks.values());
   queue: for (const block of queue) {
-    for (let ii = 0; ii < block.instructions.length; ii++) {
-      const instr = block.instructions[ii]!;
-      switch (instr.value.kind) {
-        case 'FunctionExpression': {
-          if (instr.lvalue.identifier.name === null) {
-            functions.set(instr.lvalue.identifier.id, instr.value);
+    /*
+     * We can't handle labels inside expressions yet, so we don't inline IIFEs if they are in an
+     * expression block.
+     */
+    if (isStatementBlockKind(block.kind)) {
+      for (let ii = 0; ii < block.instructions.length; ii++) {
+        const instr = block.instructions[ii]!;
+        switch (instr.value.kind) {
+          case 'FunctionExpression': {
+            if (instr.lvalue.identifier.name === null) {
+              functions.set(instr.lvalue.identifier.id, instr.value);
+            }
+            break;
           }
-          break;
-        }
-        case 'CallExpression': {
-          if (instr.value.args.length !== 0) {
-            // We don't support inlining when there are arguments
-            continue;
+          case 'CallExpression': {
+            if (instr.value.args.length !== 0) {
+              // We don't support inlining when there are arguments
+              continue;
+            }
+            const body = functions.get(instr.value.callee.identifier.id);
+            if (body === undefined) {
+              // Not invoking a local function expression, can't inline
+              continue;
+            }
+
+            if (
+              body.loweredFunc.func.params.length > 0 ||
+              body.loweredFunc.func.async ||
+              body.loweredFunc.func.generator
+            ) {
+              // Can't inline functions with params, or async/generator functions
+              continue;
+            }
+
+            // We know this function is used for an IIFE and can prune it later
+            inlinedFunctions.add(instr.value.callee.identifier.id);
+
+            // Create a new block which will contain code following the IIFE call
+            const continuationBlockId = fn.env.nextBlockId;
+            const continuationBlock: BasicBlock = {
+              id: continuationBlockId,
+              instructions: block.instructions.slice(ii + 1),
+              kind: block.kind,
+              phis: new Set(),
+              preds: new Set(),
+              terminal: block.terminal,
+            };
+            fn.body.blocks.set(continuationBlockId, continuationBlock);
+
+            /*
+             * Trim the original block to contain instructions up to (but not including)
+             * the IIFE
+             */
+            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;
+
+              // We store the result in the IIFE temporary
+              const result = instr.lvalue;
+
+              // 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);
+              }
+
+              /*
+               * 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);
+              }
+            }
+
+            /*
+             * Ensure we visit the continuation block, since there may have been
+             * sequential IIFEs that need to be visited.
+             */
+            queue.push(continuationBlock);
+            continue queue;
           }
-          const body = functions.get(instr.value.callee.identifier.id);
-          if (body === undefined) {
-            // Not invoking a local function expression, can't inline
-            continue;
-          }
-
-          if (
-            body.loweredFunc.func.params.length > 0 ||
-            body.loweredFunc.func.async ||
-            body.loweredFunc.func.generator
-          ) {
-            // Can't inline functions with params, or async/generator functions
-            continue;
-          }
-
-          // We know this function is used for an IIFE and can prune it later
-          inlinedFunctions.add(instr.value.callee.identifier.id);
-
-          // Create a new block which will contain code following the IIFE call
-          const continuationBlockId = fn.env.nextBlockId;
-          const continuationBlock: BasicBlock = {
-            id: continuationBlockId,
-            instructions: block.instructions.slice(ii + 1),
-            kind: block.kind,
-            phis: new Set(),
-            preds: new Set(),
-            terminal: block.terminal,
-          };
-          fn.body.blocks.set(continuationBlockId, continuationBlock);
-
-          /*
-           * Trim the original block to contain instructions up to (but not including)
-           * the IIFE
-           */
-          block.instructions.length = ii;
-
-          /*
-           * 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;
-
-          // Declare the IIFE temporary
-          declareTemporary(fn.env, block, result);
-
-          // 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);
-          }
-
-          /*
-           * Ensure we visit the continuation block, since there may have been
-           * sequential IIFEs that need to be visited.
-           */
-          queue.push(continuationBlock);
-          continue queue;
-        }
-        default: {
-          for (const place of eachInstructionValueOperand(instr.value)) {
-            // Any other use of a function expression means it isn't an IIFE
-            functions.delete(place.identifier.id);
+          default: {
+            for (const place of eachInstructionValueOperand(instr.value)) {
+              // Any other use of a function expression means it isn't an IIFE
+              functions.delete(place.identifier.id);
+            }
           }
         }
       }
@@ -192,7 +243,7 @@ export function inlineImmediatelyInvokedFunctionExpressions(
 
   if (inlinedFunctions.size !== 0) {
     // Remove instructions that define lambdas which we inlined
-    for (const [, block] of fn.body.blocks) {
+    for (const block of fn.body.blocks.values()) {
       retainWhere(
         block.instructions,
         instr => !inlinedFunctions.has(instr.lvalue.identifier.id),
@@ -206,9 +257,25 @@ 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>
@@ -235,6 +302,7 @@ function rewriteBlock(
       type: null,
       loc: terminal.loc,
     },
+    effects: null,
   });
   block.terminal = {
     kind: 'goto',
@@ -263,5 +331,6 @@ function declareTemporary(
       type: null,
       loc: result.loc,
     },
+    effects: null,
   });
 }

compiler/packages/babel-plugin-react-compiler/src/Inference/MUTABILITY_ALIASING_MODEL.md

@@ -0,0 +1,559 @@
+# 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
+```

compiler/packages/babel-plugin-react-compiler/src/Optimization/InlineJsxTransform.ts

@@ -151,6 +151,7 @@ export function inlineJsxTransform(
               type: null,
               loc: instr.value.loc,
             },
+            effects: null,
             loc: instr.loc,
           };
           currentBlockInstructions.push(varInstruction);
@@ -167,6 +168,7 @@ export function inlineJsxTransform(
               },
               loc: instr.value.loc,
             },
+            effects: null,
             loc: instr.loc,
           };
           currentBlockInstructions.push(devGlobalInstruction);
@@ -220,6 +222,7 @@ export function inlineJsxTransform(
               type: null,
               loc: instr.value.loc,
             },
+            effects: null,
             loc: instr.loc,
           };
           thenBlockInstructions.push(reassignElseInstruction);
@@ -292,6 +295,7 @@ export function inlineJsxTransform(
               ],
               loc: instr.value.loc,
             },
+            effects: null,
             loc: instr.loc,
           };
           elseBlockInstructions.push(reactElementInstruction);
@@ -309,6 +313,7 @@ export function inlineJsxTransform(
               type: null,
               loc: instr.value.loc,
             },
+            effects: null,
             loc: instr.loc,
           };
           elseBlockInstructions.push(reassignConditionalInstruction);
@@ -436,6 +441,7 @@ function createSymbolProperty(
       binding: {kind: 'Global', name: 'Symbol'},
       loc: instr.value.loc,
     },
+    effects: null,
     loc: instr.loc,
   };
   nextInstructions.push(symbolInstruction);
@@ -450,6 +456,7 @@ function createSymbolProperty(
       property: makePropertyLiteral('for'),
       loc: instr.value.loc,
     },
+    effects: null,
     loc: instr.loc,
   };
   nextInstructions.push(symbolForInstruction);
@@ -463,6 +470,7 @@ function createSymbolProperty(
       value: symbolName,
       loc: instr.value.loc,
     },
+    effects: null,
     loc: instr.loc,
   };
   nextInstructions.push(symbolValueInstruction);
@@ -478,6 +486,7 @@ function createSymbolProperty(
       args: [symbolValueInstruction.lvalue],
       loc: instr.value.loc,
     },
+    effects: null,
     loc: instr.loc,
   };
   const $$typeofProperty: ObjectProperty = {
@@ -508,6 +517,7 @@ function createTagProperty(
           value: componentTag.name,
           loc: instr.value.loc,
         },
+        effects: null,
         loc: instr.loc,
       };
       tagProperty = {
@@ -634,6 +644,7 @@ function createPropsProperties(
           elements: [...children],
           loc: instr.value.loc,
         },
+        effects: null,
         loc: instr.loc,
       };
       nextInstructions.push(childrenPropInstruction);
@@ -657,6 +668,7 @@ function createPropsProperties(
         value: null,
         loc: instr.value.loc,
       },
+      effects: null,
       loc: instr.loc,
     };
     refProperty = {
@@ -678,6 +690,7 @@ function createPropsProperties(
         value: null,
         loc: instr.value.loc,
       },
+      effects: null,
       loc: instr.loc,
     };
     keyProperty = {
@@ -711,6 +724,7 @@ function createPropsProperties(
         properties: props,
         loc: instr.value.loc,
       },
+      effects: null,
       loc: instr.loc,
     };
     propsProperty = {

compiler/packages/babel-plugin-react-compiler/src/Optimization/LowerContextAccess.ts

@@ -25,7 +25,6 @@ import {
   makeBlockId,
   makeInstructionId,
   makePropertyLiteral,
-  makeType,
   markInstructionIds,
   promoteTemporary,
   reversePostorderBlocks,
@@ -146,6 +145,7 @@ function emitLoadLoweredContextCallee(
     id: makeInstructionId(0),
     loc: GeneratedSource,
     lvalue: createTemporaryPlace(env, GeneratedSource),
+    effects: null,
     value: loadGlobal,
   };
 }
@@ -192,6 +192,7 @@ function emitPropertyLoad(
     lvalue: object,
     value: loadObj,
     id: makeInstructionId(0),
+    effects: null,
     loc: GeneratedSource,
   };
 
@@ -206,6 +207,7 @@ function emitPropertyLoad(
     lvalue: element,
     value: loadProp,
     id: makeInstructionId(0),
+    effects: null,
     loc: GeneratedSource,
   };
   return {
@@ -235,8 +237,10 @@ function emitSelectorFn(env: Environment, keys: Array<string>): Instruction {
     terminal: {
       id: makeInstructionId(0),
       kind: 'return',
+      returnVariant: 'Explicit',
       loc: GeneratedSource,
       value: arrayInstr.lvalue,
+      effects: null,
     },
     preds: new Set(),
     phis: new Set(),
@@ -249,7 +253,7 @@ function emitSelectorFn(env: Environment, keys: Array<string>): Instruction {
     env,
     params: [obj],
     returnTypeAnnotation: null,
-    returnType: makeType(),
+    returns: createTemporaryPlace(env, GeneratedSource),
     context: [],
     effects: null,
     body: {
@@ -278,6 +282,7 @@ function emitSelectorFn(env: Environment, keys: Array<string>): Instruction {
       loc: GeneratedSource,
     },
     lvalue: createTemporaryPlace(env, GeneratedSource),
+    effects: null,
     loc: GeneratedSource,
   };
   return fnInstr;
@@ -294,6 +299,7 @@ function emitArrayInstr(elements: Array<Place>, env: Environment): Instruction {
     id: makeInstructionId(0),
     value: array,
     lvalue: arrayLvalue,
+    effects: null,
     loc: GeneratedSource,
   };
   return arrayInstr;

compiler/packages/babel-plugin-react-compiler/src/Optimization/OutlineJsx.ts

@@ -21,7 +21,6 @@ import {
   makeBlockId,
   makeIdentifierName,
   makeInstructionId,
-  makeType,
   ObjectProperty,
   Place,
   promoteTemporary,
@@ -297,6 +296,7 @@ function emitOutlinedJsx(
       },
       loc: GeneratedSource,
     },
+    effects: null,
   };
   promoteTemporaryJsxTag(loadJsx.lvalue.identifier);
   const jsxExpr: Instruction = {
@@ -312,6 +312,7 @@ function emitOutlinedJsx(
       openingLoc: GeneratedSource,
       closingLoc: GeneratedSource,
     },
+    effects: null,
   };
 
   return [loadJsx, jsxExpr];
@@ -351,8 +352,10 @@ function emitOutlinedFn(
     terminal: {
       id: makeInstructionId(0),
       kind: 'return',
+      returnVariant: 'Explicit',
       loc: GeneratedSource,
       value: instructions.at(-1)!.lvalue,
+      effects: null,
     },
     preds: new Set(),
     phis: new Set(),
@@ -365,7 +368,7 @@ function emitOutlinedFn(
     env,
     params: [propsObj],
     returnTypeAnnotation: null,
-    returnType: makeType(),
+    returns: createTemporaryPlace(env, GeneratedSource),
     context: [],
     effects: null,
     body: {
@@ -517,6 +520,7 @@ function emitDestructureProps(
       loc: GeneratedSource,
       value: propsObj,
     },
+    effects: null,
   };
   return destructurePropsInstr;
 }

compiler/packages/babel-plugin-react-compiler/src/ReactiveScopes/CodegenReactiveFunction.ts

@@ -44,7 +44,7 @@ import {
   getHookKind,
   makeIdentifierName,
 } from '../HIR/HIR';
-import {printIdentifier, printPlace} from '../HIR/PrintHIR';
+import {printIdentifier, printInstruction, printPlace} from '../HIR/PrintHIR';
 import {eachPatternOperand} from '../HIR/visitors';
 import {Err, Ok, Result} from '../Utils/Result';
 import {GuardKind} from '../Utils/RuntimeDiagnosticConstants';
@@ -349,11 +349,9 @@ function codegenReactiveFunction(
   fn: ReactiveFunction,
 ): Result<CodegenFunction, CompilerError> {
   for (const param of fn.params) {
-    if (param.kind === 'Identifier') {
-      cx.temp.set(param.identifier.declarationId, null);
-    } else {
-      cx.temp.set(param.place.identifier.declarationId, null);
-    }
+    const place = param.kind === 'Identifier' ? param : param.place;
+    cx.temp.set(place.identifier.declarationId, null);
+    cx.declare(place.identifier);
   }
 
   const params = fn.params.map(param => convertParameter(param));
@@ -1183,7 +1181,7 @@ function codegenTerminal(
               ? codegenPlaceToExpression(cx, case_.test)
               : null;
           const block = codegenBlock(cx, case_.block!);
-          return t.switchCase(test, [block]);
+          return t.switchCase(test, block.body.length === 0 ? [] : [block]);
         }),
       );
     }
@@ -1310,7 +1308,7 @@ function codegenInstructionNullable(
         });
         CompilerError.invariant(value?.type === 'FunctionExpression', {
           reason: 'Expected a function as a function declaration value',
-          description: null,
+          description: `Got ${value == null ? String(value) : value.type} at ${printInstruction(instr)}`,
           loc: instr.value.loc,
           suggestions: null,
         });
@@ -1726,7 +1724,7 @@ function codegenInstructionValue(
     }
     case 'UnaryExpression': {
       value = t.unaryExpression(
-        instrValue.operator as 'throw', // todo
+        instrValue.operator,
         codegenPlaceToExpression(cx, instrValue.value),
       );
       break;
@@ -2582,7 +2580,16 @@ function codegenValue(
   value: boolean | number | string | null | undefined,
 ): t.Expression {
   if (typeof value === 'number') {
-    return t.numericLiteral(value);
+    if (value < 0) {
+      /**
+       * Babel's code generator produces invalid JS for negative numbers when
+       * run with { compact: true }.
+       * See repro https://codesandbox.io/p/devbox/5d47fr
+       */
+      return t.unaryExpression('-', t.numericLiteral(-value), false);
+    } else {
+      return t.numericLiteral(value);
+    }
   } else if (typeof value === 'boolean') {
     return t.booleanLiteral(value);
   } else if (typeof value === 'string') {

compiler/packages/babel-plugin-react-compiler/src/ReactiveScopes/ExtractScopeDeclarationsFromDestructuring.ts

@@ -79,6 +79,10 @@ 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);
 }
 

compiler/packages/babel-plugin-react-compiler/src/ReactiveScopes/MergeReactiveScopesThatInvalidateTogether.ts

@@ -456,6 +456,7 @@ function canMergeScopes(
       new Set(
         [...current.scope.declarations.values()].map(declaration => ({
           identifier: declaration.identifier,
+          reactive: true,
           path: [],
         })),
       ),

compiler/packages/babel-plugin-react-compiler/src/ReactiveScopes/PruneNonEscapingScopes.ts

@@ -829,12 +829,14 @@ class CollectDependenciesVisitor extends ReactiveFunctionVisitor<
         };
       }
       case 'UnsupportedNode': {
-        CompilerError.invariant(false, {
-          reason: `Unexpected unsupported node`,
-          description: null,
-          loc: value.loc,
-          suggestions: null,
-        });
+        const lvalues = [];
+        if (lvalue !== null) {
+          lvalues.push({place: lvalue, level: MemoizationLevel.Never});
+        }
+        return {
+          lvalues,
+          rvalues: [],
+        };
       }
       default: {
         assertExhaustive(
@@ -1064,12 +1066,29 @@ 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) {

compiler/packages/babel-plugin-react-compiler/src/Transform/TransformFire.ts

@@ -436,6 +436,7 @@ function makeLoadUseFireInstruction(
     value: instrValue,
     lvalue: {...useFirePlace},
     loc: GeneratedSource,
+    effects: null,
   };
 }
 
@@ -460,6 +461,7 @@ function makeLoadFireCalleeInstruction(
     },
     lvalue: {...loadedFireCallee},
     loc: GeneratedSource,
+    effects: null,
   };
 }
 
@@ -483,6 +485,7 @@ function makeCallUseFireInstruction(
     value: useFireCall,
     lvalue: {...useFireCallResultPlace},
     loc: GeneratedSource,
+    effects: null,
   };
 }
 
@@ -511,6 +514,7 @@ function makeStoreUseFireInstruction(
     },
     lvalue: fireFunctionBindingLValuePlace,
     loc: GeneratedSource,
+    effects: null,
   };
 }
 

compiler/packages/babel-plugin-react-compiler/src/TypeInference/InferTypes.ts

@@ -14,6 +14,7 @@ import {
   Identifier,
   IdentifierId,
   Instruction,
+  InstructionKind,
   makePropertyLiteral,
   makeType,
   PropType,
@@ -90,7 +91,8 @@ function apply(func: HIRFunction, unifier: Unifier): void {
       }
     }
   }
-  func.returnType = unifier.get(func.returnType);
+  const returns = func.returns.identifier;
+  returns.type = unifier.get(returns.type);
 }
 
 type TypeEquation = {
@@ -143,12 +145,12 @@ function* generate(
     }
   }
   if (returnTypes.length > 1) {
-    yield equation(func.returnType, {
+    yield equation(func.returns.identifier.type, {
       kind: 'Phi',
       operands: returnTypes,
     });
   } else if (returnTypes.length === 1) {
-    yield equation(func.returnType, returnTypes[0]!);
+    yield equation(func.returns.identifier.type, returnTypes[0]!);
   }
 }
 
@@ -193,12 +195,29 @@ function* generateInstructionTypes(
       break;
     }
 
-    // We intentionally do not infer types for context variables
+    // We intentionally do not infer types for most 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) {
@@ -359,6 +378,12 @@ 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;
           }
@@ -407,7 +432,7 @@ function* generateInstructionTypes(
       yield equation(left, {
         kind: 'Function',
         shapeId: BuiltInFunctionId,
-        return: value.loweredFunc.func.returnType,
+        return: value.loweredFunc.func.returns.identifier.type,
         isConstructor: false,
       });
       break;
@@ -441,7 +466,36 @@ function* generateInstructionTypes(
       yield equation(left, returnType);
       break;
     }
-    case 'PropertyStore':
+    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 'DeclareLocal':
     case 'RegExpLiteral':
     case 'MetaProperty':

compiler/packages/babel-plugin-react-compiler/src/Utils/TestUtils.ts

@@ -75,45 +75,57 @@ const testComplexConfigDefaults: PartialEnvironmentConfig = {
         source: 'react',
         importSpecifierName: 'useEffect',
       },
-      numRequiredArgs: 1,
+      autodepsIndex: 1,
     },
     {
       function: {
         source: 'shared-runtime',
         importSpecifierName: 'useSpecialEffect',
       },
-      numRequiredArgs: 2,
+      autodepsIndex: 2,
     },
     {
       function: {
         source: 'useEffectWrapper',
         importSpecifierName: 'default',
       },
-      numRequiredArgs: 1,
+      autodepsIndex: 1,
     },
   ],
 };
+
+function* splitPragma(
+  pragma: string,
+): Generator<{key: string; value: string | null}> {
+  for (const entry of pragma.split('@')) {
+    const keyVal = entry.trim();
+    const valIdx = keyVal.indexOf(':');
+    if (valIdx === -1) {
+      yield {key: keyVal.split(' ', 1)[0], value: null};
+    } else {
+      yield {key: keyVal.slice(0, valIdx), value: keyVal.slice(valIdx + 1)};
+    }
+  }
+}
+
 /**
  * For snap test fixtures and playground only.
  */
 function parseConfigPragmaEnvironmentForTest(
   pragma: string,
+  defaultConfig: PartialEnvironmentConfig,
 ): EnvironmentConfig {
-  const maybeConfig: Partial<Record<keyof EnvironmentConfig, unknown>> = {};
+  // throw early if the defaults are invalid
+  EnvironmentConfigSchema.parse(defaultConfig);
 
-  for (const token of pragma.split(' ')) {
-    if (!token.startsWith('@')) {
-      continue;
-    }
-    const keyVal = token.slice(1);
-    const valIdx = keyVal.indexOf(':');
-    const key = valIdx === -1 ? keyVal : keyVal.slice(0, valIdx);
-    const val = valIdx === -1 ? undefined : keyVal.slice(valIdx + 1);
-    const isSet = val === undefined || val === 'true';
+  const maybeConfig: Partial<Record<keyof EnvironmentConfig, unknown>> =
+    defaultConfig;
+
+  for (const {key, value: val} of splitPragma(pragma)) {
     if (!hasOwnProperty(EnvironmentConfigSchema.shape, key)) {
       continue;
     }
-
+    const isSet = val == null || val === 'true';
     if (isSet && key in testComplexConfigDefaults) {
       maybeConfig[key] = testComplexConfigDefaults[key];
     } else if (isSet) {
@@ -167,27 +179,24 @@ export function parseConfigPragmaForTests(
   pragma: string,
   defaults: {
     compilationMode: CompilationMode;
+    environment?: PartialEnvironmentConfig;
   },
 ): PluginOptions {
-  const environment = parseConfigPragmaEnvironmentForTest(pragma);
+  const environment = parseConfigPragmaEnvironmentForTest(
+    pragma,
+    defaults.environment ?? {},
+  );
   const options: Record<keyof PluginOptions, unknown> = {
     ...defaultOptions,
     panicThreshold: 'all_errors',
     compilationMode: defaults.compilationMode,
     environment,
   };
-  for (const token of pragma.split(' ')) {
-    if (!token.startsWith('@')) {
-      continue;
-    }
-    const keyVal = token.slice(1);
-    const idx = keyVal.indexOf(':');
-    const key = idx === -1 ? keyVal : keyVal.slice(0, idx);
-    const val = idx === -1 ? undefined : keyVal.slice(idx + 1);
+  for (const {key, value: val} of splitPragma(pragma)) {
     if (!hasOwnProperty(defaultOptions, key)) {
       continue;
     }
-    const isSet = val === undefined || val === 'true';
+    const isSet = val == null || val === 'true';
     if (isSet && key in testComplexPluginOptionDefaults) {
       options[key] = testComplexPluginOptionDefaults[key];
     } else if (isSet) {

compiler/packages/babel-plugin-react-compiler/src/Utils/utils.ts

@@ -121,6 +121,21 @@ export function Set_intersect<T>(sets: Array<ReadonlySet<T>>): Set<T> {
   return result;
 }
 
+/**
+ * @returns `true` if `a` is a superset of `b`.
+ */
+export function Set_isSuperset<T>(
+  a: ReadonlySet<T>,
+  b: ReadonlySet<T>,
+): boolean {
+  for (const v of b) {
+    if (!a.has(v)) {
+      return false;
+    }
+  }
+  return true;
+}
+
 export function Iterable_some<T>(
   iter: Iterable<T>,
   pred: (item: T) => boolean,

compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateHooksUsage.ts

@@ -452,7 +452,7 @@ function visitFunctionExpression(errors: CompilerError, fn: HIRFunction): void {
                 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)',
                 loc: callee.loc,
-                description: `Cannot call ${hookKind} within a function component`,
+                description: `Cannot call ${hookKind === 'Custom' ? 'hook' : hookKind} within a function expression`,
                 suggestions: null,
               }),
             );

compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateLocalsNotReassignedAfterRender.ts

@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {CompilerError, Effect} from '..';
+import {CompilerDiagnostic, CompilerError, Effect, ErrorSeverity} from '..';
 import {HIRFunction, IdentifierId, Place} from '../HIR';
 import {
   eachInstructionLValue,
@@ -28,16 +28,24 @@ export function validateLocalsNotReassignedAfterRender(fn: HIRFunction): void {
     false,
   );
   if (reassignment !== null) {
-    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 \`${reassignment.identifier.name.value}\` cannot be reassigned after render`
-          : '',
-      loc: reassignment.loc,
-    });
+    const errors = new CompilerError();
+    const variable =
+      reassignment.identifier.name != null &&
+      reassignment.identifier.name.kind === 'named'
+        ? `\`${reassignment.identifier.name.value}\``
+        : 'variable';
+    errors.pushDiagnostic(
+      CompilerDiagnostic.create({
+        severity: ErrorSeverity.InvalidReact,
+        category: '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;
   }
 }
 
@@ -75,16 +83,25 @@ function getContextReassignment(
           // if the function or its depends reassign, propagate that fact on the lvalue
           if (reassignment !== null) {
             if (isAsync || value.loweredFunc.func.async) {
-              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 \`${reassignment.identifier.name.value}\` cannot be reassigned after render`
-                    : '',
-                loc: reassignment.loc,
-              });
+              const errors = new CompilerError();
+              const variable =
+                reassignment.identifier.name !== null &&
+                reassignment.identifier.name.kind === 'named'
+                  ? `\`${reassignment.identifier.name.value}\``
+                  : 'variable';
+              errors.pushDiagnostic(
+                CompilerDiagnostic.create({
+                  severity: ErrorSeverity.InvalidReact,
+                  category: '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;
             }
             reassigningFunctions.set(lvalue.identifier.id, reassignment);
           }

compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoFreezingKnownMutableFunctions.ts

@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {CompilerError, Effect, ErrorSeverity} from '..';
+import {CompilerDiagnostic, CompilerError, Effect, ErrorSeverity} from '..';
 import {
   FunctionEffect,
   HIRFunction,
@@ -57,17 +57,30 @@ export function validateNoFreezingKnownMutableFunctions(
     if (operand.effect === Effect.Freeze) {
       const effect = contextMutationEffects.get(operand.identifier.id);
       if (effect != null) {
-        errors.push({
-          reason: `This argument is a function which modifies local variables when called, which can bypass memoization and cause the UI not to update`,
-          description: `Functions that are returned from hooks, passed as arguments to hooks, or passed as props to components may not mutate local variables`,
-          loc: operand.loc,
-          severity: ErrorSeverity.InvalidReact,
-        });
-        errors.push({
-          reason: `The function modifies a local variable here`,
-          loc: effect.loc,
-          severity: ErrorSeverity.InvalidReact,
-        });
+        const place = [...effect.places][0];
+        const variable =
+          place != null &&
+          place.identifier.name != null &&
+          place.identifier.name.kind === 'named'
+            ? `\`${place.identifier.name.value}\``
+            : 'a local variable';
+        errors.pushDiagnostic(
+          CompilerDiagnostic.create({
+            severity: ErrorSeverity.InvalidReact,
+            category: '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.loc,
+              message: `This modifies ${variable}`,
+            }),
+        );
       }
     }
   }
@@ -112,6 +125,55 @@ export function validateNoFreezingKnownMutableFunctions(
           );
           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),
+            );
+            effects: for (const effect of value.loweredFunc.func
+              .aliasingEffects) {
+              switch (effect.kind) {
+                case 'Mutate':
+                case 'MutateTransitive': {
+                  const knownMutation = contextMutationEffects.get(
+                    effect.value.identifier.id,
+                  );
+                  if (knownMutation != null) {
+                    contextMutationEffects.set(
+                      lvalue.identifier.id,
+                      knownMutation,
+                    );
+                  } else if (
+                    context.has(effect.value.identifier.id) &&
+                    !isRefOrRefLikeMutableType(effect.value.identifier.type)
+                  ) {
+                    contextMutationEffects.set(lvalue.identifier.id, {
+                      kind: 'ContextMutation',
+                      effect: Effect.Mutate,
+                      loc: effect.value.loc,
+                      places: new Set([effect.value]),
+                    });
+                    break effects;
+                  }
+                  break;
+                }
+                case 'MutateConditionally':
+                case 'MutateTransitiveConditionally': {
+                  const knownMutation = contextMutationEffects.get(
+                    effect.value.identifier.id,
+                  );
+                  if (knownMutation != null) {
+                    contextMutationEffects.set(
+                      lvalue.identifier.id,
+                      knownMutation,
+                    );
+                  }
+                  break;
+                }
+              }
+            }
           }
           break;
         }

compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoImpureFunctionsInRender.ts

@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {CompilerError, ErrorSeverity} from '..';
+import {CompilerDiagnostic, CompilerError, ErrorSeverity} from '..';
 import {HIRFunction} from '../HIR';
 import {getFunctionCallSignature} from '../Inference/InferReferenceEffects';
 import {Result} from '../Utils/Result';
@@ -34,17 +34,22 @@ export function validateNoImpureFunctionsInRender(
           callee.identifier.type,
         );
         if (signature != null && signature.impure === true) {
-          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
-                ? `\`${signature.canonicalName}\` is an impure function whose results may change on every call`
-                : null,
-            severity: ErrorSeverity.InvalidReact,
-            loc: callee.loc,
-            suggestions: null,
-          });
+          errors.pushDiagnostic(
+            CompilerDiagnostic.create({
+              category: 'Cannot call impure function during render',
+              description:
+                (signature.canonicalName != null
+                  ? `\`${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',
+            }),
+          );
         }
       }
     }

compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoJSXInTryStatement.ts

@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {CompilerError, ErrorSeverity} from '..';
+import {CompilerDiagnostic, CompilerError, ErrorSeverity} from '..';
 import {BlockId, HIRFunction} from '../HIR';
 import {Result} from '../Utils/Result';
 import {retainWhere} from '../Utils/utils';
@@ -34,11 +34,17 @@ export function validateNoJSXInTryStatement(
         switch (value.kind) {
           case 'JsxExpression':
           case 'JsxFragment': {
-            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,
-            });
+            errors.pushDiagnostic(
+              CompilerDiagnostic.create({
+                severity: ErrorSeverity.InvalidReact,
+                category: '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',
+              }),
+            );
             break;
           }
         }

compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoRefAccessInRender.ts

@@ -5,7 +5,11 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {CompilerError, ErrorSeverity} from '../CompilerError';
+import {
+  CompilerDiagnostic,
+  CompilerError,
+  ErrorSeverity,
+} from '../CompilerError';
 import {
   BlockId,
   HIRFunction,
@@ -385,28 +389,40 @@ 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) {
-                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,
-                });
+                didError = true;
+                errors.pushDiagnostic(
+                  CompilerDiagnostic.create({
+                    severity: ErrorSeverity.InvalidReact,
+                    category: 'Cannot access refs during render',
+                    description: ERROR_DESCRIPTION,
+                  }).withDetail({
+                    kind: 'error',
+                    loc: callee.loc,
+                    message: `This function accesses a ref value`,
+                  }),
+                );
               }
             }
-            for (const operand of eachInstructionValueOperand(instr.value)) {
-              if (hookKind != null) {
-                validateNoDirectRefValueAccess(errors, operand, env);
-              } else {
-                validateNoRefAccess(errors, env, operand, operand.loc);
+            if (!didError) {
+              /*
+               * If we already reported an error on this instruction, don't report
+               * duplicate errors
+               */
+              for (const operand of eachInstructionValueOperand(instr.value)) {
+                if (hookKind != null) {
+                  validateNoDirectRefValueAccess(errors, operand, env);
+                } else {
+                  validateNoRefPassedToFunction(
+                    errors,
+                    env,
+                    operand,
+                    operand.loc,
+                  );
+                }
               }
             }
             env.set(instr.lvalue.identifier.id, returnType);
@@ -449,7 +465,7 @@ function validateNoRefAccessInRenderImpl(
             ) {
               safeBlocks.delete(block.id);
             } else {
-              validateNoRefAccess(errors, env, instr.value.object, instr.loc);
+              validateNoRefUpdate(errors, env, instr.value.object, instr.loc);
             }
             for (const operand of eachInstructionValueOperand(instr.value)) {
               if (operand === instr.value.object) {
@@ -583,18 +599,17 @@ function destructure(
 
 function guardCheck(errors: CompilerError, operand: Place, env: Env): void {
   if (env.get(operand.identifier.id)?.kind === 'Guard') {
-    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,
-    });
+    errors.pushDiagnostic(
+      CompilerDiagnostic.create({
+        severity: ErrorSeverity.InvalidReact,
+        category: 'Cannot access refs during render',
+        description: ERROR_DESCRIPTION,
+      }).withDetail({
+        kind: 'error',
+        loc: operand.loc,
+        message: `Cannot access ref value during render`,
+      }),
+    );
   }
 }
 
@@ -608,22 +623,21 @@ function validateNoRefValueAccess(
     type?.kind === 'RefValue' ||
     (type?.kind === 'Structure' && type.fn?.readRefEffect)
   ) {
-    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,
-    });
+    errors.pushDiagnostic(
+      CompilerDiagnostic.create({
+        severity: ErrorSeverity.InvalidReact,
+        category: '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`,
+      }),
+    );
   }
 }
 
-function validateNoRefAccess(
+function validateNoRefPassedToFunction(
   errors: CompilerError,
   env: Env,
   operand: Place,
@@ -635,18 +649,43 @@ function validateNoRefAccess(
     type?.kind === 'RefValue' ||
     (type?.kind === 'Structure' && type.fn?.readRefEffect)
   ) {
-    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,
-    });
+    errors.pushDiagnostic(
+      CompilerDiagnostic.create({
+        severity: ErrorSeverity.InvalidReact,
+        category: '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' ||
+    (type?.kind === 'Structure' && type.fn?.readRefEffect)
+  ) {
+    errors.pushDiagnostic(
+      CompilerDiagnostic.create({
+        severity: ErrorSeverity.InvalidReact,
+        category: 'Cannot access refs during render',
+        description: ERROR_DESCRIPTION,
+      }).withDetail({
+        kind: 'error',
+        loc: (type.kind === 'RefValue' && type.loc) || loc,
+        message: `Cannot update ref during render`,
+      }),
+    );
   }
 }
 
@@ -657,17 +696,22 @@ function validateNoDirectRefValueAccess(
 ): void {
   const type = destructure(env.get(operand.identifier.id));
   if (type?.kind === 'RefValue') {
-    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,
-    });
+    errors.pushDiagnostic(
+      CompilerDiagnostic.create({
+        severity: ErrorSeverity.InvalidReact,
+        category: 'Cannot access refs during render',
+        description: ERROR_DESCRIPTION,
+      }).withDetail({
+        kind: 'error',
+        loc: type.loc ?? operand.loc,
+        message: `Cannot access ref value during render`,
+      }),
+    );
   }
 }
+
+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)';

compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoSetStateInEffects.ts

@@ -5,26 +5,32 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {CompilerError, ErrorSeverity} from '../CompilerError';
+import {
+  CompilerDiagnostic,
+  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 a *passive* effect (useEffect),
+ * Validates against calling setState in the body of an effect (useEffect and friends),
  * 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 validateNoSetStateInPassiveEffects(
+export function validateNoSetStateInEffects(
   fn: HIRFunction,
 ): Result<void, CompilerError> {
   const setStateFunctions: Map<IdentifierId, Place> = new Map();
@@ -79,19 +85,35 @@ export function validateNoSetStateInPassiveEffects(
             instr.value.kind === 'MethodCall'
               ? instr.value.receiver
               : instr.value.callee;
-          if (isUseEffectHookType(callee.identifier)) {
+          if (
+            isUseEffectHookType(callee.identifier) ||
+            isUseLayoutEffectHookType(callee.identifier) ||
+            isUseInsertionEffectHookType(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.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,
-                });
+                errors.pushDiagnostic(
+                  CompilerDiagnostic.create({
+                    category:
+                      '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',
+                  }),
+                );
               }
             }
           }

compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoSetStateInRender.ts

@@ -5,7 +5,11 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {CompilerError, ErrorSeverity} from '../CompilerError';
+import {
+  CompilerDiagnostic,
+  CompilerError,
+  ErrorSeverity,
+} from '../CompilerError';
 import {HIRFunction, IdentifierId, isSetStateType} from '../HIR';
 import {computeUnconditionalBlocks} from '../HIR/ComputeUnconditionalBlocks';
 import {eachInstructionValueOperand} from '../HIR/visitors';
@@ -122,23 +126,35 @@ function validateNoSetStateInRenderImpl(
             unconditionalSetStateFunctions.has(callee.identifier.id)
           ) {
             if (activeManualMemoId !== null) {
-              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,
-              });
+              errors.pushDiagnostic(
+                CompilerDiagnostic.create({
+                  category:
+                    '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()',
+                }),
+              );
             } else if (unconditionalBlocks.has(block.id)) {
-              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,
-              });
+              errors.pushDiagnostic(
+                CompilerDiagnostic.create({
+                  category:
+                    '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() within useMemo()',
+                }),
+              );
             }
           }
           break;

compiler/packages/babel-plugin-react-compiler/src/Validation/ValidatePreservedManualMemoization.ts

@@ -5,7 +5,11 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {CompilerError, ErrorSeverity} from '../CompilerError';
+import {
+  CompilerDiagnostic,
+  CompilerError,
+  ErrorSeverity,
+} from '../CompilerError';
 import {
   DeclarationId,
   Effect,
@@ -275,27 +279,37 @@ function validateInferredDep(
       errorDiagnostic = merge(errorDiagnostic ?? compareResult, compareResult);
     }
   }
-  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(', ')}]. ${
-            errorDiagnostic
-              ? getCompareDependencyResultDescription(errorDiagnostic)
-              : 'Inferred dependency not present in source'
-          }`
-        : null,
-    loc: memoLocation,
-    suggestions: null,
-  });
+  errorState.pushDiagnostic(
+    CompilerDiagnostic.create({
+      severity: ErrorSeverity.CannotPreserveMemoization,
+      category:
+        'Compilation skipped because existing memoization could not be preserved',
+      description: [
+        'React Compiler has skipped optimizing this component because the existing manual memoization could not be preserved. ',
+        'The inferred dependencies did not match the manually specified dependencies, which could cause the value to change more or less frequently than expected. ',
+        DEBUG ||
+        // If the dependency is a named variable then we can report it. Otherwise only print in debug mode
+        (dep.identifier.name != null && dep.identifier.name.kind === 'named')
+          ? `The inferred dependency was \`${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',
+    }),
+  );
 }
 
 class Visitor extends ReactiveFunctionVisitor<VisitorState> {
@@ -445,11 +459,13 @@ 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,
@@ -457,6 +473,21 @@ 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) {
@@ -502,14 +533,21 @@ class Visitor extends ReactiveFunctionVisitor<VisitorState> {
           !this.scopes.has(identifier.scope.id) &&
           !this.prunedScopes.has(identifier.scope.id)
         ) {
-          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,
-          });
+          state.errors.pushDiagnostic(
+            CompilerDiagnostic.create({
+              severity: ErrorSeverity.CannotPreserveMemoization,
+              category:
+                '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',
+            }),
+          );
         }
       }
     }
@@ -543,16 +581,25 @@ class Visitor extends ReactiveFunctionVisitor<VisitorState> {
 
           for (const identifier of decls) {
             if (isUnmemoized(identifier, this.scopes)) {
-              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
-                  ? `${printIdentifier(identifier)} was not memoized`
-                  : null,
-                severity: ErrorSeverity.CannotPreserveMemoization,
-                loc,
-                suggestions: null,
-              });
+              state.errors.pushDiagnostic(
+                CompilerDiagnostic.create({
+                  severity: ErrorSeverity.CannotPreserveMemoization,
+                  category:
+                    'Compilation skipped because existing memoization could not be preserved',
+                  description: [
+                    'React Compiler has skipped optimizing this component because the existing manual memoization could not be preserved. This value was memoized in source but not in compilation output. ',
+                    DEBUG
+                      ? `${printIdentifier(identifier)} was not memoized.`
+                      : '',
+                  ]
+                    .join('')
+                    .trim(),
+                }).withDetail({
+                  kind: 'error',
+                  loc,
+                  message: 'Could not preserve existing memoization',
+                }),
+              );
             }
           }
         }

compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateStaticComponents.ts

@@ -5,7 +5,11 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {CompilerError, ErrorSeverity} from '../CompilerError';
+import {
+  CompilerDiagnostic,
+  CompilerError,
+  ErrorSeverity,
+} from '../CompilerError';
 import {HIRFunction, IdentifierId, SourceLocation} from '../HIR';
 import {Result} from '../Utils/Result';
 
@@ -59,20 +63,23 @@ export function validateStaticComponents(
               value.tag.identifier.id,
             );
             if (location != null) {
-              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,
-              });
+              error.pushDiagnostic(
+                CompilerDiagnostic.create({
+                  severity: ErrorSeverity.InvalidReact,
+                  category: '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',
+                  }),
+              );
             }
           }
         }

compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateUseMemo.ts

@@ -5,7 +5,11 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {CompilerError, ErrorSeverity} from '..';
+import {
+  CompilerDiagnostic,
+  CompilerError,
+  ErrorSeverity,
+} from '../CompilerError';
 import {FunctionExpression, HIRFunction, IdentifierId} from '../HIR';
 import {Result} from '../Utils/Result';
 
@@ -63,24 +67,41 @@ export function validateUseMemo(fn: HIRFunction): Result<void, CompilerError> {
           }
 
           if (body.loweredFunc.func.params.length > 0) {
-            errors.push({
-              severity: ErrorSeverity.InvalidReact,
-              reason: 'useMemo callbacks may not accept any arguments',
-              description: null,
-              loc: body.loc,
-              suggestions: null,
-            });
+            const firstParam = body.loweredFunc.func.params[0];
+            const loc =
+              firstParam.kind === 'Identifier'
+                ? firstParam.loc
+                : firstParam.place.loc;
+            errors.pushDiagnostic(
+              CompilerDiagnostic.create({
+                severity: ErrorSeverity.InvalidReact,
+                category: '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',
+              }),
+            );
           }
 
           if (body.loweredFunc.func.async || body.loweredFunc.func.generator) {
-            errors.push({
-              severity: ErrorSeverity.InvalidReact,
-              reason:
-                'useMemo callbacks may not be async or generator functions',
-              description: null,
-              loc: body.loc,
-              suggestions: null,
-            });
+            errors.pushDiagnostic(
+              CompilerDiagnostic.create({
+                severity: ErrorSeverity.InvalidReact,
+                category:
+                  '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',
+              }),
+            );
           }
 
           break;

compiler/packages/babel-plugin-react-compiler/src/Validation/index.ts

@@ -9,7 +9,7 @@ export {validateContextVariableLValues} from './ValidateContextVariableLValues';
 export {validateHooksUsage} from './ValidateHooksUsage';
 export {validateMemoizedEffectDependencies} from './ValidateMemoizedEffectDependencies';
 export {validateNoCapitalizedCalls} from './ValidateNoCapitalizedCalls';
-export {validateNoRefAccessInRender} from './ValidateNoRefAccesInRender';
+export {validateNoRefAccessInRender} from './ValidateNoRefAccessInRender';
 export {validateNoSetStateInRender} from './ValidateNoSetStateInRender';
 export {validatePreservedManualMemoization} from './ValidatePreservedManualMemoization';
 export {validateUseMemo} from './ValidateUseMemo';

compiler/packages/babel-plugin-react-compiler/src/__tests__/Logger-test.ts

@@ -58,7 +58,8 @@ it('logs failed compilation', () => {
 
   expect(event.detail.severity).toEqual('InvalidReact');
   //@ts-ignore
-  const {start, end, identifierName} = event.detail.loc as t.SourceLocation;
+  const {start, end, identifierName} =
+    event.detail.primaryLocation() 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');

compiler/packages/babel-plugin-react-compiler/src/__tests__/envConfig-test.ts

@@ -20,7 +20,7 @@ describe('parseConfigPragma()', () => {
         validateHooksUsage: 1,
       } as any);
     }).toThrowErrorMatchingInlineSnapshot(
-      `"InvalidConfig: Could not validate environment config. Update React Compiler config to fix the error. Validation error: Expected boolean, received number at "validateHooksUsage""`,
+      `"Error: 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',
             },
-            numRequiredArgs: 0,
+            autodepsIndex: 0,
           },
         ],
       } as any);
     }).toThrowErrorMatchingInlineSnapshot(
-      `"InvalidConfig: Could not validate environment config. Update React Compiler config to fix the error. Validation error: numRequiredArgs must be > 0 at "inferEffectDependencies[0].numRequiredArgs""`,
+      `"Error: Could not validate environment config. Update React Compiler config to fix the error. Validation error: autodepsIndex must be > 0 at "inferEffectDependencies[0].autodepsIndex"."`,
     );
   });
 

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/aliased-nested-scope-truncated-dep.expect.md

@@ -175,21 +175,14 @@ import {
  * and mutability.
  */
 function Component(t0) {
-  const $ = _c(4);
+  const $ = _c(2);
   const { prop } = t0;
   let t1;
   if ($[0] !== prop) {
     const obj = shallowCopy(prop);
     const aliasedObj = identity(obj);
-    let t2;
-    if ($[2] !== obj) {
-      t2 = [obj.id];
-      $[2] = obj;
-      $[3] = t2;
-    } else {
-      t2 = $[3];
-    }
-    const id = t2;
+
+    const id = [obj.id];
 
     mutate(aliasedObj);
     setPropertyByKey(aliasedObj, "id", prop.id + 1);

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/align-scopes-iife-return-modified-later-logical.expect.md

@@ -26,20 +26,16 @@ import { c as _c } from "react/compiler-runtime";
 import { getNull } from "shared-runtime";
 
 function Component(props) {
-  const $ = _c(3);
-  let t0;
+  const $ = _c(2);
   let items;
   if ($[0] !== props.a) {
-    t0 = getNull() ?? [];
-    items = t0;
+    items = getNull() ?? [];
 
     items.push(props.a);
     $[0] = props.a;
     $[1] = items;
-    $[2] = t0;
   } else {
     items = $[1];
-    t0 = $[2];
   }
   return items;
 }

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/allow-modify-global-in-callback-jsx.expect.md

@@ -52,15 +52,13 @@ function Component(t0) {
   }
   const onClick = t1;
   let t2;
-  let t3;
   if ($[2] !== onClick) {
-    t3 = <div onClick={onClick}>{someGlobal.value}</div>;
+    t2 = <div onClick={onClick}>{someGlobal.value}</div>;
     $[2] = onClick;
-    $[3] = t3;
+    $[3] = t2;
   } else {
-    t3 = $[3];
+    t2 = $[3];
   }
-  t2 = t3;
   return t2;
 }
 

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/array-pattern-spread-creates-array.expect.md

@@ -0,0 +1,104 @@
+
+## Input
+
+```javascript
+// @validatePreserveExistingMemoizationGuarantees
+import {useMemo} from 'react';
+import {makeObject_Primitives, ValidateMemoization} from 'shared-runtime';
+
+function Component(props) {
+  // Should memoize independently
+  const x = useMemo(() => makeObject_Primitives(), []);
+
+  const rest = useMemo(() => {
+    const [_, ...rest] = props.array;
+
+    // Should be inferred as Array.proto.push which doesn't mutate input
+    rest.push(x);
+    return rest;
+  });
+
+  return (
+    <>
+      <ValidateMemoization inputs={[]} output={x} />
+      <ValidateMemoization inputs={[props.array]} output={rest} />
+    </>
+  );
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Component,
+  params: [{array: [0, 1, 2]}],
+};
+
+```
+
+## Code
+
+```javascript
+import { c as _c } from "react/compiler-runtime"; // @validatePreserveExistingMemoizationGuarantees
+import { useMemo } from "react";
+import { makeObject_Primitives, ValidateMemoization } from "shared-runtime";
+
+function Component(props) {
+  const $ = _c(9);
+  let t0;
+  if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
+    t0 = makeObject_Primitives();
+    $[0] = t0;
+  } else {
+    t0 = $[0];
+  }
+  const x = t0;
+  let rest;
+  if ($[1] !== props.array) {
+    [, ...rest] = props.array;
+
+    rest.push(x);
+    $[1] = props.array;
+    $[2] = rest;
+  } else {
+    rest = $[2];
+  }
+  const rest_0 = rest;
+  let t1;
+  if ($[3] === Symbol.for("react.memo_cache_sentinel")) {
+    t1 = <ValidateMemoization inputs={[]} output={x} />;
+    $[3] = t1;
+  } else {
+    t1 = $[3];
+  }
+  let t2;
+  if ($[4] !== props.array) {
+    t2 = [props.array];
+    $[4] = props.array;
+    $[5] = t2;
+  } else {
+    t2 = $[5];
+  }
+  let t3;
+  if ($[6] !== rest_0 || $[7] !== t2) {
+    t3 = (
+      <>
+        {t1}
+        <ValidateMemoization inputs={t2} output={rest_0} />
+      </>
+    );
+    $[6] = rest_0;
+    $[7] = t2;
+    $[8] = t3;
+  } else {
+    t3 = $[8];
+  }
+  return t3;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Component,
+  params: [{ array: [0, 1, 2] }],
+};
+
+```
+      
+### Eval output
+(kind: ok) <div>{"inputs":[],"output":{"a":0,"b":"value1","c":true}}</div><div>{"inputs":[[0,1,2]],"output":[1,2,{"a":0,"b":"value1","c":true}]}</div>

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/array-pattern-spread-creates-array.js

@@ -0,0 +1,28 @@
+// @validatePreserveExistingMemoizationGuarantees
+import {useMemo} from 'react';
+import {makeObject_Primitives, ValidateMemoization} from 'shared-runtime';
+
+function Component(props) {
+  // Should memoize independently
+  const x = useMemo(() => makeObject_Primitives(), []);
+
+  const rest = useMemo(() => {
+    const [_, ...rest] = props.array;
+
+    // Should be inferred as Array.proto.push which doesn't mutate input
+    rest.push(x);
+    return rest;
+  });
+
+  return (
+    <>
+      <ValidateMemoization inputs={[]} output={x} />
+      <ValidateMemoization inputs={[props.array]} output={rest} />
+    </>
+  );
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Component,
+  params: [{array: [0, 1, 2]}],
+};

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/babel-existing-react-import.expect.md

@@ -30,50 +30,46 @@ function Component(props) {
   const $ = _c(4);
   const [x] = useState(0);
   let t0;
-  let t1;
   if ($[0] !== x) {
-    t1 = calculateExpensiveNumber(x);
+    t0 = calculateExpensiveNumber(x);
     $[0] = x;
-    $[1] = t1;
+    $[1] = t0;
   } else {
-    t1 = $[1];
+    t0 = $[1];
   }
-  t0 = t1;
   const expensiveNumber = t0;
-  let t2;
+  let t1;
   if ($[2] !== expensiveNumber) {
-    t2 = <div>{expensiveNumber}</div>;
+    t1 = <div>{expensiveNumber}</div>;
     $[2] = expensiveNumber;
-    $[3] = t2;
+    $[3] = t1;
   } else {
-    t2 = $[3];
+    t1 = $[3];
   }
-  return t2;
+  return t1;
 }
 
 function Component2(props) {
   const $ = _c(4);
   const [x] = useState(0);
   let t0;
-  let t1;
   if ($[0] !== x) {
-    t1 = calculateExpensiveNumber(x);
+    t0 = calculateExpensiveNumber(x);
     $[0] = x;
-    $[1] = t1;
+    $[1] = t0;
   } else {
-    t1 = $[1];
+    t0 = $[1];
   }
-  t0 = t1;
   const expensiveNumber = t0;
-  let t2;
+  let t1;
   if ($[2] !== expensiveNumber) {
-    t2 = <div>{expensiveNumber}</div>;
+    t1 = <div>{expensiveNumber}</div>;
     $[2] = expensiveNumber;
-    $[3] = t2;
+    $[3] = t1;
   } else {
-    t2 = $[3];
+    t1 = $[3];
   }
-  return t2;
+  return t1;
 }
 
 ```

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/babel-existing-react-kitchensink-import.expect.md

@@ -32,50 +32,46 @@ function Component(props) {
   const $ = _c(4);
   const [x] = useState(0);
   let t0;
-  let t1;
   if ($[0] !== x) {
-    t1 = calculateExpensiveNumber(x);
+    t0 = calculateExpensiveNumber(x);
     $[0] = x;
-    $[1] = t1;
+    $[1] = t0;
   } else {
-    t1 = $[1];
+    t0 = $[1];
   }
-  t0 = t1;
   const expensiveNumber = t0;
-  let t2;
+  let t1;
   if ($[2] !== expensiveNumber) {
-    t2 = <div>{expensiveNumber}</div>;
+    t1 = <div>{expensiveNumber}</div>;
     $[2] = expensiveNumber;
-    $[3] = t2;
+    $[3] = t1;
   } else {
-    t2 = $[3];
+    t1 = $[3];
   }
-  return t2;
+  return t1;
 }
 
 function Component2(props) {
   const $ = _c(4);
   const [x] = useState(0);
   let t0;
-  let t1;
   if ($[0] !== x) {
-    t1 = calculateExpensiveNumber(x);
+    t0 = calculateExpensiveNumber(x);
     $[0] = x;
-    $[1] = t1;
+    $[1] = t0;
   } else {
-    t1 = $[1];
+    t0 = $[1];
   }
-  t0 = t1;
   const expensiveNumber = t0;
-  let t2;
+  let t1;
   if ($[2] !== expensiveNumber) {
-    t2 = <div>{expensiveNumber}</div>;
+    t1 = <div>{expensiveNumber}</div>;
     $[2] = expensiveNumber;
-    $[3] = t2;
+    $[3] = t1;
   } else {
-    t2 = $[3];
+    t1 = $[3];
   }
-  return t2;
+  return t1;
 }
 
 ```

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/babel-existing-react-namespace-import.expect.md

@@ -30,25 +30,23 @@ function Component(props) {
   const $ = _c(4);
   const [x] = React.useState(0);
   let t0;
-  let t1;
   if ($[0] !== x) {
-    t1 = calculateExpensiveNumber(x);
+    t0 = calculateExpensiveNumber(x);
     $[0] = x;
-    $[1] = t1;
+    $[1] = t0;
   } else {
-    t1 = $[1];
+    t0 = $[1];
   }
-  t0 = t1;
   const expensiveNumber = t0;
-  let t2;
+  let t1;
   if ($[2] !== expensiveNumber) {
-    t2 = <div>{expensiveNumber}</div>;
+    t1 = <div>{expensiveNumber}</div>;
     $[2] = expensiveNumber;
-    $[3] = t2;
+    $[3] = t1;
   } else {
-    t2 = $[3];
+    t1 = $[3];
   }
-  return t2;
+  return t1;
 }
 
 export const FIXTURE_ENTRYPOINT = {

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/babel-existing-react-runtime-import.expect.md

@@ -36,30 +36,28 @@ function Component(props) {
   const $ = _c(4);
   const [x] = React.useState(0);
   let t0;
-  let t1;
   if ($[0] !== x) {
-    t1 = calculateExpensiveNumber(x);
+    t0 = calculateExpensiveNumber(x);
     $[0] = x;
-    $[1] = t1;
+    $[1] = t0;
   } else {
-    t1 = $[1];
+    t0 = $[1];
   }
-  t0 = t1;
   const expensiveNumber = t0;
-  let t2;
+  let t1;
   if ($[2] !== expensiveNumber) {
-    t2 = (
+    t1 = (
       <div>
         {expensiveNumber}
         {`${someImport}`}
       </div>
     );
     $[2] = expensiveNumber;
-    $[3] = t2;
+    $[3] = t1;
   } else {
-    t2 = $[3];
+    t1 = $[3];
   }
-  return t2;
+  return t1;
 }
 
 export const FIXTURE_ENTRYPOINT = {

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/babel-repro-compact-negative-number.expect.md

@@ -0,0 +1,56 @@
+
+## Input
+
+```javascript
+import {Stringify} from 'shared-runtime';
+
+function Repro(props) {
+  const MY_CONST = -2;
+  return <Stringify>{props.arg - MY_CONST}</Stringify>;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Repro,
+  params: [
+    {
+      arg: 3,
+    },
+  ],
+};
+
+```
+
+## Code
+
+```javascript
+import { c as _c } from "react/compiler-runtime";
+import { Stringify } from "shared-runtime";
+
+function Repro(props) {
+  const $ = _c(2);
+
+  const t0 = props.arg - -2;
+  let t1;
+  if ($[0] !== t0) {
+    t1 = <Stringify>{t0}</Stringify>;
+    $[0] = t0;
+    $[1] = t1;
+  } else {
+    t1 = $[1];
+  }
+  return t1;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Repro,
+  params: [
+    {
+      arg: 3,
+    },
+  ],
+};
+
+```
+      
+### Eval output
+(kind: ok) <div>{"children":5}</div>

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/babel-repro-compact-negative-number.js

@@ -0,0 +1,15 @@
+import {Stringify} from 'shared-runtime';
+
+function Repro(props) {
+  const MY_CONST = -2;
+  return <Stringify>{props.arg - MY_CONST}</Stringify>;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Repro,
+  params: [
+    {
+      arg: 3,
+    },
+  ],
+};

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/block-scoping-switch-variable-scoping.expect.md

@@ -36,26 +36,22 @@ import { useMemo } from "react";
 function Component(props) {
   const $ = _c(2);
   let t0;
-  let t1;
   if ($[0] !== props.value) {
-    t1 = { value: props.value };
+    t0 = { value: props.value };
     $[0] = props.value;
-    $[1] = t1;
+    $[1] = t0;
   } else {
-    t1 = $[1];
+    t0 = $[1];
   }
-  const handlers = t1;
+  const handlers = t0;
   bb0: switch (props.test) {
     case true: {
       console.log(handlers.value);
       break bb0;
     }
-    default: {
-    }
+    default:
   }
-
-  t0 = handlers;
-  const outerHandlers = t0;
+  const outerHandlers = handlers;
   return outerHandlers;
 }
 

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/bug-aliased-capture-aliased-mutate.expect.md

@@ -2,7 +2,7 @@
 ## Input
 
 ```javascript
-// @flow @enableTransitivelyFreezeFunctionExpressions:false
+// @flow @enableTransitivelyFreezeFunctionExpressions:false @enableNewMutationAliasingModel:false
 import {arrayPush, setPropertyByKey, Stringify} from 'shared-runtime';
 
 /**

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/bug-aliased-capture-aliased-mutate.js

@@ -1,4 +1,4 @@
-// @flow @enableTransitivelyFreezeFunctionExpressions:false
+// @flow @enableTransitivelyFreezeFunctionExpressions:false @enableNewMutationAliasingModel:false
 import {arrayPush, setPropertyByKey, Stringify} from 'shared-runtime';
 
 /**

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/bug-aliased-capture-mutate.expect.md

@@ -2,7 +2,7 @@
 ## Input
 
 ```javascript
-// @flow @enableTransitivelyFreezeFunctionExpressions:false
+// @flow @enableTransitivelyFreezeFunctionExpressions:false @enableNewMutationAliasingModel:false
 import {setPropertyByKey, Stringify} from 'shared-runtime';
 
 /**

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/bug-aliased-capture-mutate.js

@@ -1,4 +1,4 @@
-// @flow @enableTransitivelyFreezeFunctionExpressions:false
+// @flow @enableTransitivelyFreezeFunctionExpressions:false @enableNewMutationAliasingModel:false
 import {setPropertyByKey, Stringify} from 'shared-runtime';
 
 /**

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/bug-capturing-func-maybealias-captured-mutate.expect.md

@@ -2,6 +2,7 @@
 ## Input
 
 ```javascript
+// @enableNewMutationAliasingModel:false
 import {makeArray, mutate} from 'shared-runtime';
 
 /**
@@ -56,7 +57,7 @@ export const FIXTURE_ENTRYPOINT = {
 ## Code
 
 ```javascript
-import { c as _c } from "react/compiler-runtime";
+import { c as _c } from "react/compiler-runtime"; // @enableNewMutationAliasingModel:false
 import { makeArray, mutate } from "shared-runtime";
 
 /**

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/bug-capturing-func-maybealias-captured-mutate.ts

@@ -1,3 +1,4 @@
+// @enableNewMutationAliasingModel:false
 import {makeArray, mutate} from 'shared-runtime';
 
 /**

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/bug-invalid-phi-as-dependency.expect.md

@@ -2,6 +2,7 @@
 ## Input
 
 ```javascript
+// @enableNewMutationAliasingModel:false
 import {CONST_TRUE, Stringify, mutate, useIdentity} from 'shared-runtime';
 
 /**
@@ -38,7 +39,7 @@ export const FIXTURE_ENTRYPOINT = {
 ## Code
 
 ```javascript
-import { c as _c } from "react/compiler-runtime";
+import { c as _c } from "react/compiler-runtime"; // @enableNewMutationAliasingModel:false
 import { CONST_TRUE, Stringify, mutate, useIdentity } from "shared-runtime";
 
 /**

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/bug-invalid-phi-as-dependency.tsx

@@ -1,3 +1,4 @@
+// @enableNewMutationAliasingModel:false
 import {CONST_TRUE, Stringify, mutate, useIdentity} from 'shared-runtime';
 
 /**

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/bug-object-expression-computed-key-modified-during-after-construction-hoisted-sequence-expr.expect.md

@@ -2,6 +2,7 @@
 ## Input
 
 ```javascript
+// @enableNewMutationAliasingModel:false
 import {identity, mutate} from 'shared-runtime';
 
 /**
@@ -39,7 +40,7 @@ export const FIXTURE_ENTRYPOINT = {
 ## Code
 
 ```javascript
-import { c as _c } from "react/compiler-runtime";
+import { c as _c } from "react/compiler-runtime"; // @enableNewMutationAliasingModel:false
 import { identity, mutate } from "shared-runtime";
 
 /**