[compiler] cleanup lints

Separated this out into its own PR since it's really a cosmetic change.

CompilerErrorDetail and CompilerDiagnostic now both expect `reason`/`category` and `description` to *not* have trailing periods.

.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',
       },
     },
@@ -608,6 +608,7 @@ module.exports = {
     symbol: 'readonly',
     SyntheticEvent: 'readonly',
     SyntheticMouseEvent: 'readonly',
+    SyntheticPointerEvent: 'readonly',
     Thenable: 'readonly',
     TimeoutID: 'readonly',
     WheelEventHandler: 'readonly',
@@ -622,6 +623,7 @@ module.exports = {
     ScrollTimeline: 'readonly',
     EventListenerOptionsOrUseCapture: 'readonly',
     FocusOptions: 'readonly',
+    OptionalEffectTiming: 'readonly',
 
     spyOnDev: 'readonly',
     spyOnDevAndProd: 'readonly',

.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'
@@ -325,7 +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'
@@ -420,7 +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'
@@ -465,7 +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'
@@ -493,7 +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__
@@ -530,7 +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'
@@ -570,7 +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'
@@ -607,7 +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'
@@ -648,7 +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'
@@ -722,7 +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'
@@ -779,7 +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'
@@ -824,7 +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'
@@ -873,7 +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

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/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/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

@@ -5,39 +5,38 @@
  * 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';
+import {ErrorSeverity} from './Utils/CompilerErrorSeverity';
+import {
+  ErrorCode,
+  ErrorCodeDetails,
+  LinterCategory,
+} from './Utils/CompilerErrorCodes';
+export {ErrorSeverity};
+export {ErrorCode, ErrorCodeDetails, LinterCategory};
 
-export enum ErrorSeverity {
+export type CompilerDiagnosticOptions = {
+  severity: ErrorSeverity;
+  category: string;
+  description?: string | null | undefined;
+  details: Array<CompilerDiagnosticDetail>;
+  suggestions?: Array<CompilerSuggestion> | null | undefined;
+  linterCategory?: LinterCategory | null | undefined;
+};
+
+export type CompilerDiagnosticDetail =
   /**
-   * Invalid JS syntax, or valid syntax that is semantically invalid which may indicate some
-   * misunderstanding on the user’s part.
+   * A/the source of the error
    */
-  InvalidJS = 'InvalidJS',
-  /**
-   * Code that breaks the rules of React.
-   */
-  InvalidReact = 'InvalidReact',
-  /**
-   * Incorrect configuration of the compiler.
-   */
-  InvalidConfig = 'InvalidConfig',
-  /**
-   * Code that can reasonably occur and that doesn't break any rules, but is unsafe to preserve
-   * memoization.
-   */
-  CannotPreserveMemoization = 'CannotPreserveMemoization',
-  /**
-   * Unhandled syntax that we don't support yet.
-   */
-  Todo = 'Todo',
-  /**
-   * An unexpected internal error in the compiler that indicates critical issues that can panic
-   * the compiler.
-   */
-  Invariant = 'Invariant',
-}
+  {
+    kind: 'error';
+    loc: SourceLocation | null;
+    message: string;
+  };
 
 export enum CompilerSuggestionOperation {
   InsertBefore,
@@ -61,13 +60,180 @@ export type CompilerSuggestion =
       description: string;
     };
 
-export type CompilerErrorDetailOptions = {
+export type PlainCompilerErrorDetailOptions = {
+  errorCode?: void;
   reason: string;
   description?: string | null | undefined;
-  severity: ErrorSeverity;
+  severity:
+    | ErrorSeverity.Invariant
+    | ErrorSeverity.Todo
+    | ErrorSeverity.InvalidConfig;
   loc: SourceLocation | null;
   suggestions?: Array<CompilerSuggestion> | null | undefined;
 };
+export type CodedCompilerErrorDetailOptions = {
+  errorCode: ErrorCode;
+  description?: string | null | undefined;
+  loc: SourceLocation | null;
+  suggestions?: Array<CompilerSuggestion> | null | undefined;
+  linterCategory?: LinterCategory | null | undefined;
+};
+
+export type CompilerErrorDetailOptions =
+  | PlainCompilerErrorDetailOptions
+  | CodedCompilerErrorDetailOptions;
+
+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 function makeCompilerDiagnostic(
+  code: ErrorCode,
+  options?: {
+    description?: string;
+    suggestions?: Array<CompilerSuggestion> | null | undefined;
+  },
+): CompilerDiagnostic {
+  return makeCompilerDiagnostic(code, options);
+}
+
+export class CompilerDiagnostic {
+  options: CompilerDiagnosticOptions;
+
+  /**
+   * Constructor is private to enforce that we either only create invariant diagnostics
+   * or use ErrorCodes
+   */
+  private constructor(options: CompilerDiagnosticOptions) {
+    this.options = options;
+  }
+
+  static create<
+    T extends CompilerDiagnosticOptions & {severity: ErrorSeverity.Invariant},
+  >(options: Omit<T, 'details'>): CompilerDiagnostic {
+    return new CompilerDiagnostic({...options, details: []});
+  }
+
+  static fromCode(
+    code: ErrorCode,
+    options?: {
+      description?: string;
+      suggestions?: Array<CompilerSuggestion> | null | undefined;
+      details?: Array<CompilerDiagnosticDetail> | null | undefined;
+    },
+  ): CompilerDiagnostic {
+    const errorEntry = ErrorCodeDetails[code];
+    let description = undefined;
+    if (errorEntry.description != null) {
+      description = endWithPeriod(errorEntry.description);
+    }
+    if (options?.description != null && options.description.length > 0) {
+      if (description != null && description.length > 0) {
+        description += ' ';
+      } else {
+        description = '';
+      }
+      description += endWithPeriod(options.description);
+    }
+
+    const diagnosticOptions: CompilerDiagnosticOptions = {
+      severity: errorEntry.severity,
+      category: errorEntry.reason,
+      description,
+      linterCategory: errorEntry.linterCategory,
+      suggestions: options?.suggestions,
+      details: options?.details ?? [],
+    };
+
+    return new CompilerDiagnostic(diagnosticOptions);
+  }
+
+  // TODO: remove after converting test fixtures to use printErrorMessage
+  serialize(): unknown {
+    return {options: {...this.options, linterCategory: undefined}};
+  }
+
+  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;
+  }
+  get linterCategory(): CompilerDiagnosticOptions['linterCategory'] {
+    return this.options.linterCategory;
+  }
+
+  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)];
+    if (this.description != null) {
+      buffer.push(`\n\n${endWithPeriod(this.description)}`);
+    }
+    for (const detail of this.options.details) {
+      switch (detail.kind) {
+        case 'error': {
+          const loc = detail.loc;
+          if (loc == null || typeof loc === 'symbol') {
+            continue;
+          }
+          let codeFrame: string;
+          try {
+            codeFrame = printCodeFrame(source, loc, detail.message);
+          } catch (e) {
+            codeFrame = detail.message;
+          }
+          buffer.push('\n\n');
+          if (loc.filename != null) {
+            const line = loc.start.line;
+            const column = options.eslint
+              ? loc.start.column + 1
+              : loc.start.column;
+            buffer.push(`${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(`. ${endWithPeriod(this.description)}`);
+    }
+    const loc = this.primaryLocation();
+    if (loc != null && typeof loc !== 'symbol') {
+      buffer.push(` (${loc.start.line}:${loc.start.column})`);
+    }
+    return buffer.join('');
+  }
+}
 
 /*
  * Each bailout or invariant in HIR lowering creates an {@link CompilerErrorDetail}, which is then
@@ -80,13 +246,68 @@ export class CompilerErrorDetail {
     this.options = options;
   }
 
-  get reason(): CompilerErrorDetailOptions['reason'] {
-    return this.options.reason;
+  static fromCode(
+    code: ErrorCode,
+    details?: {
+      description?: string | null;
+      loc?: SourceLocation | null;
+      suggestions?: Array<CompilerSuggestion> | null | undefined;
+    },
+  ): CompilerErrorDetail {
+    return new CompilerErrorDetail({
+      ...details,
+      errorCode: code,
+    } as CodedCompilerErrorDetailOptions);
   }
-  get description(): CompilerErrorDetailOptions['description'] {
-    return this.options.description;
+
+  // TODO: remove after converting test fixtures to use printErrorMessage
+  serialize(): unknown {
+    return {
+      options: {
+        reason: this.reason,
+        description: this.description,
+        severity: this.severity,
+        loc: this.loc,
+        suggestions: this.suggestions,
+      },
+    };
   }
-  get severity(): CompilerErrorDetailOptions['severity'] {
+
+  get reason(): string {
+    if (this.options.errorCode != null) {
+      return ErrorCodeDetails[this.options.errorCode].reason;
+    } else {
+      return this.options.reason;
+    }
+  }
+  get description(): string | null | undefined {
+    if (this.options.errorCode != null) {
+      let description = undefined;
+      const errorEntry = ErrorCodeDetails[this.options.errorCode];
+      if (errorEntry.description != null) {
+        description = endWithPeriod(errorEntry.description);
+      }
+      if (
+        this.options.description != null &&
+        this.options.description.length > 0
+      ) {
+        if (description != null && description.length > 0) {
+          description += ' ';
+        } else {
+          description = '';
+        }
+        description += endWithPeriod(this.options.description);
+      }
+      return description;
+    }
+    return this.options.description != null
+      ? endWithPeriod(this.options.description)
+      : this.options.description;
+  }
+  get severity(): ErrorSeverity {
+    if (this.options.errorCode != null) {
+      return ErrorCodeDetails[this.options.errorCode].severity;
+    }
     return this.options.severity;
   }
   get loc(): CompilerErrorDetailOptions['loc'] {
@@ -95,29 +316,62 @@ export class CompilerErrorDetail {
   get suggestions(): CompilerErrorDetailOptions['suggestions'] {
     return this.options.suggestions;
   }
-
-  printErrorMessage(): string {
-    const buffer = [`${this.severity}: ${this.reason}`];
-    if (this.description != null) {
-      buffer.push(`. ${this.description}`);
+  get linterCategory(): LinterCategory | null | undefined {
+    if (this.options.errorCode != null) {
+      return ErrorCodeDetails[this.options.errorCode].linterCategory;
     }
-    if (this.loc != null && typeof this.loc !== 'symbol') {
-      buffer.push(` (${this.loc.start.line}:${this.loc.end.line})`);
+    return undefined;
+  }
+
+  primaryLocation(): SourceLocation | null {
+    return this.loc;
+  }
+
+  printErrorMessage(source: string, options: PrintErrorMessageOptions): string {
+    const buffer = [printErrorSummary(this.severity, this.reason)];
+    if (this.description != null) {
+      buffer.push(`\n\n${endWithPeriod(this.description)}`);
+    }
+    const loc = this.loc;
+    if (loc != null && typeof loc !== 'symbol') {
+      let codeFrame: string;
+      try {
+        codeFrame = printCodeFrame(source, loc, this.reason);
+      } catch (e) {
+        codeFrame = '';
+      }
+      buffer.push(`\n\n`);
+      if (loc.filename != null) {
+        const line = loc.start.line;
+        const column = options.eslint ? loc.start.column + 1 : loc.start.column;
+        buffer.push(`${loc.filename}:${line}:${column}\n`);
+      }
+      buffer.push(codeFrame);
+      buffer.push('\n\n');
     }
     return buffer.join('');
   }
 
   toString(): string {
-    return this.printErrorMessage();
+    const buffer = [printErrorSummary(this.severity, this.reason)];
+    if (this.description != null) {
+      buffer.push(`. ${endWithPeriod(this.description)}`);
+    }
+    const loc = this.loc;
+    if (loc != null && typeof loc !== 'symbol') {
+      buffer.push(` (${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,
-    options: Omit<CompilerErrorDetailOptions, 'severity'>,
+    options: Omit<PlainCompilerErrorDetailOptions, 'severity'>,
   ): asserts condition {
     if (!condition) {
       const errors = new CompilerError();
@@ -131,8 +385,14 @@ export class CompilerError extends Error {
     }
   }
 
+  static throwDiagnostic(diagnostic: CompilerDiagnostic): never {
+    const errors = new CompilerError();
+    errors.pushDiagnostic(diagnostic);
+    throw errors;
+  }
+
   static throwTodo(
-    options: Omit<CompilerErrorDetailOptions, 'severity'>,
+    options: Omit<PlainCompilerErrorDetailOptions, 'severity'>,
   ): never {
     const errors = new CompilerError();
     errors.pushErrorDetail(
@@ -141,34 +401,21 @@ export class CompilerError extends Error {
     throw errors;
   }
 
-  static throwInvalidJS(
-    options: Omit<CompilerErrorDetailOptions, 'severity'>,
+  static throwFromCode(
+    code: ErrorCode,
+    options?: {
+      description?: string | null;
+      loc?: SourceLocation | null;
+      suggestions?: Array<CompilerSuggestion> | null | undefined;
+    },
   ): never {
     const errors = new CompilerError();
-    errors.pushErrorDetail(
-      new CompilerErrorDetail({
-        ...options,
-        severity: ErrorSeverity.InvalidJS,
-      }),
-    );
-    throw errors;
-  }
-
-  static throwInvalidReact(
-    options: Omit<CompilerErrorDetailOptions, 'severity'>,
-  ): never {
-    const errors = new CompilerError();
-    errors.pushErrorDetail(
-      new CompilerErrorDetail({
-        ...options,
-        severity: ErrorSeverity.InvalidReact,
-      }),
-    );
+    errors.pushErrorDetail(CompilerErrorDetail.fromCode(code, options));
     throw errors;
   }
 
   static throwInvalidConfig(
-    options: Omit<CompilerErrorDetailOptions, 'severity'>,
+    options: Omit<PlainCompilerErrorDetailOptions, 'severity'>,
   ): never {
     const errors = new CompilerError();
     errors.pushErrorDetail(
@@ -193,26 +440,54 @@ 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,
-      description: options.description ?? null,
-      severity: options.severity,
-      suggestions: options.suggestions,
-      loc: typeof options.loc === 'symbol' ? null : options.loc,
-    });
+    if (options instanceof CompilerErrorDetail) {
+      return this.pushErrorDetail(options);
+    }
+    const detail = new CompilerErrorDetail(options);
     return this.pushErrorDetail(detail);
   }
 
@@ -221,6 +496,19 @@ export class CompilerError extends Error {
     return detail;
   }
 
+  pushErrorCode(
+    code: ErrorCode,
+    details?: {
+      description?: string | null;
+      loc?: SourceLocation | null;
+      suggestions?: Array<CompilerSuggestion> | null | undefined;
+    },
+  ): CompilerErrorDetail {
+    const detail = CompilerErrorDetail.fromCode(code, details);
+    this.details.push(detail);
+    return detail;
+  }
+
   hasErrors(): boolean {
     return this.details.length > 0;
   }
@@ -241,13 +529,76 @@ 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}: ${message}`;
+}
+
+function endWithPeriod(s: string): string {
+  if (s === '' || s.endsWith('.')) {
+    return s;
+  }
+  return `${s.replace(/\.+$/, '')}.`;
+}

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

@@ -38,10 +38,10 @@ export function validateRestrictedImports(
     ImportDeclaration(importDeclPath) {
       if (restrictedImports.has(importDeclPath.node.source.value)) {
         error.push({
-          severity: ErrorSeverity.Todo,
           reason: 'Bailing out due to blocklisted import',
           description: `Import from module ${importDeclPath.node.source.value}`,
           loc: importDeclPath.node.loc ?? null,
+          severity: ErrorSeverity.Todo,
         });
       }
     },
@@ -205,10 +205,10 @@ export class ProgramContext {
     }
     const error = new CompilerError();
     error.push({
-      severity: ErrorSeverity.Todo,
       reason: 'Encountered conflicting global in generated program',
       description: `Conflict from local binding ${name}`,
       loc: scope.getBinding(name)?.path.node.loc ?? null,
+      severity: ErrorSeverity.Todo,
       suggestions: null,
     });
     return Err(error);

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,
+  PlainCompilerErrorDetailOptions,
+} from '../CompilerError';
 import {
   EnvironmentConfig,
   ExternalFunction,
@@ -102,6 +107,8 @@ export type PluginOptions = {
    * passes.
    *
    * Defaults to false
+   *
+   * TODO: rename this to lintOnly or something similar
    */
   noEmit: boolean;
 
@@ -224,12 +231,15 @@ export type LoggerEvent =
 export type CompileErrorEvent = {
   kind: 'CompileError';
   fnLoc: t.SourceLocation | null;
-  detail: CompilerErrorDetailOptions;
+  detail: CompilerErrorDetail | CompilerDiagnostic;
 };
 export type CompileDiagnosticEvent = {
   kind: 'CompileDiagnostic';
   fnLoc: t.SourceLocation | null;
-  detail: Omit<Omit<CompilerErrorDetailOptions, 'severity'>, 'suggestions'>;
+  detail: Omit<
+    Omit<PlainCompilerErrorDetailOptions, 'severity'>,
+    'suggestions'
+  >;
 };
 export type CompileSuccessEvent = {
   kind: 'CompileSuccess';

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

@@ -92,20 +92,19 @@ import {
 } from '../Validation';
 import {validateLocalsNotReassignedAfterRender} from '../Validation/ValidateLocalsNotReassignedAfterRender';
 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';
 import {optimizePropsMethodCalls} from '../Optimization/OptimizePropsMethodCalls';
 import {transformFire} from '../Transform';
 import {validateNoImpureFunctionsInRender} from '../Validation/ValidateNoImpureFunctionsInRender';
-import {CompilerError} from '..';
 import {validateStaticComponents} from '../Validation/ValidateStaticComponents';
 import {validateNoFreezingKnownMutableFunctions} from '../Validation/ValidateNoFreezingKnownMutableFunctions';
 import {inferMutationAliasingEffects} from '../Inference/InferMutationAliasingEffects';
 import {inferMutationAliasingRanges} from '../Inference/InferMutationAliasingRanges';
+import {validateNoDerivedComputationsInEffects} from '../Validation/ValidateNoDerivedComputationsInEffects';
 
 export type CompilerPipelineValue =
   | {kind: 'ast'; name: string; value: CodegenFunction}
@@ -174,7 +173,7 @@ function runWithEnvironment(
     !env.config.disableMemoizationForDebugging &&
     !env.config.enableChangeDetectionForDebugging
   ) {
-    dropManualMemoization(hir);
+    env.logOrThrowErrors(dropManualMemoization(hir));
     log({kind: 'hir', name: 'DropManualMemoization', value: hir});
   }
 
@@ -207,10 +206,10 @@ function runWithEnvironment(
 
   if (env.isInferredMemoEnabled) {
     if (env.config.validateHooksUsage) {
-      validateHooksUsage(hir).unwrap();
+      env.logOrThrowErrors(validateHooksUsage(hir));
     }
-    if (env.config.validateNoCapitalizedCalls) {
-      validateNoCapitalizedCalls(hir).unwrap();
+    if (env.config.validateNoCapitalizedCalls != null) {
+      env.logOrThrowErrors(validateNoCapitalizedCalls(hir));
     }
   }
 
@@ -230,20 +229,17 @@ function runWithEnvironment(
   log({kind: 'hir', name: 'AnalyseFunctions', value: hir});
 
   if (!env.config.enableNewMutationAliasingModel) {
-    const fnEffectErrors = inferReferenceEffects(hir);
+    const fnEffectResult = inferReferenceEffects(hir);
+
     if (env.isInferredMemoEnabled) {
-      if (fnEffectErrors.length > 0) {
-        CompilerError.throw(fnEffectErrors[0]);
-      }
+      env.logOrThrowErrors(fnEffectResult);
     }
     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();
-      }
+      env.logOrThrowErrors(mutabilityAliasingErrors);
     }
   }
 
@@ -272,10 +268,8 @@ function runWithEnvironment(
     });
     log({kind: 'hir', name: 'InferMutationAliasingRanges', value: hir});
     if (env.isInferredMemoEnabled) {
-      if (mutabilityAliasingErrors.isErr()) {
-        throw mutabilityAliasingErrors.unwrapErr();
-      }
-      validateLocalsNotReassignedAfterRender(hir);
+      env.logOrThrowErrors(mutabilityAliasingErrors.map(() => undefined));
+      env.logOrThrowErrors(validateLocalsNotReassignedAfterRender(hir));
     }
   }
 
@@ -285,30 +279,36 @@ function runWithEnvironment(
     }
 
     if (env.config.validateRefAccessDuringRender) {
-      validateNoRefAccessInRender(hir).unwrap();
+      env.logOrThrowErrors(validateNoRefAccessInRender(hir));
     }
 
     if (env.config.validateNoSetStateInRender) {
-      validateNoSetStateInRender(hir).unwrap();
+      env.logOrThrowErrors(validateNoSetStateInRender(hir));
     }
 
-    if (env.config.validateNoSetStateInPassiveEffects) {
-      env.logErrors(validateNoSetStateInPassiveEffects(hir));
+    if (env.config.validateNoDerivedComputationsInEffects) {
+      env.logOrThrowErrors(validateNoDerivedComputationsInEffects(hir));
+    }
+
+    if (env.config.validateNoSetStateInEffects) {
+      env.logErrors(validateNoSetStateInEffects(hir));
     }
 
     if (env.config.validateNoJSXInTryStatements) {
       env.logErrors(validateNoJSXInTryStatement(hir));
     }
-
-    if (env.config.validateNoImpureFunctionsInRender) {
-      validateNoImpureFunctionsInRender(hir).unwrap();
+    if (
+      env.config.validateNoImpureFunctionsInRender &&
+      !env.config.enableNewMutationAliasingModel
+    ) {
+      env.logOrThrowErrors(validateNoImpureFunctionsInRender(hir));
     }
 
     if (
       env.config.validateNoFreezingKnownMutableFunctions ||
       env.config.enableNewMutationAliasingModel
     ) {
-      validateNoFreezingKnownMutableFunctions(hir).unwrap();
+      env.logOrThrowErrors(validateNoFreezingKnownMutableFunctions(hir));
     }
   }
 
@@ -322,13 +322,6 @@ function runWithEnvironment(
     value: hir,
   });
 
-  propagatePhiTypes(hir);
-  log({
-    kind: 'hir',
-    name: 'PropagatePhiTypes',
-    value: hir,
-  });
-
   if (env.isInferredMemoEnabled) {
     if (env.config.validateStaticComponents) {
       env.logErrors(validateStaticComponents(hir));

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

@@ -7,11 +7,7 @@
 
 import {NodePath} from '@babel/core';
 import * as t from '@babel/types';
-import {
-  CompilerError,
-  CompilerErrorDetail,
-  ErrorSeverity,
-} from '../CompilerError';
+import {CompilerError, ErrorSeverity} from '../CompilerError';
 import {ExternalFunction, ReactFunctionType} from '../HIR/Environment';
 import {CodegenFunction} from '../ReactiveScopes';
 import {isComponentDeclaration} from '../Utils/ComponentDeclaration';
@@ -32,6 +28,7 @@ import {
 } from './Suppression';
 import {GeneratedSource} from '../HIR';
 import {Err, Ok, Result} from '../Utils/Result';
+import {ErrorCode} from '../Utils/CompilerErrorCodes';
 
 export type CompilerPass = {
   opts: PluginOptions;
@@ -101,12 +98,9 @@ function findDirectivesDynamicGating(
       if (t.isValidIdentifier(maybeMatch[1])) {
         result.push({directive, match: maybeMatch[1]});
       } else {
-        errors.push({
-          reason: `Dynamic gating directive is not a valid JavaScript identifier`,
+        errors.pushErrorCode(ErrorCode.DYNAMIC_GATING_IS_NOT_IDENTIFIER, {
           description: `Found '${directive.value.value}'`,
-          severity: ErrorSeverity.InvalidReact,
           loc: directive.loc ?? null,
-          suggestions: null,
         });
       }
     }
@@ -115,14 +109,11 @@ function findDirectivesDynamicGating(
     return Err(errors);
   } else if (result.length > 1) {
     const error = new CompilerError();
-    error.push({
-      reason: `Multiple dynamic gating directives found`,
+    error.pushErrorCode(ErrorCode.DYNAMIC_GATING_MULTIPLE_DIRECTIVES, {
       description: `Expected a single directive but found [${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) {
@@ -181,7 +172,7 @@ function logError(
         context.opts.logger.logEvent(context.filename, {
           kind: 'CompileError',
           fnLoc,
-          detail: detail.options,
+          detail,
         });
       }
     } else {
@@ -451,14 +442,12 @@ export function compileProgram(
   if (programContext.hasModuleScopeOptOut) {
     if (compiledFns.length > 0) {
       const error = new CompilerError();
-      error.pushErrorDetail(
-        new CompilerErrorDetail({
-          reason:
-            'Unexpected compiled functions when module scope opt-out is present',
-          severity: ErrorSeverity.Invariant,
-          loc: null,
-        }),
-      );
+      error.push({
+        reason:
+          'Unexpected compiled functions when module scope opt-out is present',
+        severity: ErrorSeverity.Invariant,
+        loc: null,
+      });
       handleError(error, programContext, null);
     }
     return null;
@@ -591,9 +580,7 @@ function processFn(
   let compiledFn: CodegenFunction;
   const compileResult = tryCompileFunction(fn, fnType, programContext);
   if (compileResult.kind === 'error') {
-    if (directives.optOut != null) {
-      logError(compileResult.error, programContext, fn.node.loc ?? null);
-    } else {
+    if (directives.optOut == null) {
       handleError(compileResult.error, programContext, fn.node.loc ?? null);
     }
     const retryResult = retryCompileFunction(fn, fnType, programContext);
@@ -692,7 +679,7 @@ function tryCompileFunction(
         fn,
         programContext.opts.environment,
         fnType,
-        'all_features',
+        programContext.opts.noEmit ? 'lint_only' : 'all_features',
         programContext,
         programContext.opts.logger,
         programContext.filename,
@@ -805,15 +792,7 @@ function shouldSkipCompilation(
   if (pass.opts.sources) {
     if (pass.filename === null) {
       const error = new CompilerError();
-      error.pushErrorDetail(
-        new CompilerErrorDetail({
-          reason: `Expected a filename but found none.`,
-          description:
-            "When the 'sources' config options is specified, the React compiler will only compile files with a name",
-          severity: ErrorSeverity.InvalidConfig,
-          loc: null,
-        }),
-      );
+      error.pushErrorCode(ErrorCode.FILENAME_NOT_SET);
       handleError(error, pass, null);
       return true;
     }

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

@@ -8,10 +8,10 @@
 import {NodePath} from '@babel/core';
 import * as t from '@babel/types';
 import {
+  CompilerDiagnostic,
   CompilerError,
-  CompilerErrorDetail,
   CompilerSuggestionOperation,
-  ErrorSeverity,
+  ErrorCode,
 } from '../CompilerError';
 import {assertExhaustive} from '../Utils/utils';
 import {GeneratedSource} from '../HIR';
@@ -165,14 +165,12 @@ export function suppressionsToCompilerError(
     let reason, suggestion;
     switch (suppressionRange.source) {
       case 'Eslint':
-        reason =
-          'React Compiler has skipped optimizing this component because one or more React ESLint rules were disabled';
+        reason = ErrorCode.BAILOUT_ESLINT_SUPPRESSION;
         suggestion =
           'Remove the ESLint suppression and address the React error';
         break;
       case 'Flow':
-        reason =
-          'React Compiler has skipped optimizing this component because one or more React rule violations were reported by Flow';
+        reason = ErrorCode.BAILOUT_FLOW_SUPPRESSION;
         suggestion = 'Remove the Flow suppression and address the React error';
         break;
       default:
@@ -181,12 +179,9 @@ export function suppressionsToCompilerError(
           'Unhandled suppression source',
         );
     }
-    error.pushErrorDetail(
-      new CompilerErrorDetail({
-        reason: `${reason}. React Compiler only works when your components follow all the rules of React, disabling them may result in unexpected or incorrect behavior`,
-        description: suppressionRange.disableComment.value.trim(),
-        severity: ErrorSeverity.InvalidReact,
-        loc: suppressionRange.disableComment.loc ?? null,
+    error.pushDiagnostic(
+      CompilerDiagnostic.fromCode(reason, {
+        description: `Found suppression \`${suppressionRange.disableComment.value.trim()}\``,
         suggestions: [
           {
             description: suggestion,
@@ -197,6 +192,10 @@ 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 +8,60 @@
 import {NodePath} from '@babel/core';
 import * as t from '@babel/types';
 
-import {
-  CompilerError,
-  CompilerErrorDetailOptions,
-  EnvironmentConfig,
-  ErrorSeverity,
-  Logger,
-} from '..';
+import {CompilerError, EnvironmentConfig, 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} from '../CompilerError';
+import {ErrorCode} from '../Utils/CompilerErrorCodes';
 
-function throwInvalidReact(
-  options: Omit<CompilerErrorDetailOptions, 'severity'>,
+function logAndThrowDiagnostic(
+  diagnostic: CompilerDiagnostic,
   {logger, filename}: TraversalState,
 ): never {
-  const detail: CompilerErrorDetailOptions = {
-    ...options,
-    severity: ErrorSeverity.InvalidReact,
-  };
   logger?.logEvent(filename, {
     kind: 'CompileError',
     fnLoc: null,
-    detail,
+    detail: diagnostic,
   });
-  CompilerError.throw(detail);
+  CompilerError.throwDiagnostic(diagnostic);
+}
+
+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 +74,10 @@ 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,
@@ -63,17 +87,17 @@ function assertValidEffectImportReference(
          * as it may have already been transformed by the compiler (and not
          * memoized).
          */
-        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: ${maybeErrorDiagnostic})`
-              : null,
-            loc: parent.node.loc ?? null,
-          },
+        logAndThrowDiagnostic(
+          CompilerDiagnostic.fromCode(ErrorCode.DID_NOT_INFER_DEPS, {
+            description: maybeErrorDiagnostic ? `${maybeErrorDiagnostic}` : '',
+            details: [
+              {
+                kind: 'error',
+                message: 'Cannot infer dependencies',
+                loc: parent.node.loc ?? GeneratedSource,
+              },
+            ],
+          }),
           context,
         );
       }
@@ -90,16 +114,21 @@ function assertValidFireImportReference(
       paths[0],
       context.transformErrors,
     );
-    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,
-      },
+    logAndThrowDiagnostic(
+      CompilerDiagnostic.fromCode(ErrorCode.CANNOT_COMPILE_FIRE, {
+        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 +157,12 @@ 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/Flood/FlowTypes.ts

@@ -0,0 +1,752 @@
+/**
+ * TypeScript definitions for Flow type JSON representations
+ * Based on the output of /data/sandcastle/boxes/fbsource/fbcode/flow/src/typing/convertTypes.ml
+ */
+
+// Base type for all Flow types with a kind field
+export interface BaseFlowType {
+  kind: string;
+}
+
+// Type for representing polarity
+export type Polarity = 'positive' | 'negative' | 'neutral';
+
+// Type for representing a name that might be null
+export type OptionalName = string | null;
+
+// Open type
+export interface OpenType extends BaseFlowType {
+  kind: 'Open';
+}
+
+// Def type
+export interface DefType extends BaseFlowType {
+  kind: 'Def';
+  def: DefT;
+}
+
+// Eval type
+export interface EvalType extends BaseFlowType {
+  kind: 'Eval';
+  type: FlowType;
+  destructor: Destructor;
+}
+
+// Generic type
+export interface GenericType extends BaseFlowType {
+  kind: 'Generic';
+  name: string;
+  bound: FlowType;
+  no_infer: boolean;
+}
+
+// ThisInstance type
+export interface ThisInstanceType extends BaseFlowType {
+  kind: 'ThisInstance';
+  instance: InstanceT;
+  is_this: boolean;
+  name: string;
+}
+
+// ThisTypeApp type
+export interface ThisTypeAppType extends BaseFlowType {
+  kind: 'ThisTypeApp';
+  t1: FlowType;
+  t2: FlowType;
+  t_list?: Array<FlowType>;
+}
+
+// TypeApp type
+export interface TypeAppType extends BaseFlowType {
+  kind: 'TypeApp';
+  type: FlowType;
+  targs: Array<FlowType>;
+  from_value: boolean;
+  use_desc: boolean;
+}
+
+// FunProto type
+export interface FunProtoType extends BaseFlowType {
+  kind: 'FunProto';
+}
+
+// ObjProto type
+export interface ObjProtoType extends BaseFlowType {
+  kind: 'ObjProto';
+}
+
+// NullProto type
+export interface NullProtoType extends BaseFlowType {
+  kind: 'NullProto';
+}
+
+// FunProtoBind type
+export interface FunProtoBindType extends BaseFlowType {
+  kind: 'FunProtoBind';
+}
+
+// Intersection type
+export interface IntersectionType extends BaseFlowType {
+  kind: 'Intersection';
+  members: Array<FlowType>;
+}
+
+// Union type
+export interface UnionType extends BaseFlowType {
+  kind: 'Union';
+  members: Array<FlowType>;
+}
+
+// Maybe type
+export interface MaybeType extends BaseFlowType {
+  kind: 'Maybe';
+  type: FlowType;
+}
+
+// Optional type
+export interface OptionalType extends BaseFlowType {
+  kind: 'Optional';
+  type: FlowType;
+  use_desc: boolean;
+}
+
+// Keys type
+export interface KeysType extends BaseFlowType {
+  kind: 'Keys';
+  type: FlowType;
+}
+
+// Annot type
+export interface AnnotType extends BaseFlowType {
+  kind: 'Annot';
+  type: FlowType;
+  use_desc: boolean;
+}
+
+// Opaque type
+export interface OpaqueType extends BaseFlowType {
+  kind: 'Opaque';
+  opaquetype: {
+    opaque_id: string;
+    underlying_t: FlowType | null;
+    super_t: FlowType | null;
+    opaque_type_args: Array<{
+      name: string;
+      type: FlowType;
+      polarity: Polarity;
+    }>;
+    opaque_name: string;
+  };
+}
+
+// Namespace type
+export interface NamespaceType extends BaseFlowType {
+  kind: 'Namespace';
+  namespace_symbol: {
+    symbol: string;
+  };
+  values_type: FlowType;
+  types_tmap: PropertyMap;
+}
+
+// Any type
+export interface AnyType extends BaseFlowType {
+  kind: 'Any';
+}
+
+// StrUtil type
+export interface StrUtilType extends BaseFlowType {
+  kind: 'StrUtil';
+  op: 'StrPrefix' | 'StrSuffix';
+  prefix?: string;
+  suffix?: string;
+  remainder?: FlowType;
+}
+
+// TypeParam definition
+export interface TypeParam {
+  name: string;
+  bound: FlowType;
+  polarity: Polarity;
+  default: FlowType | null;
+}
+
+// EnumInfo types
+export type EnumInfo = ConcreteEnum | AbstractEnum;
+
+export interface ConcreteEnum {
+  kind: 'ConcreteEnum';
+  enum_name: string;
+  enum_id: string;
+  members: Array<string>;
+  representation_t: FlowType;
+  has_unknown_members: boolean;
+}
+
+export interface AbstractEnum {
+  kind: 'AbstractEnum';
+  representation_t: FlowType;
+}
+
+// CanonicalRendersForm types
+export type CanonicalRendersForm =
+  | InstrinsicRenders
+  | NominalRenders
+  | StructuralRenders
+  | DefaultRenders;
+
+export interface InstrinsicRenders {
+  kind: 'InstrinsicRenders';
+  name: string;
+}
+
+export interface NominalRenders {
+  kind: 'NominalRenders';
+  renders_id: string;
+  renders_name: string;
+  renders_super: FlowType;
+}
+
+export interface StructuralRenders {
+  kind: 'StructuralRenders';
+  renders_variant: 'RendersNormal' | 'RendersMaybe' | 'RendersStar';
+  renders_structural_type: FlowType;
+}
+
+export interface DefaultRenders {
+  kind: 'DefaultRenders';
+}
+
+// InstanceT definition
+export interface InstanceT {
+  inst: InstType;
+  static: FlowType;
+  super: FlowType;
+  implements: Array<FlowType>;
+}
+
+// InstType definition
+export interface InstType {
+  class_name: string | null;
+  class_id: string;
+  type_args: Array<{
+    name: string;
+    type: FlowType;
+    polarity: Polarity;
+  }>;
+  own_props: PropertyMap;
+  proto_props: PropertyMap;
+  call_t: null | {
+    id: number;
+    call: FlowType;
+  };
+}
+
+// DefT types
+export type DefT =
+  | NumGeneralType
+  | StrGeneralType
+  | BoolGeneralType
+  | BigIntGeneralType
+  | EmptyType
+  | MixedType
+  | NullType
+  | VoidType
+  | SymbolType
+  | FunType
+  | ObjType
+  | ArrType
+  | ClassType
+  | InstanceType
+  | SingletonStrType
+  | NumericStrKeyType
+  | SingletonNumType
+  | SingletonBoolType
+  | SingletonBigIntType
+  | TypeType
+  | PolyType
+  | ReactAbstractComponentType
+  | RendersType
+  | EnumValueType
+  | EnumObjectType;
+
+export interface NumGeneralType extends BaseFlowType {
+  kind: 'NumGeneral';
+}
+
+export interface StrGeneralType extends BaseFlowType {
+  kind: 'StrGeneral';
+}
+
+export interface BoolGeneralType extends BaseFlowType {
+  kind: 'BoolGeneral';
+}
+
+export interface BigIntGeneralType extends BaseFlowType {
+  kind: 'BigIntGeneral';
+}
+
+export interface EmptyType extends BaseFlowType {
+  kind: 'Empty';
+}
+
+export interface MixedType extends BaseFlowType {
+  kind: 'Mixed';
+}
+
+export interface NullType extends BaseFlowType {
+  kind: 'Null';
+}
+
+export interface VoidType extends BaseFlowType {
+  kind: 'Void';
+}
+
+export interface SymbolType extends BaseFlowType {
+  kind: 'Symbol';
+}
+
+export interface FunType extends BaseFlowType {
+  kind: 'Fun';
+  static: FlowType;
+  funtype: FunTypeObj;
+}
+
+export interface ObjType extends BaseFlowType {
+  kind: 'Obj';
+  objtype: ObjTypeObj;
+}
+
+export interface ArrType extends BaseFlowType {
+  kind: 'Arr';
+  arrtype: ArrTypeObj;
+}
+
+export interface ClassType extends BaseFlowType {
+  kind: 'Class';
+  type: FlowType;
+}
+
+export interface InstanceType extends BaseFlowType {
+  kind: 'Instance';
+  instance: InstanceT;
+}
+
+export interface SingletonStrType extends BaseFlowType {
+  kind: 'SingletonStr';
+  from_annot: boolean;
+  value: string;
+}
+
+export interface NumericStrKeyType extends BaseFlowType {
+  kind: 'NumericStrKey';
+  number: string;
+  string: string;
+}
+
+export interface SingletonNumType extends BaseFlowType {
+  kind: 'SingletonNum';
+  from_annot: boolean;
+  number: string;
+  string: string;
+}
+
+export interface SingletonBoolType extends BaseFlowType {
+  kind: 'SingletonBool';
+  from_annot: boolean;
+  value: boolean;
+}
+
+export interface SingletonBigIntType extends BaseFlowType {
+  kind: 'SingletonBigInt';
+  from_annot: boolean;
+  value: string;
+}
+
+export interface TypeType extends BaseFlowType {
+  kind: 'Type';
+  type_kind: TypeTKind;
+  type: FlowType;
+}
+
+export type TypeTKind =
+  | 'TypeAliasKind'
+  | 'TypeParamKind'
+  | 'OpaqueKind'
+  | 'ImportTypeofKind'
+  | 'ImportClassKind'
+  | 'ImportEnumKind'
+  | 'InstanceKind'
+  | 'RenderTypeKind';
+
+export interface PolyType extends BaseFlowType {
+  kind: 'Poly';
+  tparams: Array<TypeParam>;
+  t_out: FlowType;
+  id: string;
+}
+
+export interface ReactAbstractComponentType extends BaseFlowType {
+  kind: 'ReactAbstractComponent';
+  config: FlowType;
+  renders: FlowType;
+  instance: ComponentInstance;
+  component_kind: ComponentKind;
+}
+
+export type ComponentInstance =
+  | {kind: 'RefSetterProp'; type: FlowType}
+  | {kind: 'Omitted'};
+
+export type ComponentKind =
+  | {kind: 'Structural'}
+  | {kind: 'Nominal'; id: string; name: string; types: Array<FlowType> | null};
+
+export interface RendersType extends BaseFlowType {
+  kind: 'Renders';
+  form: CanonicalRendersForm;
+}
+
+export interface EnumValueType extends BaseFlowType {
+  kind: 'EnumValue';
+  enum_info: EnumInfo;
+}
+
+export interface EnumObjectType extends BaseFlowType {
+  kind: 'EnumObject';
+  enum_value_t: FlowType;
+  enum_info: EnumInfo;
+}
+
+// ObjKind types
+export type ObjKind =
+  | {kind: 'Exact'}
+  | {kind: 'Inexact'}
+  | {kind: 'Indexed'; dicttype: DictType};
+
+// DictType definition
+export interface DictType {
+  dict_name: string | null;
+  key: FlowType;
+  value: FlowType;
+  dict_polarity: Polarity;
+}
+
+// ArrType types
+export type ArrTypeObj = ArrayAT | TupleAT | ROArrayAT;
+
+export interface ArrayAT {
+  kind: 'ArrayAT';
+  elem_t: FlowType;
+}
+
+export interface TupleAT {
+  kind: 'TupleAT';
+  elem_t: FlowType;
+  elements: Array<TupleElement>;
+  min_arity: number;
+  max_arity: number;
+  inexact: boolean;
+}
+
+export interface ROArrayAT {
+  kind: 'ROArrayAT';
+  elem_t: FlowType;
+}
+
+// TupleElement definition
+export interface TupleElement {
+  name: string | null;
+  t: FlowType;
+  polarity: Polarity;
+  optional: boolean;
+}
+
+// Flags definition
+export interface Flags {
+  obj_kind: ObjKind;
+}
+
+// Property types
+export type Property =
+  | FieldProperty
+  | GetProperty
+  | SetProperty
+  | GetSetProperty
+  | MethodProperty;
+
+export interface FieldProperty {
+  kind: 'Field';
+  type: FlowType;
+  polarity: Polarity;
+}
+
+export interface GetProperty {
+  kind: 'Get';
+  type: FlowType;
+}
+
+export interface SetProperty {
+  kind: 'Set';
+  type: FlowType;
+}
+
+export interface GetSetProperty {
+  kind: 'GetSet';
+  get_type: FlowType;
+  set_type: FlowType;
+}
+
+export interface MethodProperty {
+  kind: 'Method';
+  type: FlowType;
+}
+
+// PropertyMap definition
+export interface PropertyMap {
+  [key: string]: Property; // For other properties in the map
+}
+
+// ObjType definition
+export interface ObjTypeObj {
+  flags: Flags;
+  props: PropertyMap;
+  proto_t: FlowType;
+  call_t: number | null;
+}
+
+// FunType definition
+export interface FunTypeObj {
+  this_t: {
+    type: FlowType;
+    status: ThisStatus;
+  };
+  params: Array<{
+    name: string | null;
+    type: FlowType;
+  }>;
+  rest_param: null | {
+    name: string | null;
+    type: FlowType;
+  };
+  return_t: FlowType;
+  type_guard: null | {
+    inferred: boolean;
+    param_name: string;
+    type_guard: FlowType;
+    one_sided: boolean;
+  };
+  effect: Effect;
+}
+
+// ThisStatus types
+export type ThisStatus =
+  | {kind: 'This_Method'; unbound: boolean}
+  | {kind: 'This_Function'};
+
+// Effect types
+export type Effect =
+  | {kind: 'HookDecl'; id: string}
+  | {kind: 'HookAnnot'}
+  | {kind: 'ArbitraryEffect'}
+  | {kind: 'AnyEffect'};
+
+// Destructor types
+export type Destructor =
+  | NonMaybeTypeDestructor
+  | PropertyTypeDestructor
+  | ElementTypeDestructor
+  | OptionalIndexedAccessNonMaybeTypeDestructor
+  | OptionalIndexedAccessResultTypeDestructor
+  | ExactTypeDestructor
+  | ReadOnlyTypeDestructor
+  | PartialTypeDestructor
+  | RequiredTypeDestructor
+  | SpreadTypeDestructor
+  | SpreadTupleTypeDestructor
+  | RestTypeDestructor
+  | ValuesTypeDestructor
+  | ConditionalTypeDestructor
+  | TypeMapDestructor
+  | ReactElementPropsTypeDestructor
+  | ReactElementConfigTypeDestructor
+  | ReactCheckComponentConfigDestructor
+  | ReactDRODestructor
+  | MakeHooklikeDestructor
+  | MappedTypeDestructor
+  | EnumTypeDestructor;
+
+export interface NonMaybeTypeDestructor {
+  kind: 'NonMaybeType';
+}
+
+export interface PropertyTypeDestructor {
+  kind: 'PropertyType';
+  name: string;
+}
+
+export interface ElementTypeDestructor {
+  kind: 'ElementType';
+  index_type: FlowType;
+}
+
+export interface OptionalIndexedAccessNonMaybeTypeDestructor {
+  kind: 'OptionalIndexedAccessNonMaybeType';
+  index: OptionalIndexedAccessIndex;
+}
+
+export type OptionalIndexedAccessIndex =
+  | {kind: 'StrLitIndex'; name: string}
+  | {kind: 'TypeIndex'; type: FlowType};
+
+export interface OptionalIndexedAccessResultTypeDestructor {
+  kind: 'OptionalIndexedAccessResultType';
+}
+
+export interface ExactTypeDestructor {
+  kind: 'ExactType';
+}
+
+export interface ReadOnlyTypeDestructor {
+  kind: 'ReadOnlyType';
+}
+
+export interface PartialTypeDestructor {
+  kind: 'PartialType';
+}
+
+export interface RequiredTypeDestructor {
+  kind: 'RequiredType';
+}
+
+export interface SpreadTypeDestructor {
+  kind: 'SpreadType';
+  target: SpreadTarget;
+  operands: Array<SpreadOperand>;
+  operand_slice: Slice | null;
+}
+
+export type SpreadTarget =
+  | {kind: 'Value'; make_seal: 'Sealed' | 'Frozen' | 'As_Const'}
+  | {kind: 'Annot'; make_exact: boolean};
+
+export type SpreadOperand = {kind: 'Type'; type: FlowType} | Slice;
+
+export interface Slice {
+  kind: 'Slice';
+  prop_map: PropertyMap;
+  generics: Array<string>;
+  dict: DictType | null;
+  reachable_targs: Array<{
+    type: FlowType;
+    polarity: Polarity;
+  }>;
+}
+
+export interface SpreadTupleTypeDestructor {
+  kind: 'SpreadTupleType';
+  inexact: boolean;
+  resolved_rev: string;
+  unresolved: string;
+}
+
+export interface RestTypeDestructor {
+  kind: 'RestType';
+  merge_mode: RestMergeMode;
+  type: FlowType;
+}
+
+export type RestMergeMode =
+  | {kind: 'SpreadReversal'}
+  | {kind: 'ReactConfigMerge'; polarity: Polarity}
+  | {kind: 'Omit'};
+
+export interface ValuesTypeDestructor {
+  kind: 'ValuesType';
+}
+
+export interface ConditionalTypeDestructor {
+  kind: 'ConditionalType';
+  distributive_tparam_name: string | null;
+  infer_tparams: string;
+  extends_t: FlowType;
+  true_t: FlowType;
+  false_t: FlowType;
+}
+
+export interface TypeMapDestructor {
+  kind: 'ObjectKeyMirror';
+}
+
+export interface ReactElementPropsTypeDestructor {
+  kind: 'ReactElementPropsType';
+}
+
+export interface ReactElementConfigTypeDestructor {
+  kind: 'ReactElementConfigType';
+}
+
+export interface ReactCheckComponentConfigDestructor {
+  kind: 'ReactCheckComponentConfig';
+  props: {
+    [key: string]: Property;
+  };
+}
+
+export interface ReactDRODestructor {
+  kind: 'ReactDRO';
+  dro_type:
+    | 'HookReturn'
+    | 'HookArg'
+    | 'Props'
+    | 'ImmutableAnnot'
+    | 'DebugAnnot';
+}
+
+export interface MakeHooklikeDestructor {
+  kind: 'MakeHooklike';
+}
+
+export interface MappedTypeDestructor {
+  kind: 'MappedType';
+  homomorphic: Homomorphic;
+  distributive_tparam_name: string | null;
+  property_type: FlowType;
+  mapped_type_flags: {
+    variance: Polarity;
+    optional: 'MakeOptional' | 'RemoveOptional' | 'KeepOptionality';
+  };
+}
+
+export type Homomorphic =
+  | {kind: 'Homomorphic'}
+  | {kind: 'Unspecialized'}
+  | {kind: 'SemiHomomorphic'; type: FlowType};
+
+export interface EnumTypeDestructor {
+  kind: 'EnumType';
+}
+
+// Union of all possible Flow types
+export type FlowType =
+  | OpenType
+  | DefType
+  | EvalType
+  | GenericType
+  | ThisInstanceType
+  | ThisTypeAppType
+  | TypeAppType
+  | FunProtoType
+  | ObjProtoType
+  | NullProtoType
+  | FunProtoBindType
+  | IntersectionType
+  | UnionType
+  | MaybeType
+  | OptionalType
+  | KeysType
+  | AnnotType
+  | OpaqueType
+  | NamespaceType
+  | AnyType
+  | StrUtilType;

compiler/packages/babel-plugin-react-compiler/src/Flood/TypeErrors.ts

@@ -0,0 +1,132 @@
+import {CompilerError, SourceLocation} from '..';
+import {ErrorCode} from '../CompilerError';
+import {
+  ConcreteType,
+  printConcrete,
+  printType,
+  StructuralValue,
+  Type,
+  VariableId,
+} from './Types';
+
+export function unsupportedLanguageFeature(
+  desc: string,
+  loc: SourceLocation,
+): never {
+  CompilerError.throwFromCode(ErrorCode.INVALID_JAVASCRIPT_AST, {
+    description: `Typedchecker does not currently support language feature: ${desc}`,
+    loc,
+  });
+}
+
+export type UnificationError =
+  | {
+      kind: 'TypeUnification';
+      left: ConcreteType<Type>;
+      right: ConcreteType<Type>;
+    }
+  | {
+      kind: 'StructuralUnification';
+      left: StructuralValue;
+      right: ConcreteType<Type>;
+    };
+
+function printUnificationError(err: UnificationError): string {
+  if (err.kind === 'TypeUnification') {
+    return `${printConcrete(err.left, printType)} is incompatible with ${printConcrete(err.right, printType)}`;
+  } else {
+    return `structural ${err.left.kind} is incompatible with ${printConcrete(err.right, printType)}`;
+  }
+}
+
+export function raiseUnificationErrors(
+  errs: null | Array<UnificationError>,
+  loc: SourceLocation,
+): void {
+  if (errs != null) {
+    if (errs.length === 0) {
+      CompilerError.invariant(false, {
+        reason: 'Should not have array of zero errors',
+        loc,
+      });
+    } else if (errs.length === 1) {
+      CompilerError.throwFromCode(ErrorCode.INVALID_JAVASCRIPT_AST, {
+        description: `Unable to unify types because ${printUnificationError(errs[0])}`,
+        loc,
+      });
+    } else {
+      const messages = errs
+        .map(err => `\t* ${printUnificationError(err)}`)
+        .join('\n');
+      CompilerError.throwFromCode(ErrorCode.INVALID_JAVASCRIPT_AST, {
+        description: `Unable to unify types because:\n${messages}`,
+        loc,
+      });
+    }
+  }
+}
+
+export function unresolvableTypeVariable(
+  id: VariableId,
+  loc: SourceLocation,
+): never {
+  CompilerError.throwFromCode(ErrorCode.INVALID_JAVASCRIPT_AST, {
+    description: `Unable to resolve free variable ${id} to a concrete type`,
+    loc,
+  });
+}
+
+export function cannotAddVoid(explicit: boolean, loc: SourceLocation): never {
+  if (explicit) {
+    CompilerError.throwFromCode(ErrorCode.INVALID_JAVASCRIPT_AST, {
+      description: `Undefined is not a valid operand of \`+\``,
+      loc,
+    });
+  } else {
+    CompilerError.throwFromCode(ErrorCode.INVALID_JAVASCRIPT_AST, {
+      description: `Value may be undefined, which is not a valid operand of \`+\``,
+      loc,
+    });
+  }
+}
+
+export function unsupportedTypeAnnotation(
+  desc: string,
+  loc: SourceLocation,
+): never {
+  CompilerError.throwFromCode(ErrorCode.INVALID_JAVASCRIPT_AST, {
+    description: `Typedchecker does not currently support type annotation: ${desc}`,
+    loc,
+  });
+}
+
+export function checkTypeArgumentArity(
+  desc: string,
+  expected: number,
+  actual: number,
+  loc: SourceLocation,
+): void {
+  if (expected !== actual) {
+    CompilerError.throwFromCode(ErrorCode.INVALID_JAVASCRIPT_AST, {
+      description: `Expected ${desc} to have ${expected} type parameters, got ${actual}`,
+      loc,
+    });
+  }
+}
+
+export function notAFunction(desc: string, loc: SourceLocation): void {
+  CompilerError.throwFromCode(ErrorCode.INVALID_JAVASCRIPT_AST, {
+    description: `Cannot call ${desc} because it is not a function`,
+    loc,
+  });
+}
+
+export function notAPolymorphicFunction(
+  desc: string,
+  loc: SourceLocation,
+): void {
+  CompilerError.throwFromCode(ErrorCode.INVALID_JAVASCRIPT_AST, {
+    description: `Cannot call ${desc} with type arguments because it is not a polymorphic function`,
+    loc,
+  });
+}

compiler/packages/babel-plugin-react-compiler/src/Flood/TypeUtils.ts

@@ -0,0 +1,312 @@
+import {GeneratedSource} from '../HIR';
+import {assertExhaustive} from '../Utils/utils';
+import {unsupportedLanguageFeature} from './TypeErrors';
+import {
+  ConcreteType,
+  ResolvedType,
+  TypeParameter,
+  TypeParameterId,
+  DEBUG,
+  printConcrete,
+  printType,
+} from './Types';
+
+export function substitute(
+  type: ConcreteType<ResolvedType>,
+  typeParameters: Array<TypeParameter<ResolvedType>>,
+  typeArguments: Array<ResolvedType>,
+): ResolvedType {
+  const substMap = new Map<TypeParameterId, ResolvedType>();
+  for (let i = 0; i < typeParameters.length; i++) {
+    // TODO: Length checks to make sure type params match up with args
+    const typeParameter = typeParameters[i];
+    const typeArgument = typeArguments[i];
+    substMap.set(typeParameter.id, typeArgument);
+  }
+  const substitutionFunction = (t: ResolvedType): ResolvedType => {
+    // TODO: We really want a stateful mapper or visitor here so that we can model nested polymorphic types
+    if (t.type.kind === 'Generic' && substMap.has(t.type.id)) {
+      const substitutedType = substMap.get(t.type.id)!;
+      return substitutedType;
+    }
+
+    return {
+      kind: 'Concrete',
+      type: mapType(substitutionFunction, t.type),
+      platform: t.platform,
+    };
+  };
+
+  const substituted = mapType(substitutionFunction, type);
+
+  if (DEBUG) {
+    let substs = '';
+    for (let i = 0; i < typeParameters.length; i++) {
+      const typeParameter = typeParameters[i];
+      const typeArgument = typeArguments[i];
+      substs += `[${typeParameter.name}${typeParameter.id} := ${printType(typeArgument)}]`;
+    }
+    console.log(
+      `${printConcrete(type, printType)}${substs} = ${printConcrete(substituted, printType)}`,
+    );
+  }
+
+  return {kind: 'Concrete', type: substituted, platform: /* TODO */ 'shared'};
+}
+
+export function mapType<T, U>(
+  f: (t: T) => U,
+  type: ConcreteType<T>,
+): ConcreteType<U> {
+  switch (type.kind) {
+    case 'Mixed':
+    case 'Number':
+    case 'String':
+    case 'Boolean':
+    case 'Void':
+      return type;
+
+    case 'Nullable':
+      return {
+        kind: 'Nullable',
+        type: f(type.type),
+      };
+
+    case 'Array':
+      return {
+        kind: 'Array',
+        element: f(type.element),
+      };
+
+    case 'Set':
+      return {
+        kind: 'Set',
+        element: f(type.element),
+      };
+
+    case 'Map':
+      return {
+        kind: 'Map',
+        key: f(type.key),
+        value: f(type.value),
+      };
+
+    case 'Function':
+      return {
+        kind: 'Function',
+        typeParameters:
+          type.typeParameters?.map(param => ({
+            id: param.id,
+            name: param.name,
+            bound: f(param.bound),
+          })) ?? null,
+        params: type.params.map(f),
+        returnType: f(type.returnType),
+      };
+
+    case 'Component': {
+      return {
+        kind: 'Component',
+        children: type.children != null ? f(type.children) : null,
+        props: new Map([...type.props.entries()].map(([k, v]) => [k, f(v)])),
+      };
+    }
+
+    case 'Generic':
+      return {
+        kind: 'Generic',
+        id: type.id,
+        bound: f(type.bound),
+      };
+
+    case 'Object':
+      return type;
+
+    case 'Tuple':
+      return {
+        kind: 'Tuple',
+        id: type.id,
+        members: type.members.map(f),
+      };
+
+    case 'Structural':
+      return type;
+
+    case 'Enum':
+    case 'Union':
+    case 'Instance':
+      unsupportedLanguageFeature(type.kind, GeneratedSource);
+
+    default:
+      assertExhaustive(type, 'Unknown type kind');
+  }
+}
+
+export function diff<R, T>(
+  a: ConcreteType<T>,
+  b: ConcreteType<T>,
+  onChild: (a: T, b: T) => R,
+  onChildMismatch: (child: R, cur: R) => R,
+  onMismatch: (a: ConcreteType<T>, b: ConcreteType<T>, cur: R) => R,
+  init: R,
+): R {
+  let errors = init;
+
+  // Check if kinds match
+  if (a.kind !== b.kind) {
+    errors = onMismatch(a, b, errors);
+    return errors;
+  }
+
+  // Based on kind, check other properties
+  switch (a.kind) {
+    case 'Mixed':
+    case 'Number':
+    case 'String':
+    case 'Boolean':
+    case 'Void':
+      // Simple types, no further checks needed
+      break;
+
+    case 'Nullable':
+      // Check the nested type
+      errors = onChildMismatch(onChild(a.type, (b as typeof a).type), errors);
+      break;
+
+    case 'Array':
+    case 'Set':
+      // Check the element type
+      errors = onChildMismatch(
+        onChild(a.element, (b as typeof a).element),
+        errors,
+      );
+      break;
+
+    case 'Map':
+      // Check both key and value types
+      errors = onChildMismatch(onChild(a.key, (b as typeof a).key), errors);
+      errors = onChildMismatch(onChild(a.value, (b as typeof a).value), errors);
+      break;
+
+    case 'Function': {
+      const bFunc = b as typeof a;
+
+      // Check type parameters
+      if ((a.typeParameters == null) !== (bFunc.typeParameters == null)) {
+        errors = onMismatch(a, b, errors);
+      }
+
+      if (a.typeParameters != null && bFunc.typeParameters != null) {
+        if (a.typeParameters.length !== bFunc.typeParameters.length) {
+          errors = onMismatch(a, b, errors);
+        }
+
+        // Type parameters are just numbers, so we can compare them directly
+        for (let i = 0; i < a.typeParameters.length; i++) {
+          if (a.typeParameters[i] !== bFunc.typeParameters[i]) {
+            errors = onMismatch(a, b, errors);
+          }
+        }
+      }
+
+      // Check parameters
+      if (a.params.length !== bFunc.params.length) {
+        errors = onMismatch(a, b, errors);
+      }
+
+      for (let i = 0; i < a.params.length; i++) {
+        errors = onChildMismatch(onChild(a.params[i], bFunc.params[i]), errors);
+      }
+
+      // Check return type
+      errors = onChildMismatch(onChild(a.returnType, bFunc.returnType), errors);
+      break;
+    }
+
+    case 'Component': {
+      const bComp = b as typeof a;
+
+      // Check children
+      if (a.children !== bComp.children) {
+        errors = onMismatch(a, b, errors);
+      }
+
+      // Check props
+      if (a.props.size !== bComp.props.size) {
+        errors = onMismatch(a, b, errors);
+      }
+
+      for (const [k, v] of a.props) {
+        const bProp = bComp.props.get(k);
+        if (bProp == null) {
+          errors = onMismatch(a, b, errors);
+        } else {
+          errors = onChildMismatch(onChild(v, bProp), errors);
+        }
+      }
+
+      break;
+    }
+
+    case 'Generic': {
+      // Check that the type parameter IDs match
+      if (a.id !== (b as typeof a).id) {
+        errors = onMismatch(a, b, errors);
+      }
+      break;
+    }
+    case 'Structural': {
+      const bStruct = b as typeof a;
+
+      // Check that the structural IDs match
+      if (a.id !== bStruct.id) {
+        errors = onMismatch(a, b, errors);
+      }
+      break;
+    }
+    case 'Object': {
+      const bNom = b as typeof a;
+
+      // Check that the nominal IDs match
+      if (a.id !== bNom.id) {
+        errors = onMismatch(a, b, errors);
+      }
+      break;
+    }
+
+    case 'Tuple': {
+      const bTuple = b as typeof a;
+
+      // Check that the tuple IDs match
+      if (a.id !== bTuple.id) {
+        errors = onMismatch(a, b, errors);
+      }
+      for (let i = 0; i < a.members.length; i++) {
+        errors = onChildMismatch(
+          onChild(a.members[i], bTuple.members[i]),
+          errors,
+        );
+      }
+
+      break;
+    }
+
+    case 'Enum':
+    case 'Instance':
+    case 'Union': {
+      unsupportedLanguageFeature(a.kind, GeneratedSource);
+    }
+
+    default:
+      assertExhaustive(a, 'Unknown type kind');
+  }
+
+  return errors;
+}
+
+export function filterOptional(t: ResolvedType): ResolvedType {
+  if (t.kind === 'Concrete' && t.type.kind === 'Nullable') {
+    return t.type.type;
+  }
+  return t;
+}

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

@@ -9,8 +9,10 @@ import {NodePath, Scope} from '@babel/traverse';
 import * as t from '@babel/types';
 import invariant from 'invariant';
 import {
+  CompilerDiagnostic,
   CompilerError,
   CompilerSuggestionOperation,
+  ErrorCode,
   ErrorSeverity,
 } from '../CompilerError';
 import {Err, Ok, Result} from '../Utils/Result';
@@ -104,12 +106,17 @@ 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 = {
@@ -163,12 +170,15 @@ 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.fromCode(ErrorCode.UNKNOWN_FUNCTION_PARAMETERS, {
+          description: `[BuildHIR] Add support for ${param.node.type} parameters.`,
+        }).withDetail({
+          kind: 'error',
+          loc: param.node.loc ?? null,
+          message: `Unsupported parameter type: ${param.node.type}`,
+        }),
+      );
     }
   });
 
@@ -178,6 +188,7 @@ export function lower(
     const fallthrough = builder.reserve('block');
     const terminal: ReturnTerminal = {
       kind: 'return',
+      returnVariant: 'Implicit',
       loc: GeneratedSource,
       value: lowerExpressionToTemporary(builder, body),
       id: makeInstructionId(0),
@@ -188,13 +199,15 @@ export function lower(
     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 \`${body.type}\``,
-      loc: body.node.loc ?? null,
-      suggestions: null,
-    });
+    builder.errors.pushDiagnostic(
+      CompilerDiagnostic.fromCode(ErrorCode.INVALID_JAVASCRIPT_AST, {
+        description: `Expected function body to be an expression or a block statement, got \`${body.type}\`.`,
+      }).withDetail({
+        kind: 'error',
+        loc: body.node.loc ?? null,
+        message: 'Change this to a block statement or expression',
+      }),
+    );
   }
 
   if (builder.errors.hasErrors()) {
@@ -204,6 +217,7 @@ export function lower(
   builder.terminate(
     {
       kind: 'return',
+      returnVariant: 'Void',
       loc: GeneratedSource,
       value: lowerValueToTemporary(builder, {
         kind: 'Primitive',
@@ -221,7 +235,6 @@ export function lower(
     params,
     fnType: bindings == null ? env.fnType : 'Other',
     returnTypeAnnotation: null, // TODO: extract the actual return type node if present
-    returnType: makeType(),
     returns: createTemporaryPlace(env, func.node.loc ?? GeneratedSource),
     body: builder.build(),
     context,
@@ -288,6 +301,7 @@ function lowerStatement(
       }
       const terminal: ReturnTerminal = {
         kind: 'return',
+        returnVariant: 'Explicit',
         loc: stmt.node.loc ?? GeneratedSource,
         value,
         id: makeInstructionId(0),
@@ -752,12 +766,12 @@ function lowerStatement(
         const testExpr = case_.get('test');
         if (testExpr.node == null) {
           if (hasDefault) {
-            builder.errors.push({
-              reason: `Expected at most one \`default\` branch in a switch statement, this code should have failed to parse`,
-              severity: ErrorSeverity.InvalidJS,
-              loc: case_.node.loc ?? null,
-              suggestions: null,
-            });
+            builder.errors.pushErrorCode(
+              ErrorCode.INVALID_SYNTAX_MULTIPLE_DEFAULTS,
+              {
+                loc: case_.node.loc ?? null,
+              },
+            );
             break;
           }
           hasDefault = true;
@@ -869,19 +883,20 @@ function lowerStatement(
             if (builder.isContextIdentifier(id)) {
               if (kind === InstructionKind.Const) {
                 const declRangeStart = declaration.parentPath.node.start!;
-                builder.errors.push({
-                  reason: `Expect \`const\` declaration not to be reassigned`,
-                  severity: ErrorSeverity.InvalidJS,
-                  loc: id.node.loc ?? null,
-                  suggestions: [
-                    {
-                      description: 'Change to a `let` declaration',
-                      op: CompilerSuggestionOperation.Replace,
-                      range: [declRangeStart, declRangeStart + 5], // "const".length
-                      text: 'let',
-                    },
-                  ],
-                });
+                builder.errors.pushErrorCode(
+                  ErrorCode.INVALID_SYNTAX_REASSIGNED_CONST,
+                  {
+                    loc: id.node.loc ?? null,
+                    suggestions: [
+                      {
+                        description: 'Change to a `let` declaration',
+                        op: CompilerSuggestionOperation.Replace,
+                        range: [declRangeStart, declRangeStart + 5], // "const".length
+                        text: 'let',
+                      },
+                    ],
+                  },
+                );
               }
               lowerValueToTemporary(builder, {
                 kind: 'DeclareContext',
@@ -915,13 +930,13 @@ function lowerStatement(
             }
           }
         } else {
-          builder.errors.push({
-            reason: `Expected variable declaration to be an identifier if no initializer was provided`,
-            description: `Got a \`${id.type}\``,
-            severity: ErrorSeverity.InvalidJS,
-            loc: stmt.node.loc ?? null,
-            suggestions: null,
-          });
+          builder.errors.pushErrorCode(
+            ErrorCode.INVALID_SYNTAX_BAD_VARIABLE_DECL,
+            {
+              description: `Got a \`${id.type}\``,
+              loc: stmt.node.loc ?? null,
+            },
+          );
         }
       }
       return;
@@ -1356,13 +1371,69 @@ function lowerStatement(
 
       return;
     }
-    case 'TypeAlias':
-    case 'TSInterfaceDeclaration':
-    case 'TSTypeAliasDeclaration': {
-      // We do not preserve type annotations/syntax through transformation
+    case 'WithStatement': {
+      builder.errors.pushErrorCode(ErrorCode.UNSUPPORTED_WITH, {
+        loc: stmtPath.node.loc ?? 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.pushErrorCode(ErrorCode.UNSUPPORTED_INNER_CLASS, {
+        loc: stmtPath.node.loc ?? 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.pushErrorCode(ErrorCode.INVALID_IMPORT_EXPORT, {
+        loc: stmtPath.node.loc ?? null,
+      });
+      lowerValueToTemporary(builder, {
+        kind: 'UnsupportedNode',
+        loc: stmtPath.node.loc ?? GeneratedSource,
+        node: stmtPath.node,
+      });
+      return;
+    }
+    case 'TSNamespaceExportDeclaration': {
+      builder.errors.pushErrorCode(ErrorCode.INVALID_TS_NAMESPACE, {
+        loc: stmtPath.node.loc ?? null,
+      });
+      lowerValueToTemporary(builder, {
+        kind: 'UnsupportedNode',
+        loc: stmtPath.node.loc ?? GeneratedSource,
+        node: stmtPath.node,
+      });
       return;
     }
-    case 'ClassDeclaration':
     case 'DeclareClass':
     case 'DeclareExportAllDeclaration':
     case 'DeclareExportDeclaration':
@@ -1373,31 +1444,14 @@ 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 ${stmtPath.type} statements`,
-        severity: ErrorSeverity.Todo,
-        loc: stmtPath.node.loc ?? null,
-        suggestions: null,
-      });
-      lowerValueToTemporary(builder, {
-        kind: 'UnsupportedNode',
-        loc: stmtPath.node.loc ?? GeneratedSource,
-        node: stmtPath.node,
-      });
+    case 'TSTypeAliasDeclaration':
+    case 'TypeAlias': {
+      // We do not preserve type annotations/syntax through transformation
       return;
     }
     default: {
@@ -1626,12 +1680,8 @@ function lowerExpression(
       const expr = exprPath as NodePath<t.NewExpression>;
       const calleePath = expr.get('callee');
       if (!calleePath.isExpression()) {
-        builder.errors.push({
-          reason: `Expected an expression as the \`new\` expression receiver (v8 intrinsics are not supported)`,
-          description: `Got a \`${calleePath.node.type}\``,
-          severity: ErrorSeverity.InvalidJS,
+        builder.errors.pushErrorCode(ErrorCode.UNSUPPORTED_NEW_EXPRESSION, {
           loc: calleePath.node.loc ?? null,
-          suggestions: null,
         });
         return {kind: 'UnsupportedNode', node: exprNode, loc: exprLoc};
       }
@@ -1728,12 +1778,12 @@ function lowerExpression(
           last = lowerExpressionToTemporary(builder, item);
         }
         if (last === null) {
-          builder.errors.push({
-            reason: `Expected sequence expression to have at least one expression`,
-            severity: ErrorSeverity.InvalidJS,
-            loc: expr.node.loc ?? null,
-            suggestions: null,
-          });
+          builder.errors.pushErrorCode(
+            ErrorCode.UNSUPPORTED_EMPTY_SEQUENCE_EXPRESSION,
+            {
+              loc: expr.node.loc ?? null,
+            },
+          );
         } else {
           lowerValueToTemporary(builder, {
             kind: 'StoreLocal',
@@ -2217,12 +2267,18 @@ function lowerExpression(
         });
         for (const [name, locations] of Object.entries(fbtLocations)) {
           if (locations.length > 1) {
-            CompilerError.throwTodo({
-              reason: `Support <${tagName}> tags with multiple <${tagName}:${name}> values`,
-              loc: locations.at(-1) ?? GeneratedSource,
-              description: null,
-              suggestions: null,
-            });
+            CompilerError.throwDiagnostic(
+              CompilerDiagnostic.fromCode(ErrorCode.TODO_DUPLICATE_FBT_TAGS, {
+                description: `Support \`<${tagName}>\` tags with multiple \`<${tagName}:${name}>\` values`,
+                details: locations.map(loc => {
+                  return {
+                    kind: 'error',
+                    message: `Multiple \`<${tagName}:${name}>\` tags found`,
+                    loc,
+                  };
+                }),
+              }),
+            );
           }
         }
       }
@@ -2311,11 +2367,8 @@ function lowerExpression(
       const quasis = expr.get('quasis');
 
       if (subexprs.length !== quasis.length - 1) {
-        builder.errors.push({
-          reason: `Unexpected quasi and subexpression lengths in template literal`,
-          severity: ErrorSeverity.InvalidJS,
+        builder.errors.pushErrorCode(ErrorCode.INVALID_QUASI_LENGTHS, {
           loc: exprPath.node.loc ?? null,
-          suggestions: null,
         });
         return {kind: 'UnsupportedNode', node: exprNode, loc: exprLoc};
       }
@@ -2363,24 +2416,23 @@ function lowerExpression(
             };
           }
         } else {
-          builder.errors.push({
-            reason: `Only object properties can be deleted`,
-            severity: ErrorSeverity.InvalidJS,
-            loc: expr.node.loc ?? null,
-            suggestions: [
-              {
-                description: 'Remove this line',
-                range: [expr.node.start!, expr.node.end!],
-                op: CompilerSuggestionOperation.Remove,
-              },
-            ],
-          });
+          builder.errors.pushErrorCode(
+            ErrorCode.INVALID_SYNTAX_DELETE_EXPRESSION,
+            {
+              loc: expr.node.loc ?? null,
+              suggestions: [
+                {
+                  description: 'Remove this line',
+                  range: [expr.node.start!, expr.node.end!],
+                  op: CompilerSuggestionOperation.Remove,
+                },
+              ],
+            },
+          );
           return {kind: 'UnsupportedNode', node: expr.node, loc: exprLoc};
         }
       } else if (expr.node.operator === 'throw') {
-        builder.errors.push({
-          reason: `Throw expressions are not supported`,
-          severity: ErrorSeverity.InvalidJS,
+        builder.errors.pushErrorCode(ErrorCode.UNSUPPORTED_THROW_EXPRESSION, {
           loc: expr.node.loc ?? null,
           suggestions: [
             {
@@ -2947,6 +2999,8 @@ function isReorderableExpression(
         }
       }
     }
+    case 'TSAsExpression':
+    case 'TSNonNullExpression':
     case 'TypeCastExpression': {
       return isReorderableExpression(
         builder,
@@ -3205,10 +3259,8 @@ function lowerJsxElementName(
     const name = exprPath.node.name.name;
     const tag = `${namespace}:${name}`;
     if (namespace.indexOf(':') !== -1 || name.indexOf(':') !== -1) {
-      builder.errors.push({
-        reason: `Expected JSXNamespacedName to have no colons in the namespace or name`,
+      builder.errors.pushErrorCode(ErrorCode.INVALID_JSX_NAMESPACED_NAME, {
         description: `Got \`${namespace}\` : \`${name}\``,
-        severity: ErrorSeverity.InvalidJS,
         loc: exprPath.node.loc ?? null,
         suggestions: null,
       });
@@ -3447,9 +3499,8 @@ function lowerFunction(
   );
   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();
@@ -3503,6 +3554,12 @@ function lowerIdentifier(
       return place;
     }
     default: {
+      if (binding.kind === 'Global' && binding.name === 'eval') {
+        builder.errors.pushErrorCode(ErrorCode.UNSUPPORTED_EVAL, {
+          loc: exprPath.node.loc ?? null,
+          suggestions: null,
+        });
+      }
       return lowerValueToTemporary(builder, {
         kind: 'LoadGlobal',
         binding,
@@ -3564,9 +3621,7 @@ function lowerIdentifierForAssignment(
     binding.bindingKind === 'const' &&
     kind === InstructionKind.Reassign
   ) {
-    builder.errors.push({
-      reason: `Cannot reassign a \`const\` variable`,
-      severity: ErrorSeverity.InvalidJS,
+    builder.errors.pushErrorCode(ErrorCode.INVALID_SYNTAX_REASSIGNED_CONST, {
       loc: path.node.loc ?? null,
       description:
         binding.identifier.name != null
@@ -3621,12 +3676,13 @@ function lowerAssignment(
       let temporary;
       if (builder.isContextIdentifier(lvalue)) {
         if (kind === InstructionKind.Const && !isHoistedIdentifier) {
-          builder.errors.push({
-            reason: `Expected \`const\` declaration not to be reassigned`,
-            severity: ErrorSeverity.InvalidJS,
-            loc: lvalue.node.loc ?? null,
-            suggestions: null,
-          });
+          builder.errors.pushErrorCode(
+            ErrorCode.INVALID_SYNTAX_REASSIGNED_CONST,
+            {
+              loc: lvalue.node.loc ?? null,
+              suggestions: null,
+            },
+          );
         }
 
         if (
@@ -3637,7 +3693,8 @@ function lowerAssignment(
         ) {
           builder.errors.push({
             reason: `Unexpected context variable kind`,
-            severity: ErrorSeverity.InvalidJS,
+            description: `Expected one of Const, Reassign, Let, Function, got ${kind}`,
+            severity: ErrorSeverity.Invariant,
             loc: lvalue.node.loc ?? null,
             suggestions: null,
           });

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

@@ -49,6 +49,7 @@ import {
 } from './ObjectShape';
 import {Scope as BabelScope, NodePath} from '@babel/traverse';
 import {TypeSchema} from './TypeSchema';
+import {FlowTypeEnv} from '../Flood/Types';
 
 export const ReactElementSymbolSchema = z.object({
   elementSymbol: z.union([
@@ -92,7 +93,7 @@ export const MacroSchema = z.union([
   z.tuple([z.string(), z.array(MacroMethodSchema)]),
 ]);
 
-export type CompilerMode = 'all_features' | 'no_inferred_memo';
+export type CompilerMode = 'all_features' | 'no_inferred_memo' | 'lint_only';
 
 export type Macro = z.infer<typeof MacroSchema>;
 export type MacroMethod = z.infer<typeof MacroMethodSchema>;
@@ -243,6 +244,12 @@ export const EnvironmentConfigSchema = z.object({
    */
   enableUseTypeAnnotations: z.boolean().default(false),
 
+  /**
+   * Allows specifying a function that can populate HIR with type information from
+   * Flow
+   */
+  flowTypeProvider: z.nullable(z.function().args(z.string())).default(null),
+
   /**
    * Enable a new model for mutability and aliasing inference
    */
@@ -265,21 +272,19 @@ 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.
    */
@@ -288,7 +293,7 @@ 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'),
         }),
       ),
     )
@@ -320,10 +325,16 @@ 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 that effects are not used to calculate derived data which could instead be computed
+   * during render.
+   */
+  validateNoDerivedComputationsInEffects: z.boolean().default(false),
 
   /**
    * Validates against creating JSX within a try block and recommends using an error boundary
@@ -610,7 +621,7 @@ export const EnvironmentConfigSchema = z.object({
    *
    * Here the variables `ref` and `myRef` will be typed as Refs.
    */
-  enableTreatRefLikeIdentifiersAsRefs: z.boolean().default(false),
+  enableTreatRefLikeIdentifiersAsRefs: z.boolean().default(true),
 
   /*
    * If specified a value, the compiler lowers any calls to `useContext` to use
@@ -633,6 +644,17 @@ 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>;
@@ -682,6 +704,8 @@ export class Environment {
   #hoistedIdentifiers: Set<t.Identifier>;
   parentFunction: NodePath<t.Function>;
 
+  #flowTypeEnvironment: FlowTypeEnv | null;
+
   constructor(
     scope: BabelScope,
     fnType: ReactFunctionType,
@@ -750,6 +774,26 @@ export class Environment {
     this.parentFunction = parentFunction;
     this.#contextIdentifiers = contextIdentifiers;
     this.#hoistedIdentifiers = new Set();
+
+    if (config.flowTypeProvider != null) {
+      this.#flowTypeEnvironment = new FlowTypeEnv();
+      CompilerError.invariant(code != null, {
+        reason:
+          'Expected Environment to be initialized with source code when a Flow type provider is specified',
+        loc: null,
+      });
+      this.#flowTypeEnvironment.init(this, code);
+    } else {
+      this.#flowTypeEnvironment = null;
+    }
+  }
+
+  get typeContext(): FlowTypeEnv {
+    CompilerError.invariant(this.#flowTypeEnvironment != null, {
+      reason: 'Flow type environment not initialized',
+      loc: null,
+    });
+    return this.#flowTypeEnvironment;
   }
 
   get isInferredMemoEnabled(): boolean {
@@ -785,6 +829,14 @@ export class Environment {
     }
   }
 
+  logOrThrowErrors(errors: Result<void, CompilerError>): void {
+    if (this.compilerMode === 'lint_only') {
+      this.logErrors(errors);
+    } else {
+      errors.unwrap();
+    }
+  }
+
   isContextIdentifier(node: t.Identifier): boolean {
     return this.#contextIdentifiers.has(node);
   }

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,
@@ -113,6 +114,99 @@ const TYPED_GLOBALS: Array<[string, BuiltInType]> = [
           returnValueKind: ValueKind.Mutable,
         }),
       ],
+      [
+        'entries',
+        addFunction(DEFAULT_SHAPES, [], {
+          positionalParams: [Effect.Capture],
+          restParam: null,
+          returnType: {kind: 'Object', shapeId: BuiltInArrayId},
+          calleeEffect: Effect.Read,
+          returnValueKind: ValueKind.Mutable,
+          aliasing: {
+            receiver: '@receiver',
+            params: ['@object'],
+            rest: null,
+            returns: '@returns',
+            temporaries: [],
+            effects: [
+              {
+                kind: 'Create',
+                into: '@returns',
+                reason: ValueReason.KnownReturnSignature,
+                value: ValueKind.Mutable,
+              },
+              // Object values are captured into the return
+              {
+                kind: 'Capture',
+                from: '@object',
+                into: '@returns',
+              },
+            ],
+          },
+        }),
+      ],
+      [
+        'keys',
+        addFunction(DEFAULT_SHAPES, [], {
+          positionalParams: [Effect.Read],
+          restParam: null,
+          returnType: {kind: 'Object', shapeId: BuiltInArrayId},
+          calleeEffect: Effect.Read,
+          returnValueKind: ValueKind.Mutable,
+          aliasing: {
+            receiver: '@receiver',
+            params: ['@object'],
+            rest: null,
+            returns: '@returns',
+            temporaries: [],
+            effects: [
+              {
+                kind: 'Create',
+                into: '@returns',
+                reason: ValueReason.KnownReturnSignature,
+                value: ValueKind.Mutable,
+              },
+              // Only keys are captured, and keys are immutable
+              {
+                kind: 'ImmutableCapture',
+                from: '@object',
+                into: '@returns',
+              },
+            ],
+          },
+        }),
+      ],
+      [
+        'values',
+        addFunction(DEFAULT_SHAPES, [], {
+          positionalParams: [Effect.Capture],
+          restParam: null,
+          returnType: {kind: 'Object', shapeId: BuiltInArrayId},
+          calleeEffect: Effect.Read,
+          returnValueKind: ValueKind.Mutable,
+          aliasing: {
+            receiver: '@receiver',
+            params: ['@object'],
+            rest: null,
+            returns: '@returns',
+            temporaries: [],
+            effects: [
+              {
+                kind: 'Create',
+                into: '@returns',
+                reason: ValueReason.KnownReturnSignature,
+                value: ValueKind.Mutable,
+              },
+              // Object values are captured into the return
+              {
+                kind: 'Capture',
+                from: '@object',
+                into: '@returns',
+              },
+            ],
+          },
+        }),
+      ],
     ]),
   ],
   [
@@ -780,6 +874,7 @@ const REACT_APIS: Array<[string, BuiltInType]> = [
       BuiltInUseEffectEventId,
     ),
   ],
+  ['AUTODEPS', addObject(DEFAULT_SHAPES, BuiltInAutodepsId, [])],
 ];
 
 TYPED_GLOBALS.push(

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

@@ -14,6 +14,8 @@ import type {HookKind} from './ObjectShape';
 import {Type, makeType} from './Types';
 import {z} from 'zod';
 import type {AliasingEffect} from '../Inference/AliasingEffects';
+import {isReservedWord} from '../Utils/Keyword';
+import {ErrorCode} from '../Utils/CompilerErrorCodes';
 
 /*
  * *******************************************************************************************
@@ -279,7 +281,6 @@ 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;
@@ -447,8 +448,20 @@ 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;
@@ -1309,12 +1322,21 @@ export function forkTemporaryIdentifier(
  * original source code.
  */
 export function makeIdentifierName(name: string): ValidatedIdentifier {
-  CompilerError.invariant(t.isValidIdentifier(name), {
-    reason: `Expected a valid identifier name`,
-    loc: GeneratedSource,
-    description: `\`${name}\` is not a valid JavaScript identifier`,
-    suggestions: null,
-  });
+  if (isReservedWord(name)) {
+    CompilerError.throwFromCode(
+      ErrorCode.INVALID_SYNTAX_RESERVED_VARIABLE_NAME,
+      {
+        loc: GeneratedSource,
+        description: `\`${name}\` is a reserved word in JavaScript and cannot be used as an identifier name`,
+      },
+    );
+  } else {
+    CompilerError.invariant(t.isValidIdentifier(name), {
+      reason: `Expected a valid identifier name`,
+      loc: GeneratedSource,
+      description: `\`${name}\` is not a valid JavaScript identifier`,
+    });
+  }
   return {
     kind: 'named',
     value: name as ValidIdentifierName,

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 {CompilerDiagnostic, CompilerError} from '../CompilerError';
 import {Environment} from './Environment';
 import {
   BasicBlock,
@@ -37,6 +37,7 @@ import {
   mapTerminalSuccessors,
   terminalFallthrough,
 } from './visitors';
+import {ErrorCode} from '../Utils/CompilerErrorCodes';
 
 /*
  * *******************************************************************************************
@@ -308,10 +309,17 @@ 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(
+        CompilerDiagnostic.fromCode(ErrorCode.TODO_CONFLICTING_FBT_IDENTIFIER, {
+          details: [
+            {
+              kind: 'error',
+              message: 'Rename to avoid conflict with fbt plugin',
+              loc: node.loc ?? GeneratedSource,
+            },
+          ],
+        }),
+      );
     }
     const originalName = node.name;
     let name = originalName;

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

@@ -107,6 +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

@@ -142,6 +142,7 @@ function parseAliasingSignatureConfig(
   const effects = typeConfig.effects.map(
     (effect: AliasingEffectConfig): AliasingEffect => {
       switch (effect.kind) {
+        case 'ImmutableCapture':
         case 'CreateFrom':
         case 'Capture':
         case 'Alias':
@@ -384,6 +385,7 @@ 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';
@@ -1210,6 +1212,8 @@ addObject(BUILTIN_SHAPES, BuiltInRefValueId, [
   ['*', {kind: 'Object', shapeId: BuiltInRefValueId}],
 ]);
 
+addObject(BUILTIN_SHAPES, ReanimatedSharedValueId, []);
+
 addFunction(
   BUILTIN_SHAPES,
   [],

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';
@@ -54,6 +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 +=
@@ -71,10 +72,8 @@ export function printFunction(fn: HIRFunction): string {
   } else {
     definition += '()';
   }
-  if (definition.length !== 0) {
-    output.push(definition);
-  }
-  output.push(`: ${printType(fn.returnType)} @ ${printPlace(fn.returns)}`);
+  definition += `: ${printPlace(fn.returns)}`;
+  output.push(definition);
   output.push(...fn.directives);
   output.push(printHIR(fn.body));
   return output.join('\n');
@@ -216,7 +215,7 @@ export function printTerminal(terminal: Terminal): Array<string> | string {
       break;
     }
     case 'return': {
-      value = `[${terminal.id}] Return${
+      value = `[${terminal.id}] Return ${terminal.returnVariant}${
         terminal.value != null ? ' ' + printPlace(terminal.value) : ''
       }`;
       if (terminal.effects != null) {
@@ -466,7 +465,7 @@ export function printInstructionValue(instrValue: ReactiveValue): string {
       break;
     }
     case 'UnsupportedNode': {
-      value = `UnsupportedNode(${generate(instrValue.node).code})`;
+      value = `UnsupportedNode ${instrValue.node.type}`;
       break;
     }
     case 'LoadLocal': {
@@ -715,7 +714,7 @@ export function printInstructionValue(instrValue: ReactiveValue): string {
       break;
     }
     case 'FinishMemoize': {
-      value = `FinishMemoize decl=${printPlace(instrValue.decl)}`;
+      value = `FinishMemoize decl=${printPlace(instrValue.decl)}${instrValue.pruned ? ' pruned' : ''}`;
       break;
     }
     default: {
@@ -944,7 +943,10 @@ export function printAliasingEffect(effect: AliasingEffect): string {
       return `Assign ${printPlaceForAliasEffect(effect.into)} = ${printPlaceForAliasEffect(effect.from)}`;
     }
     case 'Alias': {
-      return `Alias ${printPlaceForAliasEffect(effect.into)} = ${printPlaceForAliasEffect(effect.from)}`;
+      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)} <- ${printPlaceForAliasEffect(effect.from)}`;
@@ -996,13 +998,13 @@ export function printAliasingEffect(effect: AliasingEffect): string {
       return `${effect.kind} ${printPlaceForAliasEffect(effect.value)}`;
     }
     case 'MutateFrozen': {
-      return `MutateFrozen ${printPlaceForAliasEffect(effect.place)} reason=${JSON.stringify(effect.error.reason)}`;
+      return `MutateFrozen ${printPlaceForAliasEffect(effect.place)} reason=${JSON.stringify(effect.error.category)}`;
     }
     case 'MutateGlobal': {
-      return `MutateGlobal ${printPlaceForAliasEffect(effect.place)} reason=${JSON.stringify(effect.error.reason)}`;
+      return `MutateGlobal ${printPlaceForAliasEffect(effect.place)} reason=${JSON.stringify(effect.error.category)}`;
     }
     case 'Impure': {
-      return `Impure ${printPlaceForAliasEffect(effect.place)} reason=${JSON.stringify(effect.error.reason)}`;
+      return `Impure ${printPlaceForAliasEffect(effect.place)} reason=${JSON.stringify(effect.error.category)}`;
     }
     case 'Render': {
       return `Render ${printPlaceForAliasEffect(effect.place)}`;

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

@@ -111,6 +111,19 @@ export const AliasEffectSchema: z.ZodType<AliasEffectConfig> = z.object({
   into: LifetimeIdSchema,
 });
 
+export type ImmutableCaptureEffectConfig = {
+  kind: 'ImmutableCapture';
+  from: string;
+  into: string;
+};
+
+export const ImmutableCaptureEffectSchema: z.ZodType<ImmutableCaptureEffectConfig> =
+  z.object({
+    kind: z.literal('ImmutableCapture'),
+    from: LifetimeIdSchema,
+    into: LifetimeIdSchema,
+  });
+
 export type CaptureEffectConfig = {
   kind: 'Capture';
   from: string;
@@ -187,6 +200,7 @@ export type AliasingEffectConfig =
   | AssignEffectConfig
   | AliasEffectConfig
   | CaptureEffectConfig
+  | ImmutableCaptureEffectConfig
   | ImpureEffectConfig
   | MutateEffectConfig
   | MutateTransitiveConditionallyConfig
@@ -199,6 +213,7 @@ export const AliasingEffectSchema: z.ZodType<AliasingEffectConfig> = z.union([
   AssignEffectSchema,
   AliasEffectSchema,
   CaptureEffectSchema,
+  ImmutableCaptureEffectSchema,
   ImpureEffectSchema,
   MutateEffectSchema,
   MutateTransitiveConditionallySchema,

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,
@@ -732,6 +777,7 @@ export function mapTerminalSuccessors(
     case 'return': {
       return {
         kind: 'return',
+        returnVariant: terminal.returnVariant,
         loc: terminal.loc,
         value: terminal.value,
         id: makeInstructionId(0),

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

@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {CompilerErrorDetailOptions} from '../CompilerError';
+import {CompilerDiagnostic} from '../CompilerError';
 import {
   FunctionExpression,
   GeneratedSource,
@@ -90,6 +90,23 @@ export type AliasingEffect =
    * c could be mutating a.
    */
   | {kind: 'Alias'; from: Place; into: Place}
+
+  /**
+   * Indicates the potential for information flow from `from` to `into`. This is used for a specific
+   * case: functions with unknown signatures. If the compiler sees a call such as `foo(x)`, it has to
+   * consider several possibilities (which may depend on the arguments):
+   * - foo(x) returns a new mutable value that does not capture any information from x.
+   * - foo(x) returns a new mutable value that *does* capture information from x.
+   * - foo(x) returns x itself, ie foo is the identity function
+   *
+   * The same is true of functions that take multiple arguments: `cond(a, b, c)` could conditionally
+   * return b or c depending on the value of a.
+   *
+   * To represent this case, MaybeAlias represents the fact that an aliasing relationship could exist.
+   * Any mutations that flow through this relationship automatically become conditional.
+   */
+  | {kind: 'MaybeAlias'; from: Place; into: Place}
+
   /**
    * Records direct assignment: `into = from`.
    */
@@ -133,19 +150,19 @@ export type AliasingEffect =
   /**
    * Mutation of a value known to be immutable
    */
-  | {kind: 'MutateFrozen'; place: Place; error: CompilerErrorDetailOptions}
+  | {kind: 'MutateFrozen'; place: Place; error: CompilerDiagnostic}
   /**
    * Mutation of a global
    */
   | {
       kind: 'MutateGlobal';
       place: Place;
-      error: CompilerErrorDetailOptions;
+      error: CompilerDiagnostic;
     }
   /**
    * Indicates a side-effect that is not safe during render
    */
-  | {kind: 'Impure'; place: Place; error: CompilerErrorDetailOptions}
+  | {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
@@ -183,7 +200,8 @@ export function hashEffect(effect: AliasingEffect): string {
     case 'ImmutableCapture':
     case 'Assign':
     case 'Alias':
-    case 'Capture': {
+    case 'Capture':
+    case 'MaybeAlias': {
       return [
         effect.kind,
         effect.from.identifier.id,
@@ -211,9 +229,9 @@ export function hashEffect(effect: AliasingEffect): string {
         effect.kind,
         effect.place.identifier.id,
         effect.error.severity,
-        effect.error.reason,
+        effect.error.category,
         effect.error.description,
-        printSourceLocation(effect.error.loc ?? GeneratedSource),
+        printSourceLocation(effect.error.primaryLocation() ?? GeneratedSource),
       ].join(':');
     }
     case 'Mutate':

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

@@ -85,7 +85,8 @@ function lowerWithMutationAliasing(fn: HIRFunction): void {
       case 'Assign':
       case 'Alias':
       case 'Capture':
-      case 'CreateFrom': {
+      case 'CreateFrom':
+      case 'MaybeAlias': {
         capturedOrMutated.add(effect.from.identifier.id);
         break;
       }

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

@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {CompilerError, SourceLocation} from '..';
+import {CompilerDiagnostic, CompilerError, SourceLocation} from '..';
 import {
   CallExpression,
   Effect,
@@ -30,6 +30,8 @@ import {
   makeInstructionId,
 } from '../HIR';
 import {createTemporaryPlace, markInstructionIds} from '../HIR/HIRBuilder';
+import {ErrorCode} from '../Utils/CompilerErrorCodes';
+import {Result} from '../Utils/Result';
 
 type ManualMemoCallee = {
   kind: 'useMemo' | 'useCallback';
@@ -283,26 +285,41 @@ 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.fromCode(
+        kind === 'useMemo'
+          ? ErrorCode.INVALID_USE_MEMO_NO_ARG0
+          : ErrorCode.INVALID_USE_CALLBACK_NO_ARG0,
+      ).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.fromCode(
+        fnPlace.kind === 'Spread'
+          ? ErrorCode.DYNAMIC_USE_MEMO_SPREAD_ARGUMENT
+          : ErrorCode.DYNAMIC_USE_CALLBACK_SPREAD_ARGUMENT,
+      ).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) {
@@ -310,23 +327,34 @@ 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.fromCode(
+          ErrorCode.DYNAMIC_MANUAL_MEMO_DEPENDENCY_LIST,
+        ).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.fromCode(
+            ErrorCode.COMPLEX_MANUAL_MEMO_DEPENDENCY_LIST_ENTRY,
+          ).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,
@@ -341,8 +369,14 @@ 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 ||
@@ -389,7 +423,47 @@ 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.fromCode(
+                    ErrorCode.INVALID_USE_MEMO_CALLBACK_RETURN,
+                    {
+                      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.`,
+                    },
+                  ).withDetail({
+                    kind: 'error',
+                    loc: instr.value.loc,
+                    message: 'useMemo() callbacks must return a value',
+                  }),
+                );
+              }
+            }
+          }
+
           instr.value = getManualMemoizationReplacement(
             fnPlace,
             instr.value.loc,
@@ -410,11 +484,16 @@ 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.fromCode(
+                  ErrorCode.DYNAMIC_MANUAL_MEMO_CALLBACK,
+                ).withDetail({
+                  kind: 'error',
+                  loc: fnPlace.loc,
+                  message: `Expected the first argument to be an inline function expression`,
+                }),
+              );
+              continue;
             }
             const memoDecl: Place =
               manualMemo.kind === 'useMemo'
@@ -486,6 +565,8 @@ export function dropManualMemoization(func: HIRFunction): void {
       markInstructionIds(func.body);
     }
   }
+
+  return errors.asResult();
 }
 
 function findOptionalPlaces(fn: HIRFunction): Set<IdentifierId> {
@@ -530,3 +611,17 @@ 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

@@ -57,6 +57,8 @@ import {
 } from '../HIR/visitors';
 import {empty} from '../Utils/Stack';
 import {getOrInsertWith} from '../Utils/utils';
+import {deadCodeElimination} from '../Optimization';
+import {BuiltInAutodepsId} from '../HIR/ObjectShape';
 
 /**
  * Infers reactive dependencies captured by useEffect lambdas and adds them as
@@ -77,7 +79,7 @@ export function inferEffectDependencies(fn: HIRFunction): void {
     );
     moduleTargets.set(
       effectTarget.function.importSpecifierName,
-      effectTarget.numRequiredArgs,
+      effectTarget.autodepsIndex,
     );
   }
   const autodepFnLoads = new Map<IdentifierId, number>();
@@ -135,7 +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';
@@ -169,8 +170,22 @@ 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
@@ -260,7 +275,10 @@ export function inferEffectDependencies(fn: HIRFunction): void {
                 effects: null,
               },
             });
-            value.args.push({...depsPlace, effect: Effect.Freeze});
+            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
@@ -275,7 +293,10 @@ export function inferEffectDependencies(fn: HIRFunction): void {
                 effects: null,
               },
             });
-            value.args.push({...depsPlace, effect: Effect.Freeze});
+            value.args[autodepsArgIndex] = {
+              ...depsPlace,
+              effect: Effect.Freeze,
+            };
             fn.env.inferredEffectLocations.add(callee.loc);
           }
         } else if (
@@ -323,6 +344,7 @@ export function inferEffectDependencies(fn: HIRFunction): void {
     // Renumber instructions and fix scope ranges
     markInstructionIds(fn.body);
     fixScopeAndIdentifierRanges(fn.body);
+    deadCodeElimination(fn);
 
     fn.env.hasInferredEffect = true;
   }
@@ -408,6 +430,7 @@ function rewriteSplices(
   rewriteBlocks.push(currBlock);
 
   let cursor = 0;
+
   for (const rewrite of splices) {
     while (originalInstrs[cursor].id < rewrite.location) {
       CompilerError.invariant(
@@ -429,7 +452,7 @@ function rewriteSplices(
 
     if (rewrite.kind === 'instr') {
       currBlock.instructions.push(rewrite.value);
-    } else {
+    } else if (rewrite.kind === 'block') {
       const {entry, blocks} = rewrite.value;
       const entryBlock = blocks.get(entry)!;
       // splice in all instructions from the entry block

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

@@ -25,6 +25,7 @@ import {
   isRefOrRefValue,
 } from '../HIR';
 import {eachInstructionOperand, eachTerminalOperand} from '../HIR/visitors';
+import {ErrorCode} from '../Utils/CompilerErrorCodes';
 import {assertExhaustive} from '../Utils/utils';
 
 interface State {
@@ -62,22 +63,20 @@ function inferOperandEffect(state: State, place: Place): null | FunctionEffect {
         // We ignore mutations of primitives since this is not a React-specific problem
         value.kind !== ValueKind.Primitive
       ) {
-        let reason = getWriteErrorReason(value);
+        let errorCode = getWriteErrorReason(value);
         return {
           kind:
             value.reason.size === 1 && value.reason.has(ValueReason.Global)
               ? 'GlobalMutation'
               : 'ReactMutation',
           error: {
-            reason,
+            errorCode,
             description:
               place.identifier.name !== null &&
               place.identifier.name.kind === 'named'
                 ? `Found mutation of \`${place.identifier.name.value}\``
                 : null,
             loc: place.loc,
-            suggestions: null,
-            severity: ErrorSeverity.InvalidReact,
           },
         };
       }
@@ -266,11 +265,8 @@ export function inferInstructionFunctionEffects(
       functionEffects.push({
         kind: 'GlobalMutation',
         error: {
-          reason:
-            'Unexpected reassignment of a variable which was defined outside of the component. Components and hooks should be pure and side-effect free, but variable reassignment is a form of side-effect. If this variable is used in rendering, use useState instead. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#side-effects-must-run-outside-of-render)',
+          errorCode: ErrorCode.INVALID_WRITE_GLOBAL,
           loc: instr.loc,
-          suggestions: null,
-          severity: ErrorSeverity.InvalidReact,
         },
       });
       break;
@@ -324,28 +320,28 @@ function isEffectSafeOutsideRender(effect: FunctionEffect): boolean {
   return effect.kind === 'GlobalMutation';
 }
 
-export function getWriteErrorReason(abstractValue: AbstractValue): string {
+export function getWriteErrorReason(abstractValue: AbstractValue): ErrorCode {
   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 ErrorCode.INVALID_WRITE_GLOBAL;
   } 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 ErrorCode.INVALID_WRITE_FROZEN_VALUE_JSX;
   } else if (abstractValue.reason.has(ValueReason.Context)) {
-    return `Mutating a value returned from 'useContext()', which should not be mutated`;
+    return ErrorCode.INVALID_WRITE_IMMUTABLE_VALUE_USE_CONTEXT;
   } else if (abstractValue.reason.has(ValueReason.KnownReturnSignature)) {
-    return 'Mutating a value returned from a function whose return value should not be mutated';
+    return ErrorCode.INVALID_WRITE_IMMUTABLE_VALUE_KNOWN_SIGNATURE;
   } else if (abstractValue.reason.has(ValueReason.ReactiveFunctionArgument)) {
-    return 'Mutating component props or hook arguments is not allowed. Consider using a local variable instead';
+    return ErrorCode.INVALID_WRITE_IMMUTABLE_ARGS;
   } 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 ErrorCode.INVALID_WRITE_STATE;
   } 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 ErrorCode.INVALID_WRITE_REDUCER_STATE;
   } else if (abstractValue.reason.has(ValueReason.Effect)) {
-    return 'Updating a value used previously in an effect function or as an effect dependency is not allowed. Consider moving the mutation before calling useEffect()';
+    return ErrorCode.INVALID_WRITE_EFFECT_DEPENDENCY;
   } else if (abstractValue.reason.has(ValueReason.HookCaptured)) {
-    return 'Updating a value previously passed as an argument to a hook is not allowed. Consider moving the mutation before calling the hook';
+    return ErrorCode.INVALID_WRITE_HOOK_CAPTURED;
   } else if (abstractValue.reason.has(ValueReason.HookReturn)) {
-    return 'Updating a value returned from a hook is not allowed. Consider moving the mutation into the hook where the value is constructed';
+    return ErrorCode.INVALID_WRITE_HOOK_RETURN;
   } else {
-    return 'This mutates a variable that React considers immutable';
+    return ErrorCode.INVALID_WRITE_GENERIC;
   }
 }

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

@@ -6,9 +6,9 @@
  */
 
 import {
+  CompilerDiagnostic,
   CompilerError,
   Effect,
-  ErrorSeverity,
   SourceLocation,
   ValueKind,
 } from '..';
@@ -36,8 +36,8 @@ import {
   ValueReason,
 } from '../HIR';
 import {
-  eachInstructionValueLValue,
   eachInstructionValueOperand,
+  eachPatternItem,
   eachTerminalOperand,
   eachTerminalSuccessor,
 } from '../HIR/visitors';
@@ -68,6 +68,7 @@ import {getWriteErrorReason} from './InferFunctionEffects';
 import prettyFormat from 'pretty-format';
 import {createTemporaryPlace} from '../HIR/HIRBuilder';
 import {AliasingEffect, AliasingSignature, hashEffect} from './AliasingEffects';
+import {ErrorCode, ErrorCodeDetails} from '../Utils/CompilerErrorCodes';
 
 const DEBUG = false;
 
@@ -441,25 +442,27 @@ function applySignature(
         const value = state.kind(effect.value);
         switch (value.kind) {
           case ValueKind.Frozen: {
-            const reason = getWriteErrorReason({
+            const errorCode = getWriteErrorReason({
               kind: value.kind,
               reason: value.reason,
               context: new Set(),
             });
+            const variable =
+              effect.value.identifier.name !== null &&
+              effect.value.identifier.name.kind === 'named'
+                ? `\`${effect.value.identifier.name.value}\``
+                : 'value';
             effects.push({
               kind: 'MutateFrozen',
               place: effect.value,
-              error: {
-                severity: ErrorSeverity.InvalidReact,
-                reason,
-                description:
-                  effect.value.identifier.name !== null &&
-                  effect.value.identifier.name.kind === 'named'
-                    ? `Found mutation of \`${effect.value.identifier.name.value}\``
-                    : null,
+              // TODO: remove ERROR_CODE.INVALID_WRITE and update test fixtures
+              error: CompilerDiagnostic.fromCode(ErrorCode.INVALID_WRITE, {
+                description: ErrorCodeDetails[errorCode].reason,
+              }).withDetail({
+                kind: 'error',
                 loc: effect.value.loc,
-                suggestions: null,
-              },
+                message: `${variable} cannot be modified`,
+              }),
             });
           }
         }
@@ -687,6 +690,7 @@ function applyEffect(
       }
       break;
     }
+    case 'MaybeAlias':
     case 'Alias':
     case 'Capture': {
       CompilerError.invariant(
@@ -951,7 +955,7 @@ function applyEffect(
             context,
             state,
             // OK: recording information flow
-            {kind: 'Alias', from: operand, into: effect.into},
+            {kind: 'MaybeAlias', from: operand, into: effect.into},
             initialized,
             effects,
           );
@@ -1013,33 +1017,29 @@ function applyEffect(
             effect.value.identifier.declarationId,
           )
         ) {
-          const description =
+          const variable =
             effect.value.identifier.name !== null &&
             effect.value.identifier.name.kind === 'named'
-              ? `Variable \`${effect.value.identifier.name.value}\` is accessed before it is declared`
+              ? `\`${effect.value.identifier.name.value}\``
               : null;
           const hoistedAccess = context.hoistedContextDeclarations.get(
             effect.value.identifier.declarationId,
           );
+          const diagnostic = CompilerDiagnostic.fromCode(
+            ErrorCode.INVALID_ACCESS_BEFORE_INIT,
+          );
           if (hoistedAccess != null && hoistedAccess.loc != effect.value.loc) {
-            applyEffect(
-              context,
-              state,
-              {
-                kind: 'MutateFrozen',
-                place: effect.value,
-                error: {
-                  severity: ErrorSeverity.InvalidReact,
-                  reason: `This variable is accessed before it is declared, which may prevent it from updating as the assigned value changes over time`,
-                  description,
-                  loc: hoistedAccess.loc,
-                  suggestions: null,
-                },
-              },
-              initialized,
-              effects,
-            );
+            diagnostic.withDetail({
+              kind: 'error',
+              loc: hoistedAccess.loc,
+              message: `${variable ?? 'This variable'} is accessed before it is declared`,
+            });
           }
+          diagnostic.withDetail({
+            kind: 'error',
+            loc: effect.value.loc,
+            message: `${variable ?? 'This variable'} is declared here`,
+          });
 
           applyEffect(
             context,
@@ -1047,28 +1047,22 @@ function applyEffect(
             {
               kind: 'MutateFrozen',
               place: effect.value,
-              error: {
-                severity: ErrorSeverity.InvalidReact,
-                reason: `This variable is accessed before it is declared, which prevents the earlier access from updating when this value changes over time`,
-                description,
-                loc: effect.value.loc,
-                suggestions: null,
-              },
+              error: diagnostic,
             },
             initialized,
             effects,
           );
         } else {
-          const reason = getWriteErrorReason({
+          const errorCode = getWriteErrorReason({
             kind: value.kind,
             reason: value.reason,
             context: new Set(),
           });
-          const description =
+          const variable =
             effect.value.identifier.name !== null &&
             effect.value.identifier.name.kind === 'named'
-              ? `Found mutation of \`${effect.value.identifier.name.value}\``
-              : null;
+              ? `\`${effect.value.identifier.name.value}\``
+              : 'value';
           applyEffect(
             context,
             state,
@@ -1078,13 +1072,14 @@ function applyEffect(
                   ? 'MutateFrozen'
                   : 'MutateGlobal',
               place: effect.value,
-              error: {
-                severity: ErrorSeverity.InvalidReact,
-                reason,
-                description,
+              // TODO: remove ERROR_CODE.INVALID_WRITE and update test fixtures
+              error: CompilerDiagnostic.fromCode(ErrorCode.INVALID_WRITE, {
+                description: ErrorCodeDetails[errorCode].reason,
+              }).withDetail({
+                kind: 'error',
                 loc: effect.value.loc,
-                suggestions: null,
-              },
+                message: `${variable} cannot be modified`,
+              }),
             },
             initialized,
             effects,
@@ -1325,7 +1320,7 @@ class InferenceState {
             return 'mutate-global';
           }
           case ValueKind.MaybeFrozen: {
-            return 'none';
+            return 'mutate-frozen';
           }
           default: {
             assertExhaustive(kind, `Unexpected kind ${kind}`);
@@ -1864,19 +1859,34 @@ function computeSignatureForInstruction(
       break;
     }
     case 'Destructure': {
-      for (const patternLValue of eachInstructionValueLValue(value)) {
-        if (isPrimitiveType(patternLValue.identifier)) {
+      for (const patternItem of eachPatternItem(value.lvalue.pattern)) {
+        const place =
+          patternItem.kind === 'Identifier' ? patternItem : patternItem.place;
+        if (isPrimitiveType(place.identifier)) {
           effects.push({
             kind: 'Create',
-            into: patternLValue,
+            into: place,
             value: ValueKind.Primitive,
             reason: ValueReason.Other,
           });
-        } else {
+        } else if (patternItem.kind === 'Identifier') {
           effects.push({
             kind: 'CreateFrom',
             from: value.value,
-            into: patternLValue,
+            into: place,
+          });
+        } else {
+          // Spread creates a new object/array that captures from the RValue
+          effects.push({
+            kind: 'Create',
+            into: place,
+            reason: ValueReason.Other,
+            value: ValueKind.Mutable,
+          });
+          effects.push({
+            kind: 'Capture',
+            from: value.value,
+            into: place,
           });
         }
       }
@@ -1988,16 +1998,17 @@ function computeSignatureForInstruction(
       break;
     }
     case 'StoreGlobal': {
+      const variable = `\`${value.name}\``;
       effects.push({
         kind: 'MutateGlobal',
         place: value.value,
-        error: {
-          reason:
-            'Unexpected reassignment of a variable which was defined outside of the component. Components and hooks should be pure and side-effect free, but variable reassignment is a form of side-effect. If this variable is used in rendering, use useState instead. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#side-effects-must-run-outside-of-render)',
+        error: CompilerDiagnostic.fromCode(
+          ErrorCode.INVALID_WRITE_GLOBAL,
+        ).withDetail({
+          kind: 'error',
           loc: instr.loc,
-          suggestions: null,
-          severity: ErrorSeverity.InvalidReact,
-        },
+          message: `${variable} should not be reassigned`,
+        }),
       });
       effects.push({kind: 'Assign', from: value.value, into: lvalue});
       break;
@@ -2087,17 +2098,16 @@ function computeEffectsForLegacySignature(
     effects.push({
       kind: 'Impure',
       place: receiver,
-      error: {
-        reason:
-          'Calling an impure function can produce unstable results. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent)',
-        description:
-          signature.canonicalName != null
-            ? `\`${signature.canonicalName}\` is an impure function whose results may change on every call`
-            : null,
-        severity: ErrorSeverity.InvalidReact,
-        loc,
-        suggestions: null,
-      },
+      error: CompilerDiagnostic.fromCode(ErrorCode.IMPURE_FUNCTIONS).withDetail(
+        {
+          kind: 'error',
+          loc,
+          message:
+            signature.canonicalName != null
+              ? `\`${signature.canonicalName}\` is an impure function. `
+              : 'This is an impure function.',
+        },
+      ),
     });
   }
   const stores: Array<Place> = [];
@@ -2357,6 +2367,7 @@ function computeEffectsForSignature(
   // Apply substitutions
   for (const effect of signature.effects) {
     switch (effect.kind) {
+      case 'MaybeAlias':
       case 'Assign':
       case 'ImmutableCapture':
       case 'Alias':

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

@@ -18,6 +18,7 @@ import {
   ValueKind,
   ValueReason,
   Place,
+  isPrimitiveType,
 } from '../HIR/HIR';
 import {
   eachInstructionLValue,
@@ -159,6 +160,8 @@ export function inferMutationAliasingRanges(
           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 (
@@ -194,7 +197,7 @@ export function inferMutationAliasingRanges(
           effect.kind === 'MutateGlobal' ||
           effect.kind === 'Impure'
         ) {
-          errors.push(effect.error);
+          errors.pushDiagnostic(effect.error);
           functionEffects.push(effect);
         } else if (effect.kind === 'Render') {
           renders.push({index: index++, place: effect.place});
@@ -246,6 +249,7 @@ export function inferMutationAliasingRanges(
   }
   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;
@@ -345,7 +349,8 @@ export function inferMutationAliasingRanges(
           case 'Assign':
           case 'Alias':
           case 'Capture':
-          case 'CreateFrom': {
+          case 'CreateFrom':
+          case 'MaybeAlias': {
             const isMutatedOrReassigned =
               effect.into.identifier.mutableRange.end > instr.id;
             if (isMutatedOrReassigned) {
@@ -471,15 +476,15 @@ export function inferMutationAliasingRanges(
    * 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:
-      fn.returnType.kind === 'Primitive'
-        ? ValueKind.Primitive
-        : isJsxType(fn.returnType)
-          ? ValueKind.Frozen
-          : ValueKind.Mutable,
+    value: isPrimitiveType(returns)
+      ? ValueKind.Primitive
+      : isJsxType(returns.type)
+        ? ValueKind.Frozen
+        : ValueKind.Mutable,
     reason: ValueReason.KnownReturnSignature,
   });
   /**
@@ -548,7 +553,7 @@ function appendFunctionErrors(errors: CompilerError, fn: HIRFunction): void {
       case 'Impure':
       case 'MutateFrozen':
       case 'MutateGlobal': {
-        errors.push(effect.error);
+        errors.pushDiagnostic(effect.error);
         break;
       }
     }
@@ -566,7 +571,12 @@ type Node = {
   createdFrom: Map<Identifier, number>;
   captures: Map<Identifier, number>;
   aliases: Map<Identifier, number>;
-  edges: Array<{index: number; node: Identifier; kind: 'capture' | 'alias'}>;
+  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;
@@ -584,6 +594,7 @@ class AliasingState {
       createdFrom: new Map(),
       captures: new Map(),
       aliases: new Map(),
+      maybeAliases: new Map(),
       edges: [],
       transitive: null,
       local: null,
@@ -629,6 +640,18 @@ class AliasingState {
     }
   }
 
+  maybeAlias(index: number, from: Place, into: Place): void {
+    const fromNode = this.nodes.get(from.identifier);
+    const toNode = this.nodes.get(into.identifier);
+    if (fromNode == null || toNode == null) {
+      return;
+    }
+    fromNode.edges.push({index, node: into.identifier, kind: 'maybeAlias'});
+    if (!toNode.maybeAliases.has(from.identifier)) {
+      toNode.maybeAliases.set(from.identifier, index);
+    }
+  }
+
   render(index: number, start: Identifier, errors: CompilerError): void {
     const seen = new Set<Identifier>();
     const queue: Array<Identifier> = [start];
@@ -672,22 +695,24 @@ class AliasingState {
     // Null is used for simulated mutations
     end: InstructionId | null,
     transitive: boolean,
-    kind: MutationKind,
+    startKind: MutationKind,
     loc: SourceLocation,
     errors: CompilerError,
   ): void {
-    const seen = new Set<Identifier>();
+    const seen = new Map<Identifier, MutationKind>();
     const queue: Array<{
       place: Identifier;
       transitive: boolean;
       direction: 'backwards' | 'forwards';
-    }> = [{place: start, transitive, direction: 'backwards'}];
+      kind: MutationKind;
+    }> = [{place: start, transitive, direction: 'backwards', kind: startKind}];
     while (queue.length !== 0) {
-      const {place: current, transitive, direction} = queue.pop()!;
-      if (seen.has(current)) {
+      const {place: current, transitive, direction, kind} = queue.pop()!;
+      const previousKind = seen.get(current);
+      if (previousKind != null && previousKind >= kind) {
         continue;
       }
-      seen.add(current);
+      seen.set(current, kind);
       const node = this.nodes.get(current);
       if (node == null) {
         continue;
@@ -723,13 +748,18 @@ class AliasingState {
         if (edge.index >= index) {
           break;
         }
-        queue.push({place: edge.node, transitive, direction: 'forwards'});
+        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'});
+        queue.push({
+          place: alias,
+          transitive: true,
+          direction: 'backwards',
+          kind,
+        });
       }
       if (direction === 'backwards' || node.value.kind !== 'Phi') {
         /**
@@ -746,7 +776,25 @@ class AliasingState {
           if (when >= index) {
             continue;
           }
-          queue.push({place: alias, transitive, direction: 'backwards'});
+          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,
+          });
         }
       }
       /**
@@ -757,7 +805,12 @@ class AliasingState {
           if (when >= index) {
             continue;
           }
-          queue.push({place: capture, transitive, direction: 'backwards'});
+          queue.push({
+            place: capture,
+            transitive,
+            direction: 'backwards',
+            kind,
+          });
         }
       }
     }

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

@@ -21,7 +21,6 @@ import {
   isStableType,
   isStableTypeContainer,
   isUseOperator,
-  isUseRefType,
 } from '../HIR';
 import {PostDominator} from '../HIR/Dominator';
 import {
@@ -70,13 +69,6 @@ class StableSidemap {
               isStable: false,
             });
           }
-        } else if (
-          this.env.config.enableTreatRefLikeIdentifiersAsRefs &&
-          isUseRefType(lvalue.identifier)
-        ) {
-          this.map.set(lvalue.identifier.id, {
-            isStable: true,
-          });
         }
         break;
       }

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

@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {CompilerError, CompilerErrorDetailOptions} from '../CompilerError';
+import {CompilerError} from '../CompilerError';
 import {Environment} from '../HIR';
 import {
   AbstractValue,
@@ -48,6 +48,7 @@ import {
   eachTerminalOperand,
   eachTerminalSuccessor,
 } from '../HIR/visitors';
+import {Err, Ok, Result} from '../Utils/Result';
 import {assertExhaustive, Set_isSuperset} from '../Utils/utils';
 import {
   inferTerminalFunctionEffects,
@@ -106,7 +107,7 @@ const UndefinedValue: InstructionValue = {
 export default function inferReferenceEffects(
   fn: HIRFunction,
   options: {isFunctionExpression: boolean} = {isFunctionExpression: false},
-): Array<CompilerErrorDetailOptions> {
+): Result<void, CompilerError> {
   /*
    * Initial state contains function params
    * TODO: include module declarations here as well
@@ -247,10 +248,17 @@ export default function inferReferenceEffects(
 
   if (options.isFunctionExpression) {
     fn.effects = functionEffects;
-    return [];
   } else {
-    return transformFunctionEffectErrors(functionEffects);
+    const errors = transformFunctionEffectErrors(functionEffects);
+    if (errors.length > 0) {
+      const compilerError = new CompilerError();
+      for (const detail of errors) {
+        compilerError.push(detail);
+      }
+      return Err(compilerError);
+    }
   }
+  return Ok(void 0);
 }
 
 type FreezeAction = {values: Set<InstructionValue>; reason: Set<ValueReason>};

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

@@ -11,6 +11,7 @@ import {
   Environment,
   FunctionExpression,
   GeneratedSource,
+  GotoTerminal,
   GotoVariant,
   HIRFunction,
   IdentifierId,
@@ -19,6 +20,7 @@ import {
   Place,
   isStatementBlockKind,
   makeInstructionId,
+  mergeConsecutiveBlocks,
   promoteTemporary,
   reversePostorderBlocks,
 } from '../HIR';
@@ -73,6 +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,
@@ -146,37 +152,75 @@ export function inlineImmediatelyInvokedFunctionExpressions(
              */
             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;
+            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;
+              // We store the result in the IIFE temporary
+              const result = instr.lvalue;
 
-            // Declare the IIFE temporary
-            declareTemporary(fn.env, block, result);
+              // Declare the IIFE temporary
+              declareTemporary(fn.env, block, result);
 
-            // Promote the temporary with a name as we require this to persist
-            promoteTemporary(result.identifier);
+              // 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);
+              /*
+               * 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);
+              }
             }
 
             /*
@@ -199,7 +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),
@@ -213,9 +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>

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

@@ -153,6 +153,10 @@ This is somewhat the inverse of `Capture`. The `CreateFrom` effect describes tha
 
 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`).
@@ -347,6 +351,17 @@ 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:

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

@@ -25,7 +25,6 @@ import {
   makeBlockId,
   makeInstructionId,
   makePropertyLiteral,
-  makeType,
   markInstructionIds,
   promoteTemporary,
   reversePostorderBlocks,
@@ -238,6 +237,7 @@ function emitSelectorFn(env: Environment, keys: Array<string>): Instruction {
     terminal: {
       id: makeInstructionId(0),
       kind: 'return',
+      returnVariant: 'Explicit',
       loc: GeneratedSource,
       value: arrayInstr.lvalue,
       effects: null,
@@ -253,7 +253,6 @@ function emitSelectorFn(env: Environment, keys: Array<string>): Instruction {
     env,
     params: [obj],
     returnTypeAnnotation: null,
-    returnType: makeType(),
     returns: createTemporaryPlace(env, GeneratedSource),
     context: [],
     effects: null,

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

@@ -21,7 +21,6 @@ import {
   makeBlockId,
   makeIdentifierName,
   makeInstructionId,
-  makeType,
   ObjectProperty,
   Place,
   promoteTemporary,
@@ -353,6 +352,7 @@ function emitOutlinedFn(
     terminal: {
       id: makeInstructionId(0),
       kind: 'return',
+      returnVariant: 'Explicit',
       loc: GeneratedSource,
       value: instructions.at(-1)!.lvalue,
       effects: null,
@@ -368,7 +368,6 @@ function emitOutlinedFn(
     env,
     params: [propsObj],
     returnTypeAnnotation: null,
-    returnType: makeType(),
     returns: createTemporaryPlace(env, GeneratedSource),
     context: [],
     effects: null,

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

@@ -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]);
         }),
       );
     }

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

@@ -119,6 +119,7 @@ class FindLastUsageVisitor extends ReactiveFunctionVisitor<void> {
 
 class Transform extends ReactiveFunctionTransform<ReactiveScopeDependencies | null> {
   lastUsage: Map<DeclarationId, InstructionId>;
+  temporaries: Map<DeclarationId, DeclarationId> = new Map();
 
   constructor(lastUsage: Map<DeclarationId, InstructionId>) {
     super();
@@ -215,6 +216,12 @@ class Transform extends ReactiveFunctionTransform<ReactiveScopeDependencies | nu
                 current.lvalues.add(
                   instr.instruction.lvalue.identifier.declarationId,
                 );
+                if (instr.instruction.value.kind === 'LoadLocal') {
+                  this.temporaries.set(
+                    instr.instruction.lvalue.identifier.declarationId,
+                    instr.instruction.value.place.identifier.declarationId,
+                  );
+                }
               }
               break;
             }
@@ -236,6 +243,13 @@ class Transform extends ReactiveFunctionTransform<ReactiveScopeDependencies | nu
                   )) {
                     current.lvalues.add(lvalue.identifier.declarationId);
                   }
+                  this.temporaries.set(
+                    instr.instruction.value.lvalue.place.identifier
+                      .declarationId,
+                    this.temporaries.get(
+                      instr.instruction.value.value.identifier.declarationId,
+                    ) ?? instr.instruction.value.value.identifier.declarationId,
+                  );
                 } else {
                   log(
                     `Reset scope @${current.block.scope.id} from StoreLocal in [${instr.instruction.id}]`,
@@ -260,7 +274,7 @@ class Transform extends ReactiveFunctionTransform<ReactiveScopeDependencies | nu
         case 'scope': {
           if (
             current !== null &&
-            canMergeScopes(current.block, instr) &&
+            canMergeScopes(current.block, instr, this.temporaries) &&
             areLValuesLastUsedByScope(
               instr.scope,
               current.lvalues,
@@ -426,6 +440,7 @@ function areLValuesLastUsedByScope(
 function canMergeScopes(
   current: ReactiveScopeBlock,
   next: ReactiveScopeBlock,
+  temporaries: Map<DeclarationId, DeclarationId>,
 ): boolean {
   // Don't merge scopes with reassignments
   if (
@@ -465,11 +480,14 @@ function canMergeScopes(
     (next.scope.dependencies.size !== 0 &&
       [...next.scope.dependencies].every(
         dep =>
+          dep.path.length === 0 &&
           isAlwaysInvalidatingType(dep.identifier.type) &&
           Iterable_some(
             current.scope.declarations.values(),
             decl =>
-              decl.identifier.declarationId === dep.identifier.declarationId,
+              decl.identifier.declarationId === dep.identifier.declarationId ||
+              decl.identifier.declarationId ===
+                temporaries.get(dep.identifier.declarationId),
           ),
       ))
   ) {
@@ -477,12 +495,16 @@ function canMergeScopes(
     return true;
   }
   log(`  cannot merge scopes:`);
-  log(`  ${printReactiveScopeSummary(current.scope)}`);
-  log(`  ${printReactiveScopeSummary(next.scope)}`);
+  log(
+    `  ${printReactiveScopeSummary(current.scope)} ${[...current.scope.declarations.values()].map(decl => decl.identifier.declarationId)}`,
+  );
+  log(
+    `  ${printReactiveScopeSummary(next.scope)} ${[...next.scope.dependencies].map(dep => `${dep.identifier.declarationId} ${temporaries.get(dep.identifier.declarationId) ?? dep.identifier.declarationId}`)}`,
+  );
   return false;
 }
 
-function isAlwaysInvalidatingType(type: Type): boolean {
+export function isAlwaysInvalidatingType(type: Type): boolean {
   switch (type.kind) {
     case 'Object': {
       switch (type.shapeId) {

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

@@ -42,6 +42,7 @@ import {
 import {eachInstructionOperand} from '../HIR/visitors';
 import {printSourceLocationLine} from '../HIR/PrintHIR';
 import {USE_FIRE_FUNCTION_NAME} from '../HIR/Environment';
+import {ErrorCode} from '../Utils/CompilerErrorCodes';
 
 /*
  * TODO(jmbrown):
@@ -50,8 +51,6 @@ import {USE_FIRE_FUNCTION_NAME} from '../HIR/Environment';
  *   - React.useEffect calls
  */
 
-const CANNOT_COMPILE_FIRE = 'Cannot compile `fire`';
-
 export function transformFire(fn: HIRFunction): void {
   const context = new Context(fn.env);
   replaceFireFunctions(fn, context);
@@ -178,9 +177,7 @@ function replaceFireFunctions(fn: HIRFunction, context: Context): void {
                 loc: value.args[1].loc,
                 description:
                   'You must use an array literal for an effect dependency array when that effect uses `fire()`',
-                severity: ErrorSeverity.Invariant,
-                reason: CANNOT_COMPILE_FIRE,
-                suggestions: null,
+                errorCode: ErrorCode.CANNOT_COMPILE_FIRE,
               });
             }
           } else if (value.args.length > 1 && value.args[1].kind === 'Spread') {
@@ -188,9 +185,7 @@ function replaceFireFunctions(fn: HIRFunction, context: Context): void {
               loc: value.args[1].place.loc,
               description:
                 'You must use an array literal for an effect dependency array when that effect uses `fire()`',
-              severity: ErrorSeverity.Invariant,
-              reason: CANNOT_COMPILE_FIRE,
-              suggestions: null,
+              errorCode: ErrorCode.CANNOT_COMPILE_FIRE,
             });
           }
         }
@@ -243,11 +238,9 @@ function replaceFireFunctions(fn: HIRFunction, context: Context): void {
           } else {
             context.pushError({
               loc: value.loc,
+              errorCode: ErrorCode.CANNOT_COMPILE_FIRE,
               description:
                 '`fire()` can only receive a function call such as `fire(fn(a,b)). Method calls and other expressions are not allowed',
-              severity: ErrorSeverity.InvalidReact,
-              reason: CANNOT_COMPILE_FIRE,
-              suggestions: null,
             });
           }
         } else {
@@ -262,10 +255,8 @@ function replaceFireFunctions(fn: HIRFunction, context: Context): void {
           }
           context.pushError({
             loc: value.loc,
+            errorCode: ErrorCode.CANNOT_COMPILE_FIRE,
             description,
-            severity: ErrorSeverity.InvalidReact,
-            reason: CANNOT_COMPILE_FIRE,
-            suggestions: null,
           });
         }
       } else if (value.kind === 'CallExpression') {
@@ -394,9 +385,7 @@ function ensureNoRemainingCalleeCaptures(
         description: `All uses of ${calleeName} must be either used with a fire() call in \
 this effect or not used with a fire() call at all. ${calleeName} was used with fire() on line \
 ${printSourceLocationLine(calleeInfo.fireLoc)} in this effect`,
-        severity: ErrorSeverity.InvalidReact,
-        reason: CANNOT_COMPILE_FIRE,
-        suggestions: null,
+        errorCode: ErrorCode.CANNOT_COMPILE_FIRE,
       });
     }
   }
@@ -411,9 +400,7 @@ function ensureNoMoreFireUses(fn: HIRFunction, context: Context): void {
       context.pushError({
         loc: place.identifier.loc,
         description: 'Cannot use `fire` outside of a useEffect function',
-        severity: ErrorSeverity.Invariant,
-        reason: CANNOT_COMPILE_FIRE,
-        suggestions: null,
+        errorCode: ErrorCode.CANNOT_COMPILE_FIRE,
       });
     }
   }

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;
@@ -426,6 +451,18 @@ function* generateInstructionTypes(
 
     case 'JsxExpression':
     case 'JsxFragment': {
+      if (env.config.enableTreatRefLikeIdentifiersAsRefs) {
+        if (value.kind === 'JsxExpression') {
+          for (const prop of value.props) {
+            if (prop.kind === 'JsxAttribute' && prop.name === 'ref') {
+              yield equation(prop.place.identifier.type, {
+                kind: 'Object',
+                shapeId: BuiltInUseRefId,
+              });
+            }
+          }
+        }
+      }
       yield equation(left, {kind: 'Object', shapeId: BuiltInJsxId});
       break;
     }
@@ -441,7 +478,36 @@ 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/TypeInference/PropagatePhiTypes.ts

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

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

@@ -0,0 +1,624 @@
+import {ErrorSeverity} from './CompilerErrorSeverity';
+
+export enum LinterCategory {
+  RULES_OF_HOOKS = 'rules-of-hooks',
+  IMPURE_FUNCTIONS = 'impure-functions',
+  JSX_IN_TRY = 'jsx-in-try',
+  NO_REF_ACCESS_IN_RENDER = 'no-ref-access-in-render',
+  VALIDATE_MANUAL_MEMO = 'validate-manual-memo',
+  DYNAMIC_MANUAL_MEMO = 'dynamic-manual-memo',
+
+  EXHAUSTIVE_DEPS = 'exhaustive-deps',
+  MEMOIZED_DEPENDENCIES = 'memoized-dependencies', // not real!
+  INVALID_WRITE = 'invalid-write',
+  CAPITALIZED_CALLS = 'capitalized-calls',
+  STATIC_COMPONENTS = 'static-components',
+  NO_SET_STATE_IN_RENDER = 'no-set-state-in-render',
+  NO_SET_STATE_IN_EFFECTS = 'no-set-state-in-effects',
+  UNNECESSARY_EFFECTS = 'unnecessary-effects',
+
+  UNSUPPORTED_SYNTAX = 'unsupported-syntax',
+
+  TODO_SYNTAX = 'todo-syntax',
+
+  COMPILER_CONFIG = 'compiler-config',
+}
+
+export enum ErrorCode {
+  HOOK_CALL_STATIC,
+  HOOK_INVALID_REFERENCE,
+  HOOK_CALL_REACTIVE,
+  HOOK_CALL_NOT_TOP_LEVEL,
+  IMPURE_FUNCTIONS,
+  JSX_IN_TRY,
+  NO_REF_ACCESS_IN_RENDER,
+  WRITE_AFTER_RENDER,
+  REASSIGN_AFTER_RENDER,
+  REASSIGN_IN_ASYNC,
+  INVALID_WRITE,
+  CAPITALIZED_CALLS,
+  STATIC_COMPONENTS,
+  INVALID_USE_MEMO_CALLBACK_RETURN,
+  INVALID_USE_MEMO_CALLBACK_PARAMETERS,
+  INVALID_USE_MEMO_CALLBACK_ASYNC,
+  INVALID_USE_MEMO_NO_ARG0,
+  INVALID_USE_CALLBACK_NO_ARG0,
+  DYNAMIC_MANUAL_MEMO_CALLBACK,
+  DYNAMIC_USE_MEMO_SPREAD_ARGUMENT,
+  DYNAMIC_USE_CALLBACK_SPREAD_ARGUMENT,
+  DYNAMIC_MANUAL_MEMO_DEPENDENCY_LIST,
+  COMPLEX_MANUAL_MEMO_DEPENDENCY_LIST_ENTRY,
+
+  INVALID_SET_STATE_IN_RENDER,
+  INVALID_SET_STATE_IN_MEMO,
+  INVALID_SET_STATE_IN_EFFECTS,
+
+  NO_DERIVED_COMPUTATIONS_IN_EFFECTS,
+
+  DYNAMIC_GATING_IS_NOT_IDENTIFIER,
+  DYNAMIC_GATING_MULTIPLE_DIRECTIVES,
+  FILENAME_NOT_SET,
+
+  INVALID_WRITE_GLOBAL,
+  INVALID_WRITE_FROZEN_VALUE_JSX,
+  INVALID_WRITE_IMMUTABLE_VALUE_USE_CONTEXT,
+  INVALID_WRITE_IMMUTABLE_VALUE_KNOWN_SIGNATURE,
+  INVALID_WRITE_IMMUTABLE_ARGS,
+  INVALID_WRITE_STATE,
+  INVALID_WRITE_REDUCER_STATE,
+  INVALID_WRITE_EFFECT_DEPENDENCY,
+  INVALID_WRITE_HOOK_CAPTURED,
+  INVALID_WRITE_HOOK_RETURN,
+  INVALID_ACCESS_BEFORE_INIT,
+  INVALID_WRITE_GENERIC,
+
+  MEMOIZED_EFFECT_DEPENDENCIES,
+
+  INVALID_SYNTAX_MULTIPLE_DEFAULTS,
+  INVALID_SYNTAX_REASSIGNED_CONST,
+  INVALID_SYNTAX_BAD_VARIABLE_DECL,
+  UNSUPPORTED_WITH,
+  UNSUPPORTED_INNER_CLASS,
+  INVALID_IMPORT_EXPORT,
+  INVALID_TS_NAMESPACE,
+  UNSUPPORTED_NEW_EXPRESSION,
+  UNSUPPORTED_EMPTY_SEQUENCE_EXPRESSION,
+  INVALID_QUASI_LENGTHS,
+  INVALID_SYNTAX_DELETE_EXPRESSION,
+  UNSUPPORTED_THROW_EXPRESSION,
+  INVALID_JSX_NAMESPACED_NAME,
+  UNSUPPORTED_EVAL,
+  INVALID_SYNTAX_RESERVED_VARIABLE_NAME,
+  INVALID_JAVASCRIPT_AST,
+  BAILOUT_ESLINT_SUPPRESSION,
+  BAILOUT_FLOW_SUPPRESSION,
+  MANUAL_MEMO_MUTATED_LATER,
+  MANUAL_MEMO_REMOVED,
+  MANUAL_MEMO_DEPENDENCIES_CONFLICT,
+
+  CANNOT_COMPILE_FIRE,
+  DID_NOT_INFER_DEPS,
+
+  /** Todo syntax */
+  TODO_CONFLICTING_FBT_IDENTIFIER,
+  TODO_DUPLICATE_FBT_TAGS,
+  UNKNOWN_FUNCTION_PARAMETERS,
+}
+
+type ErrorCodeType = {
+  code: ErrorCode;
+  description?: string;
+  severity: ErrorSeverity;
+  reason: string;
+  linterCategory: LinterCategory | null;
+};
+
+export const ErrorCodeDetails: Record<ErrorCode, ErrorCodeType> = {
+  [ErrorCode.HOOK_CALL_STATIC]: {
+    code: ErrorCode.HOOK_CALL_STATIC,
+    severity: ErrorSeverity.InvalidReact,
+    reason:
+      'Hooks must always be called in a consistent order, and may not be called conditionally. See the Rules of Hooks (https://react.dev/warnings/invalid-hook-call-warning)',
+    linterCategory: LinterCategory.RULES_OF_HOOKS,
+  },
+  [ErrorCode.HOOK_INVALID_REFERENCE]: {
+    code: ErrorCode.HOOK_INVALID_REFERENCE,
+    severity: ErrorSeverity.InvalidReact,
+    reason:
+      'Hooks may not be referenced as normal values, they must be called. See https://react.dev/reference/rules/react-calls-components-and-hooks#never-pass-around-hooks-as-regular-values',
+    linterCategory: LinterCategory.RULES_OF_HOOKS,
+  },
+  [ErrorCode.HOOK_CALL_REACTIVE]: {
+    code: ErrorCode.HOOK_CALL_REACTIVE,
+    severity: ErrorSeverity.InvalidReact,
+    reason:
+      'Hooks must be the same function on every render, but this value may change over time to a different function. See https://react.dev/reference/rules/react-calls-components-and-hooks#dont-dynamically-use-hooks',
+    linterCategory: LinterCategory.RULES_OF_HOOKS,
+  },
+  [ErrorCode.HOOK_CALL_NOT_TOP_LEVEL]: {
+    code: ErrorCode.HOOK_CALL_NOT_TOP_LEVEL,
+    severity: ErrorSeverity.InvalidReact,
+    reason:
+      'Hooks must be called at the top level in the body of a function component or custom hook, and may not be called within function expressions. See the Rules of Hooks (https://react.dev/warnings/invalid-hook-call-warning)',
+    linterCategory: LinterCategory.RULES_OF_HOOKS,
+  },
+  [ErrorCode.IMPURE_FUNCTIONS]: {
+    code: ErrorCode.IMPURE_FUNCTIONS,
+    severity: ErrorSeverity.InvalidReact,
+    reason: 'Cannot call impure functions during render',
+    description:
+      'Calling an impure function can produce unstable results that change 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)',
+    linterCategory: LinterCategory.IMPURE_FUNCTIONS,
+  },
+  [ErrorCode.JSX_IN_TRY]: {
+    code: ErrorCode.JSX_IN_TRY,
+    severity: ErrorSeverity.InvalidReact,
+    reason: 'Avoid constructing JSX within try/catch',
+    description: `React does not immediately render components when JSX is rendered, so any errors from this component will not be caught by the try/catch. To catch errors in rendering a given component, wrap that component in an error boundary. (https://react.dev/reference/react/Component#catching-rendering-errors-with-an-error-boundary)`,
+    linterCategory: LinterCategory.JSX_IN_TRY,
+  },
+  [ErrorCode.NO_REF_ACCESS_IN_RENDER]: {
+    code: ErrorCode.NO_REF_ACCESS_IN_RENDER,
+    severity: ErrorSeverity.InvalidReact,
+    reason: 'Cannot access refs during render',
+    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)',
+    linterCategory: LinterCategory.NO_REF_ACCESS_IN_RENDER,
+  },
+  [ErrorCode.INVALID_SET_STATE_IN_EFFECTS]: {
+    code: ErrorCode.INVALID_SET_STATE_IN_EFFECTS,
+    severity: ErrorSeverity.InvalidReact,
+    reason:
+      'Calling setState synchronously within an effect can trigger cascading renders',
+    description:
+      'Effects are intended to synchronize state between React and external systems such as manually updating the DOM, state management libraries, or other platform APIs. ' +
+      'In general, the body of an effect should do one or both of the following:\n' +
+      '* Update external systems with the latest state from React.\n' +
+      '* Subscribe for updates from some external system, calling setState in a callback function when external state changes.\n\n' +
+      'Calling setState synchronously within an effect body causes cascading renders that can hurt performance, and is not recommended. ' +
+      '(https://react.dev/learn/you-might-not-need-an-effect)',
+    linterCategory: LinterCategory.NO_SET_STATE_IN_EFFECTS,
+  },
+  [ErrorCode.WRITE_AFTER_RENDER]: {
+    code: ErrorCode.WRITE_AFTER_RENDER,
+    severity: ErrorSeverity.InvalidReact,
+    reason: 'Cannot modify local variables after render completes',
+    description: `This argument is a function which may reassign or mutate a variable after render, which can cause inconsistent behavior on subsequent renders. Consider using state instead`,
+    linterCategory: LinterCategory.INVALID_WRITE,
+  },
+  [ErrorCode.REASSIGN_AFTER_RENDER]: {
+    code: ErrorCode.REASSIGN_AFTER_RENDER,
+    severity: ErrorSeverity.InvalidReact,
+    reason: 'Cannot reassign local variables after render completes',
+    description: `Reassigning local variables after render has completed can cause inconsistent behavior on subsequent renders. Consider using state instead`,
+    linterCategory: LinterCategory.INVALID_WRITE,
+  },
+  [ErrorCode.REASSIGN_IN_ASYNC]: {
+    code: ErrorCode.REASSIGN_IN_ASYNC,
+    severity: ErrorSeverity.InvalidReact,
+    reason: 'Cannot reassign variable in async function',
+    description:
+      'Reassigning a variable in an async function can cause inconsistent behavior on subsequent renders. Consider using state instead',
+    linterCategory: LinterCategory.INVALID_WRITE,
+  },
+  [ErrorCode.INVALID_WRITE]: {
+    code: ErrorCode.INVALID_WRITE,
+    severity: ErrorSeverity.InvalidReact,
+    reason: 'This value cannot be modified',
+    linterCategory: LinterCategory.INVALID_WRITE,
+  },
+  [ErrorCode.CAPITALIZED_CALLS]: {
+    code: ErrorCode.CAPITALIZED_CALLS,
+    severity: ErrorSeverity.InvalidReact,
+    reason:
+      'Capitalized functions are reserved for components, which must be invoked with JSX. If this is a component, render it with JSX. Otherwise, ensure that it has no hook calls and rename it to begin with a lowercase letter. Alternatively, if you know for a fact that this function is not a component, you can allowlist it via the compiler config',
+    linterCategory: LinterCategory.CAPITALIZED_CALLS,
+  },
+  [ErrorCode.STATIC_COMPONENTS]: {
+    code: ErrorCode.STATIC_COMPONENTS,
+    severity: ErrorSeverity.InvalidReact,
+    reason: 'Cannot create components during render',
+    linterCategory: LinterCategory.STATIC_COMPONENTS,
+  },
+  [ErrorCode.INVALID_USE_MEMO_NO_ARG0]: {
+    code: ErrorCode.INVALID_USE_MEMO_NO_ARG0,
+    severity: ErrorSeverity.InvalidReact,
+    reason: `Expected a callback function to be passed to useMemo`,
+    linterCategory: LinterCategory.VALIDATE_MANUAL_MEMO,
+  },
+  [ErrorCode.INVALID_USE_CALLBACK_NO_ARG0]: {
+    code: ErrorCode.INVALID_USE_CALLBACK_NO_ARG0,
+    severity: ErrorSeverity.InvalidReact,
+    reason: `Expected a callback function to be passed to useCallback`,
+    linterCategory: LinterCategory.VALIDATE_MANUAL_MEMO,
+  },
+  [ErrorCode.DYNAMIC_USE_MEMO_SPREAD_ARGUMENT]: {
+    code: ErrorCode.DYNAMIC_USE_MEMO_SPREAD_ARGUMENT,
+    severity: ErrorSeverity.InvalidReact,
+    reason: 'Unexpected spread argument to useMemo',
+    linterCategory: LinterCategory.DYNAMIC_MANUAL_MEMO,
+  },
+
+  [ErrorCode.DYNAMIC_USE_CALLBACK_SPREAD_ARGUMENT]: {
+    code: ErrorCode.DYNAMIC_USE_CALLBACK_SPREAD_ARGUMENT,
+    severity: ErrorSeverity.InvalidReact,
+    reason: 'Unexpected spread argument to useCallback',
+    linterCategory: LinterCategory.DYNAMIC_MANUAL_MEMO,
+  },
+  [ErrorCode.INVALID_USE_MEMO_CALLBACK_PARAMETERS]: {
+    code: ErrorCode.INVALID_USE_MEMO_CALLBACK_PARAMETERS,
+    severity: ErrorSeverity.InvalidReact,
+    reason: 'useMemo() callbacks may not accept parameters',
+    description:
+      'useMemo() callbacks are called by React to cache calculations across re-renders. They cannot accept parameters. Instead, directly reference the props, state, or local variables needed for the computation',
+    linterCategory: LinterCategory.VALIDATE_MANUAL_MEMO,
+  },
+  [ErrorCode.INVALID_USE_MEMO_CALLBACK_ASYNC]: {
+    code: ErrorCode.INVALID_USE_MEMO_CALLBACK_ASYNC,
+    severity: ErrorSeverity.InvalidReact,
+    reason: 'useMemo() callbacks may not be async or generator functions',
+    description:
+      'useMemo() callbacks are called once and must synchronously return a value',
+    linterCategory: LinterCategory.VALIDATE_MANUAL_MEMO,
+  },
+  [ErrorCode.INVALID_USE_MEMO_CALLBACK_RETURN]: {
+    code: ErrorCode.INVALID_USE_MEMO_CALLBACK_RETURN,
+    severity: ErrorSeverity.InvalidReact,
+    reason: 'useMemo() callbacks must return a value',
+    linterCategory: LinterCategory.VALIDATE_MANUAL_MEMO,
+  },
+  [ErrorCode.DYNAMIC_MANUAL_MEMO_CALLBACK]: {
+    code: ErrorCode.DYNAMIC_MANUAL_MEMO_CALLBACK,
+    severity: ErrorSeverity.InvalidReact,
+    reason: `Expected the first argument to be an inline function expression`,
+    linterCategory: LinterCategory.DYNAMIC_MANUAL_MEMO,
+  },
+  [ErrorCode.DYNAMIC_MANUAL_MEMO_DEPENDENCY_LIST]: {
+    code: ErrorCode.DYNAMIC_MANUAL_MEMO_DEPENDENCY_LIST,
+    severity: ErrorSeverity.InvalidReact,
+    reason: `Expected the dependency list of useMemo or useCallback to be an array literal`,
+    linterCategory: LinterCategory.DYNAMIC_MANUAL_MEMO,
+  },
+  [ErrorCode.COMPLEX_MANUAL_MEMO_DEPENDENCY_LIST_ENTRY]: {
+    code: ErrorCode.COMPLEX_MANUAL_MEMO_DEPENDENCY_LIST_ENTRY,
+    severity: ErrorSeverity.InvalidReact,
+    reason: `Expected the dependency list to be an array of simple expressions (e.g. \`x\`, \`x.y.z\`, \`x?.y?.z\`)`,
+    linterCategory: LinterCategory.DYNAMIC_MANUAL_MEMO,
+  },
+  [ErrorCode.INVALID_SET_STATE_IN_RENDER]: {
+    code: ErrorCode.INVALID_SET_STATE_IN_RENDER,
+    severity: ErrorSeverity.InvalidReact,
+    reason: 'Calling setState during render may trigger an infinite loop',
+    description:
+      'Calling setState during render will trigger another render, and can lead to infinite loops. (https://react.dev/reference/react/useState)',
+    linterCategory: LinterCategory.NO_SET_STATE_IN_RENDER,
+  },
+  [ErrorCode.INVALID_SET_STATE_IN_MEMO]: {
+    code: ErrorCode.INVALID_SET_STATE_IN_MEMO,
+    severity: ErrorSeverity.InvalidReact,
+    reason: 'Calling setState from useMemo may trigger an infinite loop',
+    description:
+      'Each time the memo callback is evaluated it will change state. This can cause a memoization dependency to change, running the memo function again and causing an infinite loop. Instead of setting state in useMemo(), prefer deriving the value during render. (https://react.dev/reference/react/useState)',
+    linterCategory: LinterCategory.NO_SET_STATE_IN_RENDER,
+  },
+  [ErrorCode.NO_DERIVED_COMPUTATIONS_IN_EFFECTS]: {
+    code: ErrorCode.NO_DERIVED_COMPUTATIONS_IN_EFFECTS,
+    severity: ErrorSeverity.InvalidReact,
+    reason:
+      'Values derived from props and state should be calculated during render, not in an effect. (https://react.dev/learn/you-might-not-need-an-effect#updating-state-based-on-props-or-state)',
+    linterCategory: LinterCategory.UNNECESSARY_EFFECTS,
+  },
+
+  /** Invalid writes */
+  [ErrorCode.INVALID_WRITE_GLOBAL]: {
+    code: ErrorCode.INVALID_WRITE_GLOBAL,
+    severity: ErrorSeverity.InvalidReact,
+    reason: 'Cannot reassign variables declared outside of the component/hook',
+    description:
+      'Reassigning this value during render is a form of side effect, which can cause unpredictable behavior depending on when the component happens to re-render. If this variable is used in rendering, use useState instead. Otherwise, consider updating it in an effect. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#side-effects-must-run-outside-of-render)',
+    linterCategory: LinterCategory.INVALID_WRITE,
+  },
+  [ErrorCode.INVALID_WRITE_FROZEN_VALUE_JSX]: {
+    code: ErrorCode.INVALID_WRITE_FROZEN_VALUE_JSX,
+    severity: ErrorSeverity.InvalidReact,
+    reason:
+      'Modifying a value used previously in JSX is not allowed. Consider moving the modification before the JSX',
+    linterCategory: LinterCategory.INVALID_WRITE,
+  },
+  [ErrorCode.INVALID_WRITE_IMMUTABLE_VALUE_USE_CONTEXT]: {
+    code: ErrorCode.INVALID_WRITE_IMMUTABLE_VALUE_USE_CONTEXT,
+    severity: ErrorSeverity.InvalidReact,
+    reason: `Modifying a value returned from 'useContext()' is not allowed`,
+    linterCategory: LinterCategory.INVALID_WRITE,
+  },
+  [ErrorCode.INVALID_WRITE_IMMUTABLE_VALUE_KNOWN_SIGNATURE]: {
+    code: ErrorCode.INVALID_WRITE_IMMUTABLE_VALUE_KNOWN_SIGNATURE,
+    severity: ErrorSeverity.InvalidReact,
+    reason:
+      'Modifying a value returned from a function whose return value cannot be mutated',
+    linterCategory: LinterCategory.INVALID_WRITE,
+  },
+  [ErrorCode.INVALID_WRITE_IMMUTABLE_ARGS]: {
+    code: ErrorCode.INVALID_WRITE_IMMUTABLE_ARGS,
+    severity: ErrorSeverity.InvalidReact,
+    reason:
+      'Modifying component props or hook arguments is not allowed. Consider using a local variable instead',
+    linterCategory: LinterCategory.INVALID_WRITE,
+  },
+  [ErrorCode.INVALID_WRITE_STATE]: {
+    code: ErrorCode.INVALID_WRITE_STATE,
+    severity: ErrorSeverity.InvalidReact,
+    reason:
+      "Modifying a value returned from 'useState()', which cannot be modified directly. Use the setter function to update instead",
+    linterCategory: LinterCategory.INVALID_WRITE,
+  },
+  [ErrorCode.INVALID_WRITE_REDUCER_STATE]: {
+    code: ErrorCode.INVALID_WRITE_REDUCER_STATE,
+    severity: ErrorSeverity.InvalidReact,
+    reason:
+      "Modifying a value returned from 'useReducer()', which cannot be modified directly. Use the dispatch function to update instead",
+    linterCategory: LinterCategory.INVALID_WRITE,
+  },
+  [ErrorCode.INVALID_WRITE_EFFECT_DEPENDENCY]: {
+    code: ErrorCode.INVALID_WRITE_EFFECT_DEPENDENCY,
+    severity: ErrorSeverity.InvalidReact,
+    reason:
+      'Modifying a value used previously in an effect function or as an effect dependency is not allowed. Consider moving the modification before calling useEffect()',
+    linterCategory: LinterCategory.INVALID_WRITE,
+  },
+  [ErrorCode.INVALID_WRITE_HOOK_CAPTURED]: {
+    code: ErrorCode.INVALID_WRITE_HOOK_CAPTURED,
+    severity: ErrorSeverity.InvalidReact,
+    reason:
+      'Modifying a value previously passed as an argument to a hook is not allowed. Consider moving the modification before calling the hook',
+    linterCategory: LinterCategory.INVALID_WRITE,
+  },
+  [ErrorCode.INVALID_WRITE_HOOK_RETURN]: {
+    code: ErrorCode.INVALID_WRITE_HOOK_RETURN,
+    severity: ErrorSeverity.InvalidReact,
+    reason:
+      'Modifying a value returned from a hook is not allowed. Consider moving the modification into the hook where the value is constructed',
+    linterCategory: LinterCategory.INVALID_WRITE,
+  },
+  [ErrorCode.INVALID_ACCESS_BEFORE_INIT]: {
+    code: ErrorCode.INVALID_ACCESS_BEFORE_INIT,
+    severity: ErrorSeverity.InvalidReact,
+    reason: 'Cannot access variable before it is declared',
+    description: `Reading a variable before it is initialized will prevent the earlier access from updating when this value changes over time. Instead, move the variable access to after it has been initialized`,
+    linterCategory: LinterCategory.INVALID_WRITE,
+  },
+  [ErrorCode.INVALID_WRITE_GENERIC]: {
+    code: ErrorCode.INVALID_WRITE_GENERIC,
+    severity: ErrorSeverity.InvalidReact,
+    reason: 'This modifies a variable that React considers immutable',
+    linterCategory: LinterCategory.INVALID_WRITE,
+  },
+
+  /** Compiler Config */
+  [ErrorCode.DYNAMIC_GATING_IS_NOT_IDENTIFIER]: {
+    code: ErrorCode.DYNAMIC_GATING_IS_NOT_IDENTIFIER,
+    severity: ErrorSeverity.InvalidReact,
+    reason: 'Dynamic gating directive is not a valid JavaScript identifier',
+    linterCategory: LinterCategory.COMPILER_CONFIG,
+  },
+  [ErrorCode.DYNAMIC_GATING_MULTIPLE_DIRECTIVES]: {
+    code: ErrorCode.DYNAMIC_GATING_MULTIPLE_DIRECTIVES,
+    severity: ErrorSeverity.InvalidReact,
+    reason: 'Expected a single dynamic gating directive',
+    linterCategory: LinterCategory.COMPILER_CONFIG,
+  },
+  [ErrorCode.FILENAME_NOT_SET]: {
+    code: ErrorCode.FILENAME_NOT_SET,
+    severity: ErrorSeverity.InvalidConfig,
+    reason: `Expected a filename but found none`,
+    description:
+      "When the 'sources' config options is specified, the React compiler will only compile files with a name",
+    linterCategory: LinterCategory.COMPILER_CONFIG,
+  },
+
+  /** Effect dependencies */
+  [ErrorCode.MEMOIZED_EFFECT_DEPENDENCIES]: {
+    code: ErrorCode.MEMOIZED_EFFECT_DEPENDENCIES,
+    reason:
+      'React Compiler has skipped optimizing this component because the effect dependencies could not be memoized. Unmemoized effect dependencies can trigger an infinite loop or other unexpected behavior',
+    severity: ErrorSeverity.CannotPreserveMemoization,
+    linterCategory: LinterCategory.MEMOIZED_DEPENDENCIES,
+  },
+
+  /** Invalid / unsupported syntax */
+  [ErrorCode.INVALID_SYNTAX_MULTIPLE_DEFAULTS]: {
+    code: ErrorCode.INVALID_SYNTAX_MULTIPLE_DEFAULTS,
+    reason: `Expected at most one \`default\` branch in a switch statement, this code should have failed to parse`,
+    severity: ErrorSeverity.InvalidJS,
+    linterCategory: LinterCategory.UNSUPPORTED_SYNTAX,
+  },
+  [ErrorCode.INVALID_SYNTAX_REASSIGNED_CONST]: {
+    code: ErrorCode.INVALID_SYNTAX_REASSIGNED_CONST,
+    reason: `Expect \`const\` declaration not to be reassigned`,
+    severity: ErrorSeverity.InvalidJS,
+    linterCategory: LinterCategory.UNSUPPORTED_SYNTAX,
+  },
+  [ErrorCode.INVALID_SYNTAX_BAD_VARIABLE_DECL]: {
+    code: ErrorCode.INVALID_SYNTAX_BAD_VARIABLE_DECL,
+    reason: `Expected variable declaration to be an identifier if no initializer was provided`,
+    severity: ErrorSeverity.InvalidJS,
+    linterCategory: LinterCategory.UNSUPPORTED_SYNTAX,
+  },
+  [ErrorCode.UNSUPPORTED_WITH]: {
+    code: ErrorCode.UNSUPPORTED_WITH,
+    reason: `JavaScript 'with' syntax is not supported`,
+    description: `'with' syntax is considered deprecated and removed from JavaScript standards, consider alternatives`,
+    severity: ErrorSeverity.UnsupportedJS,
+    linterCategory: LinterCategory.UNSUPPORTED_SYNTAX,
+  },
+  [ErrorCode.UNSUPPORTED_INNER_CLASS]: {
+    code: ErrorCode.UNSUPPORTED_INNER_CLASS,
+    reason: 'Inline `class` declarations are not supported',
+    description: `Move class declarations outside of components/hooks`,
+    severity: ErrorSeverity.UnsupportedJS,
+    linterCategory: LinterCategory.UNSUPPORTED_SYNTAX,
+  },
+  [ErrorCode.INVALID_IMPORT_EXPORT]: {
+    code: ErrorCode.INVALID_IMPORT_EXPORT,
+    reason:
+      'JavaScript `import` and `export` statements may only appear at the top level of a module',
+    severity: ErrorSeverity.InvalidJS,
+    linterCategory: LinterCategory.UNSUPPORTED_SYNTAX,
+  },
+  [ErrorCode.INVALID_TS_NAMESPACE]: {
+    code: ErrorCode.INVALID_TS_NAMESPACE,
+    reason:
+      'TypeScript `namespace` statements may only appear at the top level of a module',
+    severity: ErrorSeverity.InvalidJS,
+    linterCategory: LinterCategory.UNSUPPORTED_SYNTAX,
+  },
+  [ErrorCode.UNSUPPORTED_NEW_EXPRESSION]: {
+    code: ErrorCode.UNSUPPORTED_NEW_EXPRESSION,
+    reason: `Expected an expression as the \`new\` expression receiver (v8 intrinsics are not supported)`,
+    severity: ErrorSeverity.InvalidJS,
+    linterCategory: LinterCategory.UNSUPPORTED_SYNTAX,
+  },
+  [ErrorCode.UNSUPPORTED_EMPTY_SEQUENCE_EXPRESSION]: {
+    code: ErrorCode.UNSUPPORTED_EMPTY_SEQUENCE_EXPRESSION,
+    reason: `Expected sequence expression to have at least one expression`,
+    severity: ErrorSeverity.InvalidJS,
+    linterCategory: LinterCategory.UNSUPPORTED_SYNTAX,
+  },
+  [ErrorCode.INVALID_QUASI_LENGTHS]: {
+    code: ErrorCode.INVALID_QUASI_LENGTHS,
+    reason: `Unexpected quasi and subexpression lengths in template literal`,
+    severity: ErrorSeverity.InvalidJS,
+    linterCategory: LinterCategory.UNSUPPORTED_SYNTAX,
+  },
+  [ErrorCode.INVALID_SYNTAX_DELETE_EXPRESSION]: {
+    code: ErrorCode.INVALID_SYNTAX_DELETE_EXPRESSION,
+    reason: `Only object properties can be deleted`,
+    severity: ErrorSeverity.InvalidJS,
+    linterCategory: LinterCategory.UNSUPPORTED_SYNTAX,
+  },
+  [ErrorCode.UNSUPPORTED_THROW_EXPRESSION]: {
+    code: ErrorCode.UNSUPPORTED_THROW_EXPRESSION,
+    reason: `Throw expressions are not supported`,
+    severity: ErrorSeverity.InvalidJS,
+    linterCategory: LinterCategory.UNSUPPORTED_SYNTAX,
+  },
+  [ErrorCode.INVALID_JSX_NAMESPACED_NAME]: {
+    code: ErrorCode.INVALID_JSX_NAMESPACED_NAME,
+    reason: `Expected JSXNamespacedName to have no colons in the namespace or name`,
+    severity: ErrorSeverity.InvalidJS,
+    linterCategory: LinterCategory.UNSUPPORTED_SYNTAX,
+  },
+  [ErrorCode.UNSUPPORTED_EVAL]: {
+    code: ErrorCode.UNSUPPORTED_EVAL,
+    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,
+    linterCategory: LinterCategory.UNSUPPORTED_SYNTAX,
+  },
+  [ErrorCode.INVALID_SYNTAX_RESERVED_VARIABLE_NAME]: {
+    code: ErrorCode.INVALID_SYNTAX_RESERVED_VARIABLE_NAME,
+    reason: 'Expected a non-reserved identifier name',
+    severity: ErrorSeverity.InvalidJS,
+    linterCategory: LinterCategory.UNSUPPORTED_SYNTAX,
+  },
+  [ErrorCode.INVALID_JAVASCRIPT_AST]: {
+    code: ErrorCode.INVALID_JAVASCRIPT_AST,
+    reason: 'Encountered invalid JavaScript',
+    severity: ErrorSeverity.InvalidJS,
+    linterCategory: LinterCategory.UNSUPPORTED_SYNTAX,
+  },
+  [ErrorCode.BAILOUT_ESLINT_SUPPRESSION]: {
+    code: ErrorCode.BAILOUT_ESLINT_SUPPRESSION,
+    reason:
+      'React Compiler has skipped optimizing this component because one or more React ESLint rules were disabled',
+    description:
+      'React Compiler only works when your components follow all the rules of React, disabling them may result in unexpected or incorrect behavior',
+    severity: ErrorSeverity.InvalidReact,
+    linterCategory: LinterCategory.UNSUPPORTED_SYNTAX,
+  },
+  [ErrorCode.MANUAL_MEMO_REMOVED]: {
+    code: ErrorCode.MANUAL_MEMO_REMOVED,
+    reason:
+      'Compilation skipped because existing memoization could not be preserved',
+    description:
+      'React Compiler has skipped optimizing this component because the existing manual memoization could not be preserved. This value was memoized in source but not in compilation output',
+    severity: ErrorSeverity.CannotPreserveMemoization,
+    linterCategory: LinterCategory.TODO_SYNTAX,
+  },
+
+  /**
+   * This is left vague as fire is very experimental
+   */
+  [ErrorCode.CANNOT_COMPILE_FIRE]: {
+    code: ErrorCode.CANNOT_COMPILE_FIRE,
+    reason: 'Cannot compile `fire`',
+    severity: ErrorSeverity.InvalidReact,
+    linterCategory: LinterCategory.UNSUPPORTED_SYNTAX,
+  },
+  [ErrorCode.DID_NOT_INFER_DEPS]: {
+    code: ErrorCode.DID_NOT_INFER_DEPS,
+    reason:
+      'Cannot infer dependencies of this effect. This will break your build!',
+    description:
+      'To resolve, either pass a dependency array or fix reported compiler bailout diagnostics',
+    severity: ErrorSeverity.InvalidReact,
+    linterCategory: LinterCategory.UNSUPPORTED_SYNTAX,
+  },
+
+  [ErrorCode.BAILOUT_FLOW_SUPPRESSION]: {
+    code: ErrorCode.BAILOUT_FLOW_SUPPRESSION,
+    reason:
+      'React Compiler has skipped optimizing this component because one or more React rule violations were reported by Flow',
+    description:
+      'React Compiler only works when your components follow all the rules of React, disabling them may result in unexpected or incorrect behavior',
+    severity: ErrorSeverity.InvalidReact,
+    linterCategory: LinterCategory.UNSUPPORTED_SYNTAX,
+  },
+
+  /** Syntax React Compiler may eventually support */
+  [ErrorCode.TODO_CONFLICTING_FBT_IDENTIFIER]: {
+    code: ErrorCode.TODO_CONFLICTING_FBT_IDENTIFIER,
+    reason: 'Support local variables named `fbt`',
+    description:
+      'Local variables named `fbt` may conflict with the fbt plugin and are not yet supported',
+    severity: ErrorSeverity.Todo,
+    linterCategory: LinterCategory.TODO_SYNTAX,
+  },
+  [ErrorCode.TODO_DUPLICATE_FBT_TAGS]: {
+    code: ErrorCode.TODO_DUPLICATE_FBT_TAGS,
+    reason: 'Support duplicate fbt tags',
+    severity: ErrorSeverity.Todo,
+    linterCategory: LinterCategory.TODO_SYNTAX,
+  },
+  [ErrorCode.UNKNOWN_FUNCTION_PARAMETERS]: {
+    code: ErrorCode.UNKNOWN_FUNCTION_PARAMETERS,
+    severity: ErrorSeverity.Todo,
+    reason: 'Currently unsupported function parameter syntax',
+    linterCategory: LinterCategory.TODO_SYNTAX,
+  },
+  [ErrorCode.MANUAL_MEMO_MUTATED_LATER]: {
+    code: ErrorCode.MANUAL_MEMO_MUTATED_LATER,
+    reason:
+      'Compilation skipped because existing memoization could not be preserved',
+    description: [
+      'React Compiler has skipped optimizing this component because the existing manual memoization could not be preserved. ',
+      'This dependency may be mutated later, which could cause the value to change unexpectedly',
+    ].join(''),
+    severity: ErrorSeverity.CannotPreserveMemoization,
+    linterCategory: LinterCategory.UNSUPPORTED_SYNTAX,
+  },
+  [ErrorCode.MANUAL_MEMO_DEPENDENCIES_CONFLICT]: {
+    code: ErrorCode.MANUAL_MEMO_DEPENDENCIES_CONFLICT,
+    reason:
+      'Compilation skipped because existing memoization could not be preserved',
+    description:
+      'React Compiler has skipped optimizing this component because the existing manual memoization could not be preserved. ' +
+      'The inferred dependencies did not match the manually specified dependencies, which could cause the value to change more or less frequently than expected',
+    severity: ErrorSeverity.CannotPreserveMemoization,
+    linterCategory: LinterCategory.UNSUPPORTED_SYNTAX,
+  },
+};

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

@@ -0,0 +1,34 @@
+export enum ErrorSeverity {
+  /**
+   * Invalid JS syntax, or valid syntax that is semantically invalid which may indicate some
+   * 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.
+   */
+  InvalidReact = 'InvalidReact',
+  /**
+   * Incorrect configuration of the compiler.
+   */
+  InvalidConfig = 'InvalidConfig',
+  /**
+   * Code that can reasonably occur and that doesn't break any rules, but is unsafe to preserve
+   * memoization.
+   */
+  CannotPreserveMemoization = 'CannotPreserveMemoization',
+  /**
+   * Unhandled syntax that we don't support yet.
+   */
+  Todo = 'Todo',
+  /**
+   * An unexpected internal error in the compiler that indicates critical issues that can panic
+   * the compiler.
+   */
+  Invariant = 'Invariant',
+}

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

@@ -78,6 +78,10 @@ export default class DisjointSet<T> {
     return root;
   }
 
+  has(item: T): boolean {
+    return this.#entries.has(item);
+  }
+
   /*
    * Forces the set into canonical form, ie with all items pointing directly to
    * their root, and returns a Map representing the mapping of items to their roots.

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

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

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

@@ -75,21 +75,21 @@ 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,
     },
   ],
 };
@@ -113,8 +113,13 @@ function* splitPragma(
  */
 function parseConfigPragmaEnvironmentForTest(
   pragma: string,
+  defaultConfig: PartialEnvironmentConfig,
 ): EnvironmentConfig {
-  const maybeConfig: Partial<Record<keyof EnvironmentConfig, unknown>> = {};
+  // throw early if the defaults are invalid
+  EnvironmentConfigSchema.parse(defaultConfig);
+
+  const maybeConfig: Partial<Record<keyof EnvironmentConfig, unknown>> =
+    defaultConfig;
 
   for (const {key, value: val} of splitPragma(pragma)) {
     if (!hasOwnProperty(EnvironmentConfigSchema.shape, key)) {
@@ -174,9 +179,13 @@ 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',

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

@@ -33,12 +33,12 @@ export function assertExhaustive(_: never, errorMsg: string): never {
 // Modifies @param array in place, retaining only the items where the predicate returns true.
 export function retainWhere<T>(
   array: Array<T>,
-  predicate: (item: T) => boolean,
+  predicate: (item: T, index: number) => boolean,
 ): void {
   let writeIndex = 0;
   for (let readIndex = 0; readIndex < array.length; readIndex++) {
     const item = array[readIndex];
-    if (predicate(item) === true) {
+    if (predicate(item, readIndex) === true) {
       array[writeIndex++] = item;
     }
   }

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

@@ -6,11 +6,7 @@
  */
 
 import * as t from '@babel/types';
-import {
-  CompilerError,
-  CompilerErrorDetail,
-  ErrorSeverity,
-} from '../CompilerError';
+import {CompilerError, CompilerErrorDetail} from '../CompilerError';
 import {computeUnconditionalBlocks} from '../HIR/ComputeUnconditionalBlocks';
 import {isHookName} from '../HIR/Environment';
 import {
@@ -27,6 +23,7 @@ import {
 } from '../HIR/visitors';
 import {assertExhaustive} from '../Utils/utils';
 import {Result} from '../Utils/Result';
+import {ErrorCode, ErrorCodeDetails} from '../Utils/CompilerErrorCodes';
 
 /**
  * Represents the possible kinds of value which may be stored at a given Place during
@@ -111,8 +108,6 @@ export function validateHooksUsage(
     // Once a particular hook has a conditional call error, don't report any further issues for this hook
     setKind(place, Kind.Error);
 
-    const reason =
-      'Hooks must always be called in a consistent order, and may not be called conditionally. See the Rules of Hooks (https://react.dev/warnings/invalid-hook-call-warning)';
     const previousError =
       typeof place.loc !== 'symbol' ? errorsByPlace.get(place.loc) : undefined;
 
@@ -120,15 +115,15 @@ export function validateHooksUsage(
      * In some circumstances such as optional calls, we may first encounter a "hook may not be referenced as normal values" error.
      * If that same place is also used as a conditional call, upgrade the error to a conditonal hook error
      */
-    if (previousError === undefined || previousError.reason !== reason) {
+    if (
+      previousError === undefined ||
+      previousError.reason !==
+        ErrorCodeDetails[ErrorCode.HOOK_CALL_STATIC].reason
+    ) {
       recordError(
         place.loc,
-        new CompilerErrorDetail({
-          description: null,
-          reason,
+        CompilerErrorDetail.fromCode(ErrorCode.HOOK_CALL_STATIC, {
           loc: place.loc,
-          severity: ErrorSeverity.InvalidReact,
-          suggestions: null,
         }),
       );
     }
@@ -139,13 +134,8 @@ export function validateHooksUsage(
     if (previousError === undefined) {
       recordError(
         place.loc,
-        new CompilerErrorDetail({
-          description: null,
-          reason:
-            'Hooks may not be referenced as normal values, they must be called. See https://react.dev/reference/rules/react-calls-components-and-hooks#never-pass-around-hooks-as-regular-values',
+        CompilerErrorDetail.fromCode(ErrorCode.HOOK_INVALID_REFERENCE, {
           loc: place.loc,
-          severity: ErrorSeverity.InvalidReact,
-          suggestions: null,
         }),
       );
     }
@@ -156,14 +146,12 @@ export function validateHooksUsage(
     if (previousError === undefined) {
       recordError(
         place.loc,
-        new CompilerErrorDetail({
-          description: null,
-          reason:
-            'Hooks must be the same function on every render, but this value may change over time to a different function. See https://react.dev/reference/rules/react-calls-components-and-hooks#dont-dynamically-use-hooks',
-          loc: place.loc,
-          severity: ErrorSeverity.InvalidReact,
-          suggestions: null,
-        }),
+        CompilerErrorDetail.fromCode(
+          ErrorCodeDetails[ErrorCode.HOOK_CALL_REACTIVE].code,
+          {
+            loc: place.loc,
+          },
+        ),
       );
     }
   }
@@ -424,7 +412,7 @@ export function validateHooksUsage(
   }
 
   for (const [, error] of errorsByPlace) {
-    errors.push(error);
+    errors.pushErrorDetail(error);
   }
   return errors.asResult();
 }
@@ -446,16 +434,10 @@ function visitFunctionExpression(errors: CompilerError, fn: HIRFunction): void {
               : instr.value.property;
           const hookKind = getHookKind(fn.env, callee.identifier);
           if (hookKind != null) {
-            errors.pushErrorDetail(
-              new CompilerErrorDetail({
-                severity: ErrorSeverity.InvalidReact,
-                reason:
-                  'Hooks must be called at the top level in the body of a function component or custom hook, and may not be called within function expressions. See the Rules of Hooks (https://react.dev/warnings/invalid-hook-call-warning)',
-                loc: callee.loc,
-                description: `Cannot call ${hookKind === 'Custom' ? 'hook' : hookKind} within a function expression`,
-                suggestions: null,
-              }),
-            );
+            errors.pushErrorCode(ErrorCode.HOOK_CALL_NOT_TOP_LEVEL, {
+              loc: callee.loc,
+              description: `Cannot call ${hookKind === 'Custom' ? 'hook' : hookKind} within a function expression`,
+            });
           }
           break;
         }

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} from '..';
 import {HIRFunction, IdentifierId, Place} from '../HIR';
 import {
   eachInstructionLValue,
@@ -13,13 +13,17 @@ import {
   eachTerminalOperand,
 } from '../HIR/visitors';
 import {getFunctionCallSignature} from '../Inference/InferReferenceEffects';
+import {ErrorCode} from '../Utils/CompilerErrorCodes';
+import {Ok, Result} from '../Utils/Result';
 
 /**
  * Validates that local variables cannot be reassigned after render.
  * This prevents a category of bugs in which a closure captures a
  * binding from one render but does not update
  */
-export function validateLocalsNotReassignedAfterRender(fn: HIRFunction): void {
+export function validateLocalsNotReassignedAfterRender(
+  fn: HIRFunction,
+): Result<void, CompilerError> {
   const contextVariables = new Set<IdentifierId>();
   const reassignment = getContextReassignment(
     fn,
@@ -28,17 +32,22 @@ 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.fromCode(ErrorCode.REASSIGN_AFTER_RENDER).withDetail({
+        kind: 'error',
+        loc: reassignment.loc,
+        message: `Cannot reassign ${variable} after render completes`,
+      }),
+    );
+    return errors.asResult();
   }
+  return Ok(undefined);
 }
 
 function getContextReassignment(
@@ -75,16 +84,22 @@ 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.fromCode(
+                  ErrorCode.REASSIGN_IN_ASYNC,
+                ).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/ValidateMemoizedEffectDependencies.ts

@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {CompilerError, ErrorSeverity} from '..';
+import {CompilerError} from '..';
 import {
   Identifier,
   Instruction,
@@ -22,6 +22,7 @@ import {
   ReactiveFunctionVisitor,
   visitReactiveFunction,
 } from '../ReactiveScopes/visitors';
+import {ErrorCode} from '../Utils/CompilerErrorCodes';
 import {Result} from '../Utils/Result';
 
 /**
@@ -108,12 +109,8 @@ class Visitor extends ReactiveFunctionVisitor<CompilerError> {
           isUnmemoized(deps.identifier, this.scopes))
       ) {
         state.push({
-          reason:
-            'React Compiler has skipped optimizing this component because the effect dependencies could not be memoized. Unmemoized effect dependencies can trigger an infinite loop or other unexpected behavior',
-          description: null,
-          severity: ErrorSeverity.CannotPreserveMemoization,
+          errorCode: ErrorCode.MEMOIZED_EFFECT_DEPENDENCIES,
           loc: typeof instruction.loc !== 'symbol' ? instruction.loc : null,
-          suggestions: null,
         });
       }
     }

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

@@ -5,9 +5,10 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {CompilerError, EnvironmentConfig, ErrorSeverity} from '..';
+import {CompilerError, EnvironmentConfig} from '..';
 import {HIRFunction, IdentifierId} from '../HIR';
 import {DEFAULT_GLOBALS} from '../HIR/Globals';
+import {ErrorCode} from '../Utils/CompilerErrorCodes';
 import {Result} from '../Utils/Result';
 
 export function validateNoCapitalizedCalls(
@@ -33,8 +34,6 @@ export function validateNoCapitalizedCalls(
   const errors = new CompilerError();
   const capitalLoadGlobals = new Map<IdentifierId, string>();
   const capitalizedProperties = new Map<IdentifierId, string>();
-  const reason =
-    'Capitalized functions are reserved for components, which must be invoked with JSX. If this is a component, render it with JSX. Otherwise, ensure that it has no hook calls and rename it to begin with a lowercase letter. Alternatively, if you know for a fact that this function is not a component, you can allowlist it via the compiler config';
   for (const [, block] of fn.body.blocks) {
     for (const {lvalue, value} of block.instructions) {
       switch (value.kind) {
@@ -55,11 +54,9 @@ export function validateNoCapitalizedCalls(
           const calleeIdentifier = value.callee.identifier.id;
           const calleeName = capitalLoadGlobals.get(calleeIdentifier);
           if (calleeName != null) {
-            CompilerError.throwInvalidReact({
-              reason,
+            errors.pushErrorCode(ErrorCode.CAPITALIZED_CALLS, {
               description: `${calleeName} may be a component.`,
               loc: value.loc,
-              suggestions: null,
             });
           }
           break;
@@ -78,12 +75,9 @@ export function validateNoCapitalizedCalls(
           const propertyIdentifier = value.property.identifier.id;
           const propertyName = capitalizedProperties.get(propertyIdentifier);
           if (propertyName != null) {
-            errors.push({
-              severity: ErrorSeverity.InvalidReact,
-              reason,
+            errors.pushErrorCode(ErrorCode.CAPITALIZED_CALLS, {
               description: `${propertyName} may be a component.`,
               loc: value.loc,
-              suggestions: null,
             });
           }
           break;

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

@@ -0,0 +1,225 @@
+/**
+ * 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 {
+  ArrayExpression,
+  BlockId,
+  FunctionExpression,
+  HIRFunction,
+  IdentifierId,
+  isSetStateType,
+  isUseEffectHookType,
+} from '../HIR';
+import {
+  eachInstructionValueOperand,
+  eachTerminalOperand,
+} from '../HIR/visitors';
+import {ErrorCode} from '../Utils/CompilerErrorCodes';
+import {Result} from '../Utils/Result';
+
+/**
+ * Validates that useEffect is not used for derived computations which could/should
+ * be performed in render.
+ *
+ * See https://react.dev/learn/you-might-not-need-an-effect#updating-state-based-on-props-or-state
+ *
+ * Example:
+ *
+ * ```
+ * // 🔴 Avoid: redundant state and unnecessary Effect
+ * const [fullName, setFullName] = useState('');
+ * useEffect(() => {
+ *   setFullName(firstName + ' ' + lastName);
+ * }, [firstName, lastName]);
+ * ```
+ *
+ * Instead use:
+ *
+ * ```
+ * // ✅ Good: calculated during rendering
+ * const fullName = firstName + ' ' + lastName;
+ * ```
+ */
+export function validateNoDerivedComputationsInEffects(
+  fn: HIRFunction,
+): Result<void, CompilerError> {
+  const candidateDependencies: Map<IdentifierId, ArrayExpression> = new Map();
+  const functions: Map<IdentifierId, FunctionExpression> = new Map();
+  const locals: Map<IdentifierId, IdentifierId> = new Map();
+
+  const errors = new CompilerError();
+
+  for (const block of fn.body.blocks.values()) {
+    for (const instr of block.instructions) {
+      const {lvalue, value} = instr;
+      if (value.kind === 'LoadLocal') {
+        locals.set(lvalue.identifier.id, value.place.identifier.id);
+      } else if (value.kind === 'ArrayExpression') {
+        candidateDependencies.set(lvalue.identifier.id, value);
+      } else if (value.kind === 'FunctionExpression') {
+        functions.set(lvalue.identifier.id, value);
+      } else if (
+        value.kind === 'CallExpression' ||
+        value.kind === 'MethodCall'
+      ) {
+        const callee =
+          value.kind === 'CallExpression' ? value.callee : value.property;
+        if (
+          isUseEffectHookType(callee.identifier) &&
+          value.args.length === 2 &&
+          value.args[0].kind === 'Identifier' &&
+          value.args[1].kind === 'Identifier'
+        ) {
+          const effectFunction = functions.get(value.args[0].identifier.id);
+          const deps = candidateDependencies.get(value.args[1].identifier.id);
+          if (
+            effectFunction != null &&
+            deps != null &&
+            deps.elements.length !== 0 &&
+            deps.elements.every(element => element.kind === 'Identifier')
+          ) {
+            const dependencies: Array<IdentifierId> = deps.elements.map(dep => {
+              CompilerError.invariant(dep.kind === 'Identifier', {
+                reason: `Dependency is checked as a place above`,
+                loc: value.loc,
+              });
+              return locals.get(dep.identifier.id) ?? dep.identifier.id;
+            });
+            validateEffect(
+              effectFunction.loweredFunc.func,
+              dependencies,
+              errors,
+            );
+          }
+        }
+      }
+    }
+  }
+  return errors.asResult();
+}
+
+function validateEffect(
+  effectFunction: HIRFunction,
+  effectDeps: Array<IdentifierId>,
+  errors: CompilerError,
+): void {
+  for (const operand of effectFunction.context) {
+    if (isSetStateType(operand.identifier)) {
+      continue;
+    } else if (effectDeps.find(dep => dep === operand.identifier.id) != null) {
+      continue;
+    } else {
+      // Captured something other than the effect dep or setState
+      return;
+    }
+  }
+  for (const dep of effectDeps) {
+    if (
+      effectFunction.context.find(operand => operand.identifier.id === dep) ==
+      null
+    ) {
+      // effect dep wasn't actually used in the function
+      return;
+    }
+  }
+
+  const seenBlocks: Set<BlockId> = new Set();
+  const values: Map<IdentifierId, Array<IdentifierId>> = new Map();
+  for (const dep of effectDeps) {
+    values.set(dep, [dep]);
+  }
+
+  const setStateLocations: Array<SourceLocation> = [];
+  for (const block of effectFunction.body.blocks.values()) {
+    for (const pred of block.preds) {
+      if (!seenBlocks.has(pred)) {
+        // skip if block has a back edge
+        return;
+      }
+    }
+    for (const phi of block.phis) {
+      const aggregateDeps: Set<IdentifierId> = new Set();
+      for (const operand of phi.operands.values()) {
+        const deps = values.get(operand.identifier.id);
+        if (deps != null) {
+          for (const dep of deps) {
+            aggregateDeps.add(dep);
+          }
+        }
+      }
+      if (aggregateDeps.size !== 0) {
+        values.set(phi.place.identifier.id, Array.from(aggregateDeps));
+      }
+    }
+    for (const instr of block.instructions) {
+      switch (instr.value.kind) {
+        case 'Primitive':
+        case 'JSXText':
+        case 'LoadGlobal': {
+          break;
+        }
+        case 'LoadLocal': {
+          const deps = values.get(instr.value.place.identifier.id);
+          if (deps != null) {
+            values.set(instr.lvalue.identifier.id, deps);
+          }
+          break;
+        }
+        case 'ComputedLoad':
+        case 'PropertyLoad':
+        case 'BinaryExpression':
+        case 'TemplateLiteral':
+        case 'CallExpression':
+        case 'MethodCall': {
+          const aggregateDeps: Set<IdentifierId> = new Set();
+          for (const operand of eachInstructionValueOperand(instr.value)) {
+            const deps = values.get(operand.identifier.id);
+            if (deps != null) {
+              for (const dep of deps) {
+                aggregateDeps.add(dep);
+              }
+            }
+          }
+          if (aggregateDeps.size !== 0) {
+            values.set(instr.lvalue.identifier.id, Array.from(aggregateDeps));
+          }
+
+          if (
+            instr.value.kind === 'CallExpression' &&
+            isSetStateType(instr.value.callee.identifier) &&
+            instr.value.args.length === 1 &&
+            instr.value.args[0].kind === 'Identifier'
+          ) {
+            const deps = values.get(instr.value.args[0].identifier.id);
+            if (deps != null && new Set(deps).size === effectDeps.length) {
+              setStateLocations.push(instr.value.callee.loc);
+            } else {
+              // doesn't depend on any deps
+              return;
+            }
+          }
+          break;
+        }
+        default: {
+          return;
+        }
+      }
+    }
+    for (const operand of eachTerminalOperand(block.terminal)) {
+      if (values.has(operand.identifier.id)) {
+        //
+        return;
+      }
+    }
+    seenBlocks.add(block.id);
+  }
+
+  for (const loc of setStateLocations) {
+    errors.pushErrorCode(ErrorCode.NO_DERIVED_COMPUTATIONS_IN_EFFECTS, {loc});
+  }
+}

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

@@ -5,7 +5,8 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {CompilerError, Effect, ErrorSeverity} from '..';
+import {CompilerDiagnostic, CompilerError, Effect} from '..';
+import {ErrorCode} from '../CompilerError';
 import {
   FunctionEffect,
   HIRFunction,
@@ -57,16 +58,26 @@ 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 may reassign or mutate local variables after render, which can cause inconsistent behavior on subsequent renders. Consider using state instead`,
-          loc: operand.loc,
-          severity: ErrorSeverity.InvalidReact,
-        });
-        errors.push({
-          reason: `The function modifies a local variable here`,
-          loc: effect.loc,
-          severity: ErrorSeverity.InvalidReact,
-        });
+        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.fromCode(ErrorCode.WRITE_AFTER_RENDER)
+            .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}`,
+            }),
+        );
       }
     }
   }

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

@@ -5,9 +5,10 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {CompilerError, ErrorSeverity} from '..';
+import {CompilerDiagnostic, CompilerError} from '..';
 import {HIRFunction} from '../HIR';
 import {getFunctionCallSignature} from '../Inference/InferReferenceEffects';
+import {ErrorCode} from '../Utils/CompilerErrorCodes';
 import {Result} from '../Utils/Result';
 
 /**
@@ -34,17 +35,16 @@ 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
-                ? `\`${signature.canonicalName}\` is an impure function whose results may change on every call`
-                : null,
-            severity: ErrorSeverity.InvalidReact,
-            loc: callee.loc,
-            suggestions: null,
-          });
+          errors.pushDiagnostic(
+            CompilerDiagnostic.fromCode(ErrorCode.IMPURE_FUNCTIONS).withDetail({
+              kind: 'error',
+              loc: callee.loc,
+              message:
+                signature.canonicalName != null
+                  ? `\`${signature.canonicalName}\` is an impure function. `
+                  : 'This is an impure function.',
+            }),
+          );
         }
       }
     }

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

@@ -5,8 +5,9 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {CompilerError, ErrorSeverity} from '..';
+import {CompilerDiagnostic, CompilerError} from '..';
 import {BlockId, HIRFunction} from '../HIR';
+import {ErrorCode} from '../Utils/CompilerErrorCodes';
 import {Result} from '../Utils/Result';
 import {retainWhere} from '../Utils/utils';
 
@@ -34,11 +35,13 @@ 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.fromCode(ErrorCode.JSX_IN_TRY).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 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {CompilerError, ErrorSeverity} from '../CompilerError';
+import {CompilerDiagnostic, CompilerError} from '../CompilerError';
 import {
   BlockId,
   HIRFunction,
@@ -22,7 +22,9 @@ import {
   eachPatternOperand,
   eachTerminalOperand,
 } from '../HIR/visitors';
+import {ErrorCode} from '../Utils/CompilerErrorCodes';
 import {Err, Ok, Result} from '../Utils/Result';
+import {retainWhere} from '../Utils/utils';
 
 /**
  * Validates that a function does not access a ref value during render. This includes a partial check
@@ -75,8 +77,18 @@ type RefAccessRefType =
 
 type RefFnType = {readRefEffect: boolean; returnType: RefAccessType};
 
-class Env extends Map<IdentifierId, RefAccessType> {
+class Env {
   #changed = false;
+  #data: Map<IdentifierId, RefAccessType> = new Map();
+  #temporaries: Map<IdentifierId, Place> = new Map();
+
+  lookup(place: Place): Place {
+    return this.#temporaries.get(place.identifier.id) ?? place;
+  }
+
+  define(place: Place, value: Place): void {
+    this.#temporaries.set(place.identifier.id, value);
+  }
 
   resetChanged(): void {
     this.#changed = false;
@@ -86,8 +98,14 @@ class Env extends Map<IdentifierId, RefAccessType> {
     return this.#changed;
   }
 
-  override set(key: IdentifierId, value: RefAccessType): this {
-    const cur = this.get(key);
+  get(key: IdentifierId): RefAccessType | undefined {
+    const operandId = this.#temporaries.get(key)?.identifier.id ?? key;
+    return this.#data.get(operandId);
+  }
+
+  set(key: IdentifierId, value: RefAccessType): this {
+    const operandId = this.#temporaries.get(key)?.identifier.id ?? key;
+    const cur = this.#data.get(operandId);
     const widenedValue = joinRefAccessTypes(value, cur ?? {kind: 'None'});
     if (
       !(cur == null && widenedValue.kind === 'None') &&
@@ -95,7 +113,8 @@ class Env extends Map<IdentifierId, RefAccessType> {
     ) {
       this.#changed = true;
     }
-    return super.set(key, widenedValue);
+    this.#data.set(operandId, widenedValue);
+    return this;
   }
 }
 
@@ -103,9 +122,48 @@ export function validateNoRefAccessInRender(
   fn: HIRFunction,
 ): Result<void, CompilerError> {
   const env = new Env();
+  collectTemporariesSidemap(fn, env);
   return validateNoRefAccessInRenderImpl(fn, env).map(_ => undefined);
 }
 
+function collectTemporariesSidemap(fn: HIRFunction, env: Env): void {
+  for (const block of fn.body.blocks.values()) {
+    for (const instr of block.instructions) {
+      const {lvalue, value} = instr;
+      switch (value.kind) {
+        case 'LoadLocal': {
+          const temp = env.lookup(value.place);
+          if (temp != null) {
+            env.define(lvalue, temp);
+          }
+          break;
+        }
+        case 'StoreLocal': {
+          const temp = env.lookup(value.value);
+          if (temp != null) {
+            env.define(lvalue, temp);
+            env.define(value.lvalue.place, temp);
+          }
+          break;
+        }
+        case 'PropertyLoad': {
+          if (
+            isUseRefType(value.object.identifier) &&
+            value.property === 'current'
+          ) {
+            continue;
+          }
+          const temp = env.lookup(value.object);
+          if (temp != null) {
+            env.define(lvalue, temp);
+          }
+          break;
+        }
+      }
+    }
+  }
+}
+
 function refTypeOfType(place: Place): RefAccessType {
   if (isRefValueType(place.identifier)) {
     return {kind: 'RefValue'};
@@ -258,12 +316,27 @@ function validateNoRefAccessInRenderImpl(
     env.set(place.identifier.id, type);
   }
 
+  const interpolatedAsJsx = new Set<IdentifierId>();
+  for (const block of fn.body.blocks.values()) {
+    for (const instr of block.instructions) {
+      const {value} = instr;
+      if (value.kind === 'JsxExpression' || value.kind === 'JsxFragment') {
+        if (value.children != null) {
+          for (const child of value.children) {
+            interpolatedAsJsx.add(child.identifier.id);
+          }
+        }
+      }
+    }
+  }
+
   for (let i = 0; (i == 0 || env.hasChanged()) && i < 10; i++) {
     env.resetChanged();
     returnValues = [];
-    const safeBlocks = new Map<BlockId, RefId>();
+    const safeBlocks: Array<{block: BlockId; ref: RefId}> = [];
     const errors = new CompilerError();
     for (const [, block] of fn.body.blocks) {
+      retainWhere(safeBlocks, entry => entry.block !== block.id);
       for (const phi of block.phis) {
         env.set(
           phi.place.identifier.id,
@@ -385,28 +458,77 @@ 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.fromCode(
+                    ErrorCode.NO_REF_ACCESS_IN_RENDER,
+                  ).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 we already reported an error on this instruction, don't report
+             * duplicate errors
+             */
+            if (!didError) {
+              const isRefLValue = isUseRefType(instr.lvalue.identifier);
+              for (const operand of eachInstructionValueOperand(instr.value)) {
+                /**
+                 * By default we check that function call operands are not refs,
+                 * ref values, or functions that can access refs.
+                 */
+                if (
+                  isRefLValue ||
+                  (hookKind != null &&
+                    hookKind !== 'useState' &&
+                    hookKind !== 'useReducer')
+                ) {
+                  /**
+                   * Special cases:
+                   *
+                   * 1. the lvalue is a ref
+                   * In general passing a ref to a function may access that ref
+                   * value during render, so we disallow it.
+                   *
+                   * The main exception is the "mergeRefs" pattern, ie a function
+                   * that accepts multiple refs as arguments (or an array of refs)
+                   * and returns a new, aggregated ref. If the lvalue is a ref,
+                   * we assume that the user is doing this pattern and allow passing
+                   * refs.
+                   *
+                   * Eg `const mergedRef = mergeRefs(ref1, ref2)`
+                   *
+                   * 2. calling hooks
+                   *
+                   * Hooks are independently checked to ensure they don't access refs
+                   * during render.
+                   */
+                  validateNoDirectRefValueAccess(errors, operand, env);
+                } else if (interpolatedAsJsx.has(instr.lvalue.identifier.id)) {
+                  /**
+                   * Special case: the lvalue is passed as a jsx child
+                   *
+                   * For example `<Foo>{renderHelper(ref)}</Foo>`. Here we have more
+                   * context and infer that the ref is being passed to a component-like
+                   * render function which attempts to obey the rules.
+                   */
+                  validateNoRefValueAccess(errors, env, operand);
+                } else {
+                  validateNoRefPassedToFunction(
+                    errors,
+                    env,
+                    operand,
+                    operand.loc,
+                  );
+                }
               }
             }
             env.set(instr.lvalue.identifier.id, returnType);
@@ -439,23 +561,39 @@ function validateNoRefAccessInRenderImpl(
           case 'PropertyStore':
           case 'ComputedDelete':
           case 'ComputedStore': {
-            const safe = safeBlocks.get(block.id);
             const target = env.get(instr.value.object.identifier.id);
+            let safe: (typeof safeBlocks)['0'] | null | undefined = null;
             if (
               instr.value.kind === 'PropertyStore' &&
-              safe != null &&
-              target?.kind === 'Ref' &&
-              target.refId === safe
+              target != null &&
+              target.kind === 'Ref'
             ) {
-              safeBlocks.delete(block.id);
-            } else {
-              validateNoRefAccess(errors, env, instr.value.object, instr.loc);
+              safe = safeBlocks.find(entry => entry.ref === target.refId);
             }
-            for (const operand of eachInstructionValueOperand(instr.value)) {
-              if (operand === instr.value.object) {
-                continue;
+            if (safe != null) {
+              retainWhere(safeBlocks, entry => entry !== safe);
+            } else {
+              validateNoRefUpdate(errors, env, instr.value.object, instr.loc);
+            }
+            if (
+              instr.value.kind === 'ComputedDelete' ||
+              instr.value.kind === 'ComputedStore'
+            ) {
+              validateNoRefValueAccess(errors, env, instr.value.property);
+            }
+            if (
+              instr.value.kind === 'ComputedStore' ||
+              instr.value.kind === 'PropertyStore'
+            ) {
+              validateNoDirectRefValueAccess(errors, instr.value.value, env);
+              const type = env.get(instr.value.value.identifier.id);
+              if (type != null && type.kind === 'Structure') {
+                let objectType: RefAccessType = type;
+                if (target != null) {
+                  objectType = joinRefAccessTypes(objectType, target);
+                }
+                env.set(instr.value.object.identifier.id, objectType);
               }
-              validateNoRefValueAccess(errors, env, operand);
             }
             break;
           }
@@ -535,8 +673,11 @@ function validateNoRefAccessInRenderImpl(
 
       if (block.terminal.kind === 'if') {
         const test = env.get(block.terminal.test.identifier.id);
-        if (test?.kind === 'Guard') {
-          safeBlocks.set(block.terminal.consequent, test.refId);
+        if (
+          test?.kind === 'Guard' &&
+          safeBlocks.find(entry => entry.ref === test.refId) == null
+        ) {
+          safeBlocks.push({block: block.terminal.fallthrough, ref: test.refId});
         }
       }
 
@@ -583,18 +724,15 @@ 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.fromCode(ErrorCode.NO_REF_ACCESS_IN_RENDER).withDetail(
+        {
+          kind: 'error',
+          loc: operand.loc,
+          message: `Cannot access ref value during render`,
+        },
+      ),
+    );
   }
 }
 
@@ -608,22 +746,19 @@ 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.fromCode(ErrorCode.NO_REF_ACCESS_IN_RENDER).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 +770,35 @@ 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.fromCode(ErrorCode.NO_REF_ACCESS_IN_RENDER).withDetail(
+        {
+          kind: 'error',
+          loc: (type.kind === 'RefValue' && type.loc) || loc,
+          message: `Passing a ref to a function may read its value during render`,
+        },
+      ),
+    );
+  }
+}
+
+function validateNoRefUpdate(
+  errors: CompilerError,
+  env: Env,
+  operand: Place,
+  loc: SourceLocation,
+): void {
+  const type = destructure(env.get(operand.identifier.id));
+  if (type?.kind === 'Ref' || type?.kind === 'RefValue') {
+    errors.pushDiagnostic(
+      CompilerDiagnostic.fromCode(ErrorCode.NO_REF_ACCESS_IN_RENDER).withDetail(
+        {
+          kind: 'error',
+          loc: (type.kind === 'RefValue' && type.loc) || loc,
+          message: `Cannot update ref during render`,
+        },
+      ),
+    );
   }
 }
 
@@ -657,17 +809,14 @@ 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.fromCode(ErrorCode.NO_REF_ACCESS_IN_RENDER).withDetail(
+        {
+          kind: 'error',
+          loc: type.loc ?? operand.loc,
+          message: `Cannot access ref value during render`,
+        },
+      ),
+    );
   }
 }

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

@@ -5,26 +5,29 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {CompilerError, ErrorSeverity} from '../CompilerError';
+import {CompilerDiagnostic, CompilerError} from '../CompilerError';
 import {
   HIRFunction,
   IdentifierId,
   isSetStateType,
   isUseEffectHookType,
+  isUseInsertionEffectHookType,
+  isUseLayoutEffectHookType,
   Place,
 } from '../HIR';
 import {eachInstructionValueOperand} from '../HIR/visitors';
+import {ErrorCode} from '../Utils/CompilerErrorCodes';
 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 +82,25 @@ 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.fromCode(
+                    ErrorCode.INVALID_SET_STATE_IN_EFFECTS,
+                  ).withDetail({
+                    kind: 'error',
+                    loc: setState.loc,
+                    message:
+                      'Avoid calling setState() directly within an effect',
+                  }),
+                );
               }
             }
           }

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

@@ -5,10 +5,11 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {CompilerError, ErrorSeverity} from '../CompilerError';
+import {CompilerDiagnostic, CompilerError} from '../CompilerError';
 import {HIRFunction, IdentifierId, isSetStateType} from '../HIR';
 import {computeUnconditionalBlocks} from '../HIR/ComputeUnconditionalBlocks';
 import {eachInstructionValueOperand} from '../HIR/visitors';
+import {ErrorCode} from '../Utils/CompilerErrorCodes';
 import {Result} from '../Utils/Result';
 
 /**
@@ -122,23 +123,25 @@ 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.fromCode(
+                  ErrorCode.INVALID_SET_STATE_IN_MEMO,
+                ).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.fromCode(
+                  ErrorCode.INVALID_SET_STATE_IN_RENDER,
+                ).withDetail({
+                  kind: 'error',
+                  loc: callee.loc,
+                  message: 'Found setState() during render',
+                }),
+              );
             }
           }
           break;

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

@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {CompilerError, ErrorSeverity} from '../CompilerError';
+import {CompilerDiagnostic, CompilerError, ErrorCode} from '../CompilerError';
 import {
   DeclarationId,
   Effect,
@@ -275,27 +275,29 @@ 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(', ')}]. ${
-            errorDiagnostic
-              ? getCompareDependencyResultDescription(errorDiagnostic)
-              : 'Inferred dependency not present in source'
-          }`
-        : null,
-    loc: memoLocation,
-    suggestions: null,
-  });
+  errorState.pushDiagnostic(
+    CompilerDiagnostic.fromCode(ErrorCode.MANUAL_MEMO_DEPENDENCIES_CONFLICT, {
+      description:
+        DEBUG ||
+        // If the dependency is a named variable then we can report it. Otherwise only print in debug mode
+        (dep.identifier.name != null && dep.identifier.name.kind === 'named')
+          ? `The inferred dependency was \`${prettyPrintScopeDependency(
+              dep,
+            )}\`, but the source dependencies were [${validDepsInMemoBlock
+              .map(dep => printManualMemoDependency(dep, true))
+              .join(', ')}]. ${
+              errorDiagnostic
+                ? getCompareDependencyResultDescription(errorDiagnostic)
+                : 'Inferred dependency not present in source'
+            }`
+          : '',
+      suggestions: null,
+    }).withDetail({
+      kind: 'error',
+      loc: memoLocation,
+      message: 'Could not preserve existing manual memoization',
+    }),
+  );
 }
 
 class Visitor extends ReactiveFunctionVisitor<VisitorState> {
@@ -445,11 +447,13 @@ 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 +461,21 @@ 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 +521,15 @@ 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.fromCode(
+              ErrorCode.MANUAL_MEMO_MUTATED_LATER,
+            ).withDetail({
+              kind: 'error',
+              loc,
+              message: 'This dependency may be modified later',
+            }),
+          );
         }
       }
     }
@@ -543,16 +563,17 @@ 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
-                  ? `${printIdentifier(identifier)} was not memoized`
-                  : null,
-                severity: ErrorSeverity.CannotPreserveMemoization,
-                loc,
-                suggestions: null,
-              });
+              state.errors.pushDiagnostic(
+                CompilerDiagnostic.fromCode(ErrorCode.MANUAL_MEMO_REMOVED, {
+                  description: DEBUG
+                    ? `${printIdentifier(identifier)} was not memoized`
+                    : '',
+                }).withDetail({
+                  kind: 'error',
+                  loc,
+                  message: 'Could not preserve existing memoization',
+                }),
+              );
             }
           }
         }

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

@@ -5,8 +5,9 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {CompilerError, ErrorSeverity} from '../CompilerError';
+import {CompilerDiagnostic, CompilerError} from '../CompilerError';
 import {HIRFunction, IdentifierId, SourceLocation} from '../HIR';
+import {ErrorCode} from '../Utils/CompilerErrorCodes';
 import {Result} from '../Utils/Result';
 
 /**
@@ -59,20 +60,21 @@ 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.fromCode(ErrorCode.STATIC_COMPONENTS, {
+                  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

@@ -5,8 +5,9 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {CompilerError, ErrorSeverity} from '..';
+import {CompilerDiagnostic, CompilerError} from '../CompilerError';
 import {FunctionExpression, HIRFunction, IdentifierId} from '../HIR';
+import {ErrorCode} from '../Utils/CompilerErrorCodes';
 import {Result} from '../Utils/Result';
 
 export function validateUseMemo(fn: HIRFunction): Result<void, CompilerError> {
@@ -63,24 +64,32 @@ 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.fromCode(
+                ErrorCode.INVALID_USE_MEMO_CALLBACK_PARAMETERS,
+              ).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.fromCode(
+                ErrorCode.INVALID_USE_MEMO_CALLBACK_ASYNC,
+              ).withDetail({
+                kind: 'error',
+                loc: body.loc,
+                message: 'Async and generator functions are not supported',
+              }),
+            );
           }
 
           break;

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/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-assigning-ref-accessing-function-to-object-property-if-not-mutated.expect.md

@@ -0,0 +1,52 @@
+
+## Input
+
+```javascript
+import {useRef} from 'react';
+import {Stringify} from 'shared-runtime';
+
+function Component(props) {
+  const ref = useRef(props.value);
+  const object = {};
+  object.foo = () => ref.current;
+  return <Stringify object={object} shouldInvokeFns={true} />;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Component,
+  params: [{value: 42}],
+};
+
+```
+
+## Code
+
+```javascript
+import { c as _c } from "react/compiler-runtime";
+import { useRef } from "react";
+import { Stringify } from "shared-runtime";
+
+function Component(props) {
+  const $ = _c(1);
+  const ref = useRef(props.value);
+  let t0;
+  if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
+    const object = {};
+    object.foo = () => ref.current;
+    t0 = <Stringify object={object} shouldInvokeFns={true} />;
+    $[0] = t0;
+  } else {
+    t0 = $[0];
+  }
+  return t0;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Component,
+  params: [{ value: 42 }],
+};
+
+```
+      
+### Eval output
+(kind: ok) <div>{"object":{"foo":{"kind":"Function","result":42}},"shouldInvokeFns":true}</div>

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/allow-assigning-ref-accessing-function-to-object-property-if-not-mutated.js

@@ -0,0 +1,14 @@
+import {useRef} from 'react';
+import {Stringify} from 'shared-runtime';
+
+function Component(props) {
+  const ref = useRef(props.value);
+  const object = {};
+  object.foo = () => ref.current;
+  return <Stringify object={object} shouldInvokeFns={true} />;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Component,
+  params: [{value: 42}],
+};

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/allow-merge-refs-pattern.expect.md

@@ -0,0 +1,44 @@
+
+## Input
+
+```javascript
+// @enableTreatRefLikeIdentifiersAsRefs @validateRefAccessDuringRender
+
+import {useRef} from 'react';
+
+function Component() {
+  const ref = useRef(null);
+  const ref2 = useRef(null);
+  const mergedRef = mergeRefs([ref], ref2);
+
+  return <Stringify ref={mergedRef} />;
+}
+
+```
+
+## Code
+
+```javascript
+import { c as _c } from "react/compiler-runtime"; // @enableTreatRefLikeIdentifiersAsRefs @validateRefAccessDuringRender
+
+import { useRef } from "react";
+
+function Component() {
+  const $ = _c(1);
+  const ref = useRef(null);
+  const ref2 = useRef(null);
+  const mergedRef = mergeRefs([ref], ref2);
+  let t0;
+  if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
+    t0 = <Stringify ref={mergedRef} />;
+    $[0] = t0;
+  } else {
+    t0 = $[0];
+  }
+  return t0;
+}
+
+```
+      
+### Eval output
+(kind: exception) Fixture not implemented

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/allow-merge-refs-pattern.js

@@ -0,0 +1,11 @@
+// @enableTreatRefLikeIdentifiersAsRefs @validateRefAccessDuringRender
+
+import {useRef} from 'react';
+
+function Component() {
+  const ref = useRef(null);
+  const ref2 = useRef(null);
+  const mergedRef = mergeRefs([ref], ref2);
+
+  return <Stringify ref={mergedRef} />;
+}

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/allow-passing-ref-to-render-helper-props-object.expect.md

@@ -0,0 +1,45 @@
+
+## Input
+
+```javascript
+// @enableTreatRefLikeIdentifiersAsRefs @validateRefAccessDuringRender
+
+import {useRef} from 'react';
+
+function Component(props) {
+  const ref = useRef(null);
+
+  return <Foo>{props.render({ref})}</Foo>;
+}
+
+```
+
+## Code
+
+```javascript
+import { c as _c } from "react/compiler-runtime"; // @enableTreatRefLikeIdentifiersAsRefs @validateRefAccessDuringRender
+
+import { useRef } from "react";
+
+function Component(props) {
+  const $ = _c(3);
+  const ref = useRef(null);
+
+  const T0 = Foo;
+  const t0 = props.render({ ref });
+  let t1;
+  if ($[0] !== T0 || $[1] !== t0) {
+    t1 = <T0>{t0}</T0>;
+    $[0] = T0;
+    $[1] = t0;
+    $[2] = t1;
+  } else {
+    t1 = $[2];
+  }
+  return t1;
+}
+
+```
+      
+### Eval output
+(kind: exception) Fixture not implemented

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/allow-passing-ref-to-render-helper-props-object.js

@@ -0,0 +1,9 @@
+// @enableTreatRefLikeIdentifiersAsRefs @validateRefAccessDuringRender
+
+import {useRef} from 'react';
+
+function Component(props) {
+  const ref = useRef(null);
+
+  return <Foo>{props.render({ref})}</Foo>;
+}

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/allow-passing-ref-to-render-helper.expect.md

@@ -0,0 +1,49 @@
+
+## Input
+
+```javascript
+// @enableTreatRefLikeIdentifiersAsRefs @validateRefAccessDuringRender
+
+import {useRef} from 'react';
+
+function Component(props) {
+  const ref = useRef(null);
+
+  return <Foo>{props.render(ref)}</Foo>;
+}
+
+```
+
+## Code
+
+```javascript
+import { c as _c } from "react/compiler-runtime"; // @enableTreatRefLikeIdentifiersAsRefs @validateRefAccessDuringRender
+
+import { useRef } from "react";
+
+function Component(props) {
+  const $ = _c(4);
+  const ref = useRef(null);
+  let t0;
+  if ($[0] !== props.render) {
+    t0 = props.render(ref);
+    $[0] = props.render;
+    $[1] = t0;
+  } else {
+    t0 = $[1];
+  }
+  let t1;
+  if ($[2] !== t0) {
+    t1 = <Foo>{t0}</Foo>;
+    $[2] = t0;
+    $[3] = t1;
+  } else {
+    t1 = $[3];
+  }
+  return t1;
+}
+
+```
+      
+### Eval output
+(kind: exception) Fixture not implemented

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/allow-passing-ref-to-render-helper.js

@@ -0,0 +1,9 @@
+// @enableTreatRefLikeIdentifiersAsRefs @validateRefAccessDuringRender
+
+import {useRef} from 'react';
+
+function Component(props) {
+  const ref = useRef(null);
+
+  return <Foo>{props.render(ref)}</Foo>;
+}

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/allow-ref-access-in-effect-indirect.expect.md

@@ -27,6 +27,7 @@ function Component() {
 }
 
 function Child({ref}) {
+  'use no memo';
   // This violates the rules of React, so we access the ref in a child
   // component
   return ref.current;
@@ -100,8 +101,10 @@ function Component() {
   return t6;
 }
 
-function Child(t0) {
-  const { ref } = t0;
+function Child({ ref }) {
+  "use no memo";
+  // This violates the rules of React, so we access the ref in a child
+  // component
   return ref.current;
 }
 

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/allow-ref-access-in-effect-indirect.js

@@ -23,6 +23,7 @@ function Component() {
 }
 
 function Child({ref}) {
+  'use no memo';
   // This violates the rules of React, so we access the ref in a child
   // component
   return ref.current;

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/allow-ref-access-in-effect.expect.md

@@ -23,6 +23,7 @@ function Component() {
 }
 
 function Child({ref}) {
+  'use no memo';
   // This violates the rules of React, so we access the ref in a child
   // component
   return ref.current;
@@ -86,8 +87,10 @@ function Component() {
   return t5;
 }
 
-function Child(t0) {
-  const { ref } = t0;
+function Child({ ref }) {
+  "use no memo";
+  // This violates the rules of React, so we access the ref in a child
+  // component
   return ref.current;
 }
 

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/allow-ref-access-in-effect.js

@@ -19,6 +19,7 @@ function Component() {
 }
 
 function Child({ref}) {
+  'use no memo';
   // This violates the rules of React, so we access the ref in a child
   // component
   return ref.current;

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/allow-ref-access-in-unused-callback-nested.expect.md

@@ -25,6 +25,7 @@ function Component() {
 }
 
 function Child({ref}) {
+  'use no memo';
   // This violates the rules of React, so we access the ref in a child
   // component
   return ref.current;
@@ -83,8 +84,10 @@ function Component() {
 }
 function _temp() {}
 
-function Child(t0) {
-  const { ref } = t0;
+function Child({ ref }) {
+  "use no memo";
+  // This violates the rules of React, so we access the ref in a child
+  // component
   return ref.current;
 }
 

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/allow-ref-access-in-unused-callback-nested.js

@@ -21,6 +21,7 @@ function Component() {
 }
 
 function Child({ref}) {
+  'use no memo';
   // This violates the rules of React, so we access the ref in a child
   // component
   return ref.current;

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/allow-ref-lazy-initialization-with-logical.expect.md

@@ -0,0 +1,68 @@
+
+## Input
+
+```javascript
+// @validateRefAccessDuringRender
+
+import {useRef} from 'react';
+
+function Component(props) {
+  const ref = useRef(null);
+  if (ref.current == null) {
+    // the logical means the ref write is in a different block
+    // from the if consequent. this tests that the "safe" blocks
+    // extend up to the if's fallthrough
+    ref.current = props.unknownKey ?? props.value;
+  }
+  return <Child ref={ref} />;
+}
+
+function Child({ref}) {
+  'use no memo';
+  return ref.current;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Component,
+  params: [{value: 42}],
+};
+
+```
+
+## Code
+
+```javascript
+import { c as _c } from "react/compiler-runtime"; // @validateRefAccessDuringRender
+
+import { useRef } from "react";
+
+function Component(props) {
+  const $ = _c(1);
+  const ref = useRef(null);
+  if (ref.current == null) {
+    ref.current = props.unknownKey ?? props.value;
+  }
+  let t0;
+  if ($[0] === Symbol.for("react.memo_cache_sentinel")) {
+    t0 = <Child ref={ref} />;
+    $[0] = t0;
+  } else {
+    t0 = $[0];
+  }
+  return t0;
+}
+
+function Child({ ref }) {
+  "use no memo";
+  return ref.current;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Component,
+  params: [{ value: 42 }],
+};
+
+```
+      
+### Eval output
+(kind: ok) 42

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/allow-ref-lazy-initialization-with-logical.js

@@ -0,0 +1,24 @@
+// @validateRefAccessDuringRender
+
+import {useRef} from 'react';
+
+function Component(props) {
+  const ref = useRef(null);
+  if (ref.current == null) {
+    // the logical means the ref write is in a different block
+    // from the if consequent. this tests that the "safe" blocks
+    // extend up to the if's fallthrough
+    ref.current = props.unknownKey ?? props.value;
+  }
+  return <Child ref={ref} />;
+}
+
+function Child({ref}) {
+  'use no memo';
+  return ref.current;
+}
+
+export const FIXTURE_ENTRYPOINT = {
+  fn: Component,
+  params: [{value: 42}],
+};

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/array-at-closure.expect.md

@@ -19,7 +19,7 @@ function Component(props) {
 ```javascript
 import { c as _c } from "react/compiler-runtime";
 function Component(props) {
-  const $ = _c(7);
+  const $ = _c(5);
   let t0;
   if ($[0] !== props.x) {
     t0 = foo(props.x);
@@ -31,26 +31,19 @@ function Component(props) {
   const x = t0;
   let t1;
   if ($[2] !== props || $[3] !== x) {
-    t1 = function () {
+    const fn = function () {
       const arr = [...bar(props)];
       return arr.at(x);
     };
+
+    t1 = fn();
     $[2] = props;
     $[3] = x;
     $[4] = t1;
   } else {
     t1 = $[4];
   }
-  const fn = t1;
-  let t2;
-  if ($[5] !== fn) {
-    t2 = fn();
-    $[5] = fn;
-    $[6] = t2;
-  } else {
-    t2 = $[6];
-  }
-  const fnResult = t2;
+  const fnResult = t1;
   return fnResult;
 }
 

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/array-map-captures-receiver-noAlias.expect.md

@@ -23,34 +23,18 @@ export const FIXTURE_ENTRYPOINT = {
 ```javascript
 import { c as _c } from "react/compiler-runtime";
 function Component(props) {
-  const $ = _c(6);
+  const $ = _c(2);
   let t0;
   if ($[0] !== props.a) {
-    t0 = { a: props.a };
+    const item = { a: props.a };
+    const items = [item];
+    t0 = items.map(_temp);
     $[0] = props.a;
     $[1] = t0;
   } else {
     t0 = $[1];
   }
-  const item = t0;
-  let t1;
-  if ($[2] !== item) {
-    t1 = [item];
-    $[2] = item;
-    $[3] = t1;
-  } else {
-    t1 = $[3];
-  }
-  const items = t1;
-  let t2;
-  if ($[4] !== items) {
-    t2 = items.map(_temp);
-    $[4] = items;
-    $[5] = t2;
-  } else {
-    t2 = $[5];
-  }
-  const mapped = t2;
+  const mapped = t0;
   return mapped;
 }
 function _temp(item_0) {

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/array-map-noAlias-escaping-function.expect.md

@@ -21,26 +21,18 @@ export const FIXTURE_ENTRYPOINT = {
 ```javascript
 import { c as _c } from "react/compiler-runtime";
 function Component(props) {
-  const $ = _c(4);
+  const $ = _c(2);
   const f = _temp;
   let t0;
   if ($[0] !== props.items) {
-    t0 = [...props.items].map(f);
+    const x = [...props.items].map(f);
+    t0 = [x, f];
     $[0] = props.items;
     $[1] = t0;
   } else {
     t0 = $[1];
   }
-  const x = t0;
-  let t1;
-  if ($[2] !== x) {
-    t1 = [x, f];
-    $[2] = x;
-    $[3] = t1;
-  } else {
-    t1 = $[3];
-  }
-  return t1;
+  return t0;
 }
 function _temp(item) {
   return item;

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 = {