[compiler] Improve ref validation error message

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

.eslintrc.js

@@ -608,6 +608,7 @@ module.exports = {
     symbol: 'readonly',
     SyntheticEvent: 'readonly',
     SyntheticMouseEvent: 'readonly',
+    SyntheticPointerEvent: 'readonly',
     Thenable: 'readonly',
     TimeoutID: 'readonly',
     WheelEventHandler: 'readonly',

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

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,
@@ -141,10 +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> = [];
+  const otherErrors: Array<CompilerErrorDetail | CompilerDiagnostic> = [];
   const upsert: (result: PrintedCompilerPipelineValue) => void = result => {
     const entry = results.get(result.name);
     if (Array.isArray(entry)) {
@@ -203,6 +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,
@@ -214,7 +235,7 @@ function compile(source: string): [CompilerOutput, 'flow' | 'typescript'] {
         debugLogIRs: logIR,
         logEvent: (_filename: string | null, event: LoggerEvent) => {
           if (event.kind === 'CompileError') {
-            otherErrors.push(new CompilerErrorDetail(event.detail));
+            otherErrors.push(event.detail);
           }
         },
       },
@@ -226,7 +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)
@@ -245,12 +266,15 @@ function compile(source: string): [CompilerOutput, 'flow' | 'typescript'] {
   }
   // Only include logger errors if there weren't other errors
   if (!error.hasErrors() && otherErrors.length !== 0) {
-    otherErrors.forEach(e => error.push(e));
+    otherErrors.forEach(e => error.details.push(e));
   }
   if (error.hasErrors()) {
-    return [{kind: 'err', results, error: error}, language];
+    return [{kind: 'err', results, error}, language];
   }
-  return [{kind: 'ok', results, transformOutput}, language];
+  return [
+    {kind: 'ok', results, transformOutput, errors: error.details},
+    language,
+  ];
 }
 
 export default function Editor(): JSX.Element {
@@ -259,7 +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],
   );
 
@@ -285,19 +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

@@ -84,7 +84,7 @@ export default function BabelPluginReactCompiler(
             }
           } catch (e) {
             if (e instanceof CompilerError) {
-              throw new Error(e.printErrorMessage(pass.file.code));
+              throw e.withPrintedMessage(pass.file.code, {eslint: false});
             }
             throw e;
           }

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

@@ -5,6 +5,7 @@
  * 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';
@@ -93,6 +94,14 @@ export type CompilerErrorDetailOptions = {
   suggestions?: Array<CompilerSuggestion> | null | undefined;
 };
 
+export type PrintErrorMessageOptions = {
+  /**
+   * ESLint uses 1-indexed columns and prints one error at a time
+   * So it doesn't require the "Found # error(s)" text
+   */
+  eslint: boolean;
+};
+
 export class CompilerDiagnostic {
   options: CompilerDiagnosticOptions;
 
@@ -128,7 +137,7 @@ export class CompilerDiagnostic {
     return this.options.details.filter(d => d.kind === 'error')[0]?.loc ?? null;
   }
 
-  printErrorMessage(source: string): string {
+  printErrorMessage(source: string, options: PrintErrorMessageOptions): string {
     const buffer = [
       printErrorSummary(this.severity, this.category),
       '\n\n',
@@ -143,28 +152,18 @@ export class CompilerDiagnostic {
           }
           let codeFrame: string;
           try {
-            codeFrame = codeFrameColumns(
-              source,
-              {
-                start: {
-                  line: loc.start.line,
-                  column: loc.start.column + 1,
-                },
-                end: {
-                  line: loc.end.line,
-                  column: loc.end.column + 1,
-                },
-              },
-              {
-                message: detail.message,
-              },
-            );
+            codeFrame = printCodeFrame(source, loc, detail.message);
           } catch (e) {
             codeFrame = detail.message;
           }
-          buffer.push(
-            `\n\n${loc.filename}:${loc.start.line}:${loc.start.column}\n`,
-          );
+          buffer.push('\n\n');
+          if (loc.filename != null) {
+            const line = loc.start.line;
+            const column = options.eslint
+              ? loc.start.column + 1
+              : loc.start.column;
+            buffer.push(`${loc.filename}:${line}:${column}\n`);
+          }
           buffer.push(codeFrame);
           break;
         }
@@ -223,7 +222,7 @@ export class CompilerErrorDetail {
     return this.loc;
   }
 
-  printErrorMessage(source: string): string {
+  printErrorMessage(source: string, options: PrintErrorMessageOptions): string {
     const buffer = [printErrorSummary(this.severity, this.reason)];
     if (this.description != null) {
       buffer.push(`\n\n${this.description}.`);
@@ -232,28 +231,16 @@ export class CompilerErrorDetail {
     if (loc != null && typeof loc !== 'symbol') {
       let codeFrame: string;
       try {
-        codeFrame = codeFrameColumns(
-          source,
-          {
-            start: {
-              line: loc.start.line,
-              column: loc.start.column + 1,
-            },
-            end: {
-              line: loc.end.line,
-              column: loc.end.column + 1,
-            },
-          },
-          {
-            message: this.reason,
-          },
-        );
+        codeFrame = printCodeFrame(source, loc, this.reason);
       } catch (e) {
         codeFrame = '';
       }
-      buffer.push(
-        `\n\n${loc.filename}:${loc.start.line}:${loc.start.column}\n`,
-      );
+      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');
     }
@@ -275,6 +262,7 @@ export class CompilerErrorDetail {
 
 export class CompilerError extends Error {
   details: Array<CompilerErrorDetail | CompilerDiagnostic> = [];
+  printedMessage: string | null = null;
 
   static invariant(
     condition: unknown,
@@ -360,22 +348,38 @@ 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;
   }
 
-  printErrorMessage(source: string): string {
+  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` +
-      this.details.map(detail => detail.printErrorMessage(source)).join('\n')
+      `Found ${this.details.length} error${this.details.length === 1 ? '' : 's'}:\n\n` +
+      this.details
+        .map(detail => detail.printErrorMessage(source, options).trim())
+        .join('\n\n')
     );
   }
 
@@ -438,6 +442,29 @@ export class CompilerError extends Error {
   }
 }
 
+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) {

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

@@ -174,7 +174,7 @@ function runWithEnvironment(
     !env.config.disableMemoizationForDebugging &&
     !env.config.enableChangeDetectionForDebugging
   ) {
-    dropManualMemoization(hir);
+    dropManualMemoization(hir).unwrap();
     log({kind: 'hir', name: 'DropManualMemoization', value: hir});
   }
 

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

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

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

@@ -107,10 +107,9 @@ export function lower(
       if (binding.kind !== 'Identifier') {
         builder.errors.pushDiagnostic(
           CompilerDiagnostic.create({
-            category: 'Could not find binding',
-            description: `[BuildHIR] Could not find binding for param \`${param.node.name}\``,
             severity: ErrorSeverity.Invariant,
-            suggestions: null,
+            category: 'Could not find binding',
+            description: `[BuildHIR] Could not find binding for param \`${param.node.name}\`.`,
           }).withDetail({
             kind: 'error',
             loc: param.node.loc ?? null,
@@ -172,10 +171,9 @@ export function lower(
     } else {
       builder.errors.pushDiagnostic(
         CompilerDiagnostic.create({
-          category: `Handle ${param.node.type} parameters`,
-          description: `[BuildHIR] Add support for ${param.node.type} parameters`,
           severity: ErrorSeverity.Todo,
-          suggestions: null,
+          category: `Handle ${param.node.type} parameters`,
+          description: `[BuildHIR] Add support for ${param.node.type} parameters.`,
         }).withDetail({
           kind: 'error',
           loc: param.node.loc ?? null,
@@ -191,6 +189,7 @@ export function lower(
     const fallthrough = builder.reserve('block');
     const terminal: ReturnTerminal = {
       kind: 'return',
+      returnVariant: 'Implicit',
       loc: GeneratedSource,
       value: lowerExpressionToTemporary(builder, body),
       id: makeInstructionId(0),
@@ -205,8 +204,7 @@ export function lower(
       CompilerDiagnostic.create({
         severity: ErrorSeverity.InvalidJS,
         category: `Unexpected function body kind`,
-        description: `Expected function body to be an expression or a block statement, got \`${body.type}\``,
-        suggestions: null,
+        description: `Expected function body to be an expression or a block statement, got \`${body.type}\`.`,
       }).withDetail({
         kind: 'error',
         loc: body.node.loc ?? null,
@@ -222,6 +220,7 @@ export function lower(
   builder.terminate(
     {
       kind: 'return',
+      returnVariant: 'Void',
       loc: GeneratedSource,
       value: lowerValueToTemporary(builder, {
         kind: 'Primitive',
@@ -305,6 +304,7 @@ function lowerStatement(
       }
       const terminal: ReturnTerminal = {
         kind: 'return',
+        returnVariant: 'Explicit',
         loc: stmt.node.loc ?? GeneratedSource,
         value,
         id: makeInstructionId(0),

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

@@ -631,6 +631,17 @@ export const EnvironmentConfigSchema = z.object({
    * ```
    */
   lowerContextAccess: ExternalFunctionSchema.nullable().default(null),
+
+  /**
+   * If enabled, will validate useMemos that don't return any values:
+   *
+   * Valid:
+   *   useMemo(() => foo, [foo]);
+   *   useMemo(() => { return foo }, [foo]);
+   * Invalid:
+   *   useMemo(() => { ... }, [...]);
+   */
+  validateNoVoidUseMemo: z.boolean().default(false),
 });
 
 export type EnvironmentConfig = z.infer<typeof EnvironmentConfigSchema>;

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

@@ -446,8 +446,20 @@ 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;

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

@@ -1211,6 +1211,8 @@ 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

@@ -215,7 +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) {
@@ -943,7 +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)}`;

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

@@ -777,6 +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

@@ -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`.
    */
@@ -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,

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 +5,12 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {CompilerError, SourceLocation} from '..';
+import {
+  CompilerDiagnostic,
+  CompilerError,
+  ErrorSeverity,
+  SourceLocation,
+} from '..';
 import {
   CallExpression,
   Effect,
@@ -30,6 +35,7 @@ import {
   makeInstructionId,
 } from '../HIR';
 import {createTemporaryPlace, markInstructionIds} from '../HIR/HIRBuilder';
+import {Result} from '../Utils/Result';
 
 type ManualMemoCallee = {
   kind: 'useMemo' | 'useCallback';
@@ -283,26 +289,43 @@ function extractManualMemoizationArgs(
   instr: TInstruction<CallExpression> | TInstruction<MethodCall>,
   kind: 'useCallback' | 'useMemo',
   sidemap: IdentifierSidemap,
+  errors: CompilerError,
 ): {
-  fnPlace: Place;
+  fnPlace: Place | null;
   depsList: Array<ManualMemoDependency> | null;
 } {
   const [fnPlace, depsListPlace] = instr.value.args as Array<
     Place | SpreadPattern | undefined
   >;
   if (fnPlace == null) {
-    CompilerError.throwInvalidReact({
-      reason: `Expected a callback function to be passed to ${kind}`,
-      loc: instr.value.loc,
-      suggestions: null,
-    });
+    errors.pushDiagnostic(
+      CompilerDiagnostic.create({
+        severity: ErrorSeverity.InvalidReact,
+        category: `Expected a callback function to be passed to ${kind}`,
+        description: `Expected a callback function to be passed to ${kind}`,
+        suggestions: null,
+      }).withDetail({
+        kind: 'error',
+        loc: instr.value.loc,
+        message: `Expected a callback function to be passed to ${kind}`,
+      }),
+    );
+    return {fnPlace: null, depsList: null};
   }
   if (fnPlace.kind === 'Spread' || depsListPlace?.kind === 'Spread') {
-    CompilerError.throwInvalidReact({
-      reason: `Unexpected spread argument to ${kind}`,
-      loc: instr.value.loc,
-      suggestions: null,
-    });
+    errors.pushDiagnostic(
+      CompilerDiagnostic.create({
+        severity: ErrorSeverity.InvalidReact,
+        category: `Unexpected spread argument to ${kind}`,
+        description: `Unexpected spread argument to ${kind}`,
+        suggestions: null,
+      }).withDetail({
+        kind: 'error',
+        loc: instr.value.loc,
+        message: `Unexpected spread argument to ${kind}`,
+      }),
+    );
+    return {fnPlace: null, depsList: null};
   }
   let depsList: Array<ManualMemoDependency> | null = null;
   if (depsListPlace != null) {
@@ -310,23 +333,40 @@ function extractManualMemoizationArgs(
       depsListPlace.identifier.id,
     );
     if (maybeDepsList == null) {
-      CompilerError.throwInvalidReact({
-        reason: `Expected the dependency list for ${kind} to be an array literal`,
-        suggestions: null,
-        loc: depsListPlace.loc,
-      });
+      errors.pushDiagnostic(
+        CompilerDiagnostic.create({
+          severity: ErrorSeverity.InvalidReact,
+          category: `Expected the dependency list for ${kind} to be an array literal`,
+          description: `Expected the dependency list for ${kind} to be an array literal`,
+          suggestions: null,
+        }).withDetail({
+          kind: 'error',
+          loc: depsListPlace.loc,
+          message: `Expected the dependency list for ${kind} to be an array literal`,
+        }),
+      );
+      return {fnPlace, depsList: null};
     }
-    depsList = maybeDepsList.map(dep => {
+    depsList = [];
+    for (const dep of maybeDepsList) {
       const maybeDep = sidemap.maybeDeps.get(dep.identifier.id);
       if (maybeDep == null) {
-        CompilerError.throwInvalidReact({
-          reason: `Expected the dependency list to be an array of simple expressions (e.g. \`x\`, \`x.y.z\`, \`x?.y?.z\`)`,
-          suggestions: null,
-          loc: dep.loc,
-        });
+        errors.pushDiagnostic(
+          CompilerDiagnostic.create({
+            severity: ErrorSeverity.InvalidReact,
+            category: `Expected the dependency list to be an array of simple expressions (e.g. \`x\`, \`x.y.z\`, \`x?.y?.z\`)`,
+            description: `Expected the dependency list to be an array of simple expressions (e.g. \`x\`, \`x.y.z\`, \`x?.y?.z\`)`,
+            suggestions: null,
+          }).withDetail({
+            kind: 'error',
+            loc: dep.loc,
+            message: `Expected the dependency list to be an array of simple expressions (e.g. \`x\`, \`x.y.z\`, \`x?.y?.z\`)`,
+          }),
+        );
+      } else {
+        depsList.push(maybeDep);
       }
-      return maybeDep;
-    });
+    }
   }
   return {
     fnPlace,
@@ -341,8 +381,14 @@ function extractManualMemoizationArgs(
  * rely on type inference to find useMemo/useCallback invocations, and instead does basic tracking
  * of globals and property loads to find both direct calls as well as usage via the React namespace,
  * eg `React.useMemo()`.
+ *
+ * This pass also validates that useMemo callbacks return a value (not void), ensuring that useMemo
+ * is only used for memoizing values and not for running arbitrary side effects.
  */
-export function dropManualMemoization(func: HIRFunction): void {
+export function dropManualMemoization(
+  func: HIRFunction,
+): Result<void, CompilerError> {
+  const errors = new CompilerError();
   const isValidationEnabled =
     func.env.config.validatePreserveExistingMemoizationGuarantees ||
     func.env.config.validateNoSetStateInRender ||
@@ -389,7 +435,47 @@ export function dropManualMemoization(func: HIRFunction): void {
             instr as TInstruction<CallExpression> | TInstruction<MethodCall>,
             manualMemo.kind,
             sidemap,
+            errors,
           );
+
+          if (fnPlace == null) {
+            continue;
+          }
+
+          /**
+           * Bailout on void return useMemos. This is an anti-pattern where code might be using
+           * useMemo like useEffect: running arbirtary side-effects synced to changes in specific
+           * values.
+           */
+          if (
+            func.env.config.validateNoVoidUseMemo &&
+            manualMemo.kind === 'useMemo'
+          ) {
+            const funcToCheck = sidemap.functions.get(
+              fnPlace.identifier.id,
+            )?.value;
+            if (funcToCheck !== undefined && funcToCheck.loweredFunc.func) {
+              if (!hasNonVoidReturn(funcToCheck.loweredFunc.func)) {
+                errors.pushDiagnostic(
+                  CompilerDiagnostic.create({
+                    severity: ErrorSeverity.InvalidReact,
+                    category: 'useMemo() callbacks must return a value',
+                    description: `This ${
+                      manualMemo.loadInstr.value.kind === 'PropertyLoad'
+                        ? 'React.useMemo'
+                        : 'useMemo'
+                    } callback doesn't return a value. useMemo is for computing and caching values, not for arbitrary side effects.`,
+                    suggestions: null,
+                  }).withDetail({
+                    kind: 'error',
+                    loc: instr.value.loc,
+                    message: 'useMemo() callbacks must return a value',
+                  }),
+                );
+              }
+            }
+          }
+
           instr.value = getManualMemoizationReplacement(
             fnPlace,
             instr.value.loc,
@@ -410,11 +496,19 @@ export function dropManualMemoization(func: HIRFunction): void {
              * is rare and likely sketchy.
              */
             if (!sidemap.functions.has(fnPlace.identifier.id)) {
-              CompilerError.throwInvalidReact({
-                reason: `Expected the first argument to be an inline function expression`,
-                suggestions: [],
-                loc: fnPlace.loc,
-              });
+              errors.pushDiagnostic(
+                CompilerDiagnostic.create({
+                  severity: ErrorSeverity.InvalidReact,
+                  category: `Expected the first argument to be an inline function expression`,
+                  description: `Expected the first argument to be an inline function expression`,
+                  suggestions: [],
+                }).withDetail({
+                  kind: 'error',
+                  loc: fnPlace.loc,
+                  message: `Expected the first argument to be an inline function expression`,
+                }),
+              );
+              continue;
             }
             const memoDecl: Place =
               manualMemo.kind === 'useMemo'
@@ -486,6 +580,8 @@ export function dropManualMemoization(func: HIRFunction): void {
       markInstructionIds(func.body);
     }
   }
+
+  return errors.asResult();
 }
 
 function findOptionalPlaces(fn: HIRFunction): Set<IdentifierId> {
@@ -530,3 +626,17 @@ function findOptionalPlaces(fn: HIRFunction): Set<IdentifierId> {
   }
   return optionals;
 }
+
+function hasNonVoidReturn(func: HIRFunction): boolean {
+  for (const [, block] of func.body.blocks) {
+    if (block.terminal.kind === 'return') {
+      if (
+        block.terminal.returnVariant === 'Explicit' ||
+        block.terminal.returnVariant === 'Implicit'
+      ) {
+        return true;
+      }
+    }
+  }
+  return false;
+}

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

@@ -447,23 +447,22 @@ function applySignature(
               reason: value.reason,
               context: new Set(),
             });
-            const message =
+            const variable =
               effect.value.identifier.name !== null &&
               effect.value.identifier.name.kind === 'named'
-                ? `\`${effect.value.identifier.name.value}\` cannot be modified`
-                : 'This value cannot be modified';
+                ? `\`${effect.value.identifier.name.value}\``
+                : 'value';
             effects.push({
               kind: 'MutateFrozen',
               place: effect.value,
               error: CompilerDiagnostic.create({
                 severity: ErrorSeverity.InvalidReact,
                 category: 'This value cannot be modified',
-                description: reason,
-                suggestions: null,
+                description: `${reason}.`,
               }).withDetail({
                 kind: 'error',
                 loc: effect.value.loc,
-                message,
+                message: `${variable} cannot be modified`,
               }),
             });
           }
@@ -692,6 +691,7 @@ function applyEffect(
       }
       break;
     }
+    case 'MaybeAlias':
     case 'Alias':
     case 'Capture': {
       CompilerError.invariant(
@@ -956,7 +956,7 @@ function applyEffect(
             context,
             state,
             // OK: recording information flow
-            {kind: 'Alias', from: operand, into: effect.into},
+            {kind: 'MaybeAlias', from: operand, into: effect.into},
             initialized,
             effects,
           );
@@ -1018,30 +1018,30 @@ function applyEffect(
             effect.value.identifier.declarationId,
           )
         ) {
-          const description =
+          const variable =
             effect.value.identifier.name !== null &&
             effect.value.identifier.name.kind === 'named'
-              ? `Variable \`${effect.value.identifier.name.value}\``
-              : 'This variable';
+              ? `\`${effect.value.identifier.name.value}\``
+              : null;
           const hoistedAccess = context.hoistedContextDeclarations.get(
             effect.value.identifier.declarationId,
           );
           const diagnostic = CompilerDiagnostic.create({
             severity: ErrorSeverity.InvalidReact,
             category: 'Cannot access variable before it is declared',
-            description: `${description} is accessed before it is declared, which prevents the earlier access from updating when this value changes over time`,
+            description: `${variable ?? 'This variable'} is accessed before it is declared, which prevents the earlier access from updating when this value changes over time.`,
           });
           if (hoistedAccess != null && hoistedAccess.loc != effect.value.loc) {
             diagnostic.withDetail({
               kind: 'error',
               loc: hoistedAccess.loc,
-              message: 'Variable accessed before it is declared',
+              message: `${variable ?? 'variable'} accessed before it is declared`,
             });
           }
           diagnostic.withDetail({
             kind: 'error',
             loc: effect.value.loc,
-            message: 'The variable is declared here',
+            message: `${variable ?? 'variable'} is declared here`,
           });
 
           applyEffect(
@@ -1061,11 +1061,11 @@ function applyEffect(
             reason: value.reason,
             context: new Set(),
           });
-          const message =
+          const variable =
             effect.value.identifier.name !== null &&
             effect.value.identifier.name.kind === 'named'
-              ? `\`${effect.value.identifier.name.value}\` cannot be modified`
-              : 'This value cannot be modified';
+              ? `\`${effect.value.identifier.name.value}\``
+              : 'value';
           applyEffect(
             context,
             state,
@@ -1078,11 +1078,11 @@ function applyEffect(
               error: CompilerDiagnostic.create({
                 severity: ErrorSeverity.InvalidReact,
                 category: 'This value cannot be modified',
-                description: reason,
+                description: `${reason}.`,
               }).withDetail({
                 kind: 'error',
                 loc: effect.value.loc,
-                message,
+                message: `${variable} cannot be modified`,
               }),
             },
             initialized,
@@ -1324,7 +1324,7 @@ class InferenceState {
             return 'mutate-global';
           }
           case ValueKind.MaybeFrozen: {
-            return 'none';
+            return 'mutate-frozen';
           }
           default: {
             assertExhaustive(kind, `Unexpected kind ${kind}`);
@@ -2002,6 +2002,7 @@ function computeSignatureForInstruction(
       break;
     }
     case 'StoreGlobal': {
+      const variable = `\`${value.name}\``;
       effects.push({
         kind: 'MutateGlobal',
         place: value.value,
@@ -2009,13 +2010,11 @@ function computeSignatureForInstruction(
           severity: ErrorSeverity.InvalidReact,
           category:
             'Cannot reassign variables declared outside of the component/hook',
-          description:
-            'Reassigning a variable declared outside of the component/hook 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)',
-          suggestions: null,
+          description: `Variable ${variable} is declared outside of the component/hook. Reassigning this value during render is a form of side effect, which can cause unpredictable behavior depending on when the component happens to re-render. If this variable is used in rendering, use useState instead. Otherwise, consider updating it in an effect. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#side-effects-must-run-outside-of-render)`,
         }).withDetail({
           kind: 'error',
           loc: instr.loc,
-          message: 'Cannot reassign variable',
+          message: `${variable} cannot be reassigned`,
         }),
       });
       effects.push({kind: 'Assign', from: value.value, into: lvalue});
@@ -2114,7 +2113,6 @@ function computeEffectsForLegacySignature(
             ? `\`${signature.canonicalName}\` is an impure function. `
             : '') +
           'Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent)',
-        suggestions: null,
       }).withDetail({
         kind: 'error',
         loc,
@@ -2379,6 +2377,7 @@ 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

@@ -160,6 +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 (
@@ -247,6 +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;
@@ -346,7 +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) {
@@ -567,7 +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;
@@ -585,6 +594,7 @@ class AliasingState {
       createdFrom: new Map(),
       captures: new Map(),
       aliases: new Map(),
+      maybeAliases: new Map(),
       edges: [],
       transitive: null,
       local: null,
@@ -630,6 +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];
@@ -673,22 +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;
@@ -724,13 +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') {
         /**
@@ -747,7 +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,
+          });
         }
       }
       /**
@@ -758,7 +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/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

@@ -237,6 +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,

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

@@ -352,6 +352,7 @@ function emitOutlinedFn(
     terminal: {
       id: makeInstructionId(0),
       kind: 'return',
+      returnVariant: 'Explicit',
       loc: GeneratedSource,
       value: instructions.at(-1)!.lvalue,
       effects: null,

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

@@ -14,6 +14,7 @@ import {
   Identifier,
   IdentifierId,
   Instruction,
+  InstructionKind,
   makePropertyLiteral,
   makeType,
   PropType,
@@ -194,12 +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) {
@@ -448,7 +466,36 @@ function* generateInstructionTypes(
       yield equation(left, returnType);
       break;
     }
-    case 'PropertyStore':
+    case 'PropertyStore': {
+      /**
+       * Infer types based on assignments to known object properties
+       * This is important for refs, where assignment to `<maybeRef>.current`
+       * can help us infer that an object itself is a ref
+       */
+      yield equation(
+        /**
+         * Our property type declarations are best-effort and we haven't tested
+         * using them to drive inference of rvalues from lvalues. We want to emit
+         * a Property type in order to infer refs from `.current` accesses, but
+         * stay conservative by not otherwise inferring anything about rvalues.
+         * So we use a dummy type here.
+         *
+         * TODO: consider using the rvalue type here
+         */
+        makeType(),
+        // unify() only handles properties in the second position
+        {
+          kind: 'Property',
+          objectType: value.object.identifier.type,
+          objectName: getName(names, value.object.identifier.id),
+          propertyName: {
+            kind: 'literal',
+            value: value.property,
+          },
+        },
+      );
+      break;
+    }
     case 'DeclareLocal':
     case 'RegExpLiteral':
     case 'MetaProperty':

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

@@ -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/Validation/ValidateLocalsNotReassignedAfterRender.ts

@@ -29,15 +29,20 @@ export function validateLocalsNotReassignedAfterRender(fn: HIRFunction): void {
   );
   if (reassignment !== null) {
     const errors = new CompilerError();
+    const variable =
+      reassignment.identifier.name != null &&
+      reassignment.identifier.name.kind === 'named'
+        ? `\`${reassignment.identifier.name.value}\``
+        : 'variable';
     errors.pushDiagnostic(
       CompilerDiagnostic.create({
         severity: ErrorSeverity.InvalidReact,
-        category: 'Cannot reassign a variable after render completes',
-        description: `Reassigning ${reassignment.identifier.name != null && reassignment.identifier.name.kind === 'named' ? `variable \`${reassignment.identifier.name.value}\`` : 'a variable'} after render has completed can cause inconsistent behavior on subsequent renders. Consider using state instead`,
+        category: 'Cannot reassign variable after render completes',
+        description: `Reassigning ${variable} after render has completed can cause inconsistent behavior on subsequent renders. Consider using state instead.`,
       }).withDetail({
         kind: 'error',
         loc: reassignment.loc,
-        message: 'Cannot reassign variable after render completes',
+        message: `Cannot reassign ${variable} after render completes`,
       }),
     );
     throw errors;
@@ -78,16 +83,25 @@ function getContextReassignment(
           // if the function or its depends reassign, propagate that fact on the lvalue
           if (reassignment !== null) {
             if (isAsync || value.loweredFunc.func.async) {
-              CompilerError.throwInvalidReact({
-                reason:
-                  'Reassigning a variable in an async function can cause inconsistent behavior on subsequent renders. Consider using state instead',
-                description:
-                  reassignment.identifier.name !== null &&
-                  reassignment.identifier.name.kind === 'named'
-                    ? `Variable \`${reassignment.identifier.name.value}\` cannot be reassigned after render`
-                    : '',
-                loc: reassignment.loc,
-              });
+              const errors = new CompilerError();
+              const variable =
+                reassignment.identifier.name !== null &&
+                reassignment.identifier.name.kind === 'named'
+                  ? `\`${reassignment.identifier.name.value}\``
+                  : 'variable';
+              errors.pushDiagnostic(
+                CompilerDiagnostic.create({
+                  severity: ErrorSeverity.InvalidReact,
+                  category: 'Cannot reassign variable in async function',
+                  description:
+                    'Reassigning a variable in an async function can cause inconsistent behavior on subsequent renders. Consider using state instead',
+                }).withDetail({
+                  kind: 'error',
+                  loc: reassignment.loc,
+                  message: `Cannot reassign ${variable}`,
+                }),
+              );
+              throw errors;
             }
             reassigningFunctions.set(lvalue.identifier.id, reassignment);
           }

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

@@ -57,22 +57,28 @@ export function validateNoFreezingKnownMutableFunctions(
     if (operand.effect === Effect.Freeze) {
       const effect = contextMutationEffects.get(operand.identifier.id);
       if (effect != null) {
+        const place = [...effect.places][0];
+        const variable =
+          place != null &&
+          place.identifier.name != null &&
+          place.identifier.name.kind === 'named'
+            ? `\`${place.identifier.name.value}\``
+            : 'a local variable';
         errors.pushDiagnostic(
           CompilerDiagnostic.create({
             severity: ErrorSeverity.InvalidReact,
             category: 'Cannot modify local variables after render completes',
-            description: `This argument is a function which may reassign or mutate local variables after render, which can cause inconsistent behavior on subsequent renders. Consider using state instead`,
+            description: `This argument is a function which may reassign or mutate ${variable} after render, which can cause inconsistent behavior on subsequent renders. Consider using state instead.`,
           })
             .withDetail({
               kind: 'error',
               loc: operand.loc,
-              message:
-                'This function may (indirectly) reassign or modify local variables after render',
+              message: `This function may (indirectly) reassign or modify ${variable} after render`,
             })
             .withDetail({
               kind: 'error',
               loc: effect.loc,
-              message: 'This modifies a local variable',
+              message: `This modifies ${variable}`,
             }),
         );
       }

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

@@ -5,7 +5,11 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {CompilerError, ErrorSeverity} from '../CompilerError';
+import {
+  CompilerDiagnostic,
+  CompilerError,
+  ErrorSeverity,
+} from '../CompilerError';
 import {
   BlockId,
   HIRFunction,
@@ -385,28 +389,40 @@ function validateNoRefAccessInRenderImpl(
             const hookKind = getHookKindForType(fn.env, callee.identifier.type);
             let returnType: RefAccessType = {kind: 'None'};
             const fnType = env.get(callee.identifier.id);
+            let didError = false;
             if (fnType?.kind === 'Structure' && fnType.fn !== null) {
               returnType = fnType.fn.returnType;
               if (fnType.fn.readRefEffect) {
-                errors.push({
-                  severity: ErrorSeverity.InvalidReact,
-                  reason:
-                    'This function accesses a ref value (the `current` property), which may not be accessed during render. (https://react.dev/reference/react/useRef)',
-                  loc: callee.loc,
-                  description:
-                    callee.identifier.name !== null &&
-                    callee.identifier.name.kind === 'named'
-                      ? `Function \`${callee.identifier.name.value}\` accesses a ref`
-                      : null,
-                  suggestions: null,
-                });
+                didError = true;
+                errors.pushDiagnostic(
+                  CompilerDiagnostic.create({
+                    severity: ErrorSeverity.InvalidReact,
+                    category: 'Cannot access refs during render',
+                    description: ERROR_DESCRIPTION,
+                  }).withDetail({
+                    kind: 'error',
+                    loc: callee.loc,
+                    message: `This function accesses a ref value`,
+                  }),
+                );
               }
             }
-            for (const operand of eachInstructionValueOperand(instr.value)) {
-              if (hookKind != null) {
-                validateNoDirectRefValueAccess(errors, operand, env);
-              } else {
-                validateNoRefAccess(errors, env, operand, operand.loc);
+            if (!didError) {
+              /*
+               * If we already reported an error on this instruction, don't report
+               * duplicate errors
+               */
+              for (const operand of eachInstructionValueOperand(instr.value)) {
+                if (hookKind != null) {
+                  validateNoDirectRefValueAccess(errors, operand, env);
+                } else {
+                  validateNoRefPassedToFunction(
+                    errors,
+                    env,
+                    operand,
+                    operand.loc,
+                  );
+                }
               }
             }
             env.set(instr.lvalue.identifier.id, returnType);
@@ -449,7 +465,7 @@ function validateNoRefAccessInRenderImpl(
             ) {
               safeBlocks.delete(block.id);
             } else {
-              validateNoRefAccess(errors, env, instr.value.object, instr.loc);
+              validateNoRefUpdate(errors, env, instr.value.object, instr.loc);
             }
             for (const operand of eachInstructionValueOperand(instr.value)) {
               if (operand === instr.value.object) {
@@ -583,18 +599,17 @@ function destructure(
 
 function guardCheck(errors: CompilerError, operand: Place, env: Env): void {
   if (env.get(operand.identifier.id)?.kind === 'Guard') {
-    errors.push({
-      severity: ErrorSeverity.InvalidReact,
-      reason:
-        'Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)',
-      loc: operand.loc,
-      description:
-        operand.identifier.name !== null &&
-        operand.identifier.name.kind === 'named'
-          ? `Cannot access ref value \`${operand.identifier.name.value}\``
-          : null,
-      suggestions: null,
-    });
+    errors.pushDiagnostic(
+      CompilerDiagnostic.create({
+        severity: ErrorSeverity.InvalidReact,
+        category: 'Cannot access refs during render',
+        description: ERROR_DESCRIPTION,
+      }).withDetail({
+        kind: 'error',
+        loc: operand.loc,
+        message: `Cannot access ref value during render`,
+      }),
+    );
   }
 }
 
@@ -608,22 +623,21 @@ function validateNoRefValueAccess(
     type?.kind === 'RefValue' ||
     (type?.kind === 'Structure' && type.fn?.readRefEffect)
   ) {
-    errors.push({
-      severity: ErrorSeverity.InvalidReact,
-      reason:
-        'Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)',
-      loc: (type.kind === 'RefValue' && type.loc) || operand.loc,
-      description:
-        operand.identifier.name !== null &&
-        operand.identifier.name.kind === 'named'
-          ? `Cannot access ref value \`${operand.identifier.name.value}\``
-          : null,
-      suggestions: null,
-    });
+    errors.pushDiagnostic(
+      CompilerDiagnostic.create({
+        severity: ErrorSeverity.InvalidReact,
+        category: 'Cannot access refs during render',
+        description: ERROR_DESCRIPTION,
+      }).withDetail({
+        kind: 'error',
+        loc: (type.kind === 'RefValue' && type.loc) || operand.loc,
+        message: `Cannot access ref value during render`,
+      }),
+    );
   }
 }
 
-function validateNoRefAccess(
+function validateNoRefPassedToFunction(
   errors: CompilerError,
   env: Env,
   operand: Place,
@@ -635,18 +649,43 @@ function validateNoRefAccess(
     type?.kind === 'RefValue' ||
     (type?.kind === 'Structure' && type.fn?.readRefEffect)
   ) {
-    errors.push({
-      severity: ErrorSeverity.InvalidReact,
-      reason:
-        'Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)',
-      loc: (type.kind === 'RefValue' && type.loc) || loc,
-      description:
-        operand.identifier.name !== null &&
-        operand.identifier.name.kind === 'named'
-          ? `Cannot access ref value \`${operand.identifier.name.value}\``
-          : null,
-      suggestions: null,
-    });
+    errors.pushDiagnostic(
+      CompilerDiagnostic.create({
+        severity: ErrorSeverity.InvalidReact,
+        category: 'Cannot access refs during render',
+        description: ERROR_DESCRIPTION,
+      }).withDetail({
+        kind: 'error',
+        loc: (type.kind === 'RefValue' && type.loc) || loc,
+        message: `Passing a ref to a function may read its value during render`,
+      }),
+    );
+  }
+}
+
+function validateNoRefUpdate(
+  errors: CompilerError,
+  env: Env,
+  operand: Place,
+  loc: SourceLocation,
+): void {
+  const type = destructure(env.get(operand.identifier.id));
+  if (
+    type?.kind === 'Ref' ||
+    type?.kind === 'RefValue' ||
+    (type?.kind === 'Structure' && type.fn?.readRefEffect)
+  ) {
+    errors.pushDiagnostic(
+      CompilerDiagnostic.create({
+        severity: ErrorSeverity.InvalidReact,
+        category: 'Cannot access refs during render',
+        description: ERROR_DESCRIPTION,
+      }).withDetail({
+        kind: 'error',
+        loc: (type.kind === 'RefValue' && type.loc) || loc,
+        message: `Cannot update ref during render`,
+      }),
+    );
   }
 }
 
@@ -657,17 +696,22 @@ function validateNoDirectRefValueAccess(
 ): void {
   const type = destructure(env.get(operand.identifier.id));
   if (type?.kind === 'RefValue') {
-    errors.push({
-      severity: ErrorSeverity.InvalidReact,
-      reason:
-        'Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)',
-      loc: type.loc ?? operand.loc,
-      description:
-        operand.identifier.name !== null &&
-        operand.identifier.name.kind === 'named'
-          ? `Cannot access ref value \`${operand.identifier.name.value}\``
-          : null,
-      suggestions: null,
-    });
+    errors.pushDiagnostic(
+      CompilerDiagnostic.create({
+        severity: ErrorSeverity.InvalidReact,
+        category: 'Cannot access refs during render',
+        description: ERROR_DESCRIPTION,
+      }).withDetail({
+        kind: 'error',
+        loc: type.loc ?? operand.loc,
+        message: `Cannot access ref value during render`,
+      }),
+    );
   }
 }
+
+const ERROR_DESCRIPTION =
+  'React refs are values that are not needed for rendering. Refs should only be accessed ' +
+  'outside of render, such as in event handlers or effects. ' +
+  'Accessing a ref value (the `current` property) during render can cause your component ' +
+  'not to update as expected (https://react.dev/reference/react/useRef)';

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

@@ -97,16 +97,21 @@ export function validateNoSetStateInEffects(
                 errors.pushDiagnostic(
                   CompilerDiagnostic.create({
                     category:
-                      'Calling setState within an effect can trigger cascading renders',
+                      'Calling setState synchronously within an effect can trigger cascading renders',
                     description:
-                      'Calling setState directly within a useEffect causes cascading renders that can hurt performance, and is not recommended. Consider alternatives to useEffect. (https://react.dev/learn/you-might-not-need-an-effect)',
+                      'Effects are intended to synchronize state between React and external systems such as manually updating the DOM, state management libraries, or other platform APIs. ' +
+                      'In general, the body of an effect should do one or both of the following:\n' +
+                      '* Update external systems with the latest state from React.\n' +
+                      '* Subscribe for updates from some external system, calling setState in a callback function when external state changes.\n\n' +
+                      'Calling setState synchronously within an effect body causes cascading renders that can hurt performance, and is not recommended. ' +
+                      '(https://react.dev/learn/you-might-not-need-an-effect)',
                     severity: ErrorSeverity.InvalidReact,
                     suggestions: null,
                   }).withDetail({
                     kind: 'error',
                     loc: setState.loc,
                     message:
-                      'Avoid calling setState() in the top-level of an effect',
+                      'Avoid calling setState() directly within an effect',
                   }),
                 );
               }

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

@@ -5,7 +5,11 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {CompilerError, ErrorSeverity} from '../CompilerError';
+import {
+  CompilerDiagnostic,
+  CompilerError,
+  ErrorSeverity,
+} from '../CompilerError';
 import {HIRFunction, IdentifierId, SourceLocation} from '../HIR';
 import {Result} from '../Utils/Result';
 
@@ -59,20 +63,23 @@ export function validateStaticComponents(
               value.tag.identifier.id,
             );
             if (location != null) {
-              error.push({
-                reason: `Components created during render will reset their state each time they are created. Declare components outside of render. `,
-                severity: ErrorSeverity.InvalidReact,
-                loc: value.tag.loc,
-                description: null,
-                suggestions: null,
-              });
-              error.push({
-                reason: `The component may be created during render`,
-                severity: ErrorSeverity.InvalidReact,
-                loc: location,
-                description: null,
-                suggestions: null,
-              });
+              error.pushDiagnostic(
+                CompilerDiagnostic.create({
+                  severity: ErrorSeverity.InvalidReact,
+                  category: 'Cannot create components during render',
+                  description: `Components created during render will reset their state each time they are created. Declare components outside of render. `,
+                })
+                  .withDetail({
+                    kind: 'error',
+                    loc: value.tag.loc,
+                    message: 'This component is created during render',
+                  })
+                  .withDetail({
+                    kind: 'error',
+                    loc: location,
+                    message: 'The component is created during render here',
+                  }),
+              );
             }
           }
         }

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

@@ -82,7 +82,7 @@ export function validateUseMemo(fn: HIRFunction): Result<void, CompilerError> {
               }).withDetail({
                 kind: 'error',
                 loc,
-                message: '',
+                message: 'Callbacks with parameters are not supported',
               }),
             );
           }
@@ -92,9 +92,9 @@ export function validateUseMemo(fn: HIRFunction): Result<void, CompilerError> {
               CompilerDiagnostic.create({
                 severity: ErrorSeverity.InvalidReact,
                 category:
-                  'useMemo callbacks may not be async or generator functions',
+                  'useMemo() callbacks may not be async or generator functions',
                 description:
-                  'useMemo() callbacks are called once and must synchronously return a value',
+                  'useMemo() callbacks are called once and must synchronously return a value.',
                 suggestions: null,
               }).withDetail({
                 kind: 'error',

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__/fixtures/compiler/error._todo.computed-lval-in-destructure.expect.md

@@ -16,6 +16,7 @@ function Component(props) {
 
 ```
 Found 1 error:
+
 Todo: (BuildHIR::lowerAssignment) Handle computed properties in ObjectPattern
 
 error._todo.computed-lval-in-destructure.ts:3:9
@@ -26,8 +27,6 @@ error._todo.computed-lval-in-destructure.ts:3:9
   4 |
   5 |   return x;
   6 | }
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.assign-global-in-component-tag-function.expect.md

@@ -16,15 +16,16 @@ function Component() {
 
 ```
 Found 1 error:
+
 Error: Cannot reassign variables declared outside of the component/hook
 
-Reassigning a variable declared outside of the component/hook 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)
+Variable `someGlobal` is declared outside of the component/hook. 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)
 
 error.assign-global-in-component-tag-function.ts:3:4
   1 | function Component() {
   2 |   const Foo = () => {
 > 3 |     someGlobal = true;
-    |     ^^^^^^^^^^ Cannot reassign variable
+    |     ^^^^^^^^^^ `someGlobal` cannot be reassigned
   4 |   };
   5 |   return <Foo />;
   6 | }

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.assign-global-in-jsx-children.expect.md

@@ -19,15 +19,16 @@ function Component() {
 
 ```
 Found 1 error:
+
 Error: Cannot reassign variables declared outside of the component/hook
 
-Reassigning a variable declared outside of the component/hook 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)
+Variable `someGlobal` is declared outside of the component/hook. 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)
 
 error.assign-global-in-jsx-children.ts:3:4
   1 | function Component() {
   2 |   const foo = () => {
 > 3 |     someGlobal = true;
-    |     ^^^^^^^^^^ Cannot reassign variable
+    |     ^^^^^^^^^^ `someGlobal` cannot be reassigned
   4 |   };
   5 |   // Children are generally access/called during render, so
   6 |   // modifying a global in a children function is almost

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.assign-global-in-jsx-spread-attribute.expect.md

@@ -17,6 +17,7 @@ function Component() {
 
 ```
 Found 1 error:
+
 Error: 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.assign-global-in-jsx-spread-attribute.ts:4:4
@@ -27,8 +28,6 @@ error.assign-global-in-jsx-spread-attribute.ts:4:4
   5 |   };
   6 |   return <div {...foo} />;
   7 | }
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.bailout-on-flow-suppression.expect.md

@@ -17,20 +17,19 @@ function Foo(props) {
 
 ```
 Found 1 error:
-Error: React Compiler has skipped optimizing this component because one or more React rule violations were reported by Flow. React Compiler only works when your components follow all the rules of React, disabling them may result in unexpected or incorrect behavior
 
-$FlowFixMe[react-rule-hook].
+Error: React Compiler has skipped optimizing this component because one or more React rule violations were reported by Flow
+
+React Compiler only works when your components follow all the rules of React, disabling them may result in unexpected or incorrect behavior. Found suppression `$FlowFixMe[react-rule-hook]`
 
 error.bailout-on-flow-suppression.ts:4:2
   2 |
   3 | function Foo(props) {
 > 4 |   // $FlowFixMe[react-rule-hook]
-    |   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ React Compiler has skipped optimizing this component because one or more React rule violations were reported by Flow. React Compiler only works when your components follow all the rules of React, disabling them may result in unexpected or incorrect behavior
+    |   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Found React rule suppression
   5 |   useX();
   6 |   return null;
   7 | }
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.bailout-on-suppression-of-custom-rule.expect.md

@@ -20,34 +20,32 @@ function lowercasecomponent() {
 
 ```
 Found 2 errors:
-Error: React Compiler has skipped optimizing this component because one or more React ESLint rules were disabled. React Compiler only works when your components follow all the rules of React, disabling them may result in unexpected or incorrect behavior
 
-eslint-disable my-app/react-rule.
+Error: React Compiler has skipped optimizing this component because one or more React ESLint rules were disabled
+
+React Compiler only works when your components follow all the rules of React, disabling them may result in unexpected or incorrect behavior. Found suppression `eslint-disable my-app/react-rule`
 
 error.bailout-on-suppression-of-custom-rule.ts:3:0
   1 | // @eslintSuppressionRules:["my-app","react-rule"]
   2 |
 > 3 | /* eslint-disable my-app/react-rule */
-    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ React Compiler has skipped optimizing this component because one or more React ESLint rules were disabled. React Compiler only works when your components follow all the rules of React, disabling them may result in unexpected or incorrect behavior
+    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Found React rule suppression
   4 | function lowercasecomponent() {
   5 |   'use forget';
   6 |   const x = [];
 
+Error: React Compiler has skipped optimizing this component because one or more React ESLint rules were disabled
 
-Error: React Compiler has skipped optimizing this component because one or more React ESLint rules were disabled. React Compiler only works when your components follow all the rules of React, disabling them may result in unexpected or incorrect behavior
-
-eslint-disable-next-line my-app/react-rule.
+React Compiler only works when your components follow all the rules of React, disabling them may result in unexpected or incorrect behavior. Found suppression `eslint-disable-next-line my-app/react-rule`
 
 error.bailout-on-suppression-of-custom-rule.ts:7:2
    5 |   'use forget';
    6 |   const x = [];
 >  7 |   // eslint-disable-next-line my-app/react-rule
-     |   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ React Compiler has skipped optimizing this component because one or more React ESLint rules were disabled. React Compiler only works when your components follow all the rules of React, disabling them may result in unexpected or incorrect behavior
+     |   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Found React rule suppression
    8 |   return <div>{x}</div>;
    9 | }
   10 | /* eslint-enable my-app/react-rule */
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.bug-old-inference-false-positive-ref-validation-in-use-effect.expect.md

@@ -37,9 +37,10 @@ function Component() {
 
 ```
 Found 1 error:
+
 Error: Cannot modify local variables after render completes
 
-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
+This argument is a function which may reassign or mutate a local variable after render, which can cause inconsistent behavior on subsequent renders. Consider using state instead.
 
 error.bug-old-inference-false-positive-ref-validation-in-use-effect.ts:20:12
   18 |   );
@@ -53,7 +54,7 @@ error.bug-old-inference-false-positive-ref-validation-in-use-effect.ts:20:12
 > 23 |     }
      | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 > 24 |   }, [update]);
-     | ^^^^ This function may (indirectly) reassign or modify local variables after render
+     | ^^^^ This function may (indirectly) reassign or modify a local variable after render
   25 |
   26 |   return 'ok';
   27 | }

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.call-args-destructuring-asignment-complex.expect.md

@@ -15,6 +15,7 @@ function Component(props) {
 
 ```
 Found 1 error:
+
 Invariant: Const declaration cannot be referenced as an expression
 
 error.call-args-destructuring-asignment-complex.ts:3:9
@@ -25,8 +26,6 @@ error.call-args-destructuring-asignment-complex.ts:3:9
   4 |   return x;
   5 | }
   6 |
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.capitalized-function-call-aliased.expect.md

@@ -15,6 +15,7 @@ function Foo() {
 
 ```
 Found 1 error:
+
 Error: 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
 
 Bar may be a component..
@@ -26,8 +27,6 @@ error.capitalized-function-call-aliased.ts:4:2
     |   ^^^ 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
   5 | }
   6 |
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.capitalized-function-call.expect.md

@@ -16,6 +16,7 @@ function Component() {
 
 ```
 Found 1 error:
+
 Error: 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
 
 SomeFunc may be a component..
@@ -28,8 +29,6 @@ error.capitalized-function-call.ts:3:12
   4 |
   5 |   return x;
   6 | }
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.capitalized-method-call.expect.md

@@ -16,6 +16,7 @@ function Component() {
 
 ```
 Found 1 error:
+
 Error: 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
 
 SomeFunc may be a component..
@@ -28,8 +29,6 @@ error.capitalized-method-call.ts:3:12
   4 |
   5 |   return x;
   6 | }
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.capture-ref-for-mutation.expect.md

@@ -32,55 +32,33 @@ export const FIXTURE_ENTRYPOINT = {
 ## Error
 
 ```
-Found 4 errors:
-Error: This function accesses a ref value (the `current` property), which may not be accessed during render. (https://react.dev/reference/react/useRef)
+Found 2 errors:
+
+Error: Cannot access refs during render
+
+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)
 
 error.capture-ref-for-mutation.ts:12:13
   10 |   };
   11 |   const moveLeft = {
 > 12 |     handler: handleKey('left')(),
-     |              ^^^^^^^^^^^^^^^^^ This function accesses a ref value (the `current` property), which may not be accessed during render. (https://react.dev/reference/react/useRef)
+     |              ^^^^^^^^^^^^^^^^^ This function accesses a ref value
   13 |   };
   14 |   const moveRight = {
   15 |     handler: handleKey('right')(),
 
+Error: Cannot access refs during render
 
-Error: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)
-
-error.capture-ref-for-mutation.ts:12:13
-  10 |   };
-  11 |   const moveLeft = {
-> 12 |     handler: handleKey('left')(),
-     |              ^^^^^^^^^^^^^^^^^ Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)
-  13 |   };
-  14 |   const moveRight = {
-  15 |     handler: handleKey('right')(),
-
-
-Error: This function accesses a ref value (the `current` property), which may not be accessed during render. (https://react.dev/reference/react/useRef)
+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)
 
 error.capture-ref-for-mutation.ts:15:13
   13 |   };
   14 |   const moveRight = {
 > 15 |     handler: handleKey('right')(),
-     |              ^^^^^^^^^^^^^^^^^^ This function accesses a ref value (the `current` property), which may not be accessed during render. (https://react.dev/reference/react/useRef)
+     |              ^^^^^^^^^^^^^^^^^^ This function accesses a ref value
   16 |   };
   17 |   return [moveLeft, moveRight];
   18 | }
-
-
-Error: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)
-
-error.capture-ref-for-mutation.ts:15:13
-  13 |   };
-  14 |   const moveRight = {
-> 15 |     handler: handleKey('right')(),
-     |              ^^^^^^^^^^^^^^^^^^ Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)
-  16 |   };
-  17 |   return [moveLeft, moveRight];
-  18 | }
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.conditional-hook-unknown-hook-react-namespace.expect.md

@@ -17,6 +17,7 @@ function Component(props) {
 
 ```
 Found 1 error:
+
 Error: 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)
 
 error.conditional-hook-unknown-hook-react-namespace.ts:4:8
@@ -27,8 +28,6 @@ error.conditional-hook-unknown-hook-react-namespace.ts:4:8
   5 |   }
   6 |   return x;
   7 | }
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.conditional-hooks-as-method-call.expect.md

@@ -17,6 +17,7 @@ function Component(props) {
 
 ```
 Found 1 error:
+
 Error: 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)
 
 error.conditional-hooks-as-method-call.ts:4:8
@@ -27,8 +28,6 @@ error.conditional-hooks-as-method-call.ts:4:8
   5 |   }
   6 |   return x;
   7 | }
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.context-variable-only-chained-assign.expect.md

@@ -29,15 +29,16 @@ export const FIXTURE_ENTRYPOINT = {
 
 ```
 Found 1 error:
-Error: Cannot reassign a variable after render completes
 
-Reassigning variable `x` after render has completed can cause inconsistent behavior on subsequent renders. Consider using state instead
+Error: Cannot reassign variable after render completes
+
+Reassigning `x` after render has completed can cause inconsistent behavior on subsequent renders. Consider using state instead.
 
 error.context-variable-only-chained-assign.ts:10:19
    8 |   };
    9 |   const fn2 = () => {
 > 10 |     const copy2 = (x = 4);
-     |                    ^ Cannot reassign variable after render completes
+     |                    ^ Cannot reassign `x` after render completes
   11 |     return [invoke(fn1), copy2, identity(copy2)];
   12 |   };
   13 |   return invoke(fn2);

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.declare-reassign-variable-in-function-declaration.expect.md

@@ -18,15 +18,16 @@ function Component() {
 
 ```
 Found 1 error:
-Error: Cannot reassign a variable after render completes
 
-Reassigning variable `x` after render has completed can cause inconsistent behavior on subsequent renders. Consider using state instead
+Error: Cannot reassign variable after render completes
+
+Reassigning `x` after render has completed can cause inconsistent behavior on subsequent renders. Consider using state instead.
 
 error.declare-reassign-variable-in-function-declaration.ts:4:4
   2 |   let x = null;
   3 |   function foo() {
 > 4 |     x = 9;
-    |     ^ Cannot reassign variable after render completes
+    |     ^ Cannot reassign `x` after render completes
   5 |   }
   6 |   const y = bar(foo);
   7 |   return <Child y={y} />;

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.default-param-accesses-local.expect.md

@@ -23,6 +23,7 @@ export const FIXTURE_ENTRYPOINT = {
 
 ```
 Found 1 error:
+
 Todo: (BuildHIR::node.lowerReorderableExpression) Expression type `ArrowFunctionExpression` cannot be safely reordered
 
 error.default-param-accesses-local.ts:3:6
@@ -37,8 +38,6 @@ error.default-param-accesses-local.ts:3:6
   6 | ) {
   7 |   return y();
   8 | }
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.dont-hoist-inline-reference.expect.md

@@ -20,6 +20,7 @@ export const FIXTURE_ENTRYPOINT = {
 
 ```
 Found 1 error:
+
 Todo: [hoisting] EnterSSA: Expected identifier to be defined before being used
 
 Identifier x$1 is undefined.
@@ -32,8 +33,6 @@ error.dont-hoist-inline-reference.ts:3:2
   4 |   return x;
   5 | }
   6 |
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.emit-freeze-conflicting-global.expect.md

@@ -16,6 +16,7 @@ function useFoo(props) {
 
 ```
 Found 1 error:
+
 Todo: Encountered conflicting global in generated program
 
 Conflict from local binding __DEV__.
@@ -28,8 +29,6 @@ error.emit-freeze-conflicting-global.ts:3:8
   4 |   console.log(__DEV__);
   5 |   return foo(props.x);
   6 | }
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.function-expression-references-variable-its-assigned-to.expect.md

@@ -16,15 +16,16 @@ function Component() {
 
 ```
 Found 1 error:
-Error: Cannot reassign a variable after render completes
 
-Reassigning variable `callback` after render has completed can cause inconsistent behavior on subsequent renders. Consider using state instead
+Error: Cannot reassign variable after render completes
+
+Reassigning `callback` after render has completed can cause inconsistent behavior on subsequent renders. Consider using state instead.
 
 error.function-expression-references-variable-its-assigned-to.ts:3:4
   1 | function Component() {
   2 |   let callback = () => {
 > 3 |     callback = null;
-    |     ^^^^^^^^ Cannot reassign variable after render completes
+    |     ^^^^^^^^ Cannot reassign `callback` after render completes
   4 |   };
   5 |   return <div onClick={callback} />;
   6 | }

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.hoist-optional-member-expression-with-conditional-optional.expect.md

@@ -25,6 +25,7 @@ function Component(props) {
 
 ```
 Found 1 error:
+
 Memoization: Compilation skipped because existing memoization could not be preserved
 
 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. The inferred dependency was `props.items`, but the source dependencies were [props?.items, props.cond]. Inferred different dependency than source.

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.hoist-optional-member-expression-with-conditional.expect.md

@@ -25,6 +25,7 @@ function Component(props) {
 
 ```
 Found 1 error:
+
 Memoization: Compilation skipped because existing memoization could not be preserved
 
 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. The inferred dependency was `props.items`, but the source dependencies were [props?.items, props.cond]. Inferred different dependency than source.

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.hoisting-simple-function-declaration.expect.md

@@ -25,6 +25,7 @@ export const FIXTURE_ENTRYPOINT = {
 
 ```
 Found 1 error:
+
 Todo: Support functions with unreachable code that may contain hoisted declarations
 
 error.hoisting-simple-function-declaration.ts:6:2
@@ -39,8 +40,6 @@ error.hoisting-simple-function-declaration.ts:6:2
    9 | }
   10 |
   11 | export const FIXTURE_ENTRYPOINT = {
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.hook-call-freezes-captured-identifier.expect.md

@@ -30,15 +30,16 @@ export const FIXTURE_ENTRYPOINT = {
 
 ```
 Found 1 error:
+
 Error: This value cannot be modified
 
-Modifying a value previously passed as an argument to a hook is not allowed. Consider moving the modification before calling the hook
+Modifying a value previously passed as an argument to a hook is not allowed. Consider moving the modification before calling the hook.
 
 error.hook-call-freezes-captured-identifier.ts:13:2
   11 |   });
   12 |
 > 13 |   x.value += count;
-     |   ^ This value cannot be modified
+     |   ^ value cannot be modified
   14 |   return <Stringify x={x} cb={cb} />;
   15 | }
   16 |

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.hook-call-freezes-captured-memberexpr.expect.md

@@ -30,15 +30,16 @@ export const FIXTURE_ENTRYPOINT = {
 
 ```
 Found 1 error:
+
 Error: This value cannot be modified
 
-Modifying a value previously passed as an argument to a hook is not allowed. Consider moving the modification before calling the hook
+Modifying a value previously passed as an argument to a hook is not allowed. Consider moving the modification before calling the hook.
 
 error.hook-call-freezes-captured-memberexpr.ts:13:2
   11 |   });
   12 |
 > 13 |   x.value += count;
-     |   ^ This value cannot be modified
+     |   ^ value cannot be modified
   14 |   return <Stringify x={x} cb={cb} />;
   15 | }
   16 |

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.hook-property-load-local-hook.expect.md

@@ -24,6 +24,7 @@ export const FIXTURE_ENTRYPOINT = {
 
 ```
 Found 2 errors:
+
 Error: 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
 
 error.hook-property-load-local-hook.ts:7:12
@@ -35,7 +36,6 @@ error.hook-property-load-local-hook.ts:7:12
    9 | }
   10 |
 
-
 Error: 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
 
 error.hook-property-load-local-hook.ts:8:9
@@ -46,8 +46,6 @@ error.hook-property-load-local-hook.ts:8:9
    9 | }
   10 |
   11 | export const FIXTURE_ENTRYPOINT = {
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.hook-ref-value.expect.md

@@ -21,30 +21,32 @@ export const FIXTURE_ENTRYPOINT = {
 
 ```
 Found 2 errors:
-Error: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)
+
+Error: Cannot access refs during render
+
+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)
 
 error.hook-ref-value.ts:5:23
   3 | function Component(props) {
   4 |   const ref = useRef();
 > 5 |   useEffect(() => {}, [ref.current]);
-    |                        ^^^^^^^^^^^ Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)
+    |                        ^^^^^^^^^^^ Cannot access ref value during render
   6 | }
   7 |
   8 | export const FIXTURE_ENTRYPOINT = {
 
+Error: Cannot access refs during render
 
-Error: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)
+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)
 
 error.hook-ref-value.ts:5:23
   3 | function Component(props) {
   4 |   const ref = useRef();
 > 5 |   useEffect(() => {}, [ref.current]);
-    |                        ^^^^^^^^^^^ Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)
+    |                        ^^^^^^^^^^^ Cannot access ref value during render
   6 | }
   7 |
   8 | export const FIXTURE_ENTRYPOINT = {
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-ReactUseMemo-async-callback.expect.md

@@ -16,9 +16,10 @@ function component(a, b) {
 
 ```
 Found 1 error:
-Error: useMemo callbacks may not be async or generator functions
 
-useMemo() callbacks are called once and must synchronously return a value
+Error: useMemo() callbacks may not be async or generator functions
+
+useMemo() callbacks are called once and must synchronously return a value.
 
 error.invalid-ReactUseMemo-async-callback.ts:2:24
   1 | function component(a, b) {

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-access-ref-during-render.expect.md

@@ -16,18 +16,19 @@ function Component(props) {
 
 ```
 Found 1 error:
-Error: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)
+
+Error: Cannot access refs during render
+
+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)
 
 error.invalid-access-ref-during-render.ts:4:16
   2 | function Component(props) {
   3 |   const ref = useRef(null);
 > 4 |   const value = ref.current;
-    |                 ^^^^^^^^^^^ Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)
+    |                 ^^^^^^^^^^^ Cannot access ref value during render
   5 |   return value;
   6 | }
   7 |
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-aliased-ref-in-callback-invoked-during-render-.expect.md

@@ -20,17 +20,18 @@ function Component(props) {
 
 ```
 Found 1 error:
-Error: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)
+
+Error: Cannot access refs during render
+
+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)
 
 error.invalid-aliased-ref-in-callback-invoked-during-render-.ts:9:33
    7 |     return <Foo item={item} current={current} />;
    8 |   };
 >  9 |   return <Items>{props.items.map(item => renderItem(item))}</Items>;
-     |                                  ^^^^^^^^^^^^^^^^^^^^^^^^ Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)
+     |                                  ^^^^^^^^^^^^^^^^^^^^^^^^ Passing a ref to a function may read its value during render
   10 | }
   11 |
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-array-push-frozen.expect.md

@@ -16,15 +16,16 @@ function Component(props) {
 
 ```
 Found 1 error:
+
 Error: This value cannot be modified
 
-Modifying a value used previously in JSX is not allowed. Consider moving the modification before the JSX
+Modifying a value used previously in JSX is not allowed. Consider moving the modification before the JSX.
 
 error.invalid-array-push-frozen.ts:4:2
   2 |   const x = [];
   3 |   <div>{x}</div>;
 > 4 |   x.push(props.value);
-    |   ^ This value cannot be modified
+    |   ^ value cannot be modified
   5 |   return x;
   6 | }
   7 |

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-assign-current-inferred-ref-during-render.expect.md

@@ -0,0 +1,36 @@
+
+## Input
+
+```javascript
+// @flow @enableTreatRefLikeIdentifiersAsRefs @validateRefAccessDuringRender
+import {makeObject_Primitives} from 'shared-runtime';
+
+component Example() {
+  const fooRef = makeObject_Primitives();
+  fooRef.current = true;
+
+  return <Stringify foo={fooRef} />;
+}
+
+```
+
+
+## Error
+
+```
+Found 1 error:
+
+Error: Cannot access refs during render
+
+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)
+
+  4 | component Example() {
+  5 |   const fooRef = makeObject_Primitives();
+> 6 |   fooRef.current = true;
+    |   ^^^^^^^^^^^^^^ Cannot update ref during render
+  7 |
+  8 |   return <Stringify foo={fooRef} />;
+  9 | }
+```
+          
+      

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-assign-current-inferred-ref-during-render.js

@@ -0,0 +1,9 @@
+// @flow @enableTreatRefLikeIdentifiersAsRefs @validateRefAccessDuringRender
+import {makeObject_Primitives} from 'shared-runtime';
+
+component Example() {
+  const fooRef = makeObject_Primitives();
+  fooRef.current = true;
+
+  return <Stringify foo={fooRef} />;
+}

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-assign-hook-to-local.expect.md

@@ -15,6 +15,7 @@ function Component(props) {
 
 ```
 Found 1 error:
+
 Error: 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
 
 error.invalid-assign-hook-to-local.ts:2:12
@@ -24,8 +25,6 @@ error.invalid-assign-hook-to-local.ts:2:12
   3 |   const state = x(null);
   4 |   return state[0];
   5 | }
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-computed-store-to-frozen-value.expect.md

@@ -17,15 +17,16 @@ function Component(props) {
 
 ```
 Found 1 error:
+
 Error: This value cannot be modified
 
-Modifying a value used previously in JSX is not allowed. Consider moving the modification before the JSX
+Modifying a value used previously in JSX is not allowed. Consider moving the modification before the JSX.
 
 error.invalid-computed-store-to-frozen-value.ts:5:2
   3 |   // freeze
   4 |   <div>{x}</div>;
 > 5 |   x[0] = true;
-    |   ^ This value cannot be modified
+    |   ^ value cannot be modified
   6 |   return x;
   7 | }
   8 |

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-conditional-call-aliased-hook-import.expect.md

@@ -19,6 +19,7 @@ function Component(props) {
 
 ```
 Found 1 error:
+
 Error: 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)
 
 error.invalid-conditional-call-aliased-hook-import.ts:6:11
@@ -29,8 +30,6 @@ error.invalid-conditional-call-aliased-hook-import.ts:6:11
   7 |   }
   8 |   return data;
   9 | }
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-conditional-call-aliased-react-hook.expect.md

@@ -19,6 +19,7 @@ function Component(props) {
 
 ```
 Found 1 error:
+
 Error: 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)
 
 error.invalid-conditional-call-aliased-react-hook.ts:6:10
@@ -29,8 +30,6 @@ error.invalid-conditional-call-aliased-react-hook.ts:6:10
   7 |   }
   8 |   return s;
   9 | }
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-conditional-call-non-hook-imported-as-hook.expect.md

@@ -19,6 +19,7 @@ function Component(props) {
 
 ```
 Found 1 error:
+
 Error: 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)
 
 error.invalid-conditional-call-non-hook-imported-as-hook.ts:6:11
@@ -29,8 +30,6 @@ error.invalid-conditional-call-non-hook-imported-as-hook.ts:6:11
   7 |   }
   8 |   return data;
   9 | }
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-conditional-setState-in-useMemo.expect.md

@@ -23,6 +23,7 @@ function Component({item, cond}) {
 
 ```
 Found 2 errors:
+
 Error: Calling setState from useMemo may trigger an infinite loop
 
 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)
@@ -35,6 +36,7 @@ error.invalid-conditional-setState-in-useMemo.ts:7:6
    8 |       setState(0);
    9 |     }
   10 |   }, [cond, key, init]);
+
 Error: Calling setState from useMemo may trigger an infinite loop
 
 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)

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-delete-computed-property-of-frozen-value.expect.md

@@ -17,15 +17,16 @@ function Component(props) {
 
 ```
 Found 1 error:
+
 Error: This value cannot be modified
 
-Modifying a value used previously in JSX is not allowed. Consider moving the modification before the JSX
+Modifying a value used previously in JSX is not allowed. Consider moving the modification before the JSX.
 
 error.invalid-delete-computed-property-of-frozen-value.ts:5:9
   3 |   // freeze
   4 |   <div>{x}</div>;
 > 5 |   delete x[y];
-    |          ^ This value cannot be modified
+    |          ^ value cannot be modified
   6 |   return x;
   7 | }
   8 |

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-delete-property-of-frozen-value.expect.md

@@ -17,15 +17,16 @@ function Component(props) {
 
 ```
 Found 1 error:
+
 Error: This value cannot be modified
 
-Modifying a value used previously in JSX is not allowed. Consider moving the modification before the JSX
+Modifying a value used previously in JSX is not allowed. Consider moving the modification before the JSX.
 
 error.invalid-delete-property-of-frozen-value.ts:5:9
   3 |   // freeze
   4 |   <div>{x}</div>;
 > 5 |   delete x.y;
-    |          ^ This value cannot be modified
+    |          ^ value cannot be modified
   6 |   return x;
   7 | }
   8 |

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-destructure-assignment-to-global.expect.md

@@ -14,14 +14,15 @@ function useFoo(props) {
 
 ```
 Found 1 error:
+
 Error: Cannot reassign variables declared outside of the component/hook
 
-Reassigning a variable declared outside of the component/hook 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)
+Variable `x` is declared outside of the component/hook. 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)
 
 error.invalid-destructure-assignment-to-global.ts:2:3
   1 | function useFoo(props) {
 > 2 |   [x] = props;
-    |    ^ Cannot reassign variable
+    |    ^ `x` cannot be reassigned
   3 |   return {x};
   4 | }
   5 |

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-destructure-to-local-global-variables.expect.md

@@ -16,15 +16,16 @@ function Component(props) {
 
 ```
 Found 1 error:
+
 Error: Cannot reassign variables declared outside of the component/hook
 
-Reassigning a variable declared outside of the component/hook 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)
+Variable `b` is declared outside of the component/hook. 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)
 
 error.invalid-destructure-to-local-global-variables.ts:3:6
   1 | function Component(props) {
   2 |   let a;
 > 3 |   [a, b] = props.value;
-    |       ^ Cannot reassign variable
+    |       ^ `b` cannot be reassigned
   4 |
   5 |   return [a, b];
   6 | }

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-disallow-mutating-ref-in-render.expect.md

@@ -17,18 +17,19 @@ function Component() {
 
 ```
 Found 1 error:
-Error: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)
+
+Error: Cannot access refs during render
+
+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)
 
 error.invalid-disallow-mutating-ref-in-render.ts:4:2
   2 | function Component() {
   3 |   const ref = useRef(null);
 > 4 |   ref.current = false;
-    |   ^^^^^^^^^^^ Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)
+    |   ^^^^^^^^^^^ Cannot update ref during render
   5 |
   6 |   return <button ref={ref} />;
   7 | }
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-disallow-mutating-refs-in-render-transitive.expect.md

@@ -21,31 +21,20 @@ function Component() {
 ## Error
 
 ```
-Found 2 errors:
-Error: This function accesses a ref value (the `current` property), which may not be accessed during render. (https://react.dev/reference/react/useRef)
+Found 1 error:
+
+Error: Cannot access refs during render
+
+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)
 
 error.invalid-disallow-mutating-refs-in-render-transitive.ts:9:2
    7 |   };
    8 |   const changeRef = setRef;
 >  9 |   changeRef();
-     |   ^^^^^^^^^ This function accesses a ref value (the `current` property), which may not be accessed during render. (https://react.dev/reference/react/useRef)
+     |   ^^^^^^^^^ This function accesses a ref value
   10 |
   11 |   return <button ref={ref} />;
   12 | }
-
-
-Error: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)
-
-error.invalid-disallow-mutating-refs-in-render-transitive.ts:9:2
-   7 |   };
-   8 |   const changeRef = setRef;
->  9 |   changeRef();
-     |   ^^^^^^^^^ Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)
-  10 |
-  11 |   return <button ref={ref} />;
-  12 | }
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-eval-unsupported.expect.md

@@ -14,6 +14,7 @@ function Component(props) {
 
 ```
 Found 1 error:
+
 Error: The 'eval' function is not supported
 
 Eval is an anti-pattern in JavaScript, and the code executed cannot be evaluated by React Compiler.
@@ -25,8 +26,6 @@ error.invalid-eval-unsupported.ts:2:2
   3 |   return <div />;
   4 | }
   5 |
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-function-expression-mutates-immutable-value.expect.md

@@ -19,9 +19,10 @@ function Component(props) {
 
 ```
 Found 1 error:
+
 Error: This value cannot be modified
 
-Modifying a value returned from 'useState()', which should not be modified directly. Use the setter function to update instead
+Modifying a value returned from 'useState()', which should not be modified directly. Use the setter function to update instead.
 
 error.invalid-function-expression-mutates-immutable-value.ts:5:4
   3 |   const onChange = e => {

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-global-reassignment-indirect.expect.md

@@ -36,15 +36,16 @@ export const FIXTURE_ENTRYPOINT = {
 
 ```
 Found 1 error:
+
 Error: Cannot reassign variables declared outside of the component/hook
 
-Reassigning a variable declared outside of the component/hook 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)
+Variable `someGlobal` is declared outside of the component/hook. 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)
 
 error.invalid-global-reassignment-indirect.ts:9:4
    7 |
    8 |   const setGlobal = () => {
 >  9 |     someGlobal = true;
-     |     ^^^^^^^^^^ Cannot reassign variable
+     |     ^^^^^^^^^^ `someGlobal` cannot be reassigned
   10 |   };
   11 |   const indirectSetGlobal = () => {
   12 |     setGlobal();

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-hoisting-setstate.expect.md

@@ -39,15 +39,16 @@ export const FIXTURE_ENTRYPOINT = {
 
 ```
 Found 1 error:
+
 Error: Cannot access variable before it is declared
 
-Variable `setState` is accessed before it is declared, which prevents the earlier access from updating when this value changes over time
+`setState` is accessed before it is declared, which prevents the earlier access from updating when this value changes over time.
 
 error.invalid-hoisting-setstate.ts:19:18
   17 |    * $2 = Function context=setState
   18 |    */
 > 19 |   useEffect(() => setState(2), []);
-     |                   ^^^^^^^^ Variable accessed before it is declared
+     |                   ^^^^^^^^ `setState` accessed before it is declared
   20 |
   21 |   const [state, setState] = useState(0);
   22 |   return <Stringify state={state} />;
@@ -56,7 +57,7 @@ error.invalid-hoisting-setstate.ts:21:16
   19 |   useEffect(() => setState(2), []);
   20 |
 > 21 |   const [state, setState] = useState(0);
-     |                 ^^^^^^^^ The variable is declared here
+     |                 ^^^^^^^^ `setState` is declared here
   22 |   return <Stringify state={state} />;
   23 | }
   24 |

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-hook-function-argument-mutates-local-variable.expect.md

@@ -18,9 +18,10 @@ function useFoo() {
 
 ```
 Found 1 error:
+
 Error: Cannot modify local variables after render completes
 
-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
+This argument is a function which may reassign or mutate `cache` after render, which can cause inconsistent behavior on subsequent renders. Consider using state instead.
 
 error.invalid-hook-function-argument-mutates-local-variable.ts:5:10
   3 | function useFoo() {
@@ -30,7 +31,7 @@ error.invalid-hook-function-argument-mutates-local-variable.ts:5:10
 > 6 |     cache.set('key', 'value');
     | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 > 7 |   });
-    | ^^^^ This function may (indirectly) reassign or modify local variables after render
+    | ^^^^ This function may (indirectly) reassign or modify `cache` after render
   8 | }
   9 |
 
@@ -38,7 +39,7 @@ error.invalid-hook-function-argument-mutates-local-variable.ts:6:4
   4 |   const cache = new Map();
   5 |   useHook(() => {
 > 6 |     cache.set('key', 'value');
-    |     ^^^^^ This modifies a local variable
+    |     ^^^^^ This modifies `cache`
   7 |   });
   8 | }
   9 |

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-impure-functions-in-render.expect.md

@@ -18,6 +18,7 @@ function Component() {
 
 ```
 Found 3 errors:
+
 Error: Cannot call impure function during render
 
 `Date.now` is an impure function. Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent)
@@ -30,6 +31,7 @@ error.invalid-impure-functions-in-render.ts:4:15
   5 |   const now = performance.now();
   6 |   const rand = Math.random();
   7 |   return <Foo date={date} now={now} rand={rand} />;
+
 Error: Cannot call impure function during render
 
 `performance.now` is an impure function. Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent)
@@ -42,6 +44,7 @@ error.invalid-impure-functions-in-render.ts:5:14
   6 |   const rand = Math.random();
   7 |   return <Foo date={date} now={now} rand={rand} />;
   8 | }
+
 Error: Cannot call impure function during render
 
 `Math.random` is an impure function. Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent)

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-jsx-captures-context-variable.expect.md

@@ -51,9 +51,10 @@ export const FIXTURE_ENTRYPOINT = {
 
 ```
 Found 1 error:
+
 Error: This value cannot be modified
 
-Modifying a value used previously in JSX is not allowed. Consider moving the modification before the JSX
+Modifying a value used previously in JSX is not allowed. Consider moving the modification before the JSX.
 
 error.invalid-jsx-captures-context-variable.ts:22:2
   20 |     />

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-mutate-after-aliased-freeze.expect.md

@@ -26,15 +26,16 @@ function Component(props) {
 
 ```
 Found 1 error:
+
 Error: This value cannot be modified
 
-Modifying a value used previously in JSX is not allowed. Consider moving the modification before the JSX
+Modifying a value used previously in JSX is not allowed. Consider moving the modification before the JSX.
 
 error.invalid-mutate-after-aliased-freeze.ts:13:2
   11 |   // y is MaybeFrozen at this point, since it may alias to x
   12 |   // (which is the above line freezes)
 > 13 |   y.push(props.p2);
-     |   ^ This value cannot be modified
+     |   ^ value cannot be modified
   14 |
   15 |   return <Component x={x} y={y} />;
   16 | }

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-mutate-after-freeze.expect.md

@@ -20,15 +20,16 @@ function Component(props) {
 
 ```
 Found 1 error:
+
 Error: This value cannot be modified
 
-Modifying a value used previously in JSX is not allowed. Consider moving the modification before the JSX
+Modifying a value used previously in JSX is not allowed. Consider moving the modification before the JSX.
 
 error.invalid-mutate-after-freeze.ts:7:2
    5 |
    6 |   // x is Frozen at this point
 >  7 |   x.push(props.p2);
-     |   ^ This value cannot be modified
+     |   ^ value cannot be modified
    8 |
    9 |   return <div>{_}</div>;
   10 | }

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-mutate-context-in-callback.expect.md

@@ -25,9 +25,10 @@ function Component(props) {
 
 ```
 Found 1 error:
+
 Error: This value cannot be modified
 
-Modifying a value returned from 'useContext()' is not allowed.
+Modifying a value returned from 'useContext()' is not allowed..
 
 error.invalid-mutate-context-in-callback.ts:12:4
   10 |   // independently

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-mutate-context.expect.md

@@ -15,15 +15,16 @@ function Component(props) {
 
 ```
 Found 1 error:
+
 Error: This value cannot be modified
 
-Modifying a value returned from 'useContext()' is not allowed.
+Modifying a value returned from 'useContext()' is not allowed..
 
 error.invalid-mutate-context.ts:3:2
   1 | function Component(props) {
   2 |   const context = useContext(FooContext);
 > 3 |   context.value = props.value;
-    |   ^^^^^^^ This value cannot be modified
+    |   ^^^^^^^ value cannot be modified
   4 |   return context.value;
   5 | }
   6 |

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-mutate-phi-which-could-be-frozen.expect.md

@@ -0,0 +1,39 @@
+
+## Input
+
+```javascript
+import {useHook} from 'shared-runtime';
+
+function Component(props) {
+  const frozen = useHook();
+  let x;
+  if (props.cond) {
+    x = frozen;
+  } else {
+    x = {};
+  }
+  x.property = true;
+}
+
+```
+
+
+## Error
+
+```
+Found 1 error:
+
+Error: This value cannot be modified
+
+Modifying a value returned from a hook is not allowed. Consider moving the modification into the hook where the value is constructed.
+
+error.invalid-mutate-phi-which-could-be-frozen.ts:11:2
+   9 |     x = {};
+  10 |   }
+> 11 |   x.property = true;
+     |   ^ value cannot be modified
+  12 | }
+  13 |
+```
+          
+      

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-mutate-phi-which-could-be-frozen.js

@@ -0,0 +1,12 @@
+import {useHook} from 'shared-runtime';
+
+function Component(props) {
+  const frozen = useHook();
+  let x;
+  if (props.cond) {
+    x = frozen;
+  } else {
+    x = {};
+  }
+  x.property = true;
+}

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-mutate-props-in-effect-fixpoint.expect.md

@@ -26,9 +26,10 @@ function Component(props) {
 
 ```
 Found 1 error:
+
 Error: This value cannot be modified
 
-Modifying component props or hook arguments is not allowed. Consider using a local variable instead
+Modifying component props or hook arguments is not allowed. Consider using a local variable instead.
 
 error.invalid-mutate-props-in-effect-fixpoint.ts:10:4
    8 |   let y = x;

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-mutate-props-via-for-of-iterator.expect.md

@@ -18,15 +18,16 @@ function Component(props) {
 
 ```
 Found 1 error:
+
 Error: This value cannot be modified
 
-Modifying component props or hook arguments is not allowed. Consider using a local variable instead
+Modifying component props or hook arguments is not allowed. Consider using a local variable instead.
 
 error.invalid-mutate-props-via-for-of-iterator.ts:4:4
   2 |   const items = [];
   3 |   for (const x of props.items) {
 > 4 |     x.modified = true;
-    |     ^ This value cannot be modified
+    |     ^ value cannot be modified
   5 |     items.push(x);
   6 |   }
   7 |   return items;

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-mutation-in-closure.expect.md

@@ -17,9 +17,10 @@ function useInvalidMutation(options) {
 
 ```
 Found 1 error:
+
 Error: This value cannot be modified
 
-Modifying component props or hook arguments is not allowed. Consider using a local variable instead
+Modifying component props or hook arguments is not allowed. Consider using a local variable instead.
 
 error.invalid-mutation-in-closure.ts:4:4
   2 |   function test() {

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-mutation-of-possible-props-phi-indirect.expect.md

@@ -20,9 +20,10 @@ function Component(props) {
 
 ```
 Found 1 error:
+
 Error: This value cannot be modified
 
-Modifying a variable defined outside a component or hook is not allowed. Consider using an effect
+Modifying a variable defined outside a component or hook is not allowed. Consider using an effect.
 
 error.invalid-mutation-of-possible-props-phi-indirect.ts:4:4
   2 |   let x = cond ? someGlobal : props.foo;

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-nested-function-reassign-local-variable-in-effect.expect.md

@@ -47,15 +47,16 @@ function Component() {
 
 ```
 Found 1 error:
-Error: Cannot reassign a variable after render completes
 
-Reassigning variable `local` after render has completed can cause inconsistent behavior on subsequent renders. Consider using state instead
+Error: Cannot reassign variable after render completes
+
+Reassigning `local` after render has completed can cause inconsistent behavior on subsequent renders. Consider using state instead.
 
 error.invalid-nested-function-reassign-local-variable-in-effect.ts:7:6
    5 |     // Create the reassignment function inside another function, then return it
    6 |     const reassignLocal = newValue => {
 >  7 |       local = newValue;
-     |       ^^^^^ Cannot reassign variable after render completes
+     |       ^^^^^ Cannot reassign `local` after render completes
    8 |     };
    9 |     return reassignLocal;
   10 |   };

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-non-imported-reanimated-shared-value-writes.expect.md

@@ -25,9 +25,10 @@ function SomeComponent() {
 
 ```
 Found 1 error:
+
 Error: This value cannot be modified
 
-Modifying a value returned from a hook is not allowed. Consider moving the modification into the hook where the value is constructed
+Modifying a value returned from a hook is not allowed. Consider moving the modification into the hook where the value is constructed.
 
 error.invalid-non-imported-reanimated-shared-value-writes.ts:11:22
    9 |   return (