[compiler] fix false positive "mutate frozen" validation with refs

The test case here previously reported a "Cannot modify local variables after render completes" error (from ValidateNoFreezingKnownMutableFunctions). This happens because one of the functions passed to a hook clearly mutates a ref — except that we try to ignore mutations of refs! The problem in this case is that the `const ref = ...` was getting converted to a context variable since the ref is accessed in a function before its declaration. We don't infer types for context variables at all, and our ref handling is based on types, so we failed to ignore this ref mutation.

The fix is to recognize that `StoreLocal const ...` is a special case: the variable may be referenced in code before the declaration, but at runtime it's either a TDZ error or the variable will have the type from the declaration. So we can safely infer a type.

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 +207,22 @@ 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,
+            }
+          : {
+              /* use defaults for compiler mode */
+            },
     });
     const opts: PluginOptions = parsePluginOptions({
       ...parsedOptions,
@@ -214,7 +234,7 @@ 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 +246,7 @@ 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 +265,15 @@ 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 +282,11 @@ 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 +312,26 @@ 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/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 ${param.node.type} parameters.`,
         }).withDetail({
           kind: 'error',
           loc: param.node.loc ?? null,
@@ -205,8 +203,7 @@ export function lower(
       CompilerDiagnostic.create({
         severity: ErrorSeverity.InvalidJS,
         category: `Unexpected function body kind`,
-        description: `Expected function body to be an expression or a block statement, got \`${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,

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

@@ -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)} <- ${printPlaceForAliasEffect(effect.from)}`;
@@ -995,13 +998,13 @@ export function printAliasingEffect(effect: AliasingEffect): string {
       return `${effect.kind} ${printPlaceForAliasEffect(effect.value)}`;
     }
     case 'MutateFrozen': {
-      return `MutateFrozen ${printPlaceForAliasEffect(effect.place)} reason=${JSON.stringify(effect.error.reason)}`;
+      return `MutateFrozen ${printPlaceForAliasEffect(effect.place)} reason=${JSON.stringify(effect.error.category)}`;
     }
     case 'MutateGlobal': {
-      return `MutateGlobal ${printPlaceForAliasEffect(effect.place)} reason=${JSON.stringify(effect.error.reason)}`;
+      return `MutateGlobal ${printPlaceForAliasEffect(effect.place)} reason=${JSON.stringify(effect.error.category)}`;
     }
     case 'Impure': {
-      return `Impure ${printPlaceForAliasEffect(effect.place)} reason=${JSON.stringify(effect.error.reason)}`;
+      return `Impure ${printPlaceForAliasEffect(effect.place)} reason=${JSON.stringify(effect.error.category)}`;
     }
     case 'Render': {
       return `Render ${printPlaceForAliasEffect(effect.place)}`;

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

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

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

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

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

@@ -326,26 +326,26 @@ function isEffectSafeOutsideRender(effect: FunctionEffect): boolean {
 
 export function getWriteErrorReason(abstractValue: AbstractValue): string {
   if (abstractValue.reason.has(ValueReason.Global)) {
-    return 'Writing to a variable defined outside a component or hook is not allowed. Consider using an effect';
+    return 'Modifying a variable defined outside a component or hook is not allowed. Consider using an effect';
   } else if (abstractValue.reason.has(ValueReason.JsxCaptured)) {
-    return 'Updating a value used previously in JSX is not allowed. Consider moving the mutation before the JSX';
+    return 'Modifying a value used previously in JSX is not allowed. Consider moving the modification before the JSX';
   } else if (abstractValue.reason.has(ValueReason.Context)) {
-    return `Mutating a value returned from 'useContext()', which should not be mutated`;
+    return `Modifying a value returned from 'useContext()' is not allowed.`;
   } else if (abstractValue.reason.has(ValueReason.KnownReturnSignature)) {
-    return 'Mutating a value returned from a function whose return value should not be mutated';
+    return 'Modifying a value returned from a function whose return value should not be mutated';
   } else if (abstractValue.reason.has(ValueReason.ReactiveFunctionArgument)) {
-    return 'Mutating component props or hook arguments is not allowed. Consider using a local variable instead';
+    return 'Modifying component props or hook arguments is not allowed. Consider using a local variable instead';
   } else if (abstractValue.reason.has(ValueReason.State)) {
-    return "Mutating a value returned from 'useState()', which should not be mutated. Use the setter function to update instead";
+    return "Modifying a value returned from 'useState()', which should not be modified directly. Use the setter function to update instead";
   } else if (abstractValue.reason.has(ValueReason.ReducerState)) {
-    return "Mutating a value returned from 'useReducer()', which should not be mutated. Use the dispatch function to update instead";
+    return "Modifying a value returned from 'useReducer()', which should not be modified directly. Use the dispatch function to update instead";
   } else if (abstractValue.reason.has(ValueReason.Effect)) {
-    return 'Updating a value used previously in an effect function or as an effect dependency is not allowed. Consider moving the mutation before calling useEffect()';
+    return 'Modifying a value used previously in an effect function or as an effect dependency is not allowed. Consider moving the modification before calling useEffect()';
   } else if (abstractValue.reason.has(ValueReason.HookCaptured)) {
-    return 'Updating a value previously passed as an argument to a hook is not allowed. Consider moving the mutation before calling the hook';
+    return 'Modifying a value previously passed as an argument to a hook is not allowed. Consider moving the modification before calling the hook';
   } else if (abstractValue.reason.has(ValueReason.HookReturn)) {
-    return 'Updating a value returned from a hook is not allowed. Consider moving the mutation into the hook where the value is constructed';
+    return 'Modifying a value returned from a hook is not allowed. Consider moving the modification into the hook where the value is constructed';
   } else {
-    return 'This mutates a variable that React considers immutable';
+    return 'This modifies a variable that React considers immutable';
   }
 }

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

@@ -6,6 +6,7 @@
  */
 
 import {
+  CompilerDiagnostic,
   CompilerError,
   Effect,
   ErrorSeverity,
@@ -446,20 +447,23 @@ function applySignature(
               reason: value.reason,
               context: new Set(),
             });
+            const variable =
+              effect.value.identifier.name !== null &&
+              effect.value.identifier.name.kind === 'named'
+                ? `\`${effect.value.identifier.name.value}\``
+                : 'value';
             effects.push({
               kind: 'MutateFrozen',
               place: effect.value,
-              error: {
+              error: CompilerDiagnostic.create({
                 severity: ErrorSeverity.InvalidReact,
-                reason,
-                description:
-                  effect.value.identifier.name !== null &&
-                  effect.value.identifier.name.kind === 'named'
-                    ? `Found mutation of \`${effect.value.identifier.name.value}\``
-                    : null,
+                category: 'This value cannot be modified',
+                description: `${reason}.`,
+              }).withDetail({
+                kind: 'error',
                 loc: effect.value.loc,
-                suggestions: null,
-              },
+                message: `${variable} cannot be modified`,
+              }),
             });
           }
         }
@@ -687,6 +691,7 @@ function applyEffect(
       }
       break;
     }
+    case 'MaybeAlias':
     case 'Alias':
     case 'Capture': {
       CompilerError.invariant(
@@ -951,7 +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,
           );
@@ -1013,33 +1018,31 @@ function applyEffect(
             effect.value.identifier.declarationId,
           )
         ) {
-          const description =
+          const variable =
             effect.value.identifier.name !== null &&
             effect.value.identifier.name.kind === 'named'
-              ? `Variable \`${effect.value.identifier.name.value}\` is accessed before it is declared`
+              ? `\`${effect.value.identifier.name.value}\``
               : null;
           const hoistedAccess = context.hoistedContextDeclarations.get(
             effect.value.identifier.declarationId,
           );
+          const diagnostic = CompilerDiagnostic.create({
+            severity: ErrorSeverity.InvalidReact,
+            category: 'Cannot access variable before it is declared',
+            description: `${variable ?? 'This variable'} is accessed before it is declared, which prevents the earlier access from updating when this value changes over time.`,
+          });
           if (hoistedAccess != null && hoistedAccess.loc != effect.value.loc) {
-            applyEffect(
-              context,
-              state,
-              {
-                kind: 'MutateFrozen',
-                place: effect.value,
-                error: {
-                  severity: ErrorSeverity.InvalidReact,
-                  reason: `This variable is accessed before it is declared, which may prevent it from updating as the assigned value changes over time`,
-                  description,
-                  loc: hoistedAccess.loc,
-                  suggestions: null,
-                },
-              },
-              initialized,
-              effects,
-            );
+            diagnostic.withDetail({
+              kind: 'error',
+              loc: hoistedAccess.loc,
+              message: `${variable ?? 'variable'} accessed before it is declared`,
+            });
           }
+          diagnostic.withDetail({
+            kind: 'error',
+            loc: effect.value.loc,
+            message: `${variable ?? 'variable'} is declared here`,
+          });
 
           applyEffect(
             context,
@@ -1047,13 +1050,7 @@ function applyEffect(
             {
               kind: 'MutateFrozen',
               place: effect.value,
-              error: {
-                severity: ErrorSeverity.InvalidReact,
-                reason: `This variable is accessed before it is declared, which prevents the earlier access from updating when this value changes over time`,
-                description,
-                loc: effect.value.loc,
-                suggestions: null,
-              },
+              error: diagnostic,
             },
             initialized,
             effects,
@@ -1064,11 +1061,11 @@ function applyEffect(
             reason: value.reason,
             context: new Set(),
           });
-          const description =
+          const variable =
             effect.value.identifier.name !== null &&
             effect.value.identifier.name.kind === 'named'
-              ? `Found mutation of \`${effect.value.identifier.name.value}\``
-              : null;
+              ? `\`${effect.value.identifier.name.value}\``
+              : 'value';
           applyEffect(
             context,
             state,
@@ -1078,13 +1075,15 @@ function applyEffect(
                   ? 'MutateFrozen'
                   : 'MutateGlobal',
               place: effect.value,
-              error: {
+              error: CompilerDiagnostic.create({
                 severity: ErrorSeverity.InvalidReact,
-                reason,
-                description,
+                category: 'This value cannot be modified',
+                description: `${reason}.`,
+              }).withDetail({
+                kind: 'error',
                 loc: effect.value.loc,
-                suggestions: null,
-              },
+                message: `${variable} cannot be modified`,
+              }),
             },
             initialized,
             effects,
@@ -1325,7 +1324,7 @@ class InferenceState {
             return 'mutate-global';
           }
           case ValueKind.MaybeFrozen: {
-            return 'none';
+            return 'mutate-frozen';
           }
           default: {
             assertExhaustive(kind, `Unexpected kind ${kind}`);
@@ -2003,16 +2002,20 @@ function computeSignatureForInstruction(
       break;
     }
     case 'StoreGlobal': {
+      const variable = `\`${value.name}\``;
       effects.push({
         kind: 'MutateGlobal',
         place: value.value,
-        error: {
-          reason:
-            'Unexpected reassignment of a variable which was defined outside of the component. Components and hooks should be pure and side-effect free, but variable reassignment is a form of side-effect. If this variable is used in rendering, use useState instead. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#side-effects-must-run-outside-of-render)',
-          loc: instr.loc,
-          suggestions: null,
+        error: CompilerDiagnostic.create({
           severity: ErrorSeverity.InvalidReact,
-        },
+          category:
+            'Cannot reassign variables declared outside of the component/hook',
+          description: `Variable ${variable} is declared outside of the component/hook. Reassigning this value during render is a form of side effect, which can cause unpredictable behavior depending on when the component happens to re-render. If this variable is used in rendering, use useState instead. Otherwise, consider updating it in an effect. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#side-effects-must-run-outside-of-render)`,
+        }).withDetail({
+          kind: 'error',
+          loc: instr.loc,
+          message: `${variable} cannot be reassigned`,
+        }),
       });
       effects.push({kind: 'Assign', from: value.value, into: lvalue});
       break;
@@ -2102,17 +2105,19 @@ function computeEffectsForLegacySignature(
     effects.push({
       kind: 'Impure',
       place: receiver,
-      error: {
-        reason:
-          'Calling an impure function can produce unstable results. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent)',
-        description:
-          signature.canonicalName != null
-            ? `\`${signature.canonicalName}\` is an impure function whose results may change on every call`
-            : null,
+      error: CompilerDiagnostic.create({
         severity: ErrorSeverity.InvalidReact,
+        category: 'Cannot call impure function during render',
+        description:
+          (signature.canonicalName != null
+            ? `\`${signature.canonicalName}\` is an impure function. `
+            : '') +
+          'Calling an impure function can produce unstable results that update unpredictably when the component happens to re-render. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent)',
+      }).withDetail({
+        kind: 'error',
         loc,
-        suggestions: null,
-      },
+        message: 'Cannot call impure function',
+      }),
     });
   }
   const stores: Array<Place> = [];
@@ -2372,6 +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 (
@@ -195,7 +197,7 @@ export function inferMutationAliasingRanges(
           effect.kind === 'MutateGlobal' ||
           effect.kind === 'Impure'
         ) {
-          errors.push(effect.error);
+          errors.pushDiagnostic(effect.error);
           functionEffects.push(effect);
         } else if (effect.kind === 'Render') {
           renders.push({index: index++, place: effect.place});
@@ -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) {
@@ -549,7 +553,7 @@ function appendFunctionErrors(errors: CompilerError, fn: HIRFunction): void {
       case 'Impure':
       case 'MutateFrozen':
       case 'MutateGlobal': {
-        errors.push(effect.error);
+        errors.pushDiagnostic(effect.error);
         break;
       }
     }
@@ -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/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/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) {

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/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/ValidatePreservedManualMemoization.ts

@@ -5,7 +5,11 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-import {CompilerError, ErrorSeverity} from '../CompilerError';
+import {
+  CompilerDiagnostic,
+  CompilerError,
+  ErrorSeverity,
+} from '../CompilerError';
 import {
   DeclarationId,
   Effect,
@@ -275,27 +279,37 @@ function validateInferredDep(
       errorDiagnostic = merge(errorDiagnostic ?? compareResult, compareResult);
     }
   }
-  errorState.push({
-    severity: ErrorSeverity.CannotPreserveMemoization,
-    reason:
-      'React Compiler has skipped optimizing this component because the existing manual memoization could not be preserved. The inferred dependencies did not match the manually specified dependencies, which could cause the value to change more or less frequently than expected',
-    description:
-      DEBUG ||
-      // If the dependency is a named variable then we can report it. Otherwise only print in debug mode
-      (dep.identifier.name != null && dep.identifier.name.kind === 'named')
-        ? `The inferred dependency was \`${prettyPrintScopeDependency(
-            dep,
-          )}\`, but the source dependencies were [${validDepsInMemoBlock
-            .map(dep => printManualMemoDependency(dep, true))
-            .join(', ')}]. ${
-            errorDiagnostic
-              ? getCompareDependencyResultDescription(errorDiagnostic)
-              : 'Inferred dependency not present in source'
-          }`
-        : null,
-    loc: memoLocation,
-    suggestions: null,
-  });
+  errorState.pushDiagnostic(
+    CompilerDiagnostic.create({
+      severity: ErrorSeverity.CannotPreserveMemoization,
+      category:
+        'Compilation skipped because existing memoization could not be preserved',
+      description: [
+        'React Compiler has skipped optimizing this component because the existing manual memoization could not be preserved. ',
+        'The inferred dependencies did not match the manually specified dependencies, which could cause the value to change more or less frequently than expected. ',
+        DEBUG ||
+        // If the dependency is a named variable then we can report it. Otherwise only print in debug mode
+        (dep.identifier.name != null && dep.identifier.name.kind === 'named')
+          ? `The inferred dependency was \`${prettyPrintScopeDependency(
+              dep,
+            )}\`, but the source dependencies were [${validDepsInMemoBlock
+              .map(dep => printManualMemoDependency(dep, true))
+              .join(', ')}]. ${
+              errorDiagnostic
+                ? getCompareDependencyResultDescription(errorDiagnostic)
+                : 'Inferred dependency not present in source'
+            }.`
+          : '',
+      ]
+        .join('')
+        .trim(),
+      suggestions: null,
+    }).withDetail({
+      kind: 'error',
+      loc: memoLocation,
+      message: 'Could not preserve existing manual memoization',
+    }),
+  );
 }
 
 class Visitor extends ReactiveFunctionVisitor<VisitorState> {
@@ -519,14 +533,21 @@ class Visitor extends ReactiveFunctionVisitor<VisitorState> {
           !this.scopes.has(identifier.scope.id) &&
           !this.prunedScopes.has(identifier.scope.id)
         ) {
-          state.errors.push({
-            reason:
-              'React Compiler has skipped optimizing this component because the existing manual memoization could not be preserved. This dependency may be mutated later, which could cause the value to change unexpectedly',
-            description: null,
-            severity: ErrorSeverity.CannotPreserveMemoization,
-            loc,
-            suggestions: null,
-          });
+          state.errors.pushDiagnostic(
+            CompilerDiagnostic.create({
+              severity: ErrorSeverity.CannotPreserveMemoization,
+              category:
+                'Compilation skipped because existing memoization could not be preserved',
+              description: [
+                'React Compiler has skipped optimizing this component because the existing manual memoization could not be preserved. ',
+                'This dependency may be mutated later, which could cause the value to change unexpectedly.',
+              ].join(''),
+            }).withDetail({
+              kind: 'error',
+              loc,
+              message: 'This dependency may be modified later',
+            }),
+          );
         }
       }
     }
@@ -560,16 +581,25 @@ class Visitor extends ReactiveFunctionVisitor<VisitorState> {
 
           for (const identifier of decls) {
             if (isUnmemoized(identifier, this.scopes)) {
-              state.errors.push({
-                reason:
-                  'React Compiler has skipped optimizing this component because the existing manual memoization could not be preserved. This value was memoized in source but not in compilation output.',
-                description: DEBUG
-                  ? `${printIdentifier(identifier)} was not memoized`
-                  : null,
-                severity: ErrorSeverity.CannotPreserveMemoization,
-                loc,
-                suggestions: null,
-              });
+              state.errors.pushDiagnostic(
+                CompilerDiagnostic.create({
+                  severity: ErrorSeverity.CannotPreserveMemoization,
+                  category:
+                    'Compilation skipped because existing memoization could not be preserved',
+                  description: [
+                    'React Compiler has skipped optimizing this component because the existing manual memoization could not be preserved. This value was memoized in source but not in compilation output. ',
+                    DEBUG
+                      ? `${printIdentifier(identifier)} was not memoized.`
+                      : '',
+                  ]
+                    .join('')
+                    .trim(),
+                }).withDetail({
+                  kind: 'error',
+                  loc,
+                  message: 'Could not preserve existing memoization',
+                }),
+              );
             }
           }
         }

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

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

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

@@ -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

@@ -16,18 +16,19 @@ 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: Cannot reassign variables declared outside of the component/hook
+
+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;
-    |     ^^^^^^^^^^ 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)
+    |     ^^^^^^^^^^ `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

@@ -19,18 +19,19 @@ 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: Cannot reassign variables declared outside of the component/hook
+
+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;
-    |     ^^^^^^^^^^ 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)
+    |     ^^^^^^^^^^ `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

@@ -33,6 +33,7 @@ export const FIXTURE_ENTRYPOINT = {
 
 ```
 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)
 
 error.capture-ref-for-mutation.ts:12:13
@@ -44,7 +45,6 @@ error.capture-ref-for-mutation.ts:12:13
   14 |   const moveRight = {
   15 |     handler: handleKey('right')(),
 
-
 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
@@ -56,7 +56,6 @@ error.capture-ref-for-mutation.ts:12:13
   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)
 
 error.capture-ref-for-mutation.ts:15:13
@@ -68,7 +67,6 @@ error.capture-ref-for-mutation.ts:15:13
   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
@@ -79,8 +77,6 @@ error.capture-ref-for-mutation.ts:15:13
   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

@@ -25,9 +25,10 @@ function Component(props) {
 
 ```
 Found 1 error:
-Memoization: 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.
+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.
 
 error.hoist-optional-member-expression-with-conditional-optional.ts:4:23
    2 | import {ValidateMemoization} from 'shared-runtime';
@@ -47,12 +48,10 @@ error.hoist-optional-member-expression-with-conditional-optional.ts:4:23
 > 10 |     return x;
      | ^^^^^^^^^^^^^^^^^
 > 11 |   }, [props?.items, props.cond]);
-     | ^^^^ 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
+     | ^^^^ Could not preserve existing manual memoization
   12 |   return (
   13 |     <ValidateMemoization inputs={[props?.items, props.cond]} output={data} />
   14 |   );
-
-
 ```
           
       

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

@@ -25,9 +25,10 @@ function Component(props) {
 
 ```
 Found 1 error:
-Memoization: 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.
+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.
 
 error.hoist-optional-member-expression-with-conditional.ts:4:23
    2 | import {ValidateMemoization} from 'shared-runtime';
@@ -47,12 +48,10 @@ error.hoist-optional-member-expression-with-conditional.ts:4:23
 > 10 |     return x;
      | ^^^^^^^^^^^^^^^^^
 > 11 |   }, [props?.items, props.cond]);
-     | ^^^^ 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
+     | ^^^^ Could not preserve existing manual memoization
   12 |   return (
   13 |     <ValidateMemoization inputs={[props?.items, props.cond]} output={data} />
   14 |   );
-
-
 ```
           
       

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

@@ -30,18 +30,19 @@ export const FIXTURE_ENTRYPOINT = {
 
 ```
 Found 1 error:
-Error: Updating a value previously passed as an argument to a hook is not allowed. Consider moving the mutation before calling the hook
+
+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.
 
 error.hook-call-freezes-captured-identifier.ts:13:2
   11 |   });
   12 |
 > 13 |   x.value += count;
-     |   ^ Updating a value previously passed as an argument to a hook is not allowed. Consider moving the mutation before calling the hook
+     |   ^ 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

@@ -30,18 +30,19 @@ export const FIXTURE_ENTRYPOINT = {
 
 ```
 Found 1 error:
-Error: Updating a value previously passed as an argument to a hook is not allowed. Consider moving the mutation before calling the hook
+
+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.
 
 error.hook-call-freezes-captured-memberexpr.ts:13:2
   11 |   });
   12 |
 > 13 |   x.value += count;
-     |   ^ Updating a value previously passed as an argument to a hook is not allowed. Consider moving the mutation before calling the hook
+     |   ^ 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

@@ -21,17 +21,6 @@ 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.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)
-  6 | }
-  7 |
-  8 | export const FIXTURE_ENTRYPOINT = {
-
 
 Error: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)
 
@@ -44,7 +33,16 @@ error.hook-ref-value.ts:5:23
   7 |
   8 | export const FIXTURE_ENTRYPOINT = {
 
+Error: Ref values (the `current` property) may not be accessed during render. (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)
+  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

@@ -16,6 +16,7 @@ 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.invalid-access-ref-during-render.ts:4:16
@@ -26,8 +27,6 @@ error.invalid-access-ref-during-render.ts:4:16
   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

@@ -20,6 +20,7 @@ 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.invalid-aliased-ref-in-callback-invoked-during-render-.ts:9:33
@@ -29,8 +30,6 @@ error.invalid-aliased-ref-in-callback-invoked-during-render-.ts:9:33
      |                                  ^^^^^^^^^^^^^^^^^^^^^^^^ Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)
   10 | }
   11 |
-
-
 ```
           
       

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

@@ -16,18 +16,19 @@ function Component(props) {
 
 ```
 Found 1 error:
-Error: Updating a value used previously in JSX is not allowed. Consider moving the mutation before the JSX
+
+Error: This value cannot be modified
+
+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);
-    |   ^ Updating a value used previously in JSX is not allowed. Consider moving the mutation before the JSX
+    |   ^ value cannot be modified
   5 |   return x;
   6 | }
   7 |
-
-
 ```
           
       

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

@@ -17,18 +17,19 @@ function Component(props) {
 
 ```
 Found 1 error:
-Error: Updating a value used previously in JSX is not allowed. Consider moving the mutation before the JSX
+
+Error: This value cannot be modified
+
+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;
-    |   ^ Updating a value used previously in JSX is not allowed. Consider moving the mutation before the JSX
+    |   ^ 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

@@ -17,18 +17,19 @@ function Component(props) {
 
 ```
 Found 1 error:
-Error: Updating a value used previously in JSX is not allowed. Consider moving the mutation before the JSX
+
+Error: This value cannot be modified
+
+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];
-    |          ^ Updating a value used previously in JSX is not allowed. Consider moving the mutation before the JSX
+    |          ^ 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

@@ -17,18 +17,19 @@ function Component(props) {
 
 ```
 Found 1 error:
-Error: Updating a value used previously in JSX is not allowed. Consider moving the mutation before the JSX
+
+Error: This value cannot be modified
+
+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;
-    |          ^ Updating a value used previously in JSX is not allowed. Consider moving the mutation before the JSX
+    |          ^ 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

@@ -14,17 +14,18 @@ function useFoo(props) {
 
 ```
 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: Cannot reassign variables declared outside of the component/hook
+
+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;
-    |    ^ 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)
+    |    ^ `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

@@ -16,18 +16,19 @@ function Component(props) {
 
 ```
 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: Cannot reassign variables declared outside of the component/hook
+
+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;
-    |       ^ 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)
+    |       ^ `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

@@ -17,6 +17,7 @@ function Component() {
 
 ```
 Found 1 error:
+
 Error: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)
 
 error.invalid-disallow-mutating-ref-in-render.ts:4:2
@@ -27,8 +28,6 @@ error.invalid-disallow-mutating-ref-in-render.ts:4:2
   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

@@ -22,6 +22,7 @@ function Component() {
 
 ```
 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)
 
 error.invalid-disallow-mutating-refs-in-render-transitive.ts:9:2
@@ -33,7 +34,6 @@ error.invalid-disallow-mutating-refs-in-render-transitive.ts:9:2
   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
@@ -44,8 +44,6 @@ error.invalid-disallow-mutating-refs-in-render-transitive.ts:9:2
   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

@@ -19,20 +19,19 @@ function Component(props) {
 
 ```
 Found 1 error:
-Error: Mutating a value returned from 'useState()', which should not be mutated. Use the setter function to update instead
 
-Found mutation of `x`.
+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.
 
 error.invalid-function-expression-mutates-immutable-value.ts:5:4
   3 |   const onChange = e => {
   4 |     // INVALID! should use copy-on-write and pass the new value
 > 5 |     x.value = e.target.value;
-    |     ^ Mutating a value returned from 'useState()', which should not be mutated. Use the setter function to update instead
+    |     ^ `x` cannot be modified
   6 |     setX(x);
   7 |   };
   8 |   return <input value={x.value} onChange={onChange} />;
-
-
 ```
           
       

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

@@ -36,18 +36,19 @@ export const FIXTURE_ENTRYPOINT = {
 
 ```
 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: Cannot reassign variables declared outside of the component/hook
+
+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;
-     |     ^^^^^^^^^^ 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)
+     |     ^^^^^^^^^^ `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

@@ -38,35 +38,29 @@ export const FIXTURE_ENTRYPOINT = {
 ## Error
 
 ```
-Found 2 errors:
-Error: This variable is accessed before it is declared, which may prevent it from updating as the assigned value changes over time
+Found 1 error:
 
-Variable `setState` is accessed before it is declared.
+Error: Cannot access variable before it is declared
+
+`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), []);
-     |                   ^^^^^^^^ This variable is accessed before it is declared, which may prevent it from updating as the assigned value changes over time
+     |                   ^^^^^^^^ `setState` accessed before it is declared
   20 |
   21 |   const [state, setState] = useState(0);
   22 |   return <Stringify state={state} />;
 
-
-Error: This variable is accessed before it is declared, which prevents the earlier access from updating when this value changes over time
-
-Variable `setState` is accessed before it is declared.
-
 error.invalid-hoisting-setstate.ts:21:16
   19 |   useEffect(() => setState(2), []);
   20 |
 > 21 |   const [state, setState] = useState(0);
-     |                 ^^^^^^^^ This variable is accessed before it is declared, which prevents the earlier access from updating when this value changes over time
+     |                 ^^^^^^^^ `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

@@ -18,48 +18,45 @@ function Component() {
 
 ```
 Found 3 errors:
-Error: Calling an impure function can produce unstable results. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent)
 
-`Date.now` is an impure function whose results may change on every call.
+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)
 
 error.invalid-impure-functions-in-render.ts:4:15
   2 |
   3 | function Component() {
 > 4 |   const date = Date.now();
-    |                ^^^^^^^^^^ Calling an impure function can produce unstable results. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent)
+    |                ^^^^^^^^^^ Cannot call impure function
   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
 
-Error: Calling an impure function can produce unstable results. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent)
-
-`performance.now` is an impure function whose results may change on every call.
+`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)
 
 error.invalid-impure-functions-in-render.ts:5:14
   3 | function Component() {
   4 |   const date = Date.now();
 > 5 |   const now = performance.now();
-    |               ^^^^^^^^^^^^^^^^^ Calling an impure function can produce unstable results. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent)
+    |               ^^^^^^^^^^^^^^^^^ Cannot call impure function
   6 |   const rand = Math.random();
   7 |   return <Foo date={date} now={now} rand={rand} />;
   8 | }
 
+Error: Cannot call impure function during render
 
-Error: Calling an impure function can produce unstable results. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent)
-
-`Math.random` is an impure function whose results may change on every call.
+`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)
 
 error.invalid-impure-functions-in-render.ts:6:15
   4 |   const date = Date.now();
   5 |   const now = performance.now();
 > 6 |   const rand = Math.random();
-    |                ^^^^^^^^^^^^^ Calling an impure function can produce unstable results. (https://react.dev/reference/rules/components-and-hooks-must-be-pure#components-and-hooks-must-be-idempotent)
+    |                ^^^^^^^^^^^^^ Cannot call impure function
   7 |   return <Foo date={date} now={now} rand={rand} />;
   8 | }
   9 |
-
-
 ```
           
       

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

@@ -51,20 +51,19 @@ export const FIXTURE_ENTRYPOINT = {
 
 ```
 Found 1 error:
-Error: Updating a value used previously in JSX is not allowed. Consider moving the mutation before the JSX
 
-Found mutation of `i`.
+Error: This value cannot be modified
+
+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 |     />
   21 |   );
 > 22 |   i = i + 1;
-     |   ^ Updating a value used previously in JSX is not allowed. Consider moving the mutation before the JSX
+     |   ^ `i` cannot be modified
   23 |   items.push(
   24 |     <Stringify
   25 |       key={i}
-
-
 ```
           
       

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

@@ -26,18 +26,19 @@ function Component(props) {
 
 ```
 Found 1 error:
-Error: Updating a value used previously in JSX is not allowed. Consider moving the mutation before the JSX
+
+Error: This value cannot be modified
+
+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);
-     |   ^ Updating a value used previously in JSX is not allowed. Consider moving the mutation before the JSX
+     |   ^ 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

@@ -20,18 +20,19 @@ function Component(props) {
 
 ```
 Found 1 error:
-Error: Updating a value used previously in JSX is not allowed. Consider moving the mutation before the JSX
+
+Error: This value cannot be modified
+
+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);
-     |   ^ Updating a value used previously in JSX is not allowed. Consider moving the mutation before the JSX
+     |   ^ 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

@@ -25,20 +25,19 @@ function Component(props) {
 
 ```
 Found 1 error:
-Error: Mutating a value returned from 'useContext()', which should not be mutated
 
-Found mutation of `FooContext`.
+Error: This value cannot be modified
+
+Modifying a value returned from 'useContext()' is not allowed..
 
 error.invalid-mutate-context-in-callback.ts:12:4
   10 |   // independently
   11 |   const onClick = () => {
 > 12 |     FooContext.current = true;
-     |     ^^^^^^^^^^ Mutating a value returned from 'useContext()', which should not be mutated
+     |     ^^^^^^^^^^ `FooContext` cannot be modified
   13 |   };
   14 |   return <div onClick={onClick} />;
   15 | }
-
-
 ```
           
       

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

@@ -15,18 +15,19 @@ function Component(props) {
 
 ```
 Found 1 error:
-Error: Mutating a value returned from 'useContext()', which should not be mutated
+
+Error: This value cannot be modified
+
+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;
-    |   ^^^^^^^ Mutating a value returned from 'useContext()', which should not be mutated
+    |   ^^^^^^^ 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

@@ -26,20 +26,19 @@ function Component(props) {
 
 ```
 Found 1 error:
-Error: Mutating component props or hook arguments is not allowed. Consider using a local variable instead
 
-Found mutation of `y`.
+Error: This value cannot be modified
+
+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;
    9 |   let mutateProps = () => {
 > 10 |     y.foo = true;
-     |     ^ Mutating component props or hook arguments is not allowed. Consider using a local variable instead
+     |     ^ `y` cannot be modified
   11 |   };
   12 |   let mutatePropsIndirect = () => {
   13 |     mutateProps();
-
-
 ```
           
       

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

@@ -18,18 +18,19 @@ function Component(props) {
 
 ```
 Found 1 error:
-Error: Mutating component props or hook arguments is not allowed. Consider using a local variable instead
+
+Error: This value cannot be modified
+
+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;
-    |     ^ Mutating component props or hook arguments is not allowed. Consider using a local variable instead
+    |     ^ 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

@@ -17,20 +17,19 @@ function useInvalidMutation(options) {
 
 ```
 Found 1 error:
-Error: Mutating component props or hook arguments is not allowed. Consider using a local variable instead
 
-Found mutation of `options`.
+Error: This value cannot be modified
+
+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() {
   3 |     foo(options.foo); // error should not point on this line
 > 4 |     options.foo = 'bar';
-    |     ^^^^^^^ Mutating component props or hook arguments is not allowed. Consider using a local variable instead
+    |     ^^^^^^^ `options` cannot be modified
   5 |   }
   6 |   return test;
   7 | }
-
-
 ```
           
       

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

@@ -20,20 +20,19 @@ function Component(props) {
 
 ```
 Found 1 error:
-Error: Writing to a variable defined outside a component or hook is not allowed. Consider using an effect
 
-Found mutation of `x`.
+Error: This value cannot be modified
+
+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;
   3 |   const mutatePhiThatCouldBeProps = () => {
 > 4 |     x.y = true;
-    |     ^ Writing to a variable defined outside a component or hook is not allowed. Consider using an effect
+    |     ^ `x` cannot be modified
   5 |   };
   6 |   const indirectMutateProps = () => {
   7 |     mutatePhiThatCouldBeProps();
-
-
 ```
           
       

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

@@ -25,20 +25,19 @@ function SomeComponent() {
 
 ```
 Found 1 error:
-Error: Updating a value returned from a hook is not allowed. Consider moving the mutation into the hook where the value is constructed
 
-Found mutation of `sharedVal`.
+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-non-imported-reanimated-shared-value-writes.ts:11:22
    9 |   return (
   10 |     <Button
 > 11 |       onPress={() => (sharedVal.value = Math.random())}
-     |                       ^^^^^^^^^ Updating a value returned from a hook is not allowed. Consider moving the mutation into the hook where the value is constructed
+     |                       ^^^^^^^^^ `sharedVal` cannot be modified
   12 |       title="Randomize"
   13 |     />
   14 |   );
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-optional-member-expression-as-memo-dep-non-optional-in-body.expect.md

@@ -19,9 +19,10 @@ function Component(props) {
 
 ```
 Found 1 error:
-Memoization: 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.edges.nodes`, but the source dependencies were [props.items?.edges?.nodes]. Inferred different dependency than source.
+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.edges.nodes`, but the source dependencies were [props.items?.edges?.nodes]. Inferred different dependency than source.
 
 error.invalid-optional-member-expression-as-memo-dep-non-optional-in-body.ts:3:23
    1 | // @validatePreserveExistingMemoizationGuarantees
@@ -35,12 +36,10 @@ error.invalid-optional-member-expression-as-memo-dep-non-optional-in-body.ts:3:2
 >  6 |     // deps are optional
      | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 >  7 |   }, [props.items?.edges?.nodes]);
-     | ^^^^ 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
+     | ^^^^ Could not preserve existing manual memoization
    8 |   return <Foo data={data} />;
    9 | }
   10 |
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-pass-hook-as-call-arg.expect.md

@@ -13,6 +13,7 @@ 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-pass-hook-as-call-arg.ts:2:13
@@ -21,8 +22,6 @@ error.invalid-pass-hook-as-call-arg.ts:2:13
     |              ^^^^^^ 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
   3 | }
   4 |
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-pass-hook-as-prop.expect.md

@@ -13,6 +13,7 @@ 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-pass-hook-as-prop.ts:2:21
@@ -21,8 +22,6 @@ error.invalid-pass-hook-as-prop.ts:2:21
     |                      ^^^^^^ 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
   3 | }
   4 |
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-pass-mutable-function-as-prop.expect.md

@@ -18,15 +18,16 @@ 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 `cache` after render, which can cause inconsistent behavior on subsequent renders. Consider using state instead.
 
 error.invalid-pass-mutable-function-as-prop.ts:7:18
   5 |     cache.set('key', 'value');
   6 |   };
 > 7 |   return <Foo fn={fn} />;
-    |                   ^^ This function may (indirectly) reassign or modify local variables after render
+    |                   ^^ This function may (indirectly) reassign or modify `cache` after render
   8 | }
   9 |
 
@@ -34,7 +35,7 @@ error.invalid-pass-mutable-function-as-prop.ts:5:4
   3 |   const cache = new Map();
   4 |   const fn = () => {
 > 5 |     cache.set('key', 'value');
-    |     ^^^^^ This modifies a local variable
+    |     ^^^^^ This modifies `cache`
   6 |   };
   7 |   return <Foo fn={fn} />;
   8 | }

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-pass-ref-to-function.expect.md

@@ -16,6 +16,7 @@ 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.invalid-pass-ref-to-function.ts:4:16
@@ -26,8 +27,6 @@ error.invalid-pass-ref-to-function.ts:4:16
   5 |   return x.current;
   6 | }
   7 |
-
-
 ```
           
       

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

@@ -19,20 +19,19 @@ function Component(props) {
 
 ```
 Found 1 error:
-Error: Mutating component props or hook arguments is not allowed. Consider using a local variable instead
 
-Found mutation of `props`.
+Error: This value cannot be modified
+
+Modifying component props or hook arguments is not allowed. Consider using a local variable instead.
 
 error.invalid-prop-mutation-indirect.ts:3:4
   1 | function Component(props) {
   2 |   const f = () => {
 > 3 |     props.value = true;
-    |     ^^^^^ Mutating component props or hook arguments is not allowed. Consider using a local variable instead
+    |     ^^^^^ `props` cannot be modified
   4 |   };
   5 |   const g = () => {
   6 |     f();
-
-
 ```
           
       

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

@@ -17,18 +17,19 @@ function Component(props) {
 
 ```
 Found 1 error:
-Error: Updating a value used previously in JSX is not allowed. Consider moving the mutation before the JSX
+
+Error: This value cannot be modified
+
+Modifying a value used previously in JSX is not allowed. Consider moving the modification before the JSX.
 
 error.invalid-property-store-to-frozen-value.ts:5:2
   3 |   // freeze
   4 |   <div>{x}</div>;
 > 5 |   x.y = true;
-    |   ^ Updating a value used previously in JSX is not allowed. Consider moving the mutation before the JSX
+    |   ^ value cannot be modified
   6 |   return x;
   7 | }
   8 |
-
-
 ```
           
       

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

@@ -19,20 +19,19 @@ function Component(props) {
 
 ```
 Found 1 error:
-Error: Mutating component props or hook arguments is not allowed. Consider using a local variable instead
 
-Found mutation of `props`.
+Error: This value cannot be modified
+
+Modifying component props or hook arguments is not allowed. Consider using a local variable instead.
 
 error.invalid-props-mutation-in-effect-indirect.ts:3:4
   1 | function Component(props) {
   2 |   const mutateProps = () => {
 > 3 |     props.value = true;
-    |     ^^^^^ Mutating component props or hook arguments is not allowed. Consider using a local variable instead
+    |     ^^^^^ `props` cannot be modified
   4 |   };
   5 |   const indirectMutateProps = () => {
   6 |     mutateProps();
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-read-ref-prop-in-render-destructure.expect.md

@@ -15,6 +15,7 @@ function Component({ref}) {
 
 ```
 Found 1 error:
+
 Error: Ref values (the `current` property) may not be accessed during render. (https://react.dev/reference/react/useRef)
 
 error.invalid-read-ref-prop-in-render-destructure.ts:3:16
@@ -25,8 +26,6 @@ error.invalid-read-ref-prop-in-render-destructure.ts:3:16
   4 |   return <div>{value}</div>;
   5 | }
   6 |
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-read-ref-prop-in-render-property-load.expect.md

@@ -15,6 +15,7 @@ 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.invalid-read-ref-prop-in-render-property-load.ts:3:16
@@ -25,8 +26,6 @@ error.invalid-read-ref-prop-in-render-property-load.ts:3:16
   4 |   return <div>{value}</div>;
   5 | }
   6 |
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-reassign-const.expect.md

@@ -14,6 +14,7 @@ function Component() {
 
 ```
 Found 1 error:
+
 Error: Cannot reassign a `const` variable
 
 `x` is declared as const.
@@ -25,8 +26,6 @@ error.invalid-reassign-const.ts:3:2
     |   ^ Cannot reassign a `const` variable
   4 | }
   5 |
-
-
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.invalid-reassign-local-in-hook-return-value.expect.md

@@ -16,15 +16,16 @@ function useFoo() {
 
 ```
 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.invalid-reassign-local-in-hook-return-value.ts:4:4
   2 |   let x = 0;
   3 |   return value => {
 > 4 |     x = value;
-    |     ^ Cannot reassign variable after render completes
+    |     ^ Cannot reassign `x` after render completes
   5 |   };
   6 | }
   7 |