[compiler] Remove tryRecord, add catch-all error handling, fix remaining throws

Remove `tryRecord()` from the compilation pipeline now that all passes record
errors directly via `env.recordError()` / `env.recordErrors()`. A single
catch-all try/catch in Program.ts provides the safety net for any pass that
incorrectly throws instead of recording.

Key changes:
- Remove all ~64 `env.tryRecord()` wrappers in Pipeline.ts
- Delete `tryRecord()` method from Environment.ts
- Add `CompileUnexpectedThrow` logger event so thrown errors are detectable
- Log `CompileUnexpectedThrow` in Program.ts catch-all for non-invariant throws
- Fail snap tests on `CompileUnexpectedThrow` to surface pass bugs in dev
- Convert throwTodo/throwDiagnostic calls in HIRBuilder (fbt, this),
  CodegenReactiveFunction (for-in/for-of), and BuildReactiveFunction to
  record errors or use invariants as appropriate
- Remove try/catch from BuildHIR's lower() since inner throws are now recorded
- CollectOptionalChainDependencies: return null instead of throwing on
  unsupported optional chain patterns (graceful optimization skip)

compiler/fault-tolerance-overview.md

@@ -328,4 +328,6 @@ Walk through `runWithEnvironment` and wrap each pass call site. This is the inte
 * **Partial HIR can trigger downstream invariants.** When lowering skips or partially handles constructs (e.g., unreachable hoisted functions, `var` declarations before the fix), downstream passes like `InferMutationAliasingEffects` may encounter uninitialized identifiers and throw invariants. This is acceptable since the function still correctly bails out of compilation, but error messages may be less specific. The fix for `var` (treating as `let`) demonstrates how to avoid this: continue lowering with a best-effort representation rather than skipping entirely.
 * **Errors accumulated on `env` are lost when an invariant propagates out of the pipeline.** Since invariant CompilerErrors always re-throw through `tryRecord()`, they exit the pipeline as exceptions. The caller only sees the invariant error, not any errors previously recorded on `env`. This is a design limitation that could be addressed by aggregating env errors with caught exceptions in `tryCompileFunction()`.
 * **Dedicated fault tolerance test fixtures** were added in `__tests__/fixtures/compiler/fault-tolerance/`. Each fixture combines two or more errors from different passes to verify the compiler reports all of them rather than short-circuiting on the first. Coverage includes: `var`+props mutation (BuildHIR→InferMutationAliasingEffects), `var`+ref access (BuildHIR→ValidateNoRefAccessInRender), `try/finally`+props mutation (BuildHIR→InferMutationAliasingEffects), `try/finally`+ref access (BuildHIR→ValidateNoRefAccessInRender), and a 3-error test combining try/finally+ref access+props mutation.
+* **Cleanup: consistent `tryRecord()` wrapping in Pipeline.ts.** All validation passes and inference passes are now wrapped in `env.tryRecord()` for defense-in-depth, consistent with the approach used for transform passes. Previously only transform passes were wrapped. Merged duplicate `env.enableValidations` guard blocks. Pattern B lint-only passes (`env.logErrors()`) were intentionally not wrapped since they use a different error recording strategy.
+* **Cleanup: normalized validation error recording pattern.** Four validation passes (`ValidateNoDerivedComputationsInEffects`, `ValidateMemoizedEffectDependencies`, `ValidatePreservedManualMemoization`, `ValidateSourceLocations`) were using `for (const detail of errors.details) { env.recordError(detail); }` instead of the simpler `env.recordErrors(errors)`. Normalized to use the batch method.
 

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

@@ -254,6 +254,7 @@ export type LoggerEvent =
   | CompileErrorEvent
   | CompileDiagnosticEvent
   | CompileSkipEvent
+  | CompileUnexpectedThrowEvent
   | PipelineErrorEvent
   | TimingEvent;
 
@@ -288,6 +289,11 @@ export type PipelineErrorEvent = {
   fnLoc: t.SourceLocation | null;
   data: string;
 };
+export type CompileUnexpectedThrowEvent = {
+  kind: 'CompileUnexpectedThrow';
+  fnLoc: t.SourceLocation | null;
+  data: string;
+};
 export type TimingEvent = {
   kind: 'Timing';
   measurement: PerformanceMeasure;

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

@@ -13,7 +13,6 @@ import {CompilerError} from '../CompilerError';
 import {Err, Ok, Result} from '../Utils/Result';
 import {
   HIRFunction,
-  IdentifierId,
   ReactiveFunction,
   assertConsistentIdentifiers,
   assertTerminalPredsExist,
@@ -159,9 +158,7 @@ function runWithEnvironment(
   const hir = lower(func, env);
   log({kind: 'hir', name: 'HIR', value: hir});
 
-  env.tryRecord(() => {
-    pruneMaybeThrows(hir);
-  });
+  pruneMaybeThrows(hir);
   log({kind: 'hir', name: 'PruneMaybeThrows', value: hir});
 
   validateContextVariableLValues(hir);
@@ -172,43 +169,31 @@ function runWithEnvironment(
     log({kind: 'hir', name: 'DropManualMemoization', value: hir});
   }
 
-  env.tryRecord(() => {
-    inlineImmediatelyInvokedFunctionExpressions(hir);
-  });
+  inlineImmediatelyInvokedFunctionExpressions(hir);
   log({
     kind: 'hir',
     name: 'InlineImmediatelyInvokedFunctionExpressions',
     value: hir,
   });
 
-  env.tryRecord(() => {
-    mergeConsecutiveBlocks(hir);
-  });
+  mergeConsecutiveBlocks(hir);
   log({kind: 'hir', name: 'MergeConsecutiveBlocks', value: hir});
 
   assertConsistentIdentifiers(hir);
   assertTerminalSuccessorsExist(hir);
 
-  env.tryRecord(() => {
-    enterSSA(hir);
-  });
+  enterSSA(hir);
   log({kind: 'hir', name: 'SSA', value: hir});
 
-  env.tryRecord(() => {
-    eliminateRedundantPhi(hir);
-  });
+  eliminateRedundantPhi(hir);
   log({kind: 'hir', name: 'EliminateRedundantPhi', value: hir});
 
   assertConsistentIdentifiers(hir);
 
-  env.tryRecord(() => {
-    constantPropagation(hir);
-  });
+  constantPropagation(hir);
   log({kind: 'hir', name: 'ConstantPropagation', value: hir});
 
-  env.tryRecord(() => {
-    inferTypes(hir);
-  });
+  inferTypes(hir);
   log({kind: 'hir', name: 'InferTypes', value: hir});
 
   if (env.enableValidations) {
@@ -220,34 +205,24 @@ function runWithEnvironment(
     }
   }
 
-  env.tryRecord(() => {
-    optimizePropsMethodCalls(hir);
-  });
+  optimizePropsMethodCalls(hir);
   log({kind: 'hir', name: 'OptimizePropsMethodCalls', value: hir});
 
-  env.tryRecord(() => {
-    analyseFunctions(hir);
-  });
+  analyseFunctions(hir);
   log({kind: 'hir', name: 'AnalyseFunctions', value: hir});
 
   inferMutationAliasingEffects(hir);
   log({kind: 'hir', name: 'InferMutationAliasingEffects', value: hir});
 
   if (env.outputMode === 'ssr') {
-    env.tryRecord(() => {
-      optimizeForSSR(hir);
-    });
+    optimizeForSSR(hir);
     log({kind: 'hir', name: 'OptimizeForSSR', value: hir});
   }
 
   // Note: Has to come after infer reference effects because "dead" code may still affect inference
-  env.tryRecord(() => {
-    deadCodeElimination(hir);
-  });
+  deadCodeElimination(hir);
   log({kind: 'hir', name: 'DeadCodeElimination', value: hir});
-  env.tryRecord(() => {
-    pruneMaybeThrows(hir);
-  });
+  pruneMaybeThrows(hir);
   log({kind: 'hir', name: 'PruneMaybeThrows', value: hir});
 
   inferMutationAliasingRanges(hir, {
@@ -256,9 +231,7 @@ function runWithEnvironment(
   log({kind: 'hir', name: 'InferMutationAliasingRanges', value: hir});
   if (env.enableValidations) {
     validateLocalsNotReassignedAfterRender(hir);
-  }
 
-  if (env.enableValidations) {
     if (env.config.assertValidMutableRanges) {
       assertValidMutableRanges(hir);
     }
@@ -295,9 +268,7 @@ function runWithEnvironment(
     validateNoFreezingKnownMutableFunctions(hir);
   }
 
-  env.tryRecord(() => {
-    inferReactivePlaces(hir);
-  });
+  inferReactivePlaces(hir);
   log({kind: 'hir', name: 'InferReactivePlaces', value: hir});
 
   if (env.enableValidations) {
@@ -310,9 +281,7 @@ function runWithEnvironment(
     }
   }
 
-  env.tryRecord(() => {
-    rewriteInstructionKindsBasedOnReassignment(hir);
-  });
+  rewriteInstructionKindsBasedOnReassignment(hir);
   log({
     kind: 'hir',
     name: 'RewriteInstructionKindsBasedOnReassignment',
@@ -333,16 +302,11 @@ function runWithEnvironment(
      * if inferred memoization is enabled. This makes all later passes which
      * transform reactive-scope labeled instructions no-ops.
      */
-    env.tryRecord(() => {
-      inferReactiveScopeVariables(hir);
-    });
+    inferReactiveScopeVariables(hir);
     log({kind: 'hir', name: 'InferReactiveScopeVariables', value: hir});
   }
 
-  let fbtOperands: Set<IdentifierId> = new Set();
-  env.tryRecord(() => {
-    fbtOperands = memoizeFbtAndMacroOperandsInSameScope(hir);
-  });
+  const fbtOperands = memoizeFbtAndMacroOperandsInSameScope(hir);
   log({
     kind: 'hir',
     name: 'MemoizeFbtAndMacroOperandsInSameScope',
@@ -350,15 +314,11 @@ function runWithEnvironment(
   });
 
   if (env.config.enableJsxOutlining) {
-    env.tryRecord(() => {
-      outlineJSX(hir);
-    });
+    outlineJSX(hir);
   }
 
   if (env.config.enableNameAnonymousFunctions) {
-    env.tryRecord(() => {
-      nameAnonymousFunctions(hir);
-    });
+    nameAnonymousFunctions(hir);
     log({
       kind: 'hir',
       name: 'NameAnonymousFunctions',
@@ -367,51 +327,39 @@ function runWithEnvironment(
   }
 
   if (env.config.enableFunctionOutlining) {
-    env.tryRecord(() => {
-      outlineFunctions(hir, fbtOperands);
-    });
+    outlineFunctions(hir, fbtOperands);
     log({kind: 'hir', name: 'OutlineFunctions', value: hir});
   }
 
-  env.tryRecord(() => {
-    alignMethodCallScopes(hir);
-  });
+  alignMethodCallScopes(hir);
   log({
     kind: 'hir',
     name: 'AlignMethodCallScopes',
     value: hir,
   });
 
-  env.tryRecord(() => {
-    alignObjectMethodScopes(hir);
-  });
+  alignObjectMethodScopes(hir);
   log({
     kind: 'hir',
     name: 'AlignObjectMethodScopes',
     value: hir,
   });
 
-  env.tryRecord(() => {
-    pruneUnusedLabelsHIR(hir);
-  });
+  pruneUnusedLabelsHIR(hir);
   log({
     kind: 'hir',
     name: 'PruneUnusedLabelsHIR',
     value: hir,
   });
 
-  env.tryRecord(() => {
-    alignReactiveScopesToBlockScopesHIR(hir);
-  });
+  alignReactiveScopesToBlockScopesHIR(hir);
   log({
     kind: 'hir',
     name: 'AlignReactiveScopesToBlockScopesHIR',
     value: hir,
   });
 
-  env.tryRecord(() => {
-    mergeOverlappingReactiveScopesHIR(hir);
-  });
+  mergeOverlappingReactiveScopesHIR(hir);
   log({
     kind: 'hir',
     name: 'MergeOverlappingReactiveScopesHIR',
@@ -419,9 +367,7 @@ function runWithEnvironment(
   });
   assertValidBlockNesting(hir);
 
-  env.tryRecord(() => {
-    buildReactiveScopeTerminalsHIR(hir);
-  });
+  buildReactiveScopeTerminalsHIR(hir);
   log({
     kind: 'hir',
     name: 'BuildReactiveScopeTerminalsHIR',
@@ -430,18 +376,14 @@ function runWithEnvironment(
 
   assertValidBlockNesting(hir);
 
-  env.tryRecord(() => {
-    flattenReactiveLoopsHIR(hir);
-  });
+  flattenReactiveLoopsHIR(hir);
   log({
     kind: 'hir',
     name: 'FlattenReactiveLoopsHIR',
     value: hir,
   });
 
-  env.tryRecord(() => {
-    flattenScopesWithHooksOrUseHIR(hir);
-  });
+  flattenScopesWithHooksOrUseHIR(hir);
   log({
     kind: 'hir',
     name: 'FlattenScopesWithHooksOrUseHIR',
@@ -449,19 +391,15 @@ function runWithEnvironment(
   });
   assertTerminalSuccessorsExist(hir);
   assertTerminalPredsExist(hir);
-  env.tryRecord(() => {
-    propagateScopeDependenciesHIR(hir);
-  });
+
+  propagateScopeDependenciesHIR(hir);
   log({
     kind: 'hir',
     name: 'PropagateScopeDependenciesHIR',
     value: hir,
   });
 
-  let reactiveFunction!: ReactiveFunction;
-  env.tryRecord(() => {
-    reactiveFunction = buildReactiveFunction(hir);
-  });
+  const reactiveFunction = buildReactiveFunction(hir);
   log({
     kind: 'reactive',
     name: 'BuildReactiveFunction',
@@ -470,9 +408,7 @@ function runWithEnvironment(
 
   assertWellFormedBreakTargets(reactiveFunction);
 
-  env.tryRecord(() => {
-    pruneUnusedLabels(reactiveFunction);
-  });
+  pruneUnusedLabels(reactiveFunction);
   log({
     kind: 'reactive',
     name: 'PruneUnusedLabels',
@@ -480,109 +416,84 @@ function runWithEnvironment(
   });
   assertScopeInstructionsWithinScopes(reactiveFunction);
 
-  env.tryRecord(() => {
-    pruneNonEscapingScopes(reactiveFunction);
-  });
+  pruneNonEscapingScopes(reactiveFunction);
   log({
     kind: 'reactive',
     name: 'PruneNonEscapingScopes',
     value: reactiveFunction,
   });
 
-  env.tryRecord(() => {
-    pruneNonReactiveDependencies(reactiveFunction);
-  });
+  pruneNonReactiveDependencies(reactiveFunction);
   log({
     kind: 'reactive',
     name: 'PruneNonReactiveDependencies',
     value: reactiveFunction,
   });
 
-  env.tryRecord(() => {
-    pruneUnusedScopes(reactiveFunction);
-  });
+  pruneUnusedScopes(reactiveFunction);
   log({
     kind: 'reactive',
     name: 'PruneUnusedScopes',
     value: reactiveFunction,
   });
 
-  env.tryRecord(() => {
-    mergeReactiveScopesThatInvalidateTogether(reactiveFunction);
-  });
+  mergeReactiveScopesThatInvalidateTogether(reactiveFunction);
   log({
     kind: 'reactive',
     name: 'MergeReactiveScopesThatInvalidateTogether',
     value: reactiveFunction,
   });
 
-  env.tryRecord(() => {
-    pruneAlwaysInvalidatingScopes(reactiveFunction);
-  });
+  pruneAlwaysInvalidatingScopes(reactiveFunction);
   log({
     kind: 'reactive',
     name: 'PruneAlwaysInvalidatingScopes',
     value: reactiveFunction,
   });
 
-  env.tryRecord(() => {
-    propagateEarlyReturns(reactiveFunction);
-  });
+  propagateEarlyReturns(reactiveFunction);
   log({
     kind: 'reactive',
     name: 'PropagateEarlyReturns',
     value: reactiveFunction,
   });
 
-  env.tryRecord(() => {
-    pruneUnusedLValues(reactiveFunction);
-  });
+  pruneUnusedLValues(reactiveFunction);
   log({
     kind: 'reactive',
     name: 'PruneUnusedLValues',
     value: reactiveFunction,
   });
 
-  env.tryRecord(() => {
-    promoteUsedTemporaries(reactiveFunction);
-  });
+  promoteUsedTemporaries(reactiveFunction);
   log({
     kind: 'reactive',
     name: 'PromoteUsedTemporaries',
     value: reactiveFunction,
   });
 
-  env.tryRecord(() => {
-    extractScopeDeclarationsFromDestructuring(reactiveFunction);
-  });
+  extractScopeDeclarationsFromDestructuring(reactiveFunction);
   log({
     kind: 'reactive',
     name: 'ExtractScopeDeclarationsFromDestructuring',
     value: reactiveFunction,
   });
 
-  env.tryRecord(() => {
-    stabilizeBlockIds(reactiveFunction);
-  });
+  stabilizeBlockIds(reactiveFunction);
   log({
     kind: 'reactive',
     name: 'StabilizeBlockIds',
     value: reactiveFunction,
   });
 
-  let uniqueIdentifiers: Set<string> = new Set();
-  env.tryRecord(() => {
-    uniqueIdentifiers = renameVariables(reactiveFunction);
-  });
+  const uniqueIdentifiers = renameVariables(reactiveFunction);
   log({
     kind: 'reactive',
     name: 'RenameVariables',
     value: reactiveFunction,
   });
 
-  env.tryRecord(() => {
-    pruneHoistedContexts(reactiveFunction);
-  });
+  pruneHoistedContexts(reactiveFunction);
   log({
     kind: 'reactive',
     name: 'PruneHoistedContexts',

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

@@ -720,6 +720,20 @@ function tryCompileFunction(
       return {kind: 'error', error: result.unwrapErr()};
     }
   } catch (err) {
+    /**
+     * A pass incorrectly threw instead of recording the error.
+     * Log for detection in development.
+     */
+    if (
+      err instanceof CompilerError &&
+      err.details.every(detail => detail.category !== ErrorCategory.Invariant)
+    ) {
+      programContext.logEvent({
+        kind: 'CompileUnexpectedThrow',
+        fnLoc: fn.node.loc ?? null,
+        data: err.toString(),
+      });
+    }
     return {kind: 'error', error: err};
   }
 }

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

@@ -185,51 +185,32 @@ export function lower(
 
   let directives: Array<string> = [];
   const body = func.get('body');
-  try {
-    if (body.isExpression()) {
-      const fallthrough = builder.reserve('block');
-      const terminal: ReturnTerminal = {
-        kind: 'return',
-        returnVariant: 'Implicit',
-        loc: GeneratedSource,
-        value: lowerExpressionToTemporary(builder, body),
-        id: makeInstructionId(0),
-        effects: null,
-      };
-      builder.terminateWithContinuation(terminal, fallthrough);
-    } else if (body.isBlockStatement()) {
-      lowerStatement(builder, body);
-      directives = body.get('directives').map(d => d.node.value.value);
-    } else {
-      builder.errors.pushDiagnostic(
-        CompilerDiagnostic.create({
-          category: ErrorCategory.Syntax,
-          reason: `Unexpected function body kind`,
-          description: `Expected function body to be an expression or a block statement, got \`${body.type}\``,
-        }).withDetails({
-          kind: 'error',
-          loc: body.node.loc ?? null,
-          message: 'Expected a block statement or expression',
-        }),
-      );
-    }
-  } catch (err) {
-    if (err instanceof CompilerError) {
-      // Re-throw invariant errors immediately
-      for (const detail of err.details) {
-        if (
-          (detail instanceof CompilerDiagnostic
-            ? detail.category
-            : detail.category) === ErrorCategory.Invariant
-        ) {
-          throw err;
-        }
-      }
-      // Record non-invariant errors and continue to produce partial HIR
-      builder.errors.merge(err);
-    } else {
-      throw err;
-    }
+  if (body.isExpression()) {
+    const fallthrough = builder.reserve('block');
+    const terminal: ReturnTerminal = {
+      kind: 'return',
+      returnVariant: 'Implicit',
+      loc: GeneratedSource,
+      value: lowerExpressionToTemporary(builder, body),
+      id: makeInstructionId(0),
+      effects: null,
+    };
+    builder.terminateWithContinuation(terminal, fallthrough);
+  } else if (body.isBlockStatement()) {
+    lowerStatement(builder, body);
+    directives = body.get('directives').map(d => d.node.value.value);
+  } else {
+    builder.errors.pushDiagnostic(
+      CompilerDiagnostic.create({
+        category: ErrorCategory.Syntax,
+        reason: `Unexpected function body kind`,
+        description: `Expected function body to be an expression or a block statement, got \`${body.type}\``,
+      }).withDetails({
+        kind: 'error',
+        loc: body.node.loc ?? null,
+        message: 'Expected a block statement or expression',
+      }),
+    );
   }
 
   let validatedId: HIRFunction['id'] = null;

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

@@ -310,16 +310,13 @@ function traverseOptionalBlock(
      * - a optional base block with a separate nested optional-chain (e.g. a(c?.d)?.d)
      */
     const testBlock = context.blocks.get(maybeTest.terminal.fallthrough)!;
-    if (testBlock!.terminal.kind !== 'branch') {
-      /**
-       * Fallthrough of the inner optional should be a block with no
-       * instructions, terminating with Test($<temporary written to from
-       * StoreLocal>)
-       */
-      CompilerError.throwTodo({
-        reason: `Unexpected terminal kind \`${testBlock.terminal.kind}\` for optional fallthrough block`,
-        loc: maybeTest.terminal.loc,
-      });
+    /**
+     * Fallthrough of the inner optional should be a block with no
+     * instructions, terminating with Test($<temporary written to from
+     * StoreLocal>)
+     */
+    if (testBlock.terminal.kind !== 'branch') {
+      return null;
     }
     /**
      * Recurse into inner optional blocks to collect inner optional-chain

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

@@ -773,29 +773,6 @@ export class Environment {
     return this.#errors;
   }
 
-  /**
-   * Wraps a callback in try/catch: if the callback throws a CompilerError
-   * that is NOT an invariant, the error is recorded and execution continues.
-   * Non-CompilerError exceptions and invariants are re-thrown.
-   */
-  tryRecord(fn: () => void): void {
-    try {
-      fn();
-    } catch (err) {
-      if (err instanceof CompilerError) {
-        // Check if any detail is an invariant — if so, re-throw
-        for (const detail of err.details) {
-          if (detail.category === ErrorCategory.Invariant) {
-            throw err;
-          }
-        }
-        this.recordErrors(err);
-      } else {
-        throw err;
-      }
-    }
-  }
-
   isContextIdentifier(node: t.Identifier): boolean {
     return this.#contextIdentifiers.has(node);
   }

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

@@ -308,33 +308,23 @@ export default class HIRBuilder {
 
   resolveBinding(node: t.Identifier): Identifier {
     if (node.name === 'fbt') {
-      CompilerError.throwDiagnostic({
+      this.errors.push({
         category: ErrorCategory.Todo,
         reason: 'Support local variables named `fbt`',
         description:
           'Local variables named `fbt` may conflict with the fbt plugin and are not yet supported',
-        details: [
-          {
-            kind: 'error',
-            message: 'Rename to avoid conflict with fbt plugin',
-            loc: node.loc ?? GeneratedSource,
-          },
-        ],
+        loc: node.loc ?? GeneratedSource,
+        suggestions: null,
       });
     }
     if (node.name === 'this') {
-      CompilerError.throwDiagnostic({
+      this.errors.push({
         category: ErrorCategory.UnsupportedSyntax,
         reason: '`this` is not supported syntax',
         description:
           'React Compiler does not support compiling functions that use `this`',
-        details: [
-          {
-            kind: 'error',
-            message: '`this` was used here',
-            loc: node.loc ?? GeneratedSource,
-          },
-        ],
+        loc: node.loc ?? GeneratedSource,
+        suggestions: null,
       });
     }
     const originalName = node.name;

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

@@ -1007,11 +1007,10 @@ class Driver {
     const test = this.visitValueBlock(testBlockId, loc);
     const testBlock = this.cx.ir.blocks.get(test.block)!;
     if (testBlock.terminal.kind !== 'branch') {
-      CompilerError.throwTodo({
-        reason: `Unexpected terminal kind \`${testBlock.terminal.kind}\` for ${terminalKind} test block`,
-        description: null,
+      CompilerError.invariant(false, {
+        reason: `Expected a branch terminal for ${terminalKind} test block`,
+        description: `Got \`${testBlock.terminal.kind}\``,
         loc: testBlock.terminal.loc,
-        suggestions: null,
       });
     }
     return {

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

@@ -775,12 +775,13 @@ function codegenTerminal(
         loc: terminal.init.loc,
       });
       if (terminal.init.instructions.length !== 2) {
-        CompilerError.throwTodo({
+        cx.errors.push({
           reason: 'Support non-trivial for..in inits',
-          description: null,
+          category: ErrorCategory.Todo,
           loc: terminal.init.loc,
           suggestions: null,
         });
+        return t.emptyStatement();
       }
       const iterableCollection = terminal.init.instructions[0];
       const iterableItem = terminal.init.instructions[1];
@@ -795,12 +796,13 @@ function codegenTerminal(
           break;
         }
         case 'StoreContext': {
-          CompilerError.throwTodo({
+          cx.errors.push({
             reason: 'Support non-trivial for..in inits',
-            description: null,
+            category: ErrorCategory.Todo,
             loc: terminal.init.loc,
             suggestions: null,
           });
+          return t.emptyStatement();
         }
         default:
           CompilerError.invariant(false, {
@@ -870,12 +872,13 @@ function codegenTerminal(
         loc: terminal.test.loc,
       });
       if (terminal.test.instructions.length !== 2) {
-        CompilerError.throwTodo({
+        cx.errors.push({
           reason: 'Support non-trivial for..of inits',
-          description: null,
+          category: ErrorCategory.Todo,
           loc: terminal.init.loc,
           suggestions: null,
         });
+        return t.emptyStatement();
       }
       const iterableItem = terminal.test.instructions[1];
       let lval: t.LVal;
@@ -889,12 +892,13 @@ function codegenTerminal(
           break;
         }
         case 'StoreContext': {
-          CompilerError.throwTodo({
+          cx.errors.push({
             reason: 'Support non-trivial for..of inits',
-            description: null,
+            category: ErrorCategory.Todo,
             loc: terminal.init.loc,
             suggestions: null,
           });
+          return t.emptyStatement();
         }
         default:
           CompilerError.invariant(false, {

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

@@ -97,9 +97,7 @@ export function validateNoDerivedComputationsInEffects(fn: HIRFunction): void {
       }
     }
   }
-  for (const detail of errors.details) {
-    fn.env.recordError(detail);
-  }
+  fn.env.recordErrors(errors);
 }
 
 function validateEffect(

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

@@ -52,9 +52,7 @@ export function validatePreservedManualMemoization(fn: ReactiveFunction): void {
     manualMemoState: null,
   };
   visitReactiveFunction(fn, new Visitor(), state);
-  for (const detail of state.errors.details) {
-    fn.env.recordError(detail);
-  }
+  fn.env.recordErrors(state.errors);
 }
 
 const DEBUG = false;

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

@@ -310,7 +310,5 @@ export function validateSourceLocations(
     }
   }
 
-  for (const detail of errors.details) {
-    env.recordError(detail);
-  }
+  env.recordErrors(errors);
 }

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/ecma/error.reserved-words.expect.md

@@ -24,9 +24,9 @@ function useThing(fn) {
 ```
 Found 1 error:
 
-Invariant: [HIRBuilder] Unexpected null block
+Error: Expected a non-reserved identifier name
 
-expected block 0 to exist.
+`this` is a reserved word in JavaScript and cannot be used as an identifier name.
 ```
           
       

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

@@ -21,15 +21,15 @@ export const FIXTURE_ENTRYPOINT = {
 ```
 Found 1 error:
 
-Invariant: [InferMutationAliasingEffects] Expected value kind to be initialized
+Todo: [hoisting] EnterSSA: Expected identifier to be defined before being used
 
-<unknown> x$1.
+Identifier x$1 is undefined.
 
-error.dont-hoist-inline-reference.ts:3:21
+error.dont-hoist-inline-reference.ts:3:2
   1 | import {identity} from 'shared-runtime';
   2 | function useInvalid() {
 > 3 |   const x = identity(x);
-    |                      ^ this is uninitialized
+    |   ^^^^^^^^^^^^^^^^^^^^^^ [hoisting] EnterSSA: Expected identifier to be defined before being used
   4 |   return x;
   5 | }
   6 |

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.todo-optional-call-chain-in-optional.expect.md

@@ -1,39 +0,0 @@
-
-## Input
-
-```javascript
-function useFoo(props: {value: {x: string; y: string} | null}) {
-  const value = props.value;
-  return createArray(value?.x, value?.y)?.join(', ');
-}
-
-function createArray<T>(...args: Array<T>): Array<T> {
-  return args;
-}
-
-export const FIXTURE_ENTRYPONT = {
-  fn: useFoo,
-  props: [{value: null}],
-};
-
-```
-
-
-## Error
-
-```
-Found 1 error:
-
-Todo: Unexpected terminal kind `optional` for optional fallthrough block
-
-error.todo-optional-call-chain-in-optional.ts:3:21
-  1 | function useFoo(props: {value: {x: string; y: string} | null}) {
-  2 |   const value = props.value;
-> 3 |   return createArray(value?.x, value?.y)?.join(', ');
-    |                      ^^^^^^^^ Unexpected terminal kind `optional` for optional fallthrough block
-  4 | }
-  5 |
-  6 | function createArray<T>(...args: Array<T>): Array<T> {
-```
-          
-      

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.var-declaration-and-ref-access.expect.md

@@ -18,7 +18,12 @@ function Component() {
   // Error: reading ref during render
   const value = ref.current;
 
-  return <div>{value}{items.length}</div>;
+  return (
+    <div>
+      {value}
+      {items.length}
+    </div>
+  );
 }
 
 ```
@@ -50,8 +55,8 @@ error.var-declaration-and-ref-access.ts:15:16
 > 15 |   const value = ref.current;
      |                 ^^^^^^^^^^^ Cannot access ref value during render
   16 |
-  17 |   return <div>{value}{items.length}</div>;
-  18 | }
+  17 |   return (
+  18 |     <div>
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fbt/error.todo-fbt-as-local.expect.md

@@ -50,7 +50,7 @@ export const FIXTURE_ENTRYPOINT = {
 ## Error
 
 ```
-Found 1 error:
+Found 4 errors:
 
 Todo: Support local variables named `fbt`
 
@@ -60,10 +60,49 @@ error.todo-fbt-as-local.ts:18:19
   16 |
   17 | function Foo(props) {
 > 18 |   const getText1 = fbt =>
-     |                    ^^^ Rename to avoid conflict with fbt plugin
+     |                    ^^^ Support local variables named `fbt`
   19 |     fbt(
   20 |       `Hello, ${fbt.param('(key) name', identity(props.name))}!`,
   21 |       '(description) Greeting'
+
+Todo: Support local variables named `fbt`
+
+Local variables named `fbt` may conflict with the fbt plugin and are not yet supported.
+
+error.todo-fbt-as-local.ts:18:19
+  16 |
+  17 | function Foo(props) {
+> 18 |   const getText1 = fbt =>
+     |                    ^^^ Support local variables named `fbt`
+  19 |     fbt(
+  20 |       `Hello, ${fbt.param('(key) name', identity(props.name))}!`,
+  21 |       '(description) Greeting'
+
+Todo: Support local variables named `fbt`
+
+Local variables named `fbt` may conflict with the fbt plugin and are not yet supported.
+
+error.todo-fbt-as-local.ts:18:19
+  16 |
+  17 | function Foo(props) {
+> 18 |   const getText1 = fbt =>
+     |                    ^^^ Support local variables named `fbt`
+  19 |     fbt(
+  20 |       `Hello, ${fbt.param('(key) name', identity(props.name))}!`,
+  21 |       '(description) Greeting'
+
+Todo: Support local variables named `fbt`
+
+Local variables named `fbt` may conflict with the fbt plugin and are not yet supported.
+
+error.todo-fbt-as-local.ts:24:19
+  22 |     );
+  23 |
+> 24 |   const getText2 = fbt =>
+     |                    ^^^ Support local variables named `fbt`
+  25 |     fbt(
+  26 |       `Goodbye, ${fbt.param('(key) name', identity(props.name))}!`,
+  27 |       '(description) Greeting2'
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fbt/error.todo-locally-require-fbt.expect.md

@@ -16,17 +16,15 @@ function Component(props) {
 ```
 Found 1 error:
 
-Todo: Support local variables named `fbt`
+Invariant: <fbt> tags should be module-level imports
 
-Local variables named `fbt` may conflict with the fbt plugin and are not yet supported.
-
-error.todo-locally-require-fbt.ts:2:8
-  1 | function Component(props) {
-> 2 |   const fbt = require('fbt');
-    |         ^^^ Rename to avoid conflict with fbt plugin
+error.todo-locally-require-fbt.ts:4:10
+  2 |   const fbt = require('fbt');
   3 |
-  4 |   return <fbt desc="Description">{'Text'}</fbt>;
+> 4 |   return <fbt desc="Description">{'Text'}</fbt>;
+    |           ^^^ <fbt> tags should be module-level imports
   5 | }
+  6 |
 ```
           
       

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/propagate-scope-deps-hir-fork/error.todo-optional-call-chain-in-optional.expect.md

@@ -1,40 +0,0 @@
-
-## Input
-
-```javascript
-// @enablePropagateDepsInHIR
-function useFoo(props: {value: {x: string; y: string} | null}) {
-  const value = props.value;
-  return createArray(value?.x, value?.y)?.join(', ');
-}
-
-function createArray<T>(...args: Array<T>): Array<T> {
-  return args;
-}
-
-export const FIXTURE_ENTRYPONT = {
-  fn: useFoo,
-  props: [{value: null}],
-};
-
-```
-
-
-## Error
-
-```
-Found 1 error:
-
-Todo: Unexpected terminal kind `optional` for optional fallthrough block
-
-error.todo-optional-call-chain-in-optional.ts:4:21
-  2 | function useFoo(props: {value: {x: string; y: string} | null}) {
-  3 |   const value = props.value;
-> 4 |   return createArray(value?.x, value?.y)?.join(', ');
-    |                      ^^^^^^^^ Unexpected terminal kind `optional` for optional fallthrough block
-  5 | }
-  6 |
-  7 | function createArray<T>(...args: Array<T>): Array<T> {
-```
-          
-      

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/propagate-scope-deps-hir-fork/todo-optional-call-chain-in-optional.expect.md

@@ -0,0 +1,54 @@
+
+## Input
+
+```javascript
+// @enablePropagateDepsInHIR
+function useFoo(props: {value: {x: string; y: string} | null}) {
+  const value = props.value;
+  return createArray(value?.x, value?.y)?.join(', ');
+}
+
+function createArray<T>(...args: Array<T>): Array<T> {
+  return args;
+}
+
+export const FIXTURE_ENTRYPONT = {
+  fn: useFoo,
+  props: [{value: null}],
+};
+
+```
+
+## Code
+
+```javascript
+import { c as _c } from "react/compiler-runtime"; // @enablePropagateDepsInHIR
+function useFoo(props) {
+  const $ = _c(3);
+  const value = props.value;
+  let t0;
+  if ($[0] !== value?.x || $[1] !== value?.y) {
+    t0 = createArray(value?.x, value?.y)?.join(", ");
+    $[0] = value?.x;
+    $[1] = value?.y;
+    $[2] = t0;
+  } else {
+    t0 = $[2];
+  }
+  return t0;
+}
+
+function createArray(...t0) {
+  const args = t0;
+  return args;
+}
+
+export const FIXTURE_ENTRYPONT = {
+  fn: useFoo,
+  props: [{ value: null }],
+};
+
+```
+      
+### Eval output
+(kind: exception) Fixture not implemented

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/todo-optional-call-chain-in-optional.expect.md

@@ -0,0 +1,53 @@
+
+## Input
+
+```javascript
+function useFoo(props: {value: {x: string; y: string} | null}) {
+  const value = props.value;
+  return createArray(value?.x, value?.y)?.join(', ');
+}
+
+function createArray<T>(...args: Array<T>): Array<T> {
+  return args;
+}
+
+export const FIXTURE_ENTRYPONT = {
+  fn: useFoo,
+  props: [{value: null}],
+};
+
+```
+
+## Code
+
+```javascript
+import { c as _c } from "react/compiler-runtime";
+function useFoo(props) {
+  const $ = _c(3);
+  const value = props.value;
+  let t0;
+  if ($[0] !== value?.x || $[1] !== value?.y) {
+    t0 = createArray(value?.x, value?.y)?.join(", ");
+    $[0] = value?.x;
+    $[1] = value?.y;
+    $[2] = t0;
+  } else {
+    t0 = $[2];
+  }
+  return t0;
+}
+
+function createArray(...t0) {
+  const args = t0;
+  return args;
+}
+
+export const FIXTURE_ENTRYPONT = {
+  fn: useFoo,
+  props: [{ value: null }],
+};
+
+```
+      
+### Eval output
+(kind: exception) Fixture not implemented

compiler/packages/snap/src/compiler.ts

@@ -378,6 +378,17 @@ export async function transformFixtureInput(
       msg: 'Expected nothing to be compiled (from `// @expectNothingCompiled`), but some functions compiled or errored',
     };
   }
+  const unexpectedThrows = logs.filter(
+    log => log.event.kind === 'CompileUnexpectedThrow',
+  );
+  if (unexpectedThrows.length > 0) {
+    return {
+      kind: 'err',
+      msg:
+        `Compiler pass(es) threw instead of recording errors:\n` +
+        unexpectedThrows.map(l => (l.event as any).data).join('\n'),
+    };
+  }
   return {
     kind: 'ok',
     value: {