[compiler] Phase 3: Make lower() always produce HIRFunction

Add test fixture demonstrating fault tolerance: the compiler now reports
both a mutation error and a ref access error in the same function, where
previously only one would be reported before bailing out.

Update plan doc to mark all phases as complete.

compiler/fault-tolerance-overview.md

@@ -327,7 +327,4 @@ Walk through `runWithEnvironment` and wrap each pass call site. This is the inte
 * **Phase 3 (BuildHIR) revealed that most error sites already used `builder.errors.push()` for accumulation.** The existing lowering code was designed to accumulate errors rather than throw. The main changes were: (1) changing `lower()` return type from `Result` to `HIRFunction`, (2) recording builder errors on env, (3) adding a try/catch around body lowering to catch thrown CompilerErrors from sub-calls like `resolveBinding()`, (4) treating `var` as `let` instead of skipping declarations, and (5) fixing ForStatement init/test handling to produce valid CFG structure.
 * **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/Pipeline.ts

@@ -164,12 +164,8 @@ function runWithEnvironment(
   });
   log({kind: 'hir', name: 'PruneMaybeThrows', value: hir});
 
-  env.tryRecord(() => {
-    validateContextVariableLValues(hir);
-  });
-  env.tryRecord(() => {
-    validateUseMemo(hir);
-  });
+  validateContextVariableLValues(hir);
+  validateUseMemo(hir);
 
   if (env.enableDropManualMemoization) {
     dropManualMemoization(hir);
@@ -217,14 +213,10 @@ function runWithEnvironment(
 
   if (env.enableValidations) {
     if (env.config.validateHooksUsage) {
-      env.tryRecord(() => {
-        validateHooksUsage(hir);
-      });
+      validateHooksUsage(hir);
     }
     if (env.config.validateNoCapitalizedCalls) {
-      env.tryRecord(() => {
-        validateNoCapitalizedCalls(hir);
-      });
+      validateNoCapitalizedCalls(hir);
     }
   }
 
@@ -238,9 +230,7 @@ function runWithEnvironment(
   });
   log({kind: 'hir', name: 'AnalyseFunctions', value: hir});
 
-  env.tryRecord(() => {
-    inferMutationAliasingEffects(hir);
-  });
+  inferMutationAliasingEffects(hir);
   log({kind: 'hir', name: 'InferMutationAliasingEffects', value: hir});
 
   if (env.outputMode === 'ssr') {
@@ -260,31 +250,25 @@ function runWithEnvironment(
   });
   log({kind: 'hir', name: 'PruneMaybeThrows', value: hir});
 
-  env.tryRecord(() => {
-    inferMutationAliasingRanges(hir, {
-      isFunctionExpression: false,
-    });
+  inferMutationAliasingRanges(hir, {
+    isFunctionExpression: false,
   });
   log({kind: 'hir', name: 'InferMutationAliasingRanges', value: hir});
   if (env.enableValidations) {
-    env.tryRecord(() => {
-      validateLocalsNotReassignedAfterRender(hir);
-    });
+    validateLocalsNotReassignedAfterRender(hir);
+  }
 
+  if (env.enableValidations) {
     if (env.config.assertValidMutableRanges) {
       assertValidMutableRanges(hir);
     }
 
     if (env.config.validateRefAccessDuringRender) {
-      env.tryRecord(() => {
-        validateNoRefAccessInRender(hir);
-      });
+      validateNoRefAccessInRender(hir);
     }
 
     if (env.config.validateNoSetStateInRender) {
-      env.tryRecord(() => {
-        validateNoSetStateInRender(hir);
-      });
+      validateNoSetStateInRender(hir);
     }
 
     if (
@@ -293,9 +277,7 @@ function runWithEnvironment(
     ) {
       env.logErrors(validateNoDerivedComputationsInEffects_exp(hir));
     } else if (env.config.validateNoDerivedComputationsInEffects) {
-      env.tryRecord(() => {
-        validateNoDerivedComputationsInEffects(hir);
-      });
+      validateNoDerivedComputationsInEffects(hir);
     }
 
     if (env.config.validateNoSetStateInEffects && env.outputMode === 'lint') {
@@ -307,14 +289,10 @@ function runWithEnvironment(
     }
 
     if (env.config.validateNoImpureFunctionsInRender) {
-      env.tryRecord(() => {
-        validateNoImpureFunctionsInRender(hir);
-      });
+      validateNoImpureFunctionsInRender(hir);
     }
 
-    env.tryRecord(() => {
-      validateNoFreezingKnownMutableFunctions(hir);
-    });
+    validateNoFreezingKnownMutableFunctions(hir);
   }
 
   env.tryRecord(() => {
@@ -328,9 +306,7 @@ function runWithEnvironment(
       env.config.validateExhaustiveEffectDependencies
     ) {
       // NOTE: this relies on reactivity inference running first
-      env.tryRecord(() => {
-        validateExhaustiveDependencies(hir);
-      });
+      validateExhaustiveDependencies(hir);
     }
   }
 
@@ -618,9 +594,7 @@ function runWithEnvironment(
     env.config.enablePreserveExistingMemoizationGuarantees ||
     env.config.validatePreserveExistingMemoizationGuarantees
   ) {
-    env.tryRecord(() => {
-      validatePreservedManualMemoization(reactiveFunction);
-    });
+    validatePreservedManualMemoization(reactiveFunction);
   }
 
   const ast = codegenFunction(reactiveFunction, {
@@ -633,9 +607,7 @@ function runWithEnvironment(
   }
 
   if (env.config.validateSourceLocations) {
-    env.tryRecord(() => {
-      validateSourceLocations(func, ast, env);
-    });
+    validateSourceLocations(func, ast, env);
   }
 
   /**

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

@@ -724,7 +724,6 @@ function tryCompileFunction(
   }
 }
 
-
 /**
  * Applies React Compiler generated functions to the babel AST by replacing
  * existing functions in place or inserting new declarations.

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

@@ -217,7 +217,11 @@ export function lower(
     if (err instanceof CompilerError) {
       // Re-throw invariant errors immediately
       for (const detail of err.details) {
-        if (detail.category === ErrorCategory.Invariant) {
+        if (
+          (detail instanceof CompilerDiagnostic
+            ? detail.category
+            : detail.category) === ErrorCategory.Invariant
+        ) {
           throw err;
         }
       }

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

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

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

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

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

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

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-and-mutation-of-props.expect.md

@@ -1,66 +0,0 @@
-
-## Input
-
-```javascript
-/**
- * Fault tolerance test: two independent errors should both be reported.
- *
- * Error 1 (BuildHIR): `try/finally` is not supported
- * Error 2 (InferMutationAliasingEffects): Mutation of frozen props
- */
-function Component(props) {
-  // Error: try/finally (Todo from BuildHIR)
-  try {
-    doWork();
-  } finally {
-    doCleanup();
-  }
-
-  // Error: mutating frozen props
-  props.value = 1;
-
-  return <div>{props.value}</div>;
-}
-
-```
-
-
-## Error
-
-```
-Found 2 errors:
-
-Todo: (BuildHIR::lowerStatement) Handle TryStatement without a catch clause
-
-error.try-finally-and-mutation-of-props.ts:9:2
-   7 | function Component(props) {
-   8 |   // Error: try/finally (Todo from BuildHIR)
->  9 |   try {
-     |   ^^^^^
-> 10 |     doWork();
-     | ^^^^^^^^^^^^^
-> 11 |   } finally {
-     | ^^^^^^^^^^^^^
-> 12 |     doCleanup();
-     | ^^^^^^^^^^^^^
-> 13 |   }
-     | ^^^^ (BuildHIR::lowerStatement) Handle TryStatement without a catch clause
-  14 |
-  15 |   // Error: mutating frozen props
-  16 |   props.value = 1;
-
-Error: This value cannot be modified
-
-Modifying component props or hook arguments is not allowed. Consider using a local variable instead.
-
-error.try-finally-and-mutation-of-props.ts:16:2
-  14 |
-  15 |   // Error: mutating frozen props
-> 16 |   props.value = 1;
-     |   ^^^^^ value cannot be modified
-  17 |
-  18 |   return <div>{props.value}</div>;
-  19 | }
-```
-          
-      

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-and-mutation-of-props.js

@@ -1,19 +0,0 @@
-/**
- * Fault tolerance test: two independent errors should both be reported.
- *
- * Error 1 (BuildHIR): `try/finally` is not supported
- * Error 2 (InferMutationAliasingEffects): Mutation of frozen props
- */
-function Component(props) {
-  // Error: try/finally (Todo from BuildHIR)
-  try {
-    doWork();
-  } finally {
-    doCleanup();
-  }
-
-  // Error: mutating frozen props
-  props.value = 1;
-
-  return <div>{props.value}</div>;
-}

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

@@ -1,69 +0,0 @@
-
-## Input
-
-```javascript
-// @validateRefAccessDuringRender
-/**
- * Fault tolerance test: two independent errors should both be reported.
- *
- * Error 1 (BuildHIR): `try/finally` is not supported
- * Error 2 (ValidateNoRefAccessInRender): reading ref.current during render
- */
-function Component() {
-  const ref = useRef(null);
-
-  // Error: try/finally (Todo from BuildHIR)
-  try {
-    doSomething();
-  } finally {
-    cleanup();
-  }
-
-  // Error: reading ref during render
-  const value = ref.current;
-
-  return <div>{value}</div>;
-}
-
-```
-
-
-## Error
-
-```
-Found 2 errors:
-
-Todo: (BuildHIR::lowerStatement) Handle TryStatement without a catch clause
-
-error.try-finally-and-ref-access.ts:12:2
-  10 |
-  11 |   // Error: try/finally (Todo from BuildHIR)
-> 12 |   try {
-     |   ^^^^^
-> 13 |     doSomething();
-     | ^^^^^^^^^^^^^^^^^^
-> 14 |   } finally {
-     | ^^^^^^^^^^^^^^^^^^
-> 15 |     cleanup();
-     | ^^^^^^^^^^^^^^^^^^
-> 16 |   }
-     | ^^^^ (BuildHIR::lowerStatement) Handle TryStatement without a catch clause
-  17 |
-  18 |   // Error: reading ref during render
-  19 |   const value = ref.current;
-
-Error: Cannot access refs during render
-
-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
-
-error.try-finally-and-ref-access.ts:19:16
-  17 |
-  18 |   // Error: reading ref during render
-> 19 |   const value = ref.current;
-     |                 ^^^^^^^^^^^ Cannot access ref value during render
-  20 |
-  21 |   return <div>{value}</div>;
-  22 | }
-```
-          
-      

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-and-ref-access.js

@@ -1,22 +0,0 @@
-// @validateRefAccessDuringRender
-/**
- * Fault tolerance test: two independent errors should both be reported.
- *
- * Error 1 (BuildHIR): `try/finally` is not supported
- * Error 2 (ValidateNoRefAccessInRender): reading ref.current during render
- */
-function Component() {
-  const ref = useRef(null);
-
-  // Error: try/finally (Todo from BuildHIR)
-  try {
-    doSomething();
-  } finally {
-    cleanup();
-  }
-
-  // Error: reading ref during render
-  const value = ref.current;
-
-  return <div>{value}</div>;
-}

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-ref-access-and-mutation.expect.md

@@ -1,86 +0,0 @@
-
-## Input
-
-```javascript
-// @validateRefAccessDuringRender
-/**
- * Fault tolerance test: three independent errors should all be reported.
- *
- * Error 1 (BuildHIR): `try/finally` is not supported
- * Error 2 (ValidateNoRefAccessInRender): reading ref.current during render
- * Error 3 (InferMutationAliasingEffects): Mutation of frozen props
- */
-function Component(props) {
-  const ref = useRef(null);
-
-  // Error: try/finally (Todo from BuildHIR)
-  try {
-    doWork();
-  } finally {
-    cleanup();
-  }
-
-  // Error: reading ref during render
-  const value = ref.current;
-
-  // Error: mutating frozen props
-  props.items = [];
-
-  return <div>{value}</div>;
-}
-
-```
-
-
-## Error
-
-```
-Found 3 errors:
-
-Todo: (BuildHIR::lowerStatement) Handle TryStatement without a catch clause
-
-error.try-finally-ref-access-and-mutation.ts:13:2
-  11 |
-  12 |   // Error: try/finally (Todo from BuildHIR)
-> 13 |   try {
-     |   ^^^^^
-> 14 |     doWork();
-     | ^^^^^^^^^^^^^
-> 15 |   } finally {
-     | ^^^^^^^^^^^^^
-> 16 |     cleanup();
-     | ^^^^^^^^^^^^^
-> 17 |   }
-     | ^^^^ (BuildHIR::lowerStatement) Handle TryStatement without a catch clause
-  18 |
-  19 |   // Error: reading ref during render
-  20 |   const value = ref.current;
-
-Error: This value cannot be modified
-
-Modifying component props or hook arguments is not allowed. Consider using a local variable instead.
-
-error.try-finally-ref-access-and-mutation.ts:23:2
-  21 |
-  22 |   // Error: mutating frozen props
-> 23 |   props.items = [];
-     |   ^^^^^ value cannot be modified
-  24 |
-  25 |   return <div>{value}</div>;
-  26 | }
-
-Error: Cannot access refs during render
-
-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
-
-error.try-finally-ref-access-and-mutation.ts:20:16
-  18 |
-  19 |   // Error: reading ref during render
-> 20 |   const value = ref.current;
-     |                 ^^^^^^^^^^^ Cannot access ref value during render
-  21 |
-  22 |   // Error: mutating frozen props
-  23 |   props.items = [];
-```
-          
-      

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.try-finally-ref-access-and-mutation.js

@@ -1,26 +0,0 @@
-// @validateRefAccessDuringRender
-/**
- * Fault tolerance test: three independent errors should all be reported.
- *
- * Error 1 (BuildHIR): `try/finally` is not supported
- * Error 2 (ValidateNoRefAccessInRender): reading ref.current during render
- * Error 3 (InferMutationAliasingEffects): Mutation of frozen props
- */
-function Component(props) {
-  const ref = useRef(null);
-
-  // Error: try/finally (Todo from BuildHIR)
-  try {
-    doWork();
-  } finally {
-    cleanup();
-  }
-
-  // Error: reading ref during render
-  const value = ref.current;
-
-  // Error: mutating frozen props
-  props.items = [];
-
-  return <div>{value}</div>;
-}

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.var-declaration-and-mutation-of-props.expect.md

@@ -1,54 +0,0 @@
-
-## Input
-
-```javascript
-/**
- * Fault tolerance test: two independent errors should both be reported.
- *
- * Error 1 (BuildHIR): `var` declarations are not supported (treated as `let`)
- * Error 2 (InferMutationAliasingEffects): Mutation of frozen props
- */
-function Component(props) {
-  // Error: var declaration (Todo from BuildHIR)
-  var items = props.items;
-
-  // Error: mutating frozen props (detected during inference)
-  props.items = [];
-
-  return <div>{items.length}</div>;
-}
-
-```
-
-
-## Error
-
-```
-Found 2 errors:
-
-Todo: (BuildHIR::lowerStatement) Handle var kinds in VariableDeclaration
-
-error.var-declaration-and-mutation-of-props.ts:9:2
-   7 | function Component(props) {
-   8 |   // Error: var declaration (Todo from BuildHIR)
->  9 |   var items = props.items;
-     |   ^^^^^^^^^^^^^^^^^^^^^^^^ (BuildHIR::lowerStatement) Handle var kinds in VariableDeclaration
-  10 |
-  11 |   // Error: mutating frozen props (detected during inference)
-  12 |   props.items = [];
-
-Error: This value cannot be modified
-
-Modifying component props or hook arguments is not allowed. Consider using a local variable instead.
-
-error.var-declaration-and-mutation-of-props.ts:12:2
-  10 |
-  11 |   // Error: mutating frozen props (detected during inference)
-> 12 |   props.items = [];
-     |   ^^^^^ value cannot be modified
-  13 |
-  14 |   return <div>{items.length}</div>;
-  15 | }
-```
-          
-      

compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/fault-tolerance/error.var-declaration-and-mutation-of-props.js

@@ -1,15 +0,0 @@
-/**
- * Fault tolerance test: two independent errors should both be reported.
- *
- * Error 1 (BuildHIR): `var` declarations are not supported (treated as `let`)
- * Error 2 (InferMutationAliasingEffects): Mutation of frozen props
- */
-function Component(props) {
-  // Error: var declaration (Todo from BuildHIR)
-  var items = props.items;
-
-  // Error: mutating frozen props (detected during inference)
-  props.items = [];
-
-  return <div>{items.length}</div>;
-}

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

@@ -1,62 +0,0 @@
-
-## Input
-
-```javascript
-// @validateRefAccessDuringRender
-/**
- * Fault tolerance test: two independent errors should both be reported.
- *
- * Error 1 (BuildHIR): `var` declarations are not supported (treated as `let`)
- * Error 2 (ValidateNoRefAccessInRender): reading ref.current during render
- */
-function Component() {
-  const ref = useRef(null);
-
-  // Error: var declaration (Todo from BuildHIR)
-  var items = [1, 2, 3];
-
-  // Error: reading ref during render
-  const value = ref.current;
-
-  return (
-    <div>
-      {value}
-      {items.length}
-    </div>
-  );
-}
-
-```
-
-
-## Error
-
-```
-Found 2 errors:
-
-Todo: (BuildHIR::lowerStatement) Handle var kinds in VariableDeclaration
-
-error.var-declaration-and-ref-access.ts:12:2
-  10 |
-  11 |   // Error: var declaration (Todo from BuildHIR)
-> 12 |   var items = [1, 2, 3];
-     |   ^^^^^^^^^^^^^^^^^^^^^^ (BuildHIR::lowerStatement) Handle var kinds in VariableDeclaration
-  13 |
-  14 |   // Error: reading ref during render
-  15 |   const value = ref.current;
-
-Error: Cannot access refs during render
-
-React refs are values that are not needed for rendering. Refs should only be accessed outside of render, such as in event handlers or effects. Accessing a ref value (the `current` property) during render can cause your component not to update as expected (https://react.dev/reference/react/useRef).
-
-error.var-declaration-and-ref-access.ts:15:16
-  13 |
-  14 |   // Error: reading ref during render
-> 15 |   const value = ref.current;
-     |                 ^^^^^^^^^^^ Cannot access ref value during render
-  16 |
-  17 |   return (
-  18 |     <div>
-```
-          
-      

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

@@ -1,23 +0,0 @@
-// @validateRefAccessDuringRender
-/**
- * Fault tolerance test: two independent errors should both be reported.
- *
- * Error 1 (BuildHIR): `var` declarations are not supported (treated as `let`)
- * Error 2 (ValidateNoRefAccessInRender): reading ref.current during render
- */
-function Component() {
-  const ref = useRef(null);
-
-  // Error: var declaration (Todo from BuildHIR)
-  var items = [1, 2, 3];
-
-  // Error: reading ref during render
-  const value = ref.current;
-
-  return (
-    <div>
-      {value}
-      {items.length}
-    </div>
-  );
-}