[compiler] Add fault tolerance test fixtures

[everettbu]

Mirror of facebook/react#35848
Original author: josephsavona

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Stack created with Sapling. Best reviewed with ReviewStack.

• #35853
• #35852
• #35851
• #35850
• #35849
• -> #35848
• #35847
• #35845
• #35844
• #35843
• #35842
• #35841
• #35840

[greptile-apps]

Greptile Summary

This PR adds fault tolerance to the React Compiler pipeline, enabling it to continue running all passes and report multiple errors at once rather than stopping at the first error. This is a mirror of react/react#35848.

• Adds error accumulation infrastructure to Environment (recordError, tryRecord, hasErrors, aggregateErrors) with proper invariant re-throwing
• Changes runWithEnvironment and compileFn to return Result<CodegenFunction, CompilerError>, checking for accumulated errors at the end of the pipeline
• Updates lower() in BuildHIR.ts to always produce an HIRFunction (even partial) instead of returning Result, with best-effort handling for var (treated as let), for(;;) (empty init/test), and caught non-invariant errors
• Migrates all 13+ validation passes from returning Result / throwing to recording errors on fn.env, removing .unwrap() calls throughout the pipeline
• Updates inference passes (InferMutationAliasingEffects, InferMutationAliasingRanges) and codegen (codegenFunction) to record errors on env instead of returning Result
• Wraps each pipeline pass in env.tryRecord() as defense-in-depth for any passes that still throw
• Adds dedicated fault tolerance test fixtures verifying multi-error reporting across different compiler phases
• Updates ~40 existing test fixture expectations to reflect newly-surfaced errors that were previously masked

Confidence Score: 4/5

• This PR is a well-structured architectural change with comprehensive test coverage updates, though some edge cases around uninitialized variables in the fault tolerance path warrant attention.
• The changes are systematic and follow a clear phased plan documented in the overview. The core tryRecord/recordError pattern is sound, invariant errors are correctly re-thrown, and the test fixture updates demonstrate the feature works as intended. One concern is the definite assignment assertion (!:) on reactiveFunction which could cause runtime crashes if buildReactiveFunction throws a non-invariant error. The overall risk is low since this is a compiler that bails out gracefully on errors.
• Pipeline.ts deserves attention for the reactiveFunction definite assignment assertion pattern. BuildHIR.ts has the most complex changes with the partial HIR construction logic.

Important Files Changed

Filename	Overview
compiler/packages/babel-plugin-react-compiler/src/HIR/Environment.ts	Adds error accumulation infrastructure (#errors, recordError, recordErrors, tryRecord, hasErrors, aggregateErrors) to Environment. Clean implementation with proper invariant re-throwing.
compiler/packages/babel-plugin-react-compiler/src/Entrypoint/Pipeline.ts	Core pipeline changes: wraps all passes in env.tryRecord(), changes return type to Result<CodegenFunction, CompilerError>, removes .unwrap() calls. Uses definite assignment assertions (!:) for reactiveFunction and uniqueIdentifiers.
compiler/packages/babel-plugin-react-compiler/src/HIR/BuildHIR.ts	Changes lower() to always return HIRFunction instead of Result. Adds try/catch around body lowering, treats var as let, handles for(;;) empty init/test, always produces partial HIR on error. Removes unused effects field from return value.
compiler/packages/babel-plugin-react-compiler/src/Entrypoint/Program.ts	Updates tryCompileFunction to handle the new Result return type from compileFn instead of directly using the value.
compiler/packages/babel-plugin-react-compiler/src/ReactiveScopes/CodegenReactiveFunction.ts	Changes codegenFunction and codegenReactiveFunction to return CodegenFunction directly instead of Result. Records errors on env and continues. Removes .unwrap() calls from recursive codegen of outlined/nested functions.
compiler/packages/babel-plugin-react-compiler/src/Validation/ValidateNoRefAccessInRender.ts	Refactored to pass errors as a parameter instead of returning Result. Inner function errors correctly used for ref effect detection without being propagated (preserving existing behavior).
compiler/packages/babel-plugin-react-compiler/src/Inference/InferMutationAliasingRanges.ts	Changed to always return Array<AliasingEffect> instead of Result. Records errors on env when enableValidations is true and not a function expression.
compiler/packages/babel-plugin-react-compiler/src/HIR/HIRBuilder.ts	Changed CompilerError.throwTodo() for unreachable hoisted functions to this.errors.push() to allow HIR construction to complete.
compiler/fault-tolerance-overview.md	Comprehensive design document covering the fault tolerance approach, phased plan, and key learnings. Well-structured documentation of the architectural change.

_{Last reviewed commit: 6337950}

[greptile-apps]

_{68 files reviewed, 2 comments}

_{Edit Code Review Agent Settings | Greptile}

[greptile-apps]

Uninitialized variable after caught error

If buildReactiveFunction(hir) throws a non-invariant CompilerError (e.g. a Todo error — BuildReactiveFunction.ts has several CompilerError.throwTodo() calls), tryRecord will catch it and record the error. However, reactiveFunction will remain uninitialized at runtime because the assignment inside the callback never executed. The !: definite assignment assertion silences TypeScript but doesn't protect at runtime.

Subsequent code on line 471 (assertWellFormedBreakTargets(reactiveFunction)) and all later passes will operate on an undefined value, likely crashing with a confusing error that masks the original problem.

Consider initializing with a safe default before the tryRecord block (similar to how fbtOperands and uniqueIdentifiers are handled), or checking whether reactiveFunction was assigned before continuing with subsequent passes.

Prompt To Fix With AI

This is a comment left during a code review.
Path: compiler/packages/babel-plugin-react-compiler/src/Entrypoint/Pipeline.ts
Line: 461-464

Comment:
**Uninitialized variable after caught error**

If `buildReactiveFunction(hir)` throws a non-invariant `CompilerError` (e.g. a `Todo` error — `BuildReactiveFunction.ts` has several `CompilerError.throwTodo()` calls), `tryRecord` will catch it and record the error. However, `reactiveFunction` will remain uninitialized at runtime because the assignment inside the callback never executed. The `!:` definite assignment assertion silences TypeScript but doesn't protect at runtime.

Subsequent code on line 471 (`assertWellFormedBreakTargets(reactiveFunction)`) and all later passes will operate on an `undefined` value, likely crashing with a confusing error that masks the original problem.

Consider initializing with a safe default before the `tryRecord` block (similar to how `fbtOperands` and `uniqueIdentifiers` are handled), or checking whether `reactiveFunction` was assigned before continuing with subsequent passes.

How can I resolve this? If you propose a fix, please make it concise.

[greptile-apps]

Redundant ternary condition

Both branches of this ternary access detail.category, making the conditional unnecessary. This was likely intended to differentiate between CompilerDiagnostic and CompilerErrorDetail, but since both have a .category property, the ternary is a no-op.

Suggested change

	if (
	(detail instanceof CompilerDiagnostic
	? detail.category
	: detail.category) === ErrorCategory.Invariant
	) {
	detail.category === ErrorCategory.Invariant

Prompt To Fix With AI

This is a comment left during a code review.
Path: compiler/packages/babel-plugin-react-compiler/src/HIR/BuildHIR.ts
Line: 220-224

Comment:
**Redundant ternary condition**

Both branches of this ternary access `detail.category`, making the conditional unnecessary. This was likely intended to differentiate between `CompilerDiagnostic` and `CompilerErrorDetail`, but since both have a `.category` property, the ternary is a no-op.

```suggestion
          detail.category === ErrorCategory.Invariant
```

How can I resolve this? If you propose a fix, please make it concise.

[everettbu]

Upstream PR was closed or merged. Code is synced via branch mirror.