Fix : Compiler eslint suppression silent skip 35105

[everettbu]

Mirror of facebook/react#35124
Original author: manNomi

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Summary

This PR fixes #35105 where eslint-disable comments cause the React Compiler to skip entire functions, preventing important diagnostics like incompatible-library warnings from being shown.

Motivation: When developers add unrelated ESLint suppressions (e.g., for exhaustive-deps), the compiler would silently skip analyzing the entire function. This meant critical warnings about incompatible APIs would never reach the developer, leading to silent performance issues in production.

Solution: Implemented the "shorter term fix" suggested by @josephsavona - in ESLint mode (noEmit: true), suppressions are now logged as diagnostics but compilation continues to detect other issues. Build mode behavior is unchanged for backward compatibility.

Real-World Testing

As is	To be

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[greptile-apps]

Greptile Summary

This PR fixes a critical issue where ESLint suppressions caused the React Compiler to silently skip entire functions in ESLint mode, preventing important diagnostics like incompatible-library warnings from being shown.

The implementation correctly modifies tryCompileFunction in Program.ts to distinguish between build mode and ESLint mode (noEmit: true). In ESLint mode, suppressions are now logged as diagnostics but compilation continues to detect other issues. Build mode behavior remains unchanged for backward compatibility.

Key changes:

• Modified suppression handling in Program.ts:736-749 to check noEmit flag
• In build mode: returns early with suppression error (existing behavior)
• In ESLint mode: logs suppression error and continues compilation (new behavior)
• Added comprehensive test case demonstrating the fix

Issue identified:

• Test expectation file shows "Found 1 error" but will produce 2 errors in practice (both the suppression error and the incompatible-library error)

Confidence Score: 4/5

• This PR is safe to merge after fixing the test expectation mismatch
• The implementation correctly addresses the stated goal of allowing ESLint mode to continue compilation after detecting suppressions. The logic is sound and maintains backward compatibility by only changing behavior when noEmit: true. However, the test expectation needs to be corrected to match the actual behavior (2 errors instead of 1).
• Pay close attention to error.eslint-mode-detects-incompatible-library-with-suppression.expect.md - the expected output must be updated to reflect 2 errors

Important Files Changed

Filename	Overview
compiler/packages/babel-plugin-react-compiler/src/Entrypoint/Program.ts	implements ESLint mode behavior to log suppressions but continue compilation, allowing detection of other issues like incompatible-library warnings
compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.eslint-mode-detects-incompatible-library-with-suppression.js	test fixture demonstrating that ESLint mode detects incompatible-library errors even when eslint suppressions are present
compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/error.eslint-mode-detects-incompatible-library-with-suppression.expect.md	expected test output shows only 1 error, but the implementation will produce 2 errors (suppression + incompatible-library)

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[greptile-apps]

[P1] Test expectation shows "Found 1 error" but the implementation will produce 2 errors. The eslint suppression on line 9 of the test file (react-hooks/exhaustive-deps) is in DEFAULT_ESLINT_SUPPRESSIONS and will be detected. In ESLint mode, the code logs this suppression error (Program.ts:744-748) then continues compilation, which throws an incompatible-library error that also gets logged (Program.ts:647 via handleError). The expected output should state "Found 2 errors:" and include both the suppression error and the incompatible-library error.

Prompt To Fix With AI

This is a comment left during a code review.
Path: compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.eslint-mode-detects-incompatible-library-with-suppression.expect.md
Line: 30:30

Comment:
[P1] Test expectation shows "Found 1 error" but the implementation will produce 2 errors. The eslint suppression on line 9 of the test file (`react-hooks/exhaustive-deps`) is in DEFAULT_ESLINT_SUPPRESSIONS and will be detected. In ESLint mode, the code logs this suppression error (Program.ts:744-748) then continues compilation, which throws an incompatible-library error that also gets logged (Program.ts:647 via handleError). The expected output should state "Found 2 errors:" and include both the suppression error and the incompatible-library error.

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

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[greptile-apps]

syntax: expected output says "Found 1 error" but the implementation produces 2 errors: the react-hooks/exhaustive-deps suppression on line 9 is in DEFAULT_ESLINT_SUPPRESSIONS (Program.ts:338), so in ESLint mode it logs this suppression error (Program.ts:744-748), then continues compilation which throws the incompatible-library error that also gets logged (Program.ts:647). the output should state "Found 2 errors:" and include both errors

Suggested change

	Found 1 error:
	Found 2 errors:

Prompt To Fix With AI

This is a comment left during a code review.
Path: compiler/packages/babel-plugin-react-compiler/src/__tests__/fixtures/compiler/error.eslint-mode-detects-incompatible-library-with-suppression.expect.md
Line: 30:30

Comment:
**syntax:** expected output says "Found 1 error" but the implementation produces 2 errors: the `react-hooks/exhaustive-deps` suppression on line 9 is in DEFAULT_ESLINT_SUPPRESSIONS (Program.ts:338), so in ESLint mode it logs this suppression error (Program.ts:744-748), then continues compilation which throws the incompatible-library error that also gets logged (Program.ts:647). the output should state "Found 2 errors:" and include both errors

```suggestion
Found 2 errors:
```

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

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