Fix preserve-manual-memoization false positive with optional chaining deps

[everettbu]

Mirror of facebook/react#35859
Original author: sleitor

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Summary

When a dependency array uses optional chaining (e.g. [obj?.id]), the compiler may infer a less specific dependency (e.g. obj) because optional chain lowering introduces conditionals. Previously this triggered a Subpath error ("Inferred less specific property than source"), but the user's more specific optional dependency is semantically correct — using ?. acknowledges the conditionality and produces undefined when the base is nullish.

This change treats the inferred-less-specific case as OK when the source dependency continues with an optional property access from where the inferred dependency ends. Non-optional source deps that are more specific than inferred deps still correctly produce the Subpath error.

Test

Added useCallback-optional-chaining-dep test fixture that reproduces the exact pattern from #35577. All 1712 existing tests pass.

Fixes #35577
Fixes #35167

[greptile-apps]

Greptile Summary

Fixes a false positive in the React Compiler's ValidatePreservedManualMemoization pass where using optional chaining in a dependency array (e.g., [obj?.id]) would incorrectly trigger a "Subpath" error ("Inferred less specific property than source"). The compiler infers obj instead of obj?.id because optional chain lowering introduces conditionals, but the user's more specific optional dependency is semantically correct.

• Adds a new branch in compareDeps() that returns Ok when the inferred dependency is a prefix of the source and the source continues with an optional property access (?.), while preserving existing error behavior for non-optional subpath mismatches and ref-type accesses
• Adds a test fixture (useCallback-optional-chaining-dep) reproducing the exact pattern from #35577

Confidence Score: 5/5

• This PR is safe to merge — it's a narrowly scoped fix with correct logic and a test fixture.
• The change is minimal (17 lines of logic + comments), well-guarded by existing conditions, and only relaxes validation for a specific case (optional chaining deps) that was already semantically correct. Existing error cases for non-optional subpath mismatches are preserved. A new test fixture covers the exact pattern being fixed, and the PR description confirms all 1712 existing tests pass.
• No files require special attention.

Important Files Changed

Filename	Overview
compiler/packages/babel-plugin-react-compiler/src/Validation/ValidatePreservedManualMemoization.ts	Adds a new else if branch in compareDeps to return Ok when the inferred dependency is a prefix of the source and the source continues with an optional property access (?.). The logic is correct, properly guarded by ref-access checks, and preserves existing error behavior for non-optional subpath cases.
compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/preserve-memo-validation/useCallback-optional-chaining-dep.ts	New test fixture that reproduces the false positive from #35577: useCallback with [obj?.id] as a dependency where the body uses obj?.id in a conditional. Validates that the compiler no longer emits a spurious Subpath error.
compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/preserve-memo-validation/useCallback-optional-chaining-dep.expect.md	Expected output for the new test fixture — shows successful compilation (no errors) with correct memoization using obj as the cache key.

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[greptile-apps]

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