[commit] Fix for nested optional chaining within other value blocks

[everettbu]

Mirror of facebook/react#35596
Original author: josephsavona

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Fixes a longstanding issue where we didn't support code like useFoo(value?.bar(), value?.bar()) ?? {} - we would attempt to construct a ReactiveFunction, recursively processing the blocks, but the inner optional value?.bar() wouldn't match with what the outer optional was expecting to find. It's a one-line fix!

Note: memoization in the examples is not ideal, but i've confirmed that it is not strictly related to the optional issue.

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Stack created with Sapling. Best reviewed with ReviewStack.

• #35607
• #35298
• -> #35596
• #35573
• #35595
• #35539

[greptile-apps]

Greptile Summary

Fixed a longstanding bug in the React compiler where nested optional chaining within other value blocks (like ternaries, logical expressions, or nullish coalescing) would fail to compile. The issue occurred when constructing ReactiveFunction representations - the code was incorrectly using init.fallthrough instead of final.block when stitching together nested value terminals.

Key changes:

• One-line fix in BuildReactiveFunction.ts:1107 changes return block from init.fallthrough to final.block
• Renamed 4 error.todo test files to working tests (removed error prefix)
• Added 19 new comprehensive test fixtures covering various combinations of optional chaining with ternaries, logical operators, and nullish coalescing
• Added extensive documentation for all 55 compiler passes in the docs/passes/ directory

Confidence Score: 5/5

• This PR is safe to merge with minimal risk
• The fix is a precise one-line change that correctly resolves a block reference bug in the compiler. The PR includes comprehensive test coverage with 19 new test fixtures and converts 4 previously failing tests to passing. All tests validate various edge cases of nested optional chaining. The change is well-understood and directly addresses the root cause described in the PR description.
• No files require special attention

Important Files Changed

Filename	Overview
compiler/packages/babel-plugin-react-compiler/src/ReactiveScopes/BuildReactiveFunction.ts	One-line fix changes init.fallthrough to final.block to correctly handle nested optional chaining in value blocks
compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/optional-call-chain-in-logical-expr.ts	Renamed from error.todo file, now passes with the fix - tests useNoAlias(value?.x, value?.y) ?? {}
compiler/packages/babel-plugin-react-compiler/src/tests/fixtures/compiler/chained-optionals-with-nullish-coalesce.ts	New test for chained optional property access with nullish coalescing: props.obj?.a?.b?.c ?? 'default'