fix(transformer): remove unnecessary trailing expression in object rest spread assignment

[Boshen]

Summary

• Skip the trailing reference (e.g. _c) in the generated sequence expression when the destructuring assignment is directly inside an ExpressionStatement, since the expression result is not consumed
• Before: _c = c2, {a2} = _c, b2 = objectWithoutProperties(_c, ["a2"]), _c;
• After: _c = c2, {a2} = _c, b2 = objectWithoutProperties(_c, ["a2"]);
• The trailing reference is still kept when the result is consumed, e.g. console.log((..., _c))

Closes #7389 (issue 1)

🤖 Generated with Claude Code

[Boshen]

Merge activity

• Feb 11, 11:33 AM UTC: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
• Feb 11, 11:37 AM UTC: Boshen added this pull request to the Graphite merge queue.
• Feb 11, 11:49 AM UTC: Merged by the Graphite merge queue.

[Copilot]

Pull request overview

This pull request optimizes the object rest spread transformer by removing unnecessary trailing reference expressions in sequence expressions when the destructuring assignment result is not consumed.

Changes:

• Modified object_rest_spread.rs to detect when an assignment expression is directly inside an ExpressionStatement (ignoring parenthesized wrappers)
• When the result is not consumed, the trailing reference is omitted from the generated sequence expression
• Updated test fixture outputs to reflect the optimized transformation

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
crates/oxc_transformer/src/es2018/object_rest_spread.rs	Added logic to check ancestor chain and conditionally omit trailing reference when expression result is not consumed
tasks/transform_conformance/tests/babel-plugin-transform-object-rest-spread/test/fixtures/object-rest/assignment-expression/output.js	Updated expected output to remove trailing reference in line 3
tasks/transform_conformance/overrides/babel-plugin-transform-object-rest-spread/test/fixtures/object-rest/assignment-expression/output.js	Updated expected output to remove trailing reference in line 3
tasks/transform_conformance/overrides/babel-plugin-transform-object-rest-spread/test/fixtures/object-rest/impure-computed/output.js	Updated expected output to remove trailing reference in line 22
tasks/transform_conformance/overrides/babel-plugin-transform-object-rest-spread/test/fixtures/object-rest/template-literal-allLiterals-true-no-hoisting/output.js	Updated expected output to remove trailing reference in line 5
tasks/transform_conformance/snapshots/babel.snap.md	Updated snapshots showing improvements in symbol table accuracy (fewer binding/scope mismatches)

[codspeed-hq]

Merging this PR will degrade performance by 4.02%

❌ 3 regressed benchmarks
✅ 44 untouched benchmarks
⏩ 3 skipped benchmarks¹

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	transformer[binder.ts]	1.6 ms	1.6 ms	-4.02%
❌	Simulation	transformer[react.development.js]	682.8 µs	707.8 µs	-3.52%
❌	Simulation	transformer[cal.com.tsx]	25.8 ms	26.7 ms	-3.64%

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_{Comparing fix/transformer-object-rest-spread-trailing-expr (2358438) with main (740a009)²}

Footnotes

1. 3 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

2. No successful run was found on main (9195430) during the generation of this report, so 740a009 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩