fix(minifier): recognize object spread of object literals as side-effect-free

[Boshen]

Summary

• Add ObjectExpression handling in ObjectPropertyKind::SpreadProperty's may_have_side_effects — spreading an object literal is side-effect-free when all its properties are
• Fix remove_unused_object_expr to check side effects for all-spread objects instead of unconditionally bailing

Closes rolldown/rolldown#8582

[codspeed-hq]

Merging this PR will not alter performance

✅ 53 untouched benchmarks
⏩ 3 skipped benchmarks¹

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_{Comparing fix/object-spread-side-effects (c92399b) with main (1c07b3b)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 (910c941) during the generation of this report, so 1c07b3b was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[Boshen]

Merge activity

• Mar 13, 4:42 AM UTC: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
• Mar 13, 4:42 AM UTC: Boshen added this pull request to the Graphite merge queue.
• Mar 13, 5:07 AM UTC: Merged by the Graphite merge queue.

[Copilot]

Pull request overview

This PR fixes the minifier to recognize that spreading object literals (e.g., ({...{}}), ({...{a: 1}})) is side-effect-free when all the inner properties are side-effect-free. Previously, object spreads were conservatively treated as always having side effects (since they could invoke getters on unknown values), which prevented removing unused expressions like ({...{}}).

Changes:

• Add ObjectExpression handling in ObjectPropertyKind::SpreadProperty's may_have_side_effects to recursively check inner properties
• Fix remove_unused_object_expr to check side effects for all-spread objects instead of unconditionally bailing out
• Add tests for both the side-effects analysis and peephole optimization

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
crates/oxc_ecmascript/src/side_effects/expressions.rs	Adds ObjectExpression case in spread property side-effect analysis, recursively checking inner properties
crates/oxc_minifier/src/peephole/remove_unused_expression.rs	Changes the all-spread early return from return false to checking if any spread has side effects
crates/oxc_minifier/tests/ecmascript/may_have_side_effects.rs	Updates existing tests and adds new test cases for spreading object literals
crates/oxc_minifier/tests/peephole/remove_unused_expression.rs	Adds peephole optimization tests for spreading object literals

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Treat getter-backed object spreads as side-effectful

When property_read_side_effects is All (the default), spreading an object literal with accessor properties must be considered effectful because object spread performs a property read (Get) for each enumerable key. This new branch only checks property.may_have_side_effects(ctx), which does not account for PropertyKind::Get, so expressions like ({...{ get a() { foo() } }}) can be misclassified as side-effect-free and then removed by remove_unused_object_expr, dropping the getter invocation.

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