feat(ecmascript): add `property_write_side_effects` to `MayHaveSideEffectsContext` by Dunqing · Pull Request #20217 · oxc-project/oxc

Dunqing · 2026-03-11T04:28:20Z

Part of #19673

Summary

Add property_write_side_effects() to MayHaveSideEffectsContext trait with default true (conservative)
Implement MayHaveSideEffects for AssignmentExpression and UpdateExpression (previously fell through to _ => true)
When property_write_side_effects is false, member expression writes are side-effect-free
Compound assignments (+=) and updates (++) still respect property_read_side_effects for their implicit reads
Reference: https://rolldown.rs/reference/InputOptions.treeshake#propertywritesideeffects

Test plan

Added test_property_write_side_effects_support covering all combinations of write/read side-effect settings
Existing tests pass unchanged

Copilot

Pull request overview

This PR extends the ECMAScript side-effect analysis to support a property_write_side_effects() flag on MayHaveSideEffectsContext, enabling more precise classification of assignment/update expressions for treeshaking/minification scenarios.

Changes:

Add property_write_side_effects() to MayHaveSideEffectsContext with a conservative default of true.
Implement MayHaveSideEffects for AssignmentExpression and UpdateExpression, allowing member-property writes to be treated as side-effect-free when configured.
Add tests covering combinations of property read/write side-effect settings.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
crates/oxc_ecmascript/src/side_effects/context.rs	Adds the new context flag API with a default conservative behavior.
crates/oxc_ecmascript/src/side_effects/expressions.rs	Routes assignment/update expressions through dedicated side-effect logic and implements the new behavior.
crates/oxc_minifier/tests/ecmascript/may_have_side_effects.rs	Adds test coverage for the new property-write side effects option and its interaction with property-read settings.

crates/oxc_ecmascript/src/side_effects/expressions.rs

codspeed-hq · 2026-03-11T04:35:09Z

Merging this PR will not alter performance

✅ 53 untouched benchmarks
⏩ 3 skipped benchmarks¹

_{Comparing feat/property-write-side-effects (cb8b1f6) with main (36e7d29)}

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. ↩

Dunqing · 2026-03-11T04:43:06Z

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Boshen · 2026-03-12T07:14:55Z

Merge activity

Mar 12, 7:14 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 12, 7:14 AM UTC: Boshen added this pull request to the Graphite merge queue.
Mar 12, 7:36 AM UTC: Merged by the Graphite merge queue.

…fectsContext` (#20217) Part of #19673 ## Summary - Add `property_write_side_effects()` to `MayHaveSideEffectsContext` trait with default `true` (conservative) - Implement `MayHaveSideEffects` for `AssignmentExpression` and `UpdateExpression` (previously fell through to `_ => true`) - When `property_write_side_effects` is `false`, member expression writes are side-effect-free - Compound assignments (`+=`) and updates (`++`) still respect `property_read_side_effects` for their implicit reads - Reference: https://rolldown.rs/reference/InputOptions.treeshake#propertywritesideeffects ## Test plan - [x] Added `test_property_write_side_effects_support` covering all combinations of write/read side-effect settings - [x] Existing tests pass unchanged

#20212) ## Summary close: #13067 Part of #19673 Depends on #20217. Port known-globals lists from Rolldown to Oxc's side-effect detection: - **Global identifiers** (Math, Array, console, DOM classes, etc.) are now considered side-effect-free to access via `is_known_global_identifier`, matching Rolldown's `GLOBAL_IDENT` set - **Property reads** like `Math.PI`, `console.log`, `Object.keys` are considered side-effect-free via `is_known_global_property` - **3-level chains** like `Object.prototype.hasOwnProperty` are supported via `is_known_global_property_deep` ## Test plan - [x] Added tests for known global identifiers (Math, Array, Object, console, etc.) - [x] Added tests for known global property reads (Math.PI, Object.keys, etc.) - [x] Added tests for 3-level chains (Object.prototype.hasOwnProperty, etc.) - [x] Existing minifier test expectations updated for improved side-effect detection - [x] All existing tests pass 🤖 Generated with [Claude Code](https://claude.com/claude-code)

### 🚀 Features - e7163b6 ecmascript: Add known-globals to side-effect-free property reads (#20212) (Dunqing) - 139ab68 ecmascript: Add `property_write_side_effects` to `MayHaveSideEffectsContext` (#20217) (Dunqing) ### 🐛 Bug Fixes - 78c264a parser: Fix conditional expressions with arrow-function alternates in TS (#20356) (camc314) - 5c97b14 minifier: Recognize object spread of object literals as side-effect-free (#20299) (Boshen) - 1ff5c1d transformer/typescript: Rewrite extensions in dynamic `import()` expressions (#20121) (Sverre Johansen) - 1c07b3b diagnostics: Handle `WouldBlock` in stdout writes to prevent panic (#20295) (Boshen) - ade14d4 ecmascript: Enhance side-effect detection for classes, TypedArrays, computed members, and spread (#20213) (Dunqing) ### ⚡ Performance - 5474d0a semantic: V8-style walk-up reference resolution (#20292) (Boshen) ### 📚 Documentation - e4aa5b5 parser/napi, linter/plugins: Add JSDoc comments to raw transfer constants (#20286) (overlookmotel) Co-authored-by: Boshen <1430279+Boshen@users.noreply.github.com>

Copilot AI review requested due to automatic review settings March 11, 2026 04:28

github-actions bot added A-minifier Area - Minifier C-enhancement Category - New feature or request labels Mar 11, 2026

Copilot started reviewing on behalf of Dunqing March 11, 2026 04:28 View session

Copilot AI reviewed Mar 11, 2026

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Dunqing force-pushed the feat/property-write-side-effects branch from dd1d6c7 to 8172e82 Compare March 11, 2026 04:40

This was referenced Mar 11, 2026

feat(ecmascript): add known-globals to side-effect-free property reads #20212

Merged

fix(ecmascript): enhance side-effect detection for classes, TypedArrays, computed members, and spread #20213

Merged

Dunqing changed the title ~~feat(ecmascript): add property_write_side_effects to MayHaveSideEffectsContext~~ feat(ecmascript): add property_write_side_effects to MayHaveSideEffectsContext Mar 11, 2026

Dunqing requested review from Boshen and sapphi-red March 12, 2026 05:36

Boshen approved these changes Mar 12, 2026

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Dunqing force-pushed the feat/property-write-side-effects branch from 8172e82 to 7857402 Compare March 12, 2026 05:57

sapphi-red approved these changes Mar 12, 2026

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Dunqing force-pushed the feat/property-write-side-effects branch from 7857402 to cb8b1f6 Compare March 12, 2026 06:57

Boshen added the 0-merge Merge with Graphite Merge Queue label Mar 12, 2026

graphite-app bot force-pushed the feat/property-write-side-effects branch from cb8b1f6 to 139ab68 Compare March 12, 2026 07:25

graphite-app bot merged commit 139ab68 into main Mar 12, 2026
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graphite-app bot deleted the feat/property-write-side-effects branch March 12, 2026 07:36

graphite-app bot removed the 0-merge Merge with Graphite Merge Queue label Mar 12, 2026

Boshen mentioned this pull request Mar 14, 2026

release(crates): oxc v0.119.0 #20371

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feat(ecmascript): add `property_write_side_effects` to `MayHaveSideEffectsContext`#20217

feat(ecmascript): add `property_write_side_effects` to `MayHaveSideEffectsContext`#20217
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feat/property-write-side-effects

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Merging this PR will not alter performance

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Dunqing commented Mar 11, 2026 •

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