fix(allocator): `Vec::from_array_in` do not allocate zero-length array by overlookmotel · Pull Request #24628 · oxc-project/oxc

overlookmotel · 2026-07-17T13:08:26Z

Vec::from_array_in doesn't need to allocate when the array passed to it is zero-length.

This wasn't unsound as Allocator accepts zero-sized allocations, but it was pointless. Allocating a zero-sized type still aligns the bump cursor to the type's alignment, which is an allocation of sorts - it's not zero-cost.

Just delegate to Vec::new_in instead.

overlookmotel · 2026-07-17T13:08:49Z

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Pull request overview

This PR optimizes oxc_allocator::Vec::from_array_in to avoid performing a zero-sized arena allocation when the input array length is 0, delegating to Vec::new_in instead. This removes a pointless bump-cursor alignment side effect for N == 0 while preserving behavior for N > 0.

Changes:

Add an if N == 0 fast-path in Vec::from_array_in to return an empty arena Vec without allocating.
Keep the existing arena allocation path unchanged for non-empty arrays.

codspeed-hq · 2026-07-17T13:16:43Z

Merging this PR will not alter performance

✅ 67 untouched benchmarks
⏩ 9 skipped benchmarks¹

_{Comparing om/07-17-fix_allocator_vec_from_array_in_do_not_allocate_zero-length_array (40c2f43) with main (2338c13)²}

9 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. ↩
No successful run was found on main (40c2f43) during the generation of this report, so 2338c13 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

graphite-app · 2026-07-17T13:48:59Z

Merge activity

Jul 17, 1:48 PM UTC: overlookmotel added this pull request to the Graphite merge queue.
Jul 17, 1:56 PM UTC: Merged by the Graphite merge queue.

#24628) `Vec::from_array_in` doesn't need to allocate when the array passed to it is zero-length. This wasn't unsound as `Allocator` accepts zero-sized allocations, but it was pointless. Allocating a zero-sized type still aligns the bump cursor to the type's alignment, which is an allocation of sorts - it's not zero-cost. Just delegate to `Vec::new_in` instead.

### 💥 BREAKING CHANGES - 54cc121 ast: [**BREAKING**] Split `MetaProperty` into `ImportMeta` and `NewTarget` (#24557) (camc314) ### 🚀 Features - 4c71560 parser: More friendly error for spread element in dynamic imports (#24705) (sapphi-red) - 7b045cd minfier: Drop last break from last switch case (#24673) (Armano) - 7d3c178 minifier: Remove unreachable recursive functions (#24125) (Dunqing) - 94f99b3 ast: Allow `NONE` to be passed to AST builder methods where `Option<ArenaVec>` is expected (#24629) (overlookmotel) - 77230c5 ast: Accept arrays for `ArenaVec` params of AST builder methods (#24621) (overlookmotel) - f08b152 allocator: Implement `FromIn` for array to `Vec` conversion (#24620) (overlookmotel) - 2338c13 track-memory-allocations: Track heap deallocs, alloc bytes, and peak growth (#24619) (Boshen) - 7aa4739 syntax,transformer: Move JSX entity decoder to `oxc_syntax` (#24617) (camc314) - 2b097c4 str: Export `Str` as `ArenaStr` (#24604) (overlookmotel) - 3acf4c1 minifier: Expand switch optimiation to remove empty cases (#24520) (Armano) - 129b759 parser: Improve diagnostics for unparenthesized LHS on exponential expr (#24569) (camc314) - 4d0c601 minifier: Fold arithmetic over undefined and null operands (#24485) (Dunqing) - 91541dd minifier: Drop empty switch statements (#24527) (Armano) - d05224d ast_visit: Generate VisitJs visitor that skips TypeScript type-space (#24499) (Boshen) - 3d22307 parser: Add `ParseOptions::enable_ident_hashes` (#24491) (Boshen) ### 🐛 Bug Fixes - 64c2241 minifier: Align class heritage removal with assumptions (#24533) (Dunqing) - 48b59f4 parser: Span ambient generator diagnostics (#24711) (camc314) - e750a82 ecmascript: Fix false negative for may_have_side_effects on dynamic property access (#24709) (sapphi-red) - f145d73 minifier: Guard reordered identifier reads (#24698) (Dunqing) - a2ef382 isolated-declarations: Reject `window.Symbol` as global symbol reference (#24689) (camc314) - b1bcf72 minifier: Invalidate facts for redeclared bindings (#24658) (Dunqing) - 921b834 minifier: Don't treat a conditionally-assigned var as write-once (#24650) (Dunqing) - 061af1f minifier: Avoid stale pure function summaries (#24636) (Dunqing) - 40c2f43 allocator: `Vec::from_array_in` do not allocate zero-length array (#24628) (overlookmotel) - 70994ae codegen: Preserve comments before expression operands (#24510) (Dunqing) - 7b4baff parser: Reject new import member access (#23459) (camc314) - 128b385 minifier: Clippy warning with no-debug-assertions (#24547) (camc314) - 8421feb parser: Use first `as` span for imported name (#24537) (leaysgur) - c517aa0 parser: Reject invalid accessor assertions (#24504) (camc314) ### ⚡ Performance - 884d9eb parser: Pre-size cover-grammar assignment target buffers (#24683) (Boshen) - d3f07a0 diagnostics: Box OxcDiagnosticInner to reduce binary size (#24665) (Boshen) - bcc9de0 parser: Defer diagnostic creation until parse exit (#24663) (Boshen) - c35d8ab allocator: Mark `ReplaceWith` panic path cold (#24515) (camc314) - ba65790 semantic, allocator: Branchless `clone_in` for semantic IDs (#24564) (overlookmotel) - 747feec parser: Build AST nodes with the AST builder instead of cloning (#24540) (Boshen) - ba35a0d react_compiler: Use IndexVec for dense id-keyed maps (#24549) (Boshen) - b685062 react_compiler: Keep small hot-path collections inline (#24514) (Marius Schulz) - a149e95 transformer: Outline rare expression exits (#24512) (camc314) - 7808a6e react_compiler: Make aliasing effects cheap to intern and clone (#24506) (Marius Schulz) - 3a36f2a react_compiler: Store AbstractValue reasons as a u16 bitmask (#24480) (Boshen) - 1c96753 react_compiler: Use FxHashMap for the lookup-only aliasing node map (#24490) (Boshen) Co-authored-by: Cameron <[email protected]>

github-actions Bot added the A-allocator Area - Allocator label Jul 17, 2026

overlookmotel mentioned this pull request Jul 17, 2026

refactor(react_compiler): shorten code constructing ObjectPropertyKind #24627

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overlookmotel marked this pull request as ready for review July 17, 2026 13:11

Copilot AI review requested due to automatic review settings July 17, 2026 13:11

Copilot started reviewing on behalf of overlookmotel July 17, 2026 13:12 View session

Copilot AI reviewed Jul 17, 2026

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Comment thread crates/oxc_allocator/src/vec.rs

overlookmotel self-assigned this Jul 17, 2026

This was referenced Jul 17, 2026

feat(ast): allow NONE to be passed to AST builder methods where Option<ArenaVec> is expected #24629

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refactor(react_compiler): shorten code by using NONE #24630

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camc314 approved these changes Jul 17, 2026

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graphite-app Bot force-pushed the om/07-17-fix_allocator_vec_from_array_in_do_not_allocate_zero-length_array branch from 9b622dc to 40c2f43 Compare July 17, 2026 13:49

graphite-app Bot merged commit 40c2f43 into main Jul 17, 2026
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graphite-app Bot deleted the om/07-17-fix_allocator_vec_from_array_in_do_not_allocate_zero-length_array branch July 17, 2026 13:56

oxc-guard Bot mentioned this pull request Jul 20, 2026

release(crates): oxc v0.141.0 #24714

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fix(allocator): `Vec::from_array_in` do not allocate zero-length array#24628

fix(allocator): `Vec::from_array_in` do not allocate zero-length array#24628
graphite-app[bot] merged 1 commit into
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om/07-17-fix_allocator_vec_from_array_in_do_not_allocate_zero-length_array

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Merging this PR will not alter performance

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