fix(allocator): remove unsafe hacks from `from_raw_parts` methods by overlookmotel · Pull Request #21283 · oxc-project/oxc

overlookmotel · 2026-04-09T23:40:43Z

Until recently, our Allocator was based on bumpalo. Allocator::from_raw_parts (which is used by raw transfer) used some horrible hacks to determine the layout of Bump, and to reach in to ChunkFooter and mutate it, despite it not being exposed by bumpalo.

Now that we've copied bumpalo's code into oxc_allocator crate, we can remove these hacks and work with the actual Bump internals. This removes a bunch of very dodgy unsafe code.

There wasn't a bug to fix, per se, but the hacks used by Allocator::from_raw_parts were so egregious that I think we can consider removing them a fix.

overlookmotel · 2026-04-09T23:40:55Z

fix(allocator): remove unsafe hacks from from_raw_parts methods #21283 👈 (View in Graphite)
refactor(allocator): rename var #21282
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codspeed-hq · 2026-04-09T23:47:03Z

Merging this PR will not alter performance

✅ 48 untouched benchmarks
⏩ 3 skipped benchmarks¹

_{Comparing om/04-09-fix_allocator_remove_unsafe_hacks_from_from_raw_parts_methods (b463e26) with main (c3c2055)}

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. ↩

Copilot

Pull request overview

This PR removes the previous layout/offset “hacks” in Allocator::from_raw_parts by moving the raw-parts construction logic into the in-crate Bump implementation (now that bumpalo internals are locally available), reducing unsafe reach-into-private-struct behavior.

Changes:

Refactors Allocator::{from_raw_parts,set_cursor_ptr,data_end_ptr,end_ptr} to delegate to Bump APIs instead of manually constructing/mutating chunk footers.
Adds Bump::{from_raw_parts,set_cursor_ptr,data_end_ptr,end_ptr} behind the from_raw_parts feature for raw-transfer use.
Centralizes raw-transfer sizing/alignment constants in bump.rs and moves the fixed-size CHUNK_FOOTER_SIZE consistency assertion there.

Reviewed changes

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

File	Description
crates/oxc_allocator/src/from_raw_parts.rs	Removes allocator-side unsafe hacks and delegates raw-parts/cursor/end-pointer operations to `Bump`.
crates/oxc_allocator/src/bump.rs	Exposes chunk constants and implements `from_raw_parts` + cursor/end-pointer helpers under the `from_raw_parts` feature.

Copilot

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

overlookmotel · 2026-04-10T02:47:32Z

Merge activity

Apr 10, 2:47 AM UTC: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
Apr 10, 2:51 AM UTC: overlookmotel added this pull request to the Graphite merge queue.
Apr 10, 3:02 AM UTC: Merged by the Graphite merge queue.

…1283) Until recently, our `Allocator` was based on `bumpalo`. `Allocator::from_raw_parts` (which is used by raw transfer) used some horrible hacks to determine the layout of `Bump`, and to reach in to `ChunkFooter` and mutate it, despite it not being exposed by `bumpalo`. Now that we've copied `bumpalo`'s code into `oxc_allocator` crate, we can remove these hacks and work with the actual `Bump` internals. This removes a bunch of very dodgy unsafe code. There wasn't a bug to fix, per se, but the hacks used by `Allocator::from_raw_parts` were so egregious that I think we can consider removing them a fix.

### 💥 BREAKING CHANGES - 36cdc31 str: [**BREAKING**] Remove identity `FromIn` impl for `Ident` (#21251) (overlookmotel) - 382958a span: [**BREAKING**] Remove re-exports of string types from `oxc_span` crate (#21246) (overlookmotel) - c4aedfa str: [**BREAKING**] Add `static_ident!` macro (#21245) (overlookmotel) ### 🚀 Features - e7e1aea transformer/typescript: Add `optimize_enums` option for regular enum inlining (#20539) (Dunqing) - 679f57f transformer/typescript: Implement const enum inlining and declaration removal (#20508) (Dunqing) - 6dd061c semantic: Extend `MemberWriteTarget` to cover all property modification patterns (#21205) (Dunqing) - f134e24 minifier: Support `property_write_side_effects` option to drop unused property assignments (#20773) (Dunqing) - 75663c0 semantic: Add enum member value evaluation for const enum support (#20602) (Dunqing) - 3cfe8ed semantic: Add `MemberWriteTarget` flag to `ReferenceFlags` (#20772) (Dunqing) ### 🐛 Bug Fixes - af1a586 transformer/class-properties: Use correct property name when converting parameter properties (#21268) (Amal Jossy) - b43250a allocator: Move allocation tracking into `Bump` (#21342) (overlookmotel) - 36f505f allocator: `StringBuilder` use `Allocator::alloc_layout` (#21340) (overlookmotel) - 7a08a6f allocator: Fix allocation counting in `Allocator::alloc_concat_strs_array` (#21336) (overlookmotel) - 2338e28 ecmascript: Treat `this` as potentially having side effects (#21297) (sapphi-red) - bd8bd39 allocator: Remove unsafe hacks from `from_raw_parts` methods (#21283) (overlookmotel) - 8f4c340 allocator: Remove dangerous pointer const to mut cast (#21279) (overlookmotel) - aa9259f parser: Add missing error code for optional param diagnostic (#21258) (camc314) - 04b3c2f str: Fix unsound casting const pointers to mut pointers (#21242) (overlookmotel) - ceadf6c str: Make `Ident::from_raw` an unsafe function (#21241) (overlookmotel) - eab13b3 transformer/decorators: Avoid accessor storage name collisions (#21106) (Dunqing) - 07e8a30 transformer/react-refresh: Handle parenthesized variable initializers (#21047) (camc314) ### ⚡ Performance - c3ca6f6 allocator: `StringBuilder::from_strs_array_in` check for 0 length earlier (#21338) (overlookmotel) - c2422bb allocator: `Allocator::alloc_concat_strs_array` check for 0 length earlier (#21337) (overlookmotel) - 04b0fdc allocator: Mark `Allocator::alloc_layout` as `#[inline(always)]` (#21335) (overlookmotel) - 17aee9e allocator: Use `offset_from_unsigned` in `ChunkFooter::as_raw_parts` (#21280) (overlookmotel) - 61adedd minifier: Fix O(n²) perf on very many var decls (#21062) (Gunnlaugur Thor Briem) - addcd02 napi/parser, linter/plugins: Raw transfer deserializer for `Vec`s use shift instead of multiply where possible (#21142) (overlookmotel) - 3068ded napi/parser, linter/plugins: Shift before add when calculating positions in raw transfer deserializer (#21141) (overlookmotel) - eb400b8 napi/parser, linter/plugins: Remove `uint32` buffer view (#21140) (overlookmotel) - 2675085 napi/parser: Lazy deserialization use only `Int32Array` (#21139) (overlookmotel) - 5b35a53 napi/parser: Deserializing tokens use only `int32` array (#21138) (overlookmotel) - f163d10 parser: Tokens raw deserialization use `Int32Array` (#21137) (overlookmotel) - 7a86613 linter/plugins: Use `Int32Array`s for tokens and comments buffers (#21136) (overlookmotel) - 8c51121 napi/parser, linter/plugins: Raw transfer deserialize `Span` fields as `i32`s (#21135) (overlookmotel) - bc1bcdd napi/parser, linter/plugins: Inline trivial raw transfer field deserializers into node object definitions (#21134) (overlookmotel) - c0278ab napi/parser, linter/plugins: Use `Int32Array` in raw transfer deserializer (#21132) (overlookmotel) - 43482c7 linter/plugins: Use `>>` not `>>>` in binary search loops (#21129) (overlookmotel) ### 📚 Documentation - f5e1845 allocator: Upgrade headers in doc comments for `Bump` (#21263) (overlookmotel) - 2870174 allocator: Upper case `SAFETY` in comments (#21253) (overlookmotel) - 01bc269 str: Reformat `Ident` doc comments (#21240) (overlookmotel) - dd47359 allocator: Add doc comments for panics and errors (#21230) (overlookmotel)

overlookmotel mentioned this pull request Apr 9, 2026

refactor(allocator): rename var #21282

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github-actions Bot added A-allocator Area - Allocator C-bug Category - Bug labels Apr 9, 2026

overlookmotel marked this pull request as ready for review April 9, 2026 23:46

Copilot AI review requested due to automatic review settings April 9, 2026 23:46

overlookmotel self-assigned this Apr 9, 2026

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overlookmotel force-pushed the om/04-09-refactor_allocator_rename_var branch from 6b49410 to 562c8d0 Compare April 9, 2026 23:48

overlookmotel force-pushed the om/04-09-fix_allocator_remove_unsafe_hacks_from_from_raw_parts_methods branch from fc4541c to 7e805d4 Compare April 9, 2026 23:48

Copilot AI reviewed Apr 9, 2026

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Comment thread crates/oxc_allocator/src/bump.rs

Comment thread crates/oxc_allocator/src/bump.rs

graphite-app Bot changed the base branch from om/04-09-refactor_allocator_rename_var to graphite-base/21283 April 10, 2026 00:29

graphite-app Bot force-pushed the graphite-base/21283 branch from 562c8d0 to c400e99 Compare April 10, 2026 00:34

graphite-app Bot force-pushed the om/04-09-fix_allocator_remove_unsafe_hacks_from_from_raw_parts_methods branch from 7e805d4 to 570545a Compare April 10, 2026 00:34

graphite-app Bot changed the base branch from graphite-base/21283 to main April 10, 2026 00:34

graphite-app Bot force-pushed the om/04-09-fix_allocator_remove_unsafe_hacks_from_from_raw_parts_methods branch from 570545a to 2f76951 Compare April 10, 2026 00:34

overlookmotel force-pushed the om/04-09-fix_allocator_remove_unsafe_hacks_from_from_raw_parts_methods branch from 2f76951 to 86967f3 Compare April 10, 2026 01:51

overlookmotel requested a review from Copilot April 10, 2026 01:54

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Comment thread crates/oxc_allocator/src/bump.rs

Comment thread crates/oxc_allocator/src/bump.rs Outdated

Comment thread crates/oxc_allocator/src/bump.rs

Comment thread crates/oxc_allocator/src/from_raw_parts.rs

overlookmotel force-pushed the om/04-09-fix_allocator_remove_unsafe_hacks_from_from_raw_parts_methods branch from 86967f3 to b463e26 Compare April 10, 2026 02:46

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graphite-app Bot force-pushed the om/04-09-fix_allocator_remove_unsafe_hacks_from_from_raw_parts_methods branch from b463e26 to bd8bd39 Compare April 10, 2026 02:57

graphite-app Bot merged commit bd8bd39 into main Apr 10, 2026
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graphite-app Bot removed the 0-merge Merge with Graphite Merge Queue label Apr 10, 2026

graphite-app Bot deleted the om/04-09-fix_allocator_remove_unsafe_hacks_from_from_raw_parts_methods branch April 10, 2026 03:02

Boshen mentioned this pull request Apr 13, 2026

release(crates): oxc v0.125.0 #21374

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overlookmotel mentioned this pull request Apr 23, 2026

Revamp allocator #20513

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fix(allocator): remove unsafe hacks from `from_raw_parts` methods#21283

fix(allocator): remove unsafe hacks from `from_raw_parts` methods#21283
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overlookmotel commented Apr 9, 2026 •

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overlookmotel commented Apr 10, 2026 •

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