perf(napi/parser, linter/plugins): use `utf8Slice` for decoding UTF-8 strings by overlookmotel · Pull Request #21022 · oxc-project/oxc

overlookmotel · 2026-04-03T19:37:48Z

Optimize raw transfer string decoding.

Replace TextDecoder("utf8") with Buffer.prototype.utf8Slice to decode Rust UTF-8 strings to JS strings.

Benchmarks show this is an average 5% speed-up in deserializeStr, though the reason why is unclear. It skips various checks, and avoids creating a temporary Uint8Array (which is required with TextDecoder.decode) which trims 60 bytes of the size of the assembly created for deserializeStr. But that's not enough to explain the speed-up 🤷. Anyway, take the win.

overlookmotel · 2026-04-03T19:38:03Z

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Pull request overview

This PR optimizes raw-transfer UTF-8 string decoding in the Node.js JS-side deserializers by switching from TextDecoder('utf-8') to Buffer.prototype.utf8Slice, aiming to improve performance during AST deserialization.

Changes:

Replace TextDecoder(...).decode(...)-based decoding with utf8Slice.call(...) in generated raw-transfer deserializers.
Update the raw-transfer generator to emit utf8Slice-based decoding logic.
Update oxlint’s initSourceText() to decode source text via utf8Slice instead of TextDecoder.

Reviewed changes

Copilot reviewed 2 out of 11 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tasks/ast_tools/src/generators/raw_transfer.rs	Updates generator templates to use `Buffer.prototype.utf8Slice` for UTF-8 decoding.
napi/parser/src-js/generated/deserialize/ts.js	Switches string decoding fast-paths to `utf8Slice`.
napi/parser/src-js/generated/deserialize/ts_range.js	Switches string decoding fast-paths to `utf8Slice`.
napi/parser/src-js/generated/deserialize/ts_range_parent.js	Switches string decoding fast-paths to `utf8Slice`.
napi/parser/src-js/generated/deserialize/ts_parent.js	Switches string decoding fast-paths to `utf8Slice`.
napi/parser/src-js/generated/deserialize/js.js	Switches string decoding fast-paths to `utf8Slice`.
napi/parser/src-js/generated/deserialize/js_range.js	Switches string decoding fast-paths to `utf8Slice`.
napi/parser/src-js/generated/deserialize/js_range_parent.js	Switches string decoding fast-paths to `utf8Slice`.
napi/parser/src-js/generated/deserialize/js_parent.js	Switches string decoding fast-paths to `utf8Slice`.
apps/oxlint/src-js/plugins/source_code.ts	Changes source text decoding to use `utf8Slice`.
apps/oxlint/src-js/generated/deserialize.js	Switches string decoding fast-paths to `utf8Slice`.

apps/oxlint/src-js/plugins/source_code.ts

graphite-app · 2026-04-03T22:03:40Z

Merge activity

Apr 3, 10:03 PM UTC: overlookmotel added this pull request to the Graphite merge queue.
Apr 3, 10:17 PM UTC: Merged by the Graphite merge queue.

… strings (#21022) Optimize raw transfer string decoding. Replace `TextDecoder("utf8")` with `Buffer.prototype.utf8Slice` to decode Rust UTF-8 strings to JS strings. Benchmarks show this is an average 5% speed-up in `deserializeStr`, though the reason why is unclear. It skips various checks, and avoids creating a temporary `Uint8Array` (which is required with `TextDecoder.decode`) which trims 60 bytes of the size of the assembly created for `deserializeStr`. But that's not enough to explain the speed-up 🤷. Anyway, take the win.

### 🐛 Bug Fixes - fc7f60c allocator: Revert changes to `get_current_chunk_footer_field_offset` (#20964) (overlookmotel) - 31316c8 semantic: Rebind class expressions before identifier checks (#20916) (camc314) ### ⚡ Performance - fb52383 napi/parser, linter/plugins: Clear buffers and source texts earlier (#21025) (overlookmotel) - 3b7dec4 napi/parser, linter/plugins: Use `utf8Slice` for decoding UTF-8 strings (#21022) (overlookmotel) - 012c924 napi/parser, linter/plugins: Speed up decoding strings in raw transfer (#21021) (overlookmotel) - 55e1e9b napi/parser, linter/plugins: Initialize vars as 0 (#21020) (overlookmotel) - c25ef02 napi/parser, linter/plugins: Simplify branch condition in `deserializeStr` (#21019) (overlookmotel) - 9f494c3 napi/parser, linter/plugins: Raw transfer use `String.fromCharCode` in string decoding (#21018) (overlookmotel) - 91cf105 allocator: Increase initial chunk size from 512B to 16KB (#20968) (overlookmotel) - cbc0c21 allocator: Add `#[cold]` to to error handling functions (#20967) (overlookmotel) - 0503a78 napi/parser, linter/plugins: Faster deserialization of `raw` fields (#20923) (overlookmotel) - a24f75e napi/parser: Optimize string deserialization for non-ASCII sources (#20834) (Joshua Tuddenham) ### 📚 Documentation - c78a57a syntax: Fix typo (#21044) (camc314) - f5e228f allocator: Fix typo in comment (#20972) (overlookmotel) - 7159d51 allocator: Improve doc comment examples for `vec2::Vec` (#20969) (overlookmotel) - b1da750 allocator, data_structures: Correct comments (#20966) (overlookmotel) Co-authored-by: Boshen <1430279+Boshen@users.noreply.github.com>

# Oxlint ### 💥 BREAKING CHANGES - 22ce6af oxlint/lsp: [**BREAKING**] Show/fix safe suggestions by default (#19816) (Sysix) ### 🚀 Features - 7a7b7b8 oxlint/lsp: Add source.fixAllDangerous.oxc code action kind (#20526) (bab) - 9cfe57e linter/unicorn: Implement prefer-import-meta-properties rule (#20662) (Irfan - ئىرفان) - 1edb391 linter/eslint: Implement `no-restricted-exports` rule (#20592) (Nicolas Le Cam) - 0f12bcd linter/react: Implement `hook-use-state` rule (#20986) (Khaled Labeb) - 1513a9f oxlint/lsp: Show note field for lsp diagnostic (#20983) (Sysix) - 7fdf722 linter/unicorn: Implement `no-useless-iterator-to-array` rule (#20945) (Mikhail Baev) - 39c8f2c linter/jest: Implement padding-around-after-all-blocks (#21034) (Sapphire) - ac39e51 linter/eslint-vitest-plugin: Prefer importing vitest globals (#20960) (Said Atrahouch) - 0b84de1 oxlint: Support allow option for prefer-promise-reject-errors (#20934) (camc314) - 23db851 linter/consistent-return: Move rule from nursery to suspicious (#20920) (camc314) - 9a27e32 linter/no-unnecessary-type-conversion: Move rule from nursery to suspicious (#20919) (camc314) - 1ca7b58 linter/dot-notation: Move rule from nursery to style (#20918) (camc314) - 73ba81a linter/consistent-type-exports: Move rule from nursery to style (#20917) (camc314) - b9199b1 linter/unicorn: Implement switch-case-break-position (#20872) (Mikhail Baev) - 3435ff8 linter: Implements `prefer-snapshot-hint` rule in Jest and Vitest (#20870) (Said Atrahouch) - 98510d2 linter: Implement react/prefer-function-component (#19652) (Connor Shea) - 871f9d9 linter: Implement no-useless-assignment (#15466) (Zhaoting Zhou) - 0f01fbd linter: Implement eslint/object-shorthand (#17688) (yue) ### 🐛 Bug Fixes - dd2df87 npm: Export package.json for oxlint and oxfmt (#20784) (kazuya kawaguchi) - 9bc77dd linter/no-unused-private-class-members: False positive with await expr (#21067) (camc314) - 60a57cd linter/const-comparisons: Detect equality contradictions (#21065) (camc314) - 2bb2be2 linter/no-array-index-key: False positive when index is passed as function argument (#21012) (bab) - 6492953 linter/no-this-in-sfc: Only flag `this` used as member expression object (#20961) (bab) - 9446dcc oxlint/lsp: Skip `node_modules` in oxlint config walker (#21004) (copilot-swe-agent) - af89923 linter/no-namespace: Support glob pattern matching against basename (#21031) (bab) - 64a1a7e oxlint: Don't search for nested config outside base config (#21051) (Sysix) - 3b953bc linter/button-has-type: Ignore `document.createElement` calls (#21008) (Said Atrahouch) - 8c36070 linter/unicorn: Add support for `Array.from()` for `prefer-set-size` rule (#21016) (Mikhail Baev) - c1a48f0 linter: Detect vitest import from vite-plus/test (#20976) (Said Atrahouch) - 5c32fd1 lsp: Prevent corrupted autofix output from overlapping text edits (#19793) (Peter Wagenet) - ca79960 linter/no-array-index-key: Move span to `key` property (#20947) (camc314) - 2098274 linter: Add suggestion for `jest/prefer-equality-matcher` (#20925) (eryue0220) - 6eb77ec linter: Allow default-import barrels in import/named (#20757) (Bazyli Brzóska) - 9c218ef linter/eslint-vitest-plugin: Remove pending fix status for require-local-test-context-for-concurrent-snapshot (#20890) (Said Atrahouch) ### ⚡ Performance - fb52383 napi/parser, linter/plugins: Clear buffers and source texts earlier (#21025) (overlookmotel) - 3b7dec4 napi/parser, linter/plugins: Use `utf8Slice` for decoding UTF-8 strings (#21022) (overlookmotel) - 012c924 napi/parser, linter/plugins: Speed up decoding strings in raw transfer (#21021) (overlookmotel) - 55e1e9b napi/parser, linter/plugins: Initialize vars as 0 (#21020) (overlookmotel) - c25ef02 napi/parser, linter/plugins: Simplify branch condition in `deserializeStr` (#21019) (overlookmotel) - 9f494c3 napi/parser, linter/plugins: Raw transfer use `String.fromCharCode` in string decoding (#21018) (overlookmotel) - 0503a78 napi/parser, linter/plugins: Faster deserialization of `raw` fields (#20923) (overlookmotel) - a24f75e napi/parser: Optimize string deserialization for non-ASCII sources (#20834) (Joshua Tuddenham) ### 📚 Documentation - af72b80 oxlint: Fix typo for --tsconfig (#20889) (leaysgur) - 70c53b1 linter: Highlight that tsconfig is not respected in type aware linting (#20884) (camc314) # Oxfmt ### 🚀 Features - 35cf6e8 oxfmt: Add node version hint for ts config import failures (#21046) (camc314) ### 🐛 Bug Fixes - dd2df87 npm: Export package.json for oxlint and oxfmt (#20784) (kazuya kawaguchi) - 9d45511 oxfmt: Propagate file write errors instead of panicking (#20997) (leaysgur) - 139ddd9 formatter: Handle leading comment after array elision (#20987) (leaysgur) - 4216380 oxfmt: Support `.editorconfig` `tab_width` fallback (#20988) (leaysgur) - d10df39 formatter: Resolve pending space in fits measurer before expanded-mode early exit (#20954) (Dunqing) - f9ef1bd formatter: Avoid breaking after `=>` when arrow body has JSDoc type cast (#20857) (bab) Co-authored-by: Boshen <1430279+Boshen@users.noreply.github.com>

overlookmotel mentioned this pull request Apr 3, 2026

perf(napi/parser, linter/plugins): speed up decoding strings in raw transfer #21021

Merged

github-actions bot added A-linter Area - Linter A-parser Area - Parser A-cli Area - CLI A-ast-tools Area - AST tools A-linter-plugins Area - Linter JS plugins C-performance Category - Solution not expected to change functional behavior, only performance labels Apr 3, 2026

overlookmotel self-assigned this Apr 3, 2026

overlookmotel marked this pull request as ready for review April 3, 2026 20:56

overlookmotel requested a review from camc314 as a code owner April 3, 2026 20:56

Copilot AI review requested due to automatic review settings April 3, 2026 20:56

Copilot started reviewing on behalf of overlookmotel April 3, 2026 20:57 View session

Copilot AI reviewed Apr 3, 2026

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This was referenced Apr 3, 2026

perf(napi/parser, linter/plugins): clear buffers and source texts earlier #21025

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refactor(linter/plugins): import getNodeLoc instead of injecting it #21026

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graphite-app bot force-pushed the om/04-03-perf_napi_parser_linter_plugins_speed_up_decoding_strings_in_raw_transfer branch from 683d3b3 to 012c924 Compare April 3, 2026 22:07

graphite-app bot force-pushed the om/04-03-perf_napi_parser_linter_plugins_use_utf8slice_for_decoding_utf-8_strings branch from 56b273a to 3b7dec4 Compare April 3, 2026 22:07

Base automatically changed from om/04-03-perf_napi_parser_linter_plugins_speed_up_decoding_strings_in_raw_transfer to main April 3, 2026 22:15

graphite-app bot merged commit 3b7dec4 into main Apr 3, 2026
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graphite-app bot deleted the om/04-03-perf_napi_parser_linter_plugins_use_utf8slice_for_decoding_utf-8_strings branch April 3, 2026 22:17

This was referenced Apr 6, 2026

release(crates): oxc v0.124.0 #21084

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release(apps): oxlint v1.59.0 && oxfmt v0.44.0 #21085

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perf(napi/parser, linter/plugins): use `utf8Slice` for decoding UTF-8 strings#21022

perf(napi/parser, linter/plugins): use `utf8Slice` for decoding UTF-8 strings#21022
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om/04-03-perf_napi_parser_linter_plugins_use_utf8slice_for_decoding_utf-8_strings

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