perf(linter/plugins): reduce allocations for tokens and comments with accessed loc#20480
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Pull request overview
This PR reduces per-file allocations in oxlint’s JS-side token/comment infrastructure by keeping the “loc-accessed” tracking arrays at a stable capacity and using an active-count cursor instead of shrinking them to length 0 between files.
Changes:
- Track tokens/comments whose
locwas accessed viaactiveTokensWithLocCount/activeCommentsWithLocCount. - Avoid
array.length = 0on reset; reuse existing backing stores by resetting only the active counters. - Update reset loops to iterate only over the active portion of each tracking array.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
| apps/oxlint/src-js/plugins/tokens.ts | Reuses tokensWithLoc backing store across files with an active-count cursor; updates reset logic accordingly. |
| apps/oxlint/src-js/plugins/comments.ts | Mirrors the same active-count approach for commentsWithLoc and updates reset logic. |
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… accessed `loc` (#20480) Similar to #20479. `tokensWithLoc` and `commentsWithLoc` contain tokens/comments on which `loc` property has been accessed. Previously these arrays were grown with `.push(token)`, and shrunk at end of linting file with `tokensWithLoc.length = 0;`. Problem with that is that setting length to 0 frees the array's backing allocation, which means it has to reallocate again on next file when a token's `loc` is accessed. Instead, never shrink these arrays, and track the active length in separate variables. After warm-up over first batch of files, these arrays will graduate to "old space" and just sit there without further allocations. Unlike #20479, we don't use `Uint32Array`s as `loc` is calculated lazily, and `Token`'s / `Comment`s don't know what their index is in the `cachedTokens` / `cachedComments` arrays. Adding an `#index` field to `Token` and `Comment` would bloat every instance of these classes by 8 bytes.
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Possibly the most absurd optimization I've ever encountered.
```diff
- if (regexObjects.length > regexIndex) {
+ if (regexIndex < regexObjects.length) {
regex = regexObjects[regexIndex];
}
```
There is no semantic difference whatsoever between `regexObjects.length > regexIndex` and `regexIndex < regexObjects.length`. But V8's 2nd-tier Maglev compiler treats them differently. In the`>` version, `regexObjects[regexIndex]` incurs a bounds check, whereas in the new `<` version, no bounds check.
This is a micro-optimization, but this function is extremely hot, so it may actually move the needle in code that includes a lot of regexes. The same optimization is also applied in #20480.
Claude found this oddity by reading V8's source code!
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Base automatically changed from
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March 21, 2026 12:51
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Similar to #20479.
tokensWithLocandcommentsWithLoccontain tokens/comments on whichlocproperty has been accessed.Previously these arrays were grown with
.push(token), and shrunk at end of linting file withtokensWithLoc.length = 0;. Problem with that is that setting length to 0 frees the array's backing allocation, which means it has to reallocate again on next file when a token'slocis accessed.Instead, never shrink these arrays, and track the active length in separate variables. After warm-up over first batch of files, these arrays will graduate to "old space" and just sit there without further allocations.
Unlike #20479, we don't use
Uint32Arrays aslocis calculated lazily, andToken's /Comments don't know what their index is in thecachedTokens/cachedCommentsarrays. Adding an#indexfield toTokenandCommentwould bloat every instance of these classes by 8 bytes.