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perf(linter/plugins): add fast path for files with no comments #20366

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graphite-app merged 1 commit into from
Mar 14, 2026
+17 −3
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perf(linter/plugins): add fast path for files with no comments #20366

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20 changes: 17 additions & 3 deletions apps/oxlint/src-js/plugins/comments.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -42,6 +42,10 @@ let previousComments: Comment[] = [];
// Comments whose `loc` property has been accessed, and therefore needs clearing on reset.
const commentsWithLoc: Comment[] = [];

// Empty comments array.
// Reused for all files which don't have any comments. Frozen to avoid rules mutating it.
const emptyComments: CommentType[] = Object.freeze([]) as unknown as CommentType[];

// Reset `#loc` field on a `Comment` class instance.
let resetCommentLoc: (comment: Comment) => void;

Expand Down Expand Up @@ -90,6 +94,10 @@ Object.defineProperty(Comment.prototype, "loc", { enumerable: true });
export function initComments(): void {
debugAssert(comments === null, "Comments already initialized");

// We don't need to deserialize source text if there are no comments, so we could move this call to after
// the `commentsLen === 0` check. However, various comments methods rely on that if `initComments` has been called,
// then `sourceText` is initialized. Doing it eagerly here avoids having to check if `sourceText` is `null`
// in all those methods, which can be called quite frequently.
if (sourceText === null) initSourceText();
debugAssertIsNonNull(sourceText);
debugAssertIsNonNull(buffer);
Expand All @@ -99,6 +107,12 @@ export function initComments(): void {
const commentsPos = uint32[programPos32 + (COMMENTS_OFFSET >> 2)];
const commentsLen = uint32[programPos32 + (COMMENTS_LEN_OFFSET >> 2)];

// Fast path for files with no comments
if (commentsLen === 0) {
comments = emptyComments;
return;
}

// Grow cache if needed (one-time cost as cache warms up)
while (cachedComments.length < commentsLen) {
cachedComments.push(new Comment());
Expand All @@ -125,9 +139,9 @@ export function initComments(): void {

// Set first comment as `Shebang` if file has hashbang.
// Rust side adds hashbang comment to start of comments `Vec` as a `Line` comment.
if (commentsLen > 0) {
const firstComment = cachedComments[0];
if (firstComment.start === 0 && sourceText.startsWith("#!")) firstComment.type = "Shebang";
// `uint32[commentsPos >> 2]` is the start of the first comment.
if (uint32[commentsPos >> 2] === 0 && sourceText.startsWith("#!")) {
cachedComments[0].type = "Shebang";
}

// Use `slice` rather than copying comments one-by-one into a new array.
Expand Down
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