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fix(pseudos): avoid overlapping whitespace in nth parsing #1909

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Merged
fb55 merged 1 commit into from
Oct 9, 2026
Merged

fix(pseudos): avoid overlapping whitespace in nth parsing #1909

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2 changes: 1 addition & 1 deletion src/pseudo-selectors/filters.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -32,7 +32,7 @@ function extendedFilter(tag: string[], range: string[]): boolean {
}

/** @see {@link https://www.w3.org/TR/selectors-4/#the-nth-child-pseudo} */
const nthOfRegex = /^(.+?)\s+of\s+(.+)$/is;
const nthOfRegex = /^(.+?\s)of\s+(.+)$/is;

/** A pre-compiled pseudo filter. */
export type Filter = <Node, ElementNode extends Node>(
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7 changes: 7 additions & 0 deletions test/pseudo-classes.ts
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Expand Up @@ -9,6 +9,13 @@ const dom = parseDOM(
"<div><p>In the end, it doesn't really Matter.</p><div>Indeed-that's a delicate matter.</div>",
) as Element[];

// The previous pattern backtracked on long whitespace, taking minutes here.
it("should reject a long whitespace nth argument without backtracking", () => {
expect(() =>
CSSselect.compile(`:nth-child(${" ".repeat(350_000)})`),
).toThrow("n-th rule couldn't be parsed");
}, 2000);

@chatgpt-codex-connector chatgpt-codex-connector Bot Oct 9, 2026

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P2 Badge Measure the synchronous parse duration explicitly

If this regex regresses to synchronous backtracking again, the parser blocks the event loop, so Vitest cannot fire this 2-second timeout; the test eventually completes and passes once compile() throws, even if that takes minutes. Vitest's own reproduction confirms that synchronous work completing after a test timeout is still reported as passing. As a result, this test does not enforce the performance property described by its name and comment; measure elapsed time explicitly or run the parse in a worker/subprocess that can be terminated.

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describe(":icontains", () => {
describe("ignore case", () => {
it("should match full string", () => {
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