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[codex] Cache list indentation regexes #3969

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[codex] Cache list indentation regexes #3969

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26 changes: 20 additions & 6 deletions src/rules.ts
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Original file line number Diff line number Diff line change
@@ -1,5 +1,19 @@
const noopTest = { exec: () => null } as unknown as RegExp;

function cachedIndentRegex(createRegex: (indent: number) => RegExp) {
const cache: RegExp[] = [];
return (indent: number) => {
const cappedIndent = Math.min(3, indent - 1);
const cacheIndex = cappedIndent + 1;
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@gemini-code-assist gemini-code-assist Bot May 8, 2026

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medium

While indent is expected to be at least 1 in the current implementation of Tokenizer.ts, calculating cappedIndent as Math.min(3, indent - 1) can result in a negative value if indent is 0. This would cause createRegex(-1) to be called, which leads to a SyntaxError when constructing the RegExp (e.g., new RegExp("^ {0,-1}")).

Additionally, using Math.max(0, ...) ensures that cacheIndex is always a non-negative integer, making the array access more predictable.

Suggested change
const cappedIndent = Math.min(3, indent - 1);
const cacheIndex = cappedIndent + 1;
const cappedIndent = Math.max(0, Math.min(3, indent - 1));
const cacheIndex = cappedIndent;

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@gemini-code-assist gemini-code-assist Bot May 8, 2026

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medium

The current calculation of cappedIndent can result in a negative value if indent is 0 (e.g., Math.min(3, -1) returns -1). This would cause createRegex to attempt to construct a RegExp with an invalid quantifier (e.g., ^ {0,-1}), which throws a SyntaxError in JavaScript.

While the current tokenizer implementation might ensure indent >= 1, adding a Math.max(0, ...) check makes this helper more robust against future changes or external usage of the exported other rules. This also allows for a simpler cacheIndex mapping.

Suggested change
const cappedIndent = Math.min(3, indent - 1);
const cacheIndex = cappedIndent + 1;
const cappedIndent = Math.max(0, Math.min(3, indent - 1));
const cacheIndex = cappedIndent;

let regex = cache[cacheIndex];
if (!regex) {
regex = createRegex(cappedIndent);
cache[cacheIndex] = regex;
}
return regex;
};
}

function edit(regex: string | RegExp, opt = '') {
let source = typeof regex === 'string' ? regex : regex.source;
const obj = {
Expand Down Expand Up @@ -78,12 +92,12 @@ export const other = {
notSpaceStart: /^\S*/,
endingNewline: /\n$/,
listItemRegex: (bull: string) => new RegExp(`^( {0,3}${bull})((?:[\t ][^\\n]*)?(?:\\n|$))`),
nextBulletRegex: (indent: number) => new RegExp(`^ {0,${Math.min(3, indent - 1)}}(?:[*+-]|\\d{1,9}[.)])((?:[ \t][^\\n]*)?(?:\\n|$))`),
hrRegex: (indent: number) => new RegExp(`^ {0,${Math.min(3, indent - 1)}}((?:- *){3,}|(?:_ *){3,}|(?:\\* *){3,})(?:\\n+|$)`),
fencesBeginRegex: (indent: number) => new RegExp(`^ {0,${Math.min(3, indent - 1)}}(?:\`\`\`|~~~)`),
headingBeginRegex: (indent: number) => new RegExp(`^ {0,${Math.min(3, indent - 1)}}#`),
htmlBeginRegex: (indent: number) => new RegExp(`^ {0,${Math.min(3, indent - 1)}}<(?:[a-z].*>|!--)`, 'i'),
blockquoteBeginRegex: (indent: number) => new RegExp(`^ {0,${Math.min(3, indent - 1)}}>`),
nextBulletRegex: cachedIndentRegex((indent: number) => new RegExp(`^ {0,${indent}}(?:[*+-]|\\d{1,9}[.)])((?:[ \t][^\\n]*)?(?:\\n|$))`)),
hrRegex: cachedIndentRegex((indent: number) => new RegExp(`^ {0,${indent}}((?:- *){3,}|(?:_ *){3,}|(?:\\* *){3,})(?:\\n+|$)`)),
fencesBeginRegex: cachedIndentRegex((indent: number) => new RegExp(`^ {0,${indent}}(?:\`\`\`|~~~)`)),
headingBeginRegex: cachedIndentRegex((indent: number) => new RegExp(`^ {0,${indent}}#`)),
htmlBeginRegex: cachedIndentRegex((indent: number) => new RegExp(`^ {0,${indent}}<(?:[a-z].*>|!--)`, 'i')),
blockquoteBeginRegex: cachedIndentRegex((indent: number) => new RegExp(`^ {0,${indent}}>`)),
};

/**
Expand Down