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40 lines
1.4 KiB
40 lines
1.4 KiB
5 years ago
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/** @flow */
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function getRelocatable(re: RegExp): RegExp {
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// In the future, this could use a WeakMap instead of an expando.
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if (!(re: any).__matchAtRelocatable) {
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// Disjunctions are the lowest-precedence operator, so we can make any
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// pattern match the empty string by appending `|()` to it:
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// https://people.mozilla.org/~jorendorff/es6-draft.html#sec-patterns
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var source = re.source + '|()';
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// We always make the new regex global.
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var flags = 'g' + (re.ignoreCase ? 'i' : '') + (re.multiline ? 'm' : '') + ((re: any).unicode ? 'u' : '')
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// sticky (/.../y) doesn't make sense in conjunction with our relocation
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// logic, so we ignore it here.
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;
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(re: any).__matchAtRelocatable = new RegExp(source, flags);
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}
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return (re: any).__matchAtRelocatable;
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}
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function matchAt(re: RegExp, str: string, pos: number): any {
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if (re.global || (re: any).sticky) {
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throw new Error('matchAt(...): Only non-global regexes are supported');
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}
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var reloc = getRelocatable(re);
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reloc.lastIndex = pos;
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var match: Array<string> = reloc.exec(str);
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// Last capturing group is our sentinel that indicates whether the regex
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// matched at the given location.
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if (match[match.length - 1] == null) {
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// Original regex matched.
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match.length = match.length - 1;
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return match;
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} else {
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return null;
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}
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}
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module.exports = matchAt;
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