Microsoft/TypeScript
TS1518 depends on operand order in negated v-mode class unions
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#63 718 ouverte le 4 août 2026
BugDomain: ParserHelp Wanted
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Description
🔎 Search Terms
TS1518, RegExp v flag, MayContainStrings, negated character class, ClassUnion, operand order, q{}
🕗 Version & Regression Information
Occurs in every version tested: 7.0.2 and 7.1.0-dev.20260804.1 (nightly). I searched open and closed issues.
💻 Code
const a = /[^\q{xy}b]/v; // TS1518
const b = /[^b\q{xy}]/v; // no error
🙁 Actual behavior
TS1518 only considers the first union operand. The second pattern is accepted but is invalid JavaScript.
🙂 Expected behavior
Both patterns report TS1518: MayContainStrings is true when any union operand may match a string.