29 lines
765 B
TypeScript
29 lines
765 B
TypeScript
// @strict: true
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// @declaration: true
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// Repro from #17456
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type StringContains<S extends string, L extends string> = (
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{ [K in S]: 'true' } &
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{ [key: string]: 'false' }
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)[L]
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type ObjectHasKey<O, L extends string> = StringContains<Extract<keyof O, string>, L>
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type First<T> = ObjectHasKey<T, '0'>; // Should be deferred
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type T1 = ObjectHasKey<{ a: string }, 'a'>; // 'true'
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type T2 = ObjectHasKey<{ a: string }, 'b'>; // 'false'
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// Verify that mapped type isn't eagerly resolved in type-to-string operation
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declare function f1<A extends string, B extends string>(a: A, b: B): { [P in A | B]: any };
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function f2<A extends string>(a: A) {
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return f1(a, 'x');
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}
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function f3(x: 'a' | 'b') {
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return f2(x);
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}
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