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BugA bug in TypeScriptA bug in TypeScriptDomain: check: Type InferenceRelated to type inference performed during signature resolution or `infer` type resolutionRelated to type inference performed during signature resolution or `infer` type resolutionHelp WantedYou can do thisYou can do this
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Description
π Search Terms
boolean invariant type parameter literal widen union
π Version & Regression Information
- This is the behavior in every version I tried
β― Playground Link
π» Code
// Box<T> type is invariant in T
type Box<T> = {
get: () => T;
set: (value: T) => void;
};
declare function box<T>(value: T): Box<T>;
const bn1 = box({ prop: 0 }); // Box<{ prop: number }>
const bn2: Box<{ prop: number }> = box({ prop: 0 }); // Ok
const bb1 = box({ prop: false }); // Box<{ prop: boolean }>
const bb2: Box<{ prop: boolean }> = box({ prop: false }); // Error, box<{ prop: false }> not assignable to Box<{ prop: boolean }>π Actual behavior
Error on bb2 is surprising and inconsistent with lack of error on bn2.
π Expected behavior
Expected the box(false) expression to have type Box<boolean> for both bb1 and bb2.
Additional information about the issue
This issue is a small variation of #48363 that was fixed by @ahejlsberg in #48380
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BugA bug in TypeScriptA bug in TypeScriptDomain: check: Type InferenceRelated to type inference performed during signature resolution or `infer` type resolutionRelated to type inference performed during signature resolution or `infer` type resolutionHelp WantedYou can do thisYou can do this