Inconsistent boolean literal types in objects

🔎 Search Terms

boolean invariant type parameter literal widen union

🕗 Version & Regression Information

• This is the behavior in every version I tried

⏯ Playground Link

https://www.typescriptlang.org/play/?ts=5.7.0-dev.20240824&ssl=14&ssc=130&pln=1&pc=1#code/PTAECEHsA8B4BUB8oAuBPADgU1ASwM54B2AbgIYBOuZRKxo8AsAFAvrYQwLIC8oA3i1CgA5lhQAuUAAoAlKB7J4AbiGh84qdPIAbAK5Yp8eYtAlIuACarmAXxstLWAMY7KOAGZ6izlLkhEoABGXEjaZPqGDLJSUHBIDszOAfh0QUQAjArBMNL8oBgUkBhSAAygtrLKoCCccPmFxVJEegC2QVgUFYgsyUSpwUQATLFcDUUloC3tnd3ZIdB5BRNlFVU1YADyANYsvSlpQVl8C0uNkx4RGmvVtXGw4005kDpYNN37-YcjdQ-LTyEXm9ArZeDlFo8LlccJVbmAAKIUIoUAA04L+5yklx011BU0gdDI+HwuBERDIQVeqEgv0hUkBr3eoJYQA

💻 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 }>

🙁 Actual behavior

Error on bb2 is surprising and inconsistent with lack of error on bn2.

🙂 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 https://github.com/microsoft/TypeScript/issues/48363 that was fixed by @ahejlsberg in https://github.com/microsoft/TypeScript/pull/48380

リンクされている TypeScript Playground から始め、数値の Box の例と boolean の Box の例の違いを再現してください。示されている不変な Box 宣言について、型推論と代入可能性の挙動を追跡してください。boolean のケースが数値のケースと一貫して動作し、その例に対するリグレッションカバレッジがあることを完了条件とします。