Type widening for T or Promise<T>

Bug Report

🔎 Search Terms

Type widening, promise, generic type widening.

🕗 Version & Regression Information

This is the behavior in every version I tried.

⏯ Playground Link

Playground link

💻 Code

type Cb3 = <Res extends string | Promise<string>>(cb: () => Res) => Res

const c: Cb3 = {} as any;

// this don't widen the type, type of t31 is "1"
const t31 = c(() => {
  return '1';
});

// but here is the problem, type of t32 is Promise<string>
const t32 = c(async () => {
  return '1';
});

🙁 Actual behavior

Type of t32 is Promise<string>

🙂 Expected behavior

Type of t32 is Promise<"1">, by analogy with type of t31

Commencez par le TypeScript Playground lié et comparez l’inférence des callbacks génériques dans les exemples synchrone et asynchrone. Suivez l’endroit où le cas Promise perd le type littéral ; le travail est terminé lorsque l’appel asynchrone est inféré comme Promise<"1"> tandis que le résultat synchrone reste inchangé.