Promise<unknown> is not assignable to Promise<void>

[kkirby]

Bug Report

Currently unknown is assignable to void. However, Promise<unknown> is NOT assignable to Promise<void>.

🔎 Search Terms

promise, type compatibility, assignment

🕗 Version & Regression Information

This is the behavior in every version I tried, and I reviewed the FAQ

⏯ Playground Link

Playground link with relevant code

💻 Code

const voidPromiseFn = async () => {}
const voidFn = () => {};

const unknownPromiseFn = async (): Promise<unknown> => void 0;
const unknownFn = (): unknown => void 0;

const takesVoidPromiseFn = (fn: typeof voidPromiseFn) => {};
const takesVoidFn = (fn: typeof voidFn) => {};

// This works
takesVoidFn(voidFn);
// This works
takesVoidFn(unknownFn);

// This works
takesVoidPromiseFn(voidPromiseFn);
// This does NOT work
takesVoidPromiseFn(unknownPromiseFn);

const takesVoidPromise = (fn: Promise<void>) => {};

// This works
takesVoidPromise(new Promise<void>(() => {}));
// This does NOT work
takesVoidPromise(new Promise<unknown>(() => {}));

🙁 Actual behavior

A function that returns Promise<unknown> (() => Promise<unknown>) could not be passed as a function argument with the type () => Promise<void>. Contradictory, a function that returns unknown (() => unknown) can be passed to a function argument with the type () => void.

🙂 Expected behavior

I would expect that passing a () => Promise<unknown> to a function argument that accepts () => Promise<void> to be allowed.

[MartinJohns]

Duplicate of #12871.

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.