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Promise.all and Promise.allSettled infer incorrect types from Array subclasses #51993
Description
lib Update Request
Configuration Check
My compilation target is ES2020 and my lib is the default.
Missing / Incorrect Definition
Promise.all
Promise.allSettled
Sample Code
declare class ArrayChild<T> extends Array<T> {}
declare const array: Array<Promise<number>>
declare const child: ArrayChild<Promise<number>>
Promise.all(array).then(a => a /* number[] */)
Promise.allSettled(array).then(a => a /* PromiseSettledResult<number>[] */)
Promise.all(child).then(a => a /* {[K in keyof ArrayChild]: number} */)
Promise.allSettled(child).then(a => /* {[K in keyof ArrayChild]: PromiseSettledResult<number>} */) Documentation Link
Promise.all
Promise.allSettled
Possible fix
The inferred value should be of type number[] exactly like what happens with normal Array class. In the linked playground, It can be seen that Promise.all and Promise.allSettled infer the correct type with an Iterable type of object. This undesired behavior just happens with Array subclasses. I have quickly tried changing the signature from the original:
allSettled<T extends readonly unknown[] | []>(values: T): Promise<{ -readonly [P in keyof T]: PromiseSettledResult<Awaited<T[P]>> }>;
all<T extends readonly unknown[] | []>(values: T): Promise<{ -readonly [P in keyof T]: Awaited<T[P]> }>;to
allSettled<T extends Promise<unknown>[]>(values: T): Promise<T extends Promise<infer S>[] ? PromiseSettledResult<S>[] : never>
all<T extends Promise<unknown>[]>(values: T): Promise<T extends Promise<infer S>[] ? S[] : never>and it works as expected: Playground link
Activity
IllusionMH commentedon Dec 22, 2022
This would break tuples, which (I assume), are more common use case than Array subclasses in promise methods.
Example
andrewbranch commentedon Dec 22, 2022
Yeah, we definitely can’t break tuple inference here. Seems like there could be another way to write it, but we’ll have to weigh the complexity and performance cost against how useful it actually is on average in real code.
asnaeb commentedon Dec 22, 2022
Extending Array class, while uncommon is part of the language and this bug can be a wall against libraries development, for example. I'm going to spend some time in finding a solution as soon as I get the chance!
[-]Promise.all and Promise.allSettled infer incorrect types from Array child classes[/-][+]Promise.all and Promise.allSettled infer incorrect types from Array subclasses[/+]asnaeb commentedon Dec 25, 2022
While I didn't test this exhaustively, It looks like it's working
Playground Link