Better typings for promise.race based on mapped tuple types

[dubzzz]

Following the feature - Mapped tuple types #25947 - it is now possible to have better typings for Promise.race.

[dubzzz]

Actually I closed the issue because I thought that race<T>(values: (T | PromiseLike<T>)[]): Promise<T> might already handle such infinite number of parameters but my try on the playground show the contrary so I re-open the PR.

For the moment, the following code is invalid:

const waitingFirst: Promise<number|string> = Promise.race([
    Promise.resolve(1),
    Promise.resolve(1),
    Promise.resolve(1),
    Promise.resolve(1),
    Promise.resolve(1),
    Promise.resolve("e"),
    Promise.resolve(1),
    Promise.resolve(1),
    Promise.resolve(1),
    Promise.resolve("e"),
    Promise.resolve(1)
]);

But it should be fixed by this PR.

[rbuckton]

Wouldn't this be cleaner?

interface PromiseConstructor {
    // array
    race<T>(values: T[]): Promise<T extends PromiseLike<infer U> ? U : T>;
    // iterable
    race<T>(values: Iterable<T>): Promise<T extends PromiseLike<infer U> ? U : T>;
}

[dubzzz]

@rbuckton Indeed it would be cleaner. I am updating the commit accordingly

[Jessidhia]

Isn't array already Iterable? 🤔

[rbuckton]

@Kovensky: It is, but we split the definition between different lib files based on how much of ES2015 your host supports.

[dubzzz]

@rbuckton Do I need to adapt something in this PR?

[rbuckton]

@typescript-bot test this

[typescript-bot]

Heya @rbuckton, I've started to run the extended test suite on this PR at f6f4f5d. You can monitor the build here. It should now contribute to this PR's status checks.

[rbuckton]

This change may be causing a compiler crash in our RWC suite. We are investigating.

[dubzzz]

Please let me know when you get more details about the failure ;)

[rbuckton]

Unfortunately, conditional types tend to result in higher memory usage in the compiler. One of our RWC test suites is crashing due to running out of memory as a result of this change. I will continue to investigate, but unfortunately will be out of the office next week. If this is something I am unable to address before Friday, I will continue to investigate when I return to the office.

[RyanCavanaugh]

@dubzzz in an attempt to get this branch rebased with master, I broke everything (long story). Opened a new PR at #31117