Better typings for Promise.resolve(), like #31117

[jablko]

No description provided.

[sandersn]

@rbuckton Is this ready to merge now?

[rbuckton]

I'd like to run the RWC and user tests once more to be sure.

[rbuckton]

@typescript-bot run dt
@typescript-bot test this
@typescript-bot user test this

[typescript-bot]

Heya @rbuckton, I've started to run the diff-based user code test suite on this PR at 915863f. You can monitor the build here.

Update: The results are in!

[typescript-bot]

Heya @rbuckton, I've started to run the parallelized Definitely Typed test suite on this PR at 915863f. You can monitor the build here.

[typescript-bot]

Heya @rbuckton, I've started to run the extended test suite on this PR at 915863f. You can monitor the build here.

[typescript-bot]

Heya @rbuckton, I've run the RWC suite on this PR - assuming you're on the TS core team, you can view the resulting diff here.

[typescript-bot]

@rbuckton
Great news! no new errors were found between main..refs/pull/33074/merge

[rbuckton]

This still causes a build break in older versions of firebase-sdk, but since this only occurs in an outdated snapshot of firebase in our RWC tests and not in the most recent version of firebase, this change seems acceptable.

 /** * Takes an array of values and sequences them using the promise (or value) * returned by the supplied callback. The callback for each item is called * after the promise is resolved for the previous item. * The function returns a promise which is resolved after the promise for * the last item is resolved. */ export function sequence<T, R>( values: T[], fn: (value: T, result?: R) => R | Promise<R>, initialValue?: R ): Promise<R> { let result = Promise.resolve(initialValue); values.forEach(value => { result = result.then(lastResult => fn(value, lastResult)); ~~~~~~ !!! error TS2322: Type 'Promise<R | Awaited<R>>' is not assignable to type 'Promise<Awaited<R>>'. !!! error TS2322: Type 'R | Awaited<R>' is not assignable to type 'Awaited<R>'. !!! error TS2322: Type 'R' is not assignable to type 'Awaited<R>'. }); return result as AnyDuringMigration; } 

[sandersn]

Note that this breaks @types/react-test-renderer's attempt to create a type that can't be passed to Promise.resolve:

declare const UNDEFINED_VOID_ONLY: unique symbol; export function act(callback: () => void | { [UNDEFINED_VOID_ONLY]: never }): DebugPromiseLike; // Intentionally doesn't extend PromiseLike<never>. // Ideally this should be as hard to accidentally use as possible. export interface DebugPromiseLike { // the actual then() in here is 1-ary, but that doesn't count as a PromiseLike. then(onfulfilled: (value: never) => never, onrejected: (reason: never) => never): never; } // @ts-expect-error <-- this is no longer an error Promise.resolve(act(() => {}));

I think this change is still OK, I just wanted to report on the break.

[sandersn]

This breaks vscode in a few places too, so we're going to revert it for 4.8 to give us a chance to figure out what to do.