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Defer generic awaited type - #35284

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Jack Bates (jablko) wants to merge 2 commits into
microsoft:mainfrom
jablko:patch-26
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Defer generic awaited type#35284
Jack Bates (jablko) wants to merge 2 commits into
microsoft:mainfrom
jablko:patch-26

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@jablko

@jablko Jack Bates (jablko) commented Nov 22, 2019 •
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async function f<T>(x: T) {
    return x;
}
const expected: Promise<number> = f(undefined as Promise<number>);

Before

!!! error TS2322: Type 'Promise<Promise<number>>' is not assignable to type 'Promise<number>'.
!!! error TS2322:   Type 'Promise<number>' is not assignable to type 'number'.

After

getAwaitedType() returns the awaited type if it's known, or Awaited<T> if it's generic.

Fixes #27711

This proposal excludes non-A+ promises, which has the benefit of not requiring a recursive solution or a new kind of type, since an A+ promise can't resolve to another promise.

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

@jablko
Jack Bates (jablko) force-pushed the patch-26 branch 5 times, most recently from 3e596bb to 8145dda Compare November 28, 2019 14:51
@jablko Jack Bates (jablko) mentioned this pull request Jan 5, 2020
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@jablko
Jack Bates (jablko) force-pushed the patch-26 branch 3 times, most recently from b0cb02e to b96a504 Compare January 25, 2020 20:23
@orta

Orta Therox (orta) commented Jan 29, 2020

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TypeScript Bot (@typescript-bot) test this
TypeScript Bot (@typescript-bot) user test this
TypeScript Bot (@typescript-bot) run dt

@typescript-bot

TypeScript Bot (typescript-bot) commented Jan 29, 2020 •
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Heya Orta Therox (@orta), I've started to run the extended test suite on this PR at 3bab709. You can monitor the build here. It should now contribute to this PR's status checks.

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TypeScript Bot (typescript-bot) commented Jan 29, 2020 •
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Heya Orta Therox (@orta), I've started to run the parallelized Definitely Typed test suite on this PR at 3bab709. You can monitor the build here. It should now contribute to this PR's status checks.

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TypeScript Bot (typescript-bot) commented Jan 29, 2020 •
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Heya Orta Therox (@orta), I've started to run the parallelized community code test suite on this PR at 3bab709. You can monitor the build here. It should now contribute to this PR's status checks.

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TypeScript Bot (typescript-bot) commented Jan 29, 2020

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The user suite test run you requested has finished and failed. I've opened a PR with the baseline diff from master.

@jablko Jack Bates (jablko) mentioned this pull request Jan 31, 2020
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@jablko
Jack Bates (jablko) force-pushed the patch-26 branch 2 times, most recently from 4dc37b5 to e78a9aa Compare February 3, 2020 15:28
@sandersn Nathan Shively-Sanders (sandersn) added the For Backlog Bug PRs that fix a backlog bug label Feb 3, 2020
@jablko
Jack Bates (jablko) force-pushed the patch-26 branch 4 times, most recently from 866166b to fb42ba3 Compare February 10, 2020 20:01
@jablko
Jack Bates (jablko) force-pushed the patch-26 branch 4 times, most recently from 9a424b4 to 600875a Compare February 13, 2020 15:42
@rbuckton Ron Buckton (rbuckton) mentioned this pull request Jul 29, 2020
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@jcalz Joe Calzaretta (jcalz) mentioned this pull request Oct 28, 2021
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@rbuckton

Ron Buckton (rbuckton) commented Mar 18, 2022

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This was superseded by #45350

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TypeScript Bot (typescript-bot) commented Mar 18, 2022

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The TypeScript team hasn't accepted the linked issue #27711. If you can get it accepted, this PR will have a better chance of being reviewed.

@microsoft Microsoft (microsoft) locked as resolved and limited conversation to collaborators Oct 21, 2025
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Promise<Promise<T>> cannot exist in JS

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@jablko @orta @typescript-bot @rbuckton @sandersn