Cannot await on interfaces extending Promise<any> in TypeScript 2.1 RC

[thomasboyt]

For context: I ran into this bug using Knex and its type definition in TypeScript 2.1 RC. Knex's type definitions use an extended Promise interface for every value returned from a query, to allow for further chaining. Unfortunately, it looks like async/await in TypeScript does not support this.

I found several references to fixed issues and regressions in prior versions of TypeScript, but could not find an open issue for the current version. Apologies if this is a duplicate issue.

TypeScript Version: typescript@rc (2.1.1)

Code

main.ts:

interface PromiseExtender extends Promise<any> {
}

function getPromiseExtender(): PromiseExtender {
  return new Promise((resolve, reject) => {});
}

async function main() {
  await getPromiseExtender();  // error: Operand for 'await' does not have a valid callable 'then' member.
}

tsconfig.json:

{
  "compilerOptions": {
    "target": "es5",
    "lib": ["dom", "es6", "es2015.promise", "es2015.iterable", "scripthost"],
    "module": "commonjs",
    "sourceMap": true,
    "strictNullChecks": true,
    "noImplicitAny": true
  }
}

Runnable test case: https://github.com/thomasboyt/typescript-await-promise-bug-test-case

Expected behavior: TypeScript allows awaiting interfaces extending Promise<any>.

Actual behavior: TypeScript displays the error Operand for 'await' does not have a valid callable 'then' member..

My current workaround for this is to just await (promiseExtendingObject as any), so it's not the end of the world. Hopefully can be fixed before 2.1 is released, though :)

[Jessidhia]

Would interface PromiseExtender<T> extends Promise<T> {} work?

[dead-claudia]

@Kovensky It shouldn't be necessary - ES async/await operates on thenables, not just promises.

[thomasboyt]

Ran into another library with this issue: supertest-as-promised, which adds a then method to an existing interface (with the slight indirection of going through Bluebird, since that's the underlying promise implementation that library uses: https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/supertest-as-promised/supertest-as-promised.d.ts).

[itaysabato]

Same deal with superagent.
It doesn't seem like it matters what is used as the generic parameter...

[rbuckton]

Fixed in #12743

[mhegazy]

Fix should be in typescript@next later tonight. Please give it a try and let us know if you are still running into issues.

[dead-claudia]

Will it make the final release of 2.1, a patch release, or 2.2?

…

On Wed, Dec 7, 2016, 20:55 Mohamed Hegazy ***@***.***> wrote: Fix should be in ***@***.*** later tonight. Please give it a try and let us know if you are still running into issues. — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#12292 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AERrBGXvMQFz7Guc8neVDGdoLaD6sbVRks5rF2OVgaJpZM4Kza4p> .

[itaysabato]

@mhegazy seems to be fine now, thanks.