Open Can't use type aliases resolving to Promise for async/await return types

[zaoqi]

TypeScript Version: 3.5.3

Search Terms:

Code

type CPS<x> = Promise<x> // to use async/await
function callcc<T>(f: (k: (v: T) => CPS<any>) => CPS<T>): CPS<T> {
    return new Promise((resolve, reject) => {
        const resolve_packed: (v: T) => CPS<any> = (v) => {
            resolve(v)
            return new Promise((resolve, reject) => { })
        }
        f(resolve_packed).then(resolve).catch(reject)
    })
}
function new_cps<T>(x: T): CPS<T> {
    return Promise.resolve(x)
}
function un_cps<T>(x: CPS<T>): T {
    let r: [true, T] | [false, any] | null = null
    x.then((v) => { r = [true, v]; }).catch((e) => { r = [false, e]; })
    if (r === null) {
        throw 'ERR'
    } else if (r[0] === true) {
        return r[1]
    } else if (r[0] === false) {
        throw String(r[1])
    }
    throw 'ERR'
}
async function f(): CPS<any> {
    // ...
}

Expected behavior:

Actual behavior:

a.ts:26:21 - error TS1055: Type 'CPS' is not a valid async function return type in ES5/ES3 because it does not refer to a Promise-compatible constructor value.

26 async function f(): CPS<any> {
                       ~~~~~~~~


Found 1 error.

Playground Link:

Related Issues:

#27987

[RyanCavanaugh]

The error means what it says. If you want to do this, you also need a value named CPS in scope that refers to a valid Promise constructor.

const CPS = Promise;
// Proceed as expected, everything OK:

[typescript-bot]

This issue has been marked 'Working as Intended' and has seen no recent activity. It has been automatically closed for house-keeping purposes.