awaitedType.ts

// @target: esnext
// @strictNullChecks: false

type T1 = Awaited<number>;
type T2 = Awaited<Promise<number>>;
type T3 = Awaited<number | Promise<number>>;
type T4 = Awaited<number | Promise<string>>;
type T5 = Awaited<{ then: number }>;
type T6 = Awaited<{ then(): void }>; // never (non-promise "thenable")
type T7 = Awaited<{ then(x: number): void }>; // never (non-promise "thenable")
type T8 = Awaited<{ then(x: () => void): void }>; // unknown
type T9 = Awaited<any>;
type T10 = Awaited<never>;
type T11 = Awaited<unknown>;
type T12 = Awaited<Promise<Promise<number>>>;
type T13 = _Expect<Awaited<Promise<Promise<number>> | string | null>, /*expected*/ string | number | null>; // otherwise just prints T13 in types tests, which isn't very helpful
type T14 = _Expect<Awaited<Promise<Promise<number>> | string | undefined>, /*expected*/ string | number | undefined>; // otherwise just prints T14 in types tests, which isn't very helpful
type T15 = _Expect<Awaited<Promise<Promise<number>> | string | null | undefined>, /*expected*/ string | number | null | undefined>; // otherwise just prints T15 in types tests, which isn't very helpful

interface BadPromise { then(cb: (value: BadPromise) => void): void; }
type T16 = Awaited<BadPromise>; // error

interface BadPromise1 { then(cb: (value: BadPromise2) => void): void; }
interface BadPromise2 { then(cb: (value: BadPromise1) => void): void; }
type T17 = Awaited<BadPromise1>; // error

// https://github.com/microsoft/TypeScript/issues/46934
type T18 = Awaited<{ then(cb: (value: number, other: { }) => void)}>; // number

// https://github.com/microsoft/TypeScript/issues/33562
type MaybePromise<T> = T | Promise<T> | PromiseLike<T>
declare function MaybePromise<T>(value: T): MaybePromise<T>;

async function main() {
    let aaa: number;
    let bbb: string;
    [
        aaa,
        bbb,
    ] = await Promise.all([
        MaybePromise(1),
        MaybePromise('2'),
        MaybePromise(true),
    ])
}

// non-generic
async function f1(x: string) {
    // y: string
    const y = await x;
}

async function f2(x: unknown) {
    // y: unknown
    const y = await x;
}

async function f3(x: object) {
    // y: object
    const y = await x;
}

async function f4(x: Promise<string>) {
    // y: string
    const y = await x;
}

async function f5(x: Promise<unknown>) {
    // y: unknown
    const y = await x;
}

async function f6(x: Promise<object>) {
    // y: object
    const y = await x;
}

// generic

async function f7<T>(x: T) {
    // NOTE: T does not belong solely to the domain of primitive types and either does
    // not have a base constraint, its base constraint is `any`, `unknown`, `{}`, or `object`,
    // or it has a non-primitive base constraint with a callable `then`.

    // y: Awaited<T>
    const y = await x;
}

async function f8<T extends any>(x: T) {
    // NOTE: T does not belong solely to the domain of primitive types and either does
    // not have a base constraint, its base constraint is `any`, `unknown`, `{}`, or `object`,
    // or it has a non-primitive base constraint with a callable `then`.

    // y: Awaited<T>
    const y = await x;
}

async function f9<T extends unknown>(x: T) {
    // NOTE: T does not belong solely to the domain of primitive types and either does
    // not have a base constraint, its base constraint is `any`, `unknown`, `{}`, or `object`,
    // or it has a non-primitive base constraint with a callable `then`.

    // y: Awaited<T>
    const y = await x;
}

async function f10<T extends {}>(x: T) {
    // NOTE: T does not belong solely to the domain of primitive types and either does
    // not have a base constraint, its base constraint is `any`, `unknown`, `{}`, or `object`,
    // or it has a non-primitive base constraint with a callable `then`.

    // y: Awaited<T>
    const y = await x;
}

async function f11<T extends { then(onfulfilled: (value: unknown) => void): void }>(x: T) {
    // NOTE: T does not belong solely to the domain of primitive types and either does
    // not have a base constraint, its base constraint is `any`, `unknown`, `{}`, or `object`,
    // or it has a non-primitive base constraint with a callable `then`.

    // y: Awaited<T>
    const y = await x;
}

async function f12<T extends string | object>(x: T) {
    // NOTE: T does not belong solely to the domain of primitive types and either does
    // not have a base constraint, its base constraint is `any`, `unknown`, `{}`, or `object`,
    // or it has a non-primitive base constraint with a callable `then`.

    // y: Awaited<T>
    const y = await x;
}

async function f13<T extends string>(x: T) {
    // NOTE: T belongs to the domain of primitive types

    // y: T
    const y = await x;
}

async function f14<T extends { x: number }>(x: T) {
    // NOTE: T has a non-primitive base constraint without a callable `then`.

    // y: T
    const y = await x;
}

async function f15<T extends { then: number }>(x: T) {
    // NOTE: T has a non-primitive base constraint without a callable `then`.

    // y: T
    const y = await x;
}

async function f16<T extends number & { then(): void }>(x: T) {
    // NOTE: T belongs to the domain of primitive types (regardless of `then`)

    // y: T
    const y = await x;
}


// helps with tests where '.types' just prints out the type alias name
type _Expect<TActual extends TExpected, TExpected> = TActual;