async function return expressions are not contextually typed

[falsandtru]

TypeScript Version: 3.7.x-dev.20200111

Search Terms:

Code

declare function f(cb: (v: boolean) => [0] | PromiseLike<[0]>): void;
f(v => v ? [0] : Promise.reject()); // ok
f(async v => v ? [0] : Promise.reject()); // error

Expected behavior:
pass
Actual behavior:

Type 'Promise<number[]>' is not assignable to type '[0] | PromiseLike<[0]>'.
  Type 'Promise<number[]>' is not assignable to type 'PromiseLike<[0]>'.
    Types of property 'then' are incompatible.
      Type '<TResult1 = number[], TResult2 = never>(onfulfilled?: ((value: number[]) => TResult1 | PromiseLike<TResult1>) | null | undefined, onrejected?: ((reason: any) => TResult2 | PromiseLike<...>) | null | undefined) => Promise<...>' is not assignable to type '<TResult1 = [0], TResult2 = never>(onfulfilled?: ((value: [0]) => TResult1 | PromiseLike<TResult1>) | null | undefined, onrejected?: ((reason: any) => TResult2 | PromiseLike<TResult2>) | null | undefined) => PromiseLike<...>'.
        Types of parameters 'onfulfilled' and 'onfulfilled' are incompatible.
          Types of parameters 'value' and 'value' are incompatible.
            Property '0' is missing in type 'number[]' but required in type '[0]'.(2322)

Playground Link: http://www.typescriptlang.org/play/index.html?ts=3.8.0-dev.20200111#code/CYUwxgNghgTiAEAzArgOzAFwJYHtVIAowAjALngIDdziccIQpUBKeAXgD54BtABgF14AH3gAFGDgC2WAM4gAMlgDWIADx9+HZuUo4swANwAoRFXZdK8APw8B8cuKmyQAOjgArcBgLNmx01AyAJ7o8JacYda2gg4S0nJuIJ6YPn5AA

Related Issues:

[DanielRosenwasser]

Similarly

declare function g(cb: (v: boolean) => "contextuallyTypable" | PromiseLike<"contextuallyTypable">): void;
g(v => v ? "contextuallyTypable" : Promise.reject());
g(async v => v ? "contextuallyTypable" : Promise.reject());

Yields

Type 'Promise<string>' is not assignable to type '"contextuallyTypable" | PromiseLike<"contextuallyTypable">'.
  Type 'Promise<string>' is not assignable to type 'PromiseLike<"contextuallyTypable">'.
    Types of property 'then' are incompatible.
      Type '<TResult1 = string, TResult2 = never>(onfulfilled?: ((value: string) => TResult1 | PromiseLike<TResult1>) | null | undefined, onrejected?: ((reason: any) => TResult2 | PromiseLike<...>) | null | undefined) => Promise<...>' is not assignable to type '<TResult1 = "contextuallyTypable", TResult2 = never>(onfulfilled?: ((value: "contextuallyTypable") => TResult1 | PromiseLike<TResult1>) | null | undefined, onrejected?: ((reason: any) => TResult2 | PromiseLike<...>) | null | undefined) => PromiseLike<...>'.
        Types of parameters 'onfulfilled' and 'onfulfilled' are incompatible.
          Types of parameters 'value' and 'value' are incompatible.
            Type 'string' is not assignable to type '"contextuallyTypable"'.

And the following example fails under noImplicitAny.

declare function h(cb: (v: boolean) => MyCallback | PromiseLike<MyCallback>): void;
h(v => v ? (abc) => { } : Promise.reject());
h(async v => v ? (def) => { } : Promise.reject());

Parameter 'def' implicitly has an 'any' type.