Type inference fails on instance method call that returns same type

[joshuakb2]

Search Terms: infer, inferred, declaration, generic function

Code

// Things are objects that store a function
class Thing<In, Out> {
    f: (x: In) => Out;

    private constructor(f: (x: In) => Out) {
        this.f = f;
    }

    // Creates an identical thing
    public another(): Thing<In, Out> {
        return new Thing<In, Out>(this.f);
    }

    // Creates a thing with the given function
    public static create<In, Out>(f: (x: In) => Out): Thing<In, Out> {
        return new Thing<In, Out>(f);
    }
}

// Type inference works here, understands that x => x is string => string
const test: Thing<string, string> = Thing.create(x => x);

// Type inference does not work here, even though .another() returns something with the same type as the original thing
const test2: Thing<string, string> = Thing.create(x => x).another();

// Type inference works here because we helped it along by defining x: string, but it's redundant.
const test3: Thing<string, string> = Thing.create((x: string) => x).another();

Expected behavior: test, test2, and test3 would all be inferred properly.

Actual behavior: test2 produces an error: "Type 'unknown' is not assignable to type 'string'."

Playground Link: Playground Link

Related Issues: (I couldn't find any)

[RyanCavanaugh]

The contextual type of an expression can supply inference candidates via the return type, but this process is not recursive and it's very tenuous to apply that logic any further than it already goes.

#30134 would be a prerequisite to handling this in all cases.