Assignability issue in narrowed constrained key type

[tinganho]

The below code:

class M {
    __m: any;
}
class C {
    __c: any;
}
type D = typeof M | typeof C;
interface R {
    [i: string]: D;
}
function f1(p: D) {
}
interface P {
    p1: string;
    p2: string;
}
function f2<K extends keyof P>(p: K) {
    let r: R = {};
    if (p in r) {
        f1(r[p]); // Error  `R[K]` is not assignable to `D`
    }
}

Gives me the error R[K] is not assignable to D.

Though isn't R[K] equal to D?

[mhegazy]

you do not really need the generic type parameter here. this should be written as:

function f2(p: keyof P) {
    let r: R = {};
    if (p in r) {
        f1(r[p]); 
    }
}

[tinganho]

It seems to work without a generic type parameter. Though, in my actual code I'm using the following signature:

public set<K extends keyof P>(prop: K, value: P[K] | null | undefined): void;

[ahejlsberg]

This no longer reproduces in the nightly build. I believe it was fixed in #12770.