Recursive generic constraint

[NN---]

Didn't find this issue.
Will TypeScript allow recursive generic constraints known as CRTP:

interface B<T extends B> {}

There is a workaround but it is not nice.

interface A {
    f() : void;
}

interface B<T extends A> extends A {
}

class C implements B<C> {
    f() : void {}
}

[danquirk]

Recursive types and structural types like this are not a great mix. Consider your definition of B with some actual members (or else its meaningless):

interface B<T extends B> {
    foo: string;
}

Now imagine the steps the compiler has to go through to validate whether the T in a particular B instantiation satisfies the constraint T extends B. It has to inspect the shape of B to structurally check T against, which causes another elaboration of B and asking again whether this other T extends B is satisfied, and so on. Eventually the compiler ends up having to just short circuit the comparison.

[jbondc]

Seems doable, I'll keep it as a note for #3496