Typescript: Constraints cannot be proven in mapped types combination

[Igorbek]

TypeScript Version: 2.1.4 / nightly (2.2.0-dev.20161219)

Code

type A<T> = () => T;
type B<T, C extends A<T>> = C;
type As<Ts> = {
    [P in keyof Ts]: A<Ts[P]>;
};

type Failing<Ts, Cs extends As<Ts>> = {
    [P in keyof Ts]: B<Ts[P], Cs[P]>;
//                            ~~~~~ Type 'Cs[P]' does not satisfy the constraint 'A<Ts[P]>'.
};

Expected behavior:

No errors, the constraint has been proven

Actual behavior:

Error in Failing type at B<Ts[P], Cs[P]>: Type 'Cs[P]' does not satisfy the constraint 'A

Note

If I change A<T> to be just T (type A<T> = T;), all compiles just fine.

[zpdDG4gta8XKpMCd]

might be related #8459 which presumably growing from #8397 or even this one #3410

[zpdDG4gta8XKpMCd]

ha! don't downvote me, downvote the design team who is making typescript is the only language out there that sacrifices correctness for "convenience" of use, this is blatant and unprecedented

[RyanCavanaugh]

Guess what we're spending the swag budget on this year

[RyanCavanaugh]

Repro with some thing renamed / simplified a little

  interface Thing { blah };
  type B<C extends Thing> = { m: C };
  type ThingMap<M> = {
    [P in keyof M]: Thing;
  };

  type Failing<T, Cs extends ThingMap<T>> = {
    foo: B<Cs[keyof T]>;
  };

  type Passing<T> = {
    foo: B<ThingMap<T>[keyof T]>;
  };

[falsandtru]

@RyanCavanaugh Seems like your repro is fixed now, but @Igorbek 's repro still throws an error.

[zpdDG4gta8XKpMCd]

https://github.com/Microsoft/TypeScript/issues/15957

... Guess what we're spending the swag budget on this year...

[mhegazy]

should be fixed in latest.