Uncomputed generic type does not follow structural typing

Bug Report

🔎 Search Terms

generic
unassignable type
uncomputed type

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about:
  • Common "Bugs" That Aren't Bugs
  • Type System Behavior
  • Generics

⏯ Playground Link

Playground link with relevant code

💻 Code

class A {
    x: string = 'A';
    y: number = 0;
}

class B {
    x: string = 'B';
    z: boolean = true;
}

type T<X extends { x: any }> = Pick<X, 'x'>;

type C = T<A>;
type D = T<B>;

type C_extends_D = C extends D ? true : false;                                  // true
type PickA_extends_PickB = Pick<A, 'x'> extends Pick<B, 'x'> ? true : false;    // true
type TA_extends_TB = T<A> extends T<B> ? true : false;                          // false (?)

declare let a: T<A>;
declare let b: T<B>;
declare let c: C;
declare let d: D;

b = a;      // error here (?)
c = d;

🙁 Actual behavior

• Type TA_extends_TB is false.
• a is not assignable to b.

🙂 Expected behavior

• All types TA_extends_TB should be true, the same way as C_extends_D and PickA_extends_PickB.
• a should be assignable to b and vice-versa, the same way as c and d.