Constraining one associated type doesn't normalize the bounds on others

[aturon]

The trait system seems to be missing a normalization in bounds for associated items:

trait Parent {
    type Ty;
    type Assoc: Child<Self::Ty>;
}

trait Child<T> {}

struct ChildWrapper<T>(T);
impl<A, T> Child<A> for ChildWrapper<T> where T: Child<A> {}

struct ParentWrapper<T>(T);
impl<A, T: Parent<Ty = A>> Parent for ParentWrapper<T>
{
    type Ty = A;
    type Assoc = ChildWrapper<T::Assoc>;
}

produces the error:

error[E0277]: the trait bound `<T as Parent>::Assoc: Child<A>` is not satisfied
  --> wrapper.rs:12:1
   |
12 | impl<A, T: Parent<Ty = A>> Parent for ParentWrapper<T>
   | ^ the trait `Child<A>` is not implemented for `<T as Parent>::Assoc`
   |
   = help: consider adding a `where <T as Parent>::Assoc: Child<A>` bound
   = note: required by `Parent`

error[E0277]: the trait bound `<T as Parent>::Assoc: Child<A>` is not satisfied
  --> wrapper.rs:15:5
   |
15 |     type Assoc = ChildWrapper<T::Assoc>;
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Child<A>` is not implemented for `<T as Parent>::Assoc`
   |
   = help: consider adding a `where <T as Parent>::Assoc: Child<A>` bound
   = note: required by `Parent`

[aturon]

cc @nikomatsakis

[nikomatsakis]

Note that this version works: https://is.gd/MIFVFg

(Removing the A)

[estebank]

#65192 suggests impl<A, T: Parent<Ty = A>> Parent for ParentWrapper<T> where <T as Parent>::Assoc: Child<A> { /* ... */}, which compiles.

[estebank]

This now compiles.