Type::AssociatedType::AssociatedType doesn't resolve

[huonw]

trait Foo {
    type X;
}
trait Bar {
    type Y;
}

fn foo<T>(_: T::X::Y) 
    where T: Foo,
          T::X: Bar,
{}

<anon>:8:14: 8:21 error: failed to resolve. Use of undeclared type or module `T::X`
<anon>:8 fn foo<T>(_: T::X::Y) 
                      ^~~~~~~
<anon>:8:14: 8:21 error: use of undeclared type name `T::X::Y`
<anon>:8 fn foo<T>(_: T::X::Y) 
                      ^~~~~~~

[alexcrichton]

I think this is a dupe of #20300 (not using as seems to be blocked on that bug)