"associated type `T` not found for type parameter `X`" error with where clause

[mandel59]

trait A {
    type T;
}

impl A for () {
    type T = i32;
}

fn foo<X>(_x: X::T) where X: A {
}

fn main() {
    foo::<()>(42);
}

This fails to compile with:

assoc.rs:9:15: 9:19 error: associated type `T` not found for type parameter `X`
assoc.rs:9 fn foo<X>(_x: X::T) where X: A {
                         ^~~~
error: aborting due to previous error

It passes with tweaking the definition:

fn foo<X: A>(_x: X::T) {
}

[mandel59]

a dup of #20300