#![feature(existential_type)]

trait Bar {
    type A;
}

impl Bar for () {
    type A = ();
}

trait Foo {
    type A;
    type B: Bar<A = Self::A>;

    fn foo() -> Self::B;
}

impl Foo for () {
    type A = ();
    existential type B: Bar<A = Self::A>;

    fn foo() -> Self::B {
        ()
    }
}