associated type bounds in traits

desugared-2.rs

trait Foo where <Self::Bar as Iterator>: Send {
    type Bar: Iterator;
}

impl Foo for () {
    type Bar = Iteerator<Item = ()>;
}

desugared.rs

trait Foo {
    type Bar: Iterator<Item = _0>;
    type _0: Send;
}

impl Foo for () {
    type Bar = Iterator<Item = _0>;
    type _0 = ();
}

original.rs

trait Foo {
    type Bar: Iterator<Item: Send>;
}

impl Foo for () {
    type Bar = Iterator<Item = ()>;
}