E0269 (not all control paths return a value) misfiring on an () associated type.

[eddyb]

Try on playpen:

trait Make {
    type Out;

    fn make() -> Self::Out;
}

impl Make for () {
    type Out = ();

    fn make() -> Self::Out {}
}

This looks like missing normalization when checking for the return type.
fn make() -> Self::Out { () } and fn make() -> Self::Out { return; } work just fine.