#![feature(type_alias_impl_trait)] mod a { type Foo = impl PartialEq<(Foo, i32)>; struct Bar; impl PartialEq<(Bar, i32)> for Bar { fn eq(&self, _other: &(Foo, i32)) -> bool { true } } } mod b { type Foo = impl PartialEq<(Foo, i32)>; struct Bar; impl PartialEq<(Foo, i32)> for Bar { //~^ ERROR cannot implement trait on type alias impl trait fn eq(&self, _other: &(Bar, i32)) -> bool { true } } } fn main() {}