//@ revisions: current next //@[next] compile-flags: -Znext-solver //@[next] check-pass #![feature(type_alias_impl_trait)] type A = impl Foo; type B = impl Foo; trait Foo {} fn muh(x: A) -> B { if false { return x; // B's hidden type is A (opaquely) //[current]~^ ERROR opaque type's hidden type cannot be another opaque type } Bar // A's hidden type is `Bar`, because all the return types are compared with each other } struct Bar; impl Foo for Bar {} fn main() {}