rust/tests/ui/type-alias-impl-trait/impl_for_weak_alias.rs

#![feature(type_alias_impl_trait)]
#![feature(auto_traits)]

type Alias = (impl Sized, u8);

auto trait Trait {}
impl Trait for Alias {}
//~^ ERROR traits with a default impl, like `Trait`, cannot be implemented for type alias `Alias`

fn _def() -> Alias {
    (42, 42)
}

fn main() {}