src/test/ui/type-alias-impl-trait/no_inferrable_concrete_type.rs

// Issue 52985: user code provides no use case that allows a type alias `impl Trait`
// We now emit a 'could not find defining uses' error

#![feature(type_alias_impl_trait)]

type Foo = impl Copy; //~ could not find defining uses

// make compiler happy about using 'Foo'
fn bar(x: Foo) -> Foo { x }

fn main() {
    let _: Foo = std::mem::transmute(0u8);
}