// compile-pass #![feature(underscore_const_names)] trait Trt {} struct Str {} impl Trt for Str {} macro_rules! check_impl { ($struct:ident,$trait:ident) => { const _ : () = { use std::marker::PhantomData; struct ImplementsTrait(PhantomData); let _ = ImplementsTrait::<$struct>(PhantomData); () }; } } #[deny(unused)] const _ : () = (); const _ : i32 = 42; const _ : Str = Str{}; check_impl!(Str, Trt); check_impl!(Str, Trt); fn main() { check_impl!(Str, Trt); check_impl!(Str, Trt); }