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// build-pass #![feature(const_trait_impl, effects)] #[const_trait] trait Func<T> { type Output; fn call_once(self, arg: T) -> Self::Output; } struct Closure; impl const Func<&usize> for Closure { type Output = usize; fn call_once(self, arg: &usize) -> Self::Output { *arg } } enum Bug<T = [(); Closure.call_once(&0) ]> { V(T), } fn main() {}