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#[lang = "sized"] pub trait Sized {} trait Foo<T> { type Output; fn test(self, slice: &T) -> &Self::Output; } struct Bar<T>(T); // { dg-warning "struct is never constructed" "" { target *-*-* } .-1 } impl<T> Foo<[T]> for Bar<usize> { type Output = [T]; fn test(self, slice: &[T]) -> &[T] { slice } }