src/test/ui/conservative_impl_trait.rs - third_party/rust - Git at Google

 // #39872, #39553

 fn will_ice(something: &u32) -> impl Iterator<Item = &u32> {
     //~^ ERROR `()` is not an iterator
 }

 fn main() {}
	// #39872, #39553

	fn will_ice(something: &u32) -> impl Iterator<Item = &u32> {
	//~^ ERROR `()` is not an iterator
	}

	fn main() {}