tests/ui/impl-trait/issue-51185.rs - toolchain/rustc - Git at Google

 //@ run-pass
 fn foo() -> impl Into<for<'a> fn(&'a ())> {
     (|_| {}) as for<'a> fn(&'a ())
 }

 fn main() {
     foo().into()(&());
 }
	//@ run-pass
	fn foo() -> impl Into<for<'a> fn(&'a ())> {
	(\|_\| {}) as for<'a> fn(&'a ())
	}

	fn main() {
	foo().into()(&());
	}