tests/ui/label/label-underscore.rs - rust-lang/rust - Git at Google

 fn main() {
     '_: loop { //~ ERROR labels cannot use keyword names
         break '_ //~ ERROR labels cannot use keyword names
     }
 }
	fn main() {
	'_: loop { //~ ERROR labels cannot use keyword names
	break '_ //~ ERROR labels cannot use keyword names
	}
	}