src/test/ui/parser/macro/macro-repeat.rs - toolchain/rustc - Git at Google

 macro_rules! mac {
     ( $($v:tt)* ) => (
         $v  //~ ERROR still repeating at this depth
     )
 }

 fn main() {
     mac!(0);
 }
	macro_rules! mac {
	( $($v:tt)* ) => (
	$v //~ ERROR still repeating at this depth
	)
	}

	fn main() {
	mac!(0);
	}