tests/ui/macros/issue-39404.rs - toolchain/rustc - Git at Google

 #![allow(unused)]

 macro_rules! m { ($i) => {} }
 //~^ ERROR missing fragment specifier
 //~| WARN previously accepted

 fn main() {}
	#![allow(unused)]

	macro_rules! m { ($i) => {} }
	//~^ ERROR missing fragment specifier
	//~\| WARN previously accepted

	fn main() {}