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

 // `/**/` was previously regarded as a doc comment because it starts with `/**` and ends with `*/`.
 // This could break some internal logic that assumes the length of a doc comment is at least 5,
 // leading to an ICE.

 macro_rules! one_arg_macro {
     ($fmt:expr) => (print!(concat!($fmt, "\n")));
 }

 fn main() {
     one_arg_macro!(/**/); //~ ERROR unexpected end
 }
	// `//` was previously regarded as a doc comment because it starts with `/` and ends with `*/`.
	// This could break some internal logic that assumes the length of a doc comment is at least 5,
	// leading to an ICE.

	macro_rules! one_arg_macro {
	($fmt:expr) => (print!(concat!($fmt, "\n")));
	}

	fn main() {
	one_arg_macro!(/**/); //~ ERROR unexpected end
	}