...
LL | one_arg_macro!(/**/);
| ^^^^^^^^^^^^^^^^^^^^ missing tokens in macro arguments
+ |
+note: while trying to match meta-variable `$fmt:expr`
+ --> $DIR/empty-comment.rs:6:6
+ |
+LL | ($fmt:expr) => (print!(concat!($fmt, "\n")));
+ | ^^^^^^^^^
error: aborting due to previous error