error[E0603]: macro `mac` is private
  --> $DIR/decl-macro.rs:8:8
   |
LL |     m::mac!();
   |        ^^^ private macro
   |
note: the macro `mac` is defined here
  --> $DIR/decl-macro.rs:4:5
   |
LL |     macro mac() {}
   |     ^^^^^^^^^^^

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0603`.