How can I use a non-public function from within a macro?

Question

I have a macro that is getting too big so I wanted to extract part of the code into a function. When I do that, I have a problem because the function is not in scope when the macro is expanded at the call-site:

#[macro_use]
mod macros {
    fn hi() {
        println!("Hello")
    }

    #[macro_export]
    macro_rules! say_hi {
        () => {
            hi();
        };
    }
}

fn main() {
    say_hi!();
}

This does not compile:

error[E0425]: cannot find function `hi` in this scope
  --> src/main.rs:10:13
   |
10 |             hi();
   |             ^^ not found in this scope
...
16 |     say_hi!();
   |     ---------- in this macro invocation
   |
help: possible candidate is found in another module, you can import it into scope
   |
15 | fn main() use macros::hi;
   |

I tried making hi public (though I didn't want to) but since it is not imported in the context of the caller, it doesn't work anyway.

How can I solve this problem?

Answer 1

The first problem is that in the context of the caller of the macro, the function cannot be visible unless the function is public, thus I'm afraid it's not possible to call non-pub functions from macros.

Another problem is that functions referred to by macros should always use their fully qualified paths (so that they work from any context). Assuming the function hi is made pub, this will work:

#[macro_export]
macro_rules! say_hi {
    () => {
        $crate::macros::hi();
    };
}

Note: use $crate to make sure the macro works when used from any crate, see the $crate documentation for details.