How do I use a macro across module files?

Question

I have two modules in separate files within the same crate, where the crate has macro_rules enabled. I want to use the macros defined in one module in another m

Answer 1

I have came across the same problem in Rust 1.44.1, and this solution works for later versions (known working for Rust 1.7).

Say you have a new project as:

src/
    main.rs
    memory.rs
    chunk.rs

In main.rs, you need to annotate that you are importing macros from the source, otherwise, it will not do for you.

#[macro_use]
mod memory;
mod chunk;

fn main() {
    println!("Hello, world!");
}

So in memory.rs you can define the macros, and you don't need annotations:

macro_rules! grow_capacity {
    ( $x:expr ) => {
        {
            if $x < 8 { 8 } else { $x * 2 }
        }
    };
}

Finally you can use it in chunk.rs, and you don't need to include the macro here, because it's done in main.rs:

grow_capacity!(8);

The upvoted answer caused confusion for me, with this doc by example, it would be helpful too.