Is there a way to get the file and the module path of where a procedural macro is attached at compile-time?

Question

I'm looking for the equivalent of file!() & module_path!() in a procedural macro context.

For example, the following doesn't work:

file.rs:

#[some_attribute]
const A: bool = true;

macro.rs:

#[proc_macro_attribute]
pub fn some_attribute(attr: TokenStream, input: TokenStream) -> TokenStream {
    println!("{}", file!());

    input
}

This prints macro.rs which makes sense, but what I want is file.rs. Is there a way to achieve this? Is there also a similar way for module_path!()?

A requirement of this is that has to happen at compile-time.

I'm trying to create a file in the OUT_DIR containing constant values where the attribute is added with the module and the file that they are in.

Answer 1

I had the same problem and found out that Rust added a new experimential API to Rust macros (#54725) which allows exactly what you want:

#![feature(proc_macro_span)]

#[proc_macro]
pub(crate) fn do_something(item: TokenStream) -> TokenStream {
    let span = Span::call_site();
    let source = span.source_file();
    format!("println!(r#\"Path: {}\"#)", source.path().to_str().unwrap())
        .parse()
        .unwrap()
}

use my_macro_crate::*;

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

Will output:

Hello, world!
Path: src\main.rs

Important

Apart from this API being experimential, the path might not be a real OS path. This can be the case if the Span was generated by a macro. Visit the documentation here.