Use macro inside proc_macro crate

1

Hello,

I have a crate with proc-macro = true inside Cargo.toml, because it exposes a procedural macro.

There is also a normal macro that is only used inside this crate.

How can I use this macro in one module of this crate if it is defined in another module of this crate?

Because if I write

#[macro_export]
macro_rules! internal_macro {...}

I get

error: cannot export macro_rules! macros from a `proc-macro` crate type currently
2

You can use the #[macro_use] attribute to import a macro from another module. The #[macro_export] attribute is just if you want to export it as part of the crate's public API.

// src/lib.rs

#[macro_use]
mod macros;

internal_macro! { ... }

// src/macros.rs

macro_rules! internal_macro { ... }
1 Like
3

Sorry, I forget that #[macro_use] belongs above mod modname instead of above use modname.
Thank you

4

Also, FWIW, I recommend people stop using #[macro_use] and that they use, instead, the more future-compatible and other-items-in-the-language-consistent mechanism of re-exporting a macro_rules! macro:

//! `src/macros.rs`

macro_rules! internal_macro { … }
pub(crate) use internal_macro;

and then you can use crate::macros::internal_macro! anywhere in the crate :wink:

7 Likes
5

I'm mostly wondering how I missed the existence of this, managing the macro namespace can be a bit of a nightmare due to the way they're resolved. The use of pub use might improve on that if it means I can then import and use the macro anywhere in the crate (or dependent crates) like any other regular old item.

1 Like
6

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