Use macro inside proc_macro crate

Volker_Weissmann · 2021-06-14T05:01:03.580Z

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

Michael-F-Bryan · 2021-06-14T05:29:41.918Z

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 { ... }

Volker_Weissmann · 2021-06-14T07:29:26.966Z

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

Yandros · 2021-06-14T10:20:52.276Z

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

jjpe · 2021-06-14T16:31:02.837Z

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.

system · 2021-09-12T16:31:55.540Z

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