Using $crate in Rust's procedural macros?

Question

I know what the $crate variable is, but as far as I can tell, it can\'t be used inside procedural macros. Is there another way to achieve a similar effect?

I have an ex

Answer 1

In Edition 2015 (classic Rust), you can do this (but it's hacky):

• use ::defining_crate::SomeTrait in the macro
• within third-party crates depending on defining_crate, the above works fine

• within defining_crate itself, add a module in the root:

  mod defining_crate { pub use super::*; }

In Edition 2018 even more hacky solutions are required (see this issue), though #55275 may give us a simple workaround.

Answer 2

Based on replies from https://github.com/rust-lang/rust/issues/38356#issuecomment-412920528, it looks like there is no way to do this (as of 2018-08), neither to refer to the proc-macro crate nor to refer to any other crate unambiguously.

Answer 3

Since Rust 1.34, you can use extern my_crate as self, and use my_crate::Foo instead of $crate::Foo.

https://github.com/rust-lang/rust/issues/54647

https://github.com/rust-lang/rust/pull/57407

(Credit: Neptunepink ##rust irc.freenode.net)