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# proc-macro-crate
[](https://docs.rs/proc-macro-crate/) [](https://crates.io/crates/proc-macro-crate) [](https://crates.io/crates/proc-macro-crate) [](https://travis-ci.org/bkchr/proc-macro-crate)
Providing support for `$crate` in procedural macros.
* [Introduction](#introduction)
* [Example](#example)
* [License](#license)
### Introduction
In `macro_rules!` `$crate` is used to get the path of the crate where a macro is declared in. In
procedural macros there is currently no easy way to get this path. A common hack is to import the
desired crate with a know name and use this. However, with rust edition 2018 and dropping
`extern crate` declarations from `lib.rs`, people start to rename crates in `Cargo.toml` directly.
However, this breaks importing the crate, as the proc-macro developer does not know the renamed
name of the crate that should be imported.
This crate provides a way to get the name of a crate, even if it renamed in `Cargo.toml`. For this
purpose a single function `crate_name` is provided. This function needs to be called in the context
of a proc-macro with the name of the desired crate. `CARGO_MANIFEST_DIR` will be used to find the
current active `Cargo.toml` and this `Cargo.toml` is searched for the desired crate.
### Example
```rust
use quote::quote;
use syn::Ident;
use proc_macro2::Span;
use proc_macro_crate::{crate_name, FoundCrate};
fn import_my_crate() {
let found_crate = crate_name("my-crate").expect("my-crate is present in `Cargo.toml`");
match found_crate {
FoundCrate::Itself => quote!( crate::Something ),
FoundCrate::Name(name) => {
let ident = Ident::new(&name, Span::call_site());
quote!( #ident::Something )
}
};
}
```
### Edge cases
There are multiple edge cases when it comes to determining the correct crate. If you for example
import a crate as its own dependency, like this:
```toml
[package]
name = "my_crate"
[dev-dependencies]
my_crate = { version = "0.1", features = [ "test-feature" ] }
```
The crate will return `FoundCrate::Itself` and you will not be able to find the other instance
of your crate in `dev-dependencies`. Other similar cases are when one crate is imported multiple
times:
```toml
[package]
name = "my_crate"
[dependencies]
some-crate = { version = "0.5" }
some-crate-old = { package = "some-crate", version = "0.1" }
```
When searching for `some-crate` in this `Cargo.toml` it will return `FoundCrate::Name("some_old_crate")`,
aka the last definition of the crate in the `Cargo.toml`.
### License
Licensed under either of
* [Apache License, Version 2.0](https://www.apache.org/licenses/LICENSE-2.0)
* [MIT license](https://opensource.org/licenses/MIT)
at your option.
License: MIT OR Apache-2.0
|
