Add support for reexporting the derive proc macro?

[LHolten]

Hi, my library has a proc macro that generates code that uses #[derive(::my_library::RefCast)].
Here ::my_library::RefCast reexports ::ref_cast::RefCast, but sadly the RefCast macro generates hardcoded references to the ::ref_cast crate.
This means that users of my_library have to add a dependency on both my-library and ref-cast.

Could you make the RefCast derive macro accept a path to the location where it has been reexported from and then use that for the generated code?

[LHolten]

Oh and I can make a PR if that is desired.

[dtolnay]

I would prefer not to support that in this crate. But if you are interested in working on it, rust-lang/rust#54363 (comment) describes a design for how I would like for proc macro re-exporting to work instead.