$crate is not a valid identifier inside paste::item!

[softprops]

demo reproduction here https://github.com/dtolnay/paste/pull/2/files

I found that Im not able to refer to a crate local macro inside a paste::item! block, that is the ability to express $crate::foo! which is required to enable rust 2018 style imports ( aka ditching #[macro_use].

The specific context is here where I'm using paste to generate idents which are inputs for another crate local macro

[dtolnay]

This looks like a rustc bug because I can reproduce it without any libraries.

repro/src/lib.rs

extern crate proc_macro;
use self::proc_macro::TokenStream;

#[proc_macro]
pub fn repro(input: TokenStream) -> TokenStream {
    input.into_iter().next();
    unimplemented!()
}

testing/src/lib.rs

macro_rules! m {
    () => {
        repro::repro!($crate);
    };
}

m!();

error: proc macro panicked                                                                                                     
 --> src/main.rs:3:9                                                                                                           
  |                                                                                                                            
3 |         repro::repro!($crate);                                                                                             
  |         ^^^^^^^^^^^^^^^^^^^^^^                                                                                             
...                                                                                                                            
7 | m!();                                                                                                                      
  | ----- in this macro invocation                                                                                             
  |                                                                                                                            
  = help: message: `"$crate"` is not a valid identifier

[dtolnay]

Moved upstream: rust-lang/rust#55640.

[softprops]

Thanks @dtolnay