use impl trait in grammar paramater

[AphrosDelos532]

I have a question about a simplified version of my project. Below is the project structure.

├── Cargo.lock
├── Cargo.toml
└── src
    ├── grammar.lalrpop
    ├── main.rs
    └── traits.rs

The traits.rs file contains the following content. I have defined and exposed a trait named AccessCache.

struct Cache {}

pub trait AccessCache {}

impl AccessCache for Cache {}

pub fn fun(cache: &impl AccessCache) {}

However, when I attempt to add it to the parser, I encounter the following error:

use crate::traits::AccessCache;

grammar(pool: &impl AccessCache);

...

Caused by:
  process didn't exit successfully: `.../build-script-build` (exit status: 1)
  
  --- stdout
  processing file `src/parser/parser.lalrpop`
  src/parser/parser.lalrpop:17:21: 17:31 error: unexpected token: `AccessCache`

  --- stderr
    grammar(pool: &impl AccessCache);
                        ~~~~~~~~~~~

However, I can use it well in other Rust functions. I'm puzzled. Is it not possible to use it in this way?

[Pat-Lafon]

Yes, unfortunately grammar parameters are incomplete in their handling of more advanced rust functionality. See this similar issue: #134 Please open an issue and we would be very interested in pr's on this.