Compilation Error When Using ref Keyword in Attribute for External File Reference

[shishidosoichiro]

Describe the bug
When I try to use #[endpoint(request_body = ref("./external.json"))] to reference an external file, as per the Salvo documentation, I encounter a compilation error. It appears that the ref keyword may be causing a conflict, possibly because it's also a reserved word in Rust.

To Reproduce
Steps to reproduce:

1. Add the following code:

   use salvo::{oapi::extract::JsonBody, prelude::*};
   
   #[endpoint(request_body = ref("./external.json"))]
   async fn hello(name: JsonBody<String>) -> String {
       format!("Hello World, {}", name)
   }
   
   #[tokio::main]
   async fn main() {
       let router = Router::new().get(hello);
       let acceptor = TcpListener::new("127.0.0.1:5800").bind().await;
       Server::new(acceptor).serve(router).await;
   }

2. Run cargo build.
3. Compilation fails with the following error:

   error: unexpected token, expected type such as String, expected identifier
    --> src/main.rs:3:31
     |
   3 | #[endpoint(request_body = ref("./external.json"))]
     |                               ^^^^^^^^^^^^^^^^^
   

Expected behavior
I expected this code to compile successfully, allowing ref("./external.json") to refer to an external JSON file as the request body.

Screenshots
Not applicable.

Desktop (please complete the following information):

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Additional context
It seems that ref might be causing a conflict due to its status as a Rust reserved word, but I’m not certain. I’d appreciate any guidance on how best to approach this or if there’s a workaround. Thank you for all the hard work on Salvo—it's a great framework, and any help would be greatly appreciated!