[debug_handler] is causing compilation error for correct handler

[eipi1]

• I have looked for existing issues (including closed) about this

Bug Report

Version

├── axum v0.6.18
│   ├── axum-core v0.3.4
├── axum-macros v0.3.7 (proc-macro)

Platform

Linux x1 5.15.0-76-generic #83-Ubuntu SMP Thu Jun 15 19:16:32 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux

Description

I have a simple axum router -

let shared_state = Arc::new(Client::new());

let _: Router = Router::new().route(
    "/agg",
    get({
        let shared_state = shared_state.clone();
        move || root_agg(shared_state, Uri::from_static("/"))
    }),
);
async fn root_agg(client: Arc<Client<HttpConnector>>, uri: Uri) -> Bytes {
    let res = client.get(uri.clone()).await.unwrap();
    // let buf = hyper::body::aggregate(res).await.unwrap();
    let buf = hyper::body::to_bytes(res).await.unwrap();
    buf
}

It compiles without any errors.
But if I add #[axum_macros::debug_handler] to the handler method, it causes compilation failure.

#[axum_macros::debug_handler]
async fn root_agg(client: Arc<Client<HttpConnector>>, uri: Uri) -> Bytes {
    let res = client.get(uri.clone()).await.unwrap();
    // let buf = hyper::body::aggregate(res).await.unwrap();
    let buf = hyper::body::to_bytes(res).await.unwrap();
    buf
}

Compiler output -

error[E0277]: the trait bound `Arc<Client<HttpConnector>>: FromRequestParts<()>` is not satisfied
  --> src/main.rs:51:27
   |
51 | async fn root_agg(client: Arc<Client<HttpConnector>>, uri: Uri) -> Bytes {
   |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `FromRequestParts<()>` is not implemented for `Arc<Client<HttpConnector>>`
   |
   = note: Function argument is not a valid axum extractor. 
           See `https://docs.rs/axum/latest/axum/extract/index.html` for details
   = help: the following other types implement trait `FromRequestParts<S>`:
             <() as FromRequestParts<S>>
             <(T1, T2) as FromRequestParts<S>>
             <(T1, T2, T3) as FromRequestParts<S>>
             <(T1, T2, T3, T4) as FromRequestParts<S>>
             <(T1, T2, T3, T4, T5) as FromRequestParts<S>>
             <(T1, T2, T3, T4, T5, T6) as FromRequestParts<S>>
             <(T1, T2, T3, T4, T5, T6, T7) as FromRequestParts<S>>
             <(T1, T2, T3, T4, T5, T6, T7, T8) as FromRequestParts<S>>
           and 25 others
   = help: see issue #48214
   = help: add `#![feature(trivial_bounds)]` to the crate attributes to enable

For more information about this error, try `rustc --explain E0277`.
warning: `playground` (bin "playground") generated 1 warning
error: could not compile `playground` (bin "playground") due to previous error; 1 warning emitted

Link to sample code

[jplatte]

debug_handler can only be used for actual handler funtions. In your case, the handler is the move || ... closure, not root_agg. You would also get an error trying to pass root_agg directly to get.

I guess debug_handler could be told to ignore specific function arguments, but I'm not sure whether it's worth it since it's not a very common use case.