Can't make generic Router, handler issue

[sergeda]

Summary

I'm trying to make generic router like this:

pub fn routes<T: Translator + Send + 'static>() -> Router {
    Router::new()
        .route(
            &format!("/:lang([a-z]{{2}})/{}", AUTH_PAGE),
            get(auth::<T>),
        )
}

async fn auth<T: Translator>(
    Extension(available_languages): Extension<Arc<AvailableLanguages>>,
    Extension(translator): Extension<Arc<T>>,
) -> Result<Response, AppError> 

This doesn't compile with error:

 the trait bound `fn(axum::Extension<std::sync::Arc<AvailableLanguages>>, axum::Extension<std::sync::Arc<T>>) -> impl futures::Future<Output = Result<axum::http::Response<axum::body::Body>, AppError>> {auth::<T>}: Handler<_, _>` is not satisfied
    --> src/routes.rs:104:17
     |
 104 |             get(auth::<T>),
     |             --- ^^^^^^^^^ the trait `Handler<_, _>` is not implemented for fn item `fn(Extension<Arc<AvailableLanguages>>, Extension<Arc<T>>) -> impl Future<Output = ...> {auth::<...>}`
     |             |
     |             required by a bound introduced by this call
     |
     = note: the full name for the type has been written to '/home/project/target/debug/deps/project-6b749d28f673aaa8.long-type-4099543736153440462.txt'
     = note: consider using `--verbose` to print the full type name to the console
     = note: Consider using `#[axum::debug_handler]` to improve the error message
     = help: the following other types implement trait `Handler<T, S>`:
               <IntoHandler<H, T, S> as Handler<T, S>>
               <Layered<L, H, T, S> as Handler<T, S>>
               <MethodRouter<S> as Handler<(), S>>
               <Or<L, R, Lt, Rt, S> as Handler<(M, Lt, Rt), S>>
 note: required by a bound in `axum::routing::get`

But if I specify some trait implementation on handler it compiles fine:

pub fn routes<T: Translator + Send + 'static>() -> Router {
    Router::new()
        .route(
            &format!("/:lang([a-z]{{2}})/{}", AUTH_PAGE),
            get(auth::<FluentTranslator>),
        )
}

axum version

0.7.5

[mladedav]

Did you try the third note in the error output concerning the debug attribute? I think it should help here.

[sergeda]

I tried #[axum::debug_handler] doesn't support handlers with generics

[mladedav]

Ah, ok. I think the issue is that FromRequestParts isn't implemented for Extension<T> for all T. The implementation has more constraints than your handler. Try adding Clone and any other bounds that the implementation has and you don't.

[sergeda]

Adding Sync helped. The end result is: <T: Translator + Send + Sync + 'static>