Code can compile even debug_handler give error

[kouhe3]

Summary

This is my code
https://github.com/kouhe3/FerrumLaunche/blob/648c5389560358058aab54ec5462d47d2dee8abd/play-back/src/lib.rs#L56
If remove comment this line.I will got

   --> play-back\src\lib.rs:56:38
    |
 56 |             .route("/minecraft", get(Self::version_list))
    |                                  --- ^^^^^^^^^^^^^^^^^^ the trait `Handler<_, _>` is not implemented for fn item `fn(State<Arc<AxumSever<A, B, C, D, E>>>) -> ... {...::version_list}`
    |                                  |
    |                                  required by a bound introduced by this call
    |

but Self::config_get can pass check. i don't know why

And, when add #[debug_handler] on config_get, it will give error

error[E0401]: can't use `Self` from outer item
  --> play-back\src\lib.rs:75:49
   |
66 | impl<A, B, C, D, E> AxumSever<A, B, C, D, E>
   | ---- `Self` type implicitly declared here, by this `impl`
...
75 |     async fn config_get(State(state): State<Arc<Self>>) -> Json<Option<LauncherConfig>> {
   |                                                 ^^^^
   |                                                 |
   |                                                 use of `Self` from outer item
   |                                                 refer to the type directly here instead

So why can this code be compiled? Even if it not pass debug_handler?

axum version

0.8.4

[yanns]

the purpose of #[debug_handler] is to give a more precise error message. This should guide you how to fix the issue.
Here, State<Arc<Self>> is mot permitted. Try to focus on fixing the error while keeping #[debug_handler].

[kouhe3]

Your suggestion is a good approach. By moving the function implementation outside, it provides more useful information to identify the real issue.

Self::config_get can compile because b.set is Syncand Send. So by changing the GetVersion trait to Impl Fuiture + Send, axum can work with the Self type in the handle — even though you advised against doing that.

[yanns]

Don't get me wrong, I have not advised against anything.
Is your issue fixed now?

[kouhe3]

yeah fixed. I just want to say, Self can use in here, maybe we should change debug_handle?

[yanns]

debug_handle is just a way to force the rust compiler to give better diagnostics.
The error message is coming from the rust compiler itself.
If you want to change this, you need to approach the rust compiler team.

[mladedav]

If I understand correctly, the code compiles, but if debug_handler is added, it gives false negative errors.

Maybe the macro generates some code that does not work well with Self in signatures?

[yanns]

I understood that the code does not compile, with or without debug_handler. But maybe I misunderstood the first description of the issue.