ErrorResponse conflicts with impl IntoResponse

[scotow]

Since the merge of this PR, it has become more difficult to use the impl IntoReponse syntax (as highly presented in the doc). It was pretty useful to not write the whole response type.

Here is an example of an over simplified handler:

async fn handler() -> impl IntoResponse {
    Err("error")?;
    Ok("success")
}

and here is the associated error:

error[E0283]: type annotations needed
  --> src/main.rs:40:41
   |
40 |   async fn handler() -> impl IntoResponse {
   |  _________________________________________^
41 | |     Err("error")?;
42 | |     Ok("success")
43 | | }
   | |_^ cannot infer type for enum `Result<&str, _>`
   |
   = note: multiple `impl`s satisfying `Result<&str, _>: IntoResponse` found in the `axum_core` crate:
           - impl<T, E> IntoResponse for Result<T, E>
             where T: IntoResponse, E: IntoResponse;
           - impl<T> IntoResponse for Result<T, ErrorResponse>
             where T: IntoResponse;

In this example, the return type can be specified as Result<&'static str, &'static str>, but when working with complex response types, writing the full types can be a pain.

Am I missing something, or is not possible to use the impl IntoResponse for returning Result<_, _> anymore?

[jplatte]

I'm surprised this ever worked. I would recommend writing the return types of fallible handler functions as Result<impl IntoResponse, Error> or Result<impl IntoResponse> given a Result type alias like the one in axum::response.