feat: add #[diagnostic::on_unimplemented] to IntoResponse and IntoResponseParts (#3723)

axum-core/src/response/into_response.rs

@@ -109,6 +109,9 @@ use std::{
 /// let app = Router::new().route("/", get(|| async { MyBody }));
 /// # let _: Router = app;
 /// ```
+#[diagnostic::on_unimplemented(
+    note = "See `https://docs.rs/axum/0.8/axum/response/trait.IntoResponse.html` for details"
+)]
 pub trait IntoResponse {
     /// Create a response.
     #[must_use]

axum-core/src/response/into_response_parts.rs

@@ -70,6 +70,9 @@ use std::{convert::Infallible, fmt};
 ///     SetHeader("x-foo", "custom")
 /// }
 /// ```
+#[diagnostic::on_unimplemented(
+    note = "See `https://docs.rs/axum/0.8/axum/response/trait.IntoResponseParts.html` for details"
+)]
 pub trait IntoResponseParts {
     /// The type returned in the event of an error.
     ///

axum-macros/tests/debug_handler/fail/single_wrong_return_tuple.stderr

@@ -9,6 +9,7 @@ help: the trait `IntoResponse` is not implemented for `NotIntoResponse`
   |
 3 | struct NotIntoResponse;
   | ^^^^^^^^^^^^^^^^^^^^^^
+  = note: See `https://docs.rs/axum/0.8/axum/response/trait.IntoResponse.html` for details
   = help: the following other types implement trait `IntoResponse`:
             &'static [u8; N]
             &'static [u8]

axum-macros/tests/debug_handler/fail/wrong_return_tuple.stderr

@@ -15,6 +15,7 @@ help: the trait `IntoResponseParts` is not implemented for `CustomIntoResponse`
    |
 12 | struct CustomIntoResponse {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: See `https://docs.rs/axum/0.8/axum/response/trait.IntoResponseParts.html` for details
    = help: the following other types implement trait `IntoResponseParts`:
              ()
              (T1, T2)
@@ -42,6 +43,7 @@ help: the trait `IntoResponseParts` is not implemented for `CustomIntoResponse`
    |
 12 | struct CustomIntoResponse {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^
+   = note: See `https://docs.rs/axum/0.8/axum/response/trait.IntoResponseParts.html` for details
    = help: the following other types implement trait `IntoResponseParts`:
              ()
              (T1, T2)

axum-macros/tests/debug_handler/fail/wrong_return_type.stderr

@@ -4,6 +4,7 @@ error[E0277]: the trait bound `bool: IntoResponse` is not satisfied
 4 | async fn handler() -> bool {
   |                       ^^^^ the trait `IntoResponse` is not implemented for `bool`
   |
+  = note: See `https://docs.rs/axum/0.8/axum/response/trait.IntoResponse.html` for details
   = help: the following other types implement trait `IntoResponse`:
             &'static [u8; N]
             &'static [u8]