Improve debug_handler on tuple response types (#2201)

Co-authored-by: David Pedersen <[email protected]>
Co-authored-by: Jonas Platte <[email protected]>

axum-macros/tests/debug_handler/fail/output_tuple_too_many.rs

@@ -0,0 +1,29 @@
+use axum::response::AppendHeaders;
+
+#[axum::debug_handler]
+async fn handler(
+) -> (
+    axum::http::StatusCode,
+    AppendHeaders<[(axum::http::HeaderName, &'static str); 1]>,
+    AppendHeaders<[(axum::http::HeaderName, &'static str); 1]>,
+    AppendHeaders<[(axum::http::HeaderName, &'static str); 1]>,
+    AppendHeaders<[(axum::http::HeaderName, &'static str); 1]>,
+    AppendHeaders<[(axum::http::HeaderName, &'static str); 1]>,
+    AppendHeaders<[(axum::http::HeaderName, &'static str); 1]>,
+    AppendHeaders<[(axum::http::HeaderName, &'static str); 1]>,
+    AppendHeaders<[(axum::http::HeaderName, &'static str); 1]>,
+    AppendHeaders<[(axum::http::HeaderName, &'static str); 1]>,
+    AppendHeaders<[(axum::http::HeaderName, &'static str); 1]>,
+    AppendHeaders<[(axum::http::HeaderName, &'static str); 1]>,
+    AppendHeaders<[(axum::http::HeaderName, &'static str); 1]>,
+    AppendHeaders<[(axum::http::HeaderName, &'static str); 1]>,
+    AppendHeaders<[(axum::http::HeaderName, &'static str); 1]>,
+    AppendHeaders<[(axum::http::HeaderName, &'static str); 1]>,
+    AppendHeaders<[(axum::http::HeaderName, &'static str); 1]>,
+    AppendHeaders<[(axum::http::HeaderName, &'static str); 1]>,
+    axum::http::StatusCode,
+) {
+    panic!()
+}
+
+fn main() {}

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

@@ -0,0 +1,12 @@
+error: Cannot return tuples with more than 17 elements
+  --> tests/debug_handler/fail/output_tuple_too_many.rs:5:3
+   |
+5  |   ) -> (
+   |  ___^
+6  | |     axum::http::StatusCode,
+7  | |     AppendHeaders<[(axum::http::HeaderName, &'static str); 1]>,
+8  | |     AppendHeaders<[(axum::http::HeaderName, &'static str); 1]>,
+...  |
+24 | |     axum::http::StatusCode,
+25 | | ) {
+   | |_^

axum-macros/tests/debug_handler/fail/returning_request_parts.rs

@@ -0,0 +1,10 @@
+#[axum::debug_handler]
+async fn handler(
+) -> (
+    axum::http::request::Parts, // this should be response parts, not request parts
+    axum::http::StatusCode,
+) {
+    panic!()
+}
+
+fn main(){}

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

@@ -0,0 +1,8 @@
+error[E0308]: mismatched types
+ --> tests/debug_handler/fail/returning_request_parts.rs:4:5
+  |
+4 |     axum::http::request::Parts, // this should be response parts, not request parts
+  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
+  |     |
+  |     expected `axum::http::response::Parts`, found `axum::http::request::Parts`
+  |     expected `axum::http::response::Parts` because of return type

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

@@ -0,0 +1,10 @@
+#![allow(unused_parens)]
+
+struct NotIntoResponse;
+
+#[axum::debug_handler]
+async fn handler() -> (NotIntoResponse) {
+    panic!()
+}
+
+fn main() {}

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

@@ -0,0 +1,21 @@
+error[E0277]: the trait bound `NotIntoResponse: IntoResponse` is not satisfied
+ --> tests/debug_handler/fail/single_wrong_return_tuple.rs:6:23
+  |
+6 | async fn handler() -> (NotIntoResponse) {
+  |                       ^^^^^^^^^^^^^^^^^ the trait `IntoResponse` is not implemented for `NotIntoResponse`
+  |
+  = help: the following other types implement trait `IntoResponse`:
+            Box<str>
+            Box<[u8]>
+            axum::body::Bytes
+            Body
+            axum::extract::rejection::FailedToBufferBody
+            axum::extract::rejection::LengthLimitError
+            axum::extract::rejection::UnknownBodyError
+            bytes::bytes_mut::BytesMut
+          and $N others
+note: required by a bound in `__axum_macros_check_handler_into_response::{closure#0}::check`
+ --> tests/debug_handler/fail/single_wrong_return_tuple.rs:6:23
+  |
+6 | async fn handler() -> (NotIntoResponse) {
+  |                       ^^^^^^^^^^^^^^^^^ required by this bound in `check`

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

@@ -0,0 +1,30 @@
+#![allow(unused_parens)]
+
+#[axum::debug_handler]
+async fn named_type() -> (
+    axum::http::StatusCode,
+    axum::Json<&'static str>,
+    axum::response::AppendHeaders<[( axum::http::HeaderName,&'static str); 1]>,
+) {
+    panic!()
+}
+
+
+struct CustomIntoResponse{
+
+}
+impl axum::response::IntoResponse for CustomIntoResponse{
+    fn into_response(self) -> axum::response::Response {
+        todo!()
+    }
+}
+#[axum::debug_handler]
+async fn custom_type() -> (
+    axum::http::StatusCode,
+    CustomIntoResponse,
+    axum::response::AppendHeaders<[( axum::http::HeaderName,&'static str); 1]>,
+) {
+    panic!()
+}
+
+fn main() {}

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

@@ -0,0 +1,24 @@
+error: `Json<_>` must be the last element in a response tuple
+ --> tests/debug_handler/fail/wrong_return_tuple.rs:6:5
+  |
+6 |     axum::Json<&'static str>,
+  |     ^^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0277]: the trait bound `CustomIntoResponse: IntoResponseParts` is not satisfied
+  --> tests/debug_handler/fail/wrong_return_tuple.rs:24:5
+   |
+24 |     CustomIntoResponse,
+   |     ^^^^^^^^^^^^^^^^^^ the trait `IntoResponseParts` is not implemented for `CustomIntoResponse`
+   |
+   = help: the following other types implement trait `IntoResponseParts`:
+             AppendHeaders<I>
+             HeaderMap
+             Extension<T>
+             Extensions
+             Option<T>
+             [(K, V); N]
+             ()
+             (T1,)
+           and $N others
+   = help: see issue #48214
+   = help: add `#![feature(trivial_bounds)]` to the crate attributes to enable