Improve debug_handler message for generic request-consuming extractors (#1826)

Co-authored-by: David Pedersen <david.pdrsn@gmail.com>

axum-macros/CHANGELOG.md

@@ -7,7 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 # Unreleased
 
-- None.
+- **fixed:** Improve `#[debug_handler]` message for known generic
+  request-consuming extractors ([#1826])
+
+[#1826]: https://github.com/tokio-rs/axum/pull/1826
 
 # 0.3.5 (03. March, 2023)
 

axum-macros/src/debug_handler.rs

@@ -228,6 +228,8 @@ fn check_inputs_impls_from_request(
                 }
             };
 
+            let consumes_request = request_consuming_type_name(&ty).is_some();
+
             let check_fn = format_ident!(
                 "__axum_macros_check_{}_{}_from_request_check",
                 item_fn.sig.ident,
@@ -252,7 +254,7 @@ fn check_inputs_impls_from_request(
                 }
             };
 
-            let check_fn_generics = if must_impl_from_request_parts {
+            let check_fn_generics = if must_impl_from_request_parts || consumes_request {
                 quote! {}
             } else {
                 quote! { <M> }
@@ -262,6 +264,10 @@ fn check_inputs_impls_from_request(
                 quote_spanned! {span=>
                     #ty: ::axum::extract::FromRequestParts<#state_ty> + Send
                 }
+            } else if consumes_request {
+                quote_spanned! {span=>
+                    #ty: ::axum::extract::FromRequest<#state_ty, #body_ty> + Send
+                }
             } else {
                 quote_spanned! {span=>
                     #ty: ::axum::extract::FromRequest<#state_ty, #body_ty, M> + Send
@@ -300,35 +306,9 @@ fn check_input_order(item_fn: &ItemFn) -> Option<TokenStream> {
                 FnArg::Typed(pat_type) => &*pat_type.ty,
                 FnArg::Receiver(_) => return None,
             };
-            let span = ty.span();
+            let type_name = request_consuming_type_name(ty)?;
 
-            let path = match ty {
-                Type::Path(type_path) => &type_path.path,
-                _ => return None,
-            };
-
-            let ident = match path.segments.last() {
-                Some(path_segment) => &path_segment.ident,
-                None => return None,
-            };
-
-            let type_name = match &*ident.to_string() {
-                "Json" => "Json<_>",
-                "BodyStream" => "BodyStream",
-                "RawBody" => "RawBody<_>",
-                "RawForm" => "RawForm",
-                "Multipart" => "Multipart",
-                "Protobuf" => "Protobuf",
-                "JsonLines" => "JsonLines<_>",
-                "Form" => "Form<_>",
-                "Request" => "Request<_>",
-                "Bytes" => "Bytes",
-                "String" => "String",
-                "Parts" => "Parts",
-                _ => return None,
-            };
-
-            Some((idx, type_name, span))
+            Some((idx, type_name, ty.span()))
         })
         .collect::<Vec<_>>();
 
@@ -343,7 +323,7 @@ fn check_input_order(item_fn: &ItemFn) -> Option<TokenStream> {
             let (_idx, type_name, span) = &types_that_consume_the_request[0];
             let error = format!(
                 "`{type_name}` consumes the request body and thus must be \
-            the last argument to the handler function"
+                the last argument to the handler function"
             );
             return Some(quote_spanned! {*span=>
                 compile_error!(#error);
@@ -386,6 +366,36 @@ fn check_input_order(item_fn: &ItemFn) -> Option<TokenStream> {
     }
 }
 
+fn request_consuming_type_name(ty: &Type) -> Option<&'static str> {
+    let path = match ty {
+        Type::Path(type_path) => &type_path.path,
+        _ => return None,
+    };
+
+    let ident = match path.segments.last() {
+        Some(path_segment) => &path_segment.ident,
+        None => return None,
+    };
+
+    let type_name = match &*ident.to_string() {
+        "Json" => "Json<_>",
+        "BodyStream" => "BodyStream",
+        "RawBody" => "RawBody<_>",
+        "RawForm" => "RawForm",
+        "Multipart" => "Multipart",
+        "Protobuf" => "Protobuf",
+        "JsonLines" => "JsonLines<_>",
+        "Form" => "Form<_>",
+        "Request" => "Request<_>",
+        "Bytes" => "Bytes",
+        "String" => "String",
+        "Parts" => "Parts",
+        _ => return None,
+    };
+
+    Some(type_name)
+}
+
 fn check_output_impls_into_response(item_fn: &ItemFn) -> TokenStream {
     let ty = match &item_fn.sig.output {
         syn::ReturnType::Default => return quote! {},

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

@@ -0,0 +1,9 @@
+use axum::Json;
+use axum_macros::debug_handler;
+
+struct Struct {}
+
+#[debug_handler]
+async fn handler(foo: Json<Struct>) {}
+
+fn main() {}

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

@@ -0,0 +1,20 @@
+error[E0277]: the trait bound `for<'de> Struct: serde::de::Deserialize<'de>` is not satisfied
+ --> tests/debug_handler/fail/json_not_deserialize.rs:7:23
+  |
+7 | async fn handler(foo: Json<Struct>) {}
+  |                       ^^^^^^^^^^^^ the trait `for<'de> serde::de::Deserialize<'de>` is not implemented for `Struct`
+  |
+  = help: the following other types implement trait `serde::de::Deserialize<'de>`:
+            &'a [u8]
+            &'a serde_json::raw::RawValue
+            &'a std::path::Path
+            &'a str
+            ()
+            (T0, T1)
+            (T0, T1, T2)
+            (T0, T1, T2, T3)
+          and $N others
+  = note: required for `Struct` to implement `serde::de::DeserializeOwned`
+  = note: required for `Json<Struct>` to implement `FromRequest<(), Body>`
+  = help: see issue #48214
+  = help: add `#![feature(trivial_bounds)]` to the crate attributes to enable