Improve UI when the custom schema fn accepts the wrong argument (#300)

derive/src/endpoint.rs

@@ -531,14 +531,16 @@ fn expand_endpoint_type(
 		)
 	});
 	let output_struct = schema.map(|schema_fn| {
-		let output_struct_ident = output_struct_ident.as_ref().unwrap_or_else(|| unreachable!());
+		let output_struct_ident = output_struct_ident
+			.as_ref()
+			.unwrap_or_else(|| unreachable!());
 		let status_codes_fn = status_codes.unwrap_or_else(|| unreachable!());
 
 		let schema_call = quote_spanned! { schema_fn.span() =>
-			let schema: ::gotham_restful::private::OpenapiSchema = #schema_fn(code);
+			let schema = ::gotham_restful::private::CustomSchema::schema(#schema_fn, code);
 		};
 		let status_codes_call = quote_spanned! { status_codes_fn.span() =>
-			let status_codes: ::std::vec::Vec<::gotham_restful::gotham::hyper::StatusCode> = #status_codes_fn();
+			let status_codes = ::gotham_restful::private::CustomStatusCodes::status_codes(#status_codes_fn);
 		};
 
 		quote! {
@@ -563,7 +565,9 @@ fn expand_endpoint_type(
 					::gotham_restful::IntoResponse::into_response(self.0)
 				}
 
-				fn accepted_types() -> ::core::option::Option<::std::vec::Vec<::gotham_restful::gotham::mime::Mime>> {
+				fn accepted_types() -> ::core::option::Option<
+						::std::vec::Vec<::gotham_restful::gotham::mime::Mime>>
+				{
 					<#output_ty as ::gotham_restful::IntoResponse>::accepted_types()
 				}
 			}

src/lib.rs

@@ -496,14 +496,57 @@ pub mod private {
 	pub use openapi_type::{OpenapiSchema, OpenapiType, Visitor};
 	pub use serde_json;
 
+	#[cfg(feature = "openapi")]
+	use gotham::hyper::StatusCode;
+	#[cfg(feature = "auth")]
 	use gotham::state::{FromState, State};
 
+	/// This method is used by the endpoint macro to generate a good error message
+	/// when the used AuthData type does not implement Clone.
+	#[cfg(feature = "auth")]
+	#[inline]
 	pub fn clone_from_state<T>(state: &State) -> T
 	where
 		T: FromState + Clone
 	{
 		T::borrow_from(state).clone()
 	}
+
+	/// This trait is used by the endpoint macro to generate a good error message
+	/// when the schema function has the wrong signature.
+	#[cfg(feature = "openapi")]
+	pub trait CustomSchema {
+		fn schema(self, code: StatusCode) -> OpenapiSchema;
+	}
+
+	#[cfg(feature = "openapi")]
+	impl<F> CustomSchema for F
+	where
+		F: FnOnce(StatusCode) -> OpenapiSchema
+	{
+		#[inline]
+		fn schema(self, code: StatusCode) -> OpenapiSchema {
+			self(code)
+		}
+	}
+
+	/// This trait is used by the endpoint macro to generate a good error message
+	/// when the status_codes function has the wrong signature.
+	#[cfg(feature = "openapi")]
+	pub trait CustomStatusCodes {
+		fn status_codes(self) -> Vec<StatusCode>;
+	}
+
+	#[cfg(feature = "openapi")]
+	impl<F> CustomStatusCodes for F
+	where
+		F: FnOnce() -> Vec<StatusCode>
+	{
+		#[inline]
+		fn status_codes(self) -> Vec<StatusCode> {
+			self()
+		}
+	}
 }
 
 #[cfg(feature = "auth")]

tests/ui/endpoint/dynamic_schema_wrong_type.stderr

@@ -1,39 +1,22 @@
-error[E0308]: mismatched types
+error[E0631]: type mismatch in function arguments
   --> tests/ui/endpoint/dynamic_schema_wrong_type.rs:16:21
    |
-16 | #[read_all(schema = "schema", status_codes = "status_codes")]
-   |                     ^^^^^^^^
-   |                     |
-   |                     expected `u16`, found struct `StatusCode`
-   |                     arguments to this function are incorrect
-   |
-note: function defined here
-  --> tests/ui/endpoint/dynamic_schema_wrong_type.rs:8:4
-   |
 8  | fn schema(_: u16) -> String {
-   |    ^^^^^^ ------
-help: call `Into::into` on this expression to convert `StatusCode` into `u16`
-   |
-16 | #[read_all(schema = "schema".into(), status_codes = "status_codes")]
-   |                             +++++++
-
-error[E0308]: mismatched types
-  --> tests/ui/endpoint/dynamic_schema_wrong_type.rs:16:21
-   |
+   | --------------------------- found signature defined here
+...
 16 | #[read_all(schema = "schema", status_codes = "status_codes")]
-   |                     ^^^^^^^^
-   |                     |
-   |                     expected struct `OpenapiSchema`, found struct `std::string::String`
-   |                     expected due to this
+   |                     ^^^^^^^^ expected due to this
+   |
+   = note: expected function signature `fn(StatusCode) -> _`
+              found function signature `fn(u16) -> _`
+   = note: required for `fn(u16) -> std::string::String {schema}` to implement `CustomSchema`
 
-error[E0308]: mismatched types
+error[E0271]: expected `fn() -> Vec<u16> {status_codes}` to be a fn item that returns `Vec<StatusCode>`, but it returns `Vec<u16>`
   --> tests/ui/endpoint/dynamic_schema_wrong_type.rs:16:46
    |
 16 | #[read_all(schema = "schema", status_codes = "status_codes")]
-   |                                              ^^^^^^^^^^^^^^
-   |                                              |
-   |                                              expected struct `StatusCode`, found `u16`
-   |                                              expected due to this
+   |                                              ^^^^^^^^^^^^^^ expected struct `StatusCode`, found `u16`
    |
    = note: expected struct `Vec<StatusCode>`
               found struct `Vec<u16>`
+   = note: required for `fn() -> Vec<u16> {status_codes}` to implement `CustomStatusCodes`