Fix generating XML doc comments for query parameters in gRPC JSON transcoding (#55482)

Author: JamesNK

src/Grpc/JsonTranscoding/src/Microsoft.AspNetCore.Grpc.Swagger/Internal/GrpcJsonTranscodingDescriptionProvider.cs

@@ -146,12 +146,18 @@ private static ApiDescription CreateApiDescription(RouteEndpoint routeEndpoint,
         var queryParameters = ServiceDescriptorHelpers.ResolveQueryParameterDescriptors(routeParameters, methodDescriptor, bodyDescriptor?.Descriptor, bodyDescriptor?.FieldDescriptor);
         foreach (var queryDescription in queryParameters)
         {
-            var fieldType = MessageDescriptorHelpers.ResolveFieldType(queryDescription.Value);
+            var field = queryDescription.Value;
+            var propertyInfo = field.ContainingType.ClrType.GetProperty(field.PropertyName);
+
+            // If from a property, create model as property to get its XML comments.
+            var identity = propertyInfo != null
+                ? ModelMetadataIdentity.ForProperty(propertyInfo, MessageDescriptorHelpers.ResolveFieldType(field), field.ContainingType.ClrType)
+                : ModelMetadataIdentity.ForType(MessageDescriptorHelpers.ResolveFieldType(field));
 
             apiDescription.ParameterDescriptions.Add(new ApiParameterDescription
             {
                 Name = queryDescription.Key,
-                ModelMetadata = new GrpcModelMetadata(ModelMetadataIdentity.ForType(fieldType)),
+                ModelMetadata = new GrpcModelMetadata(identity),
                 Source = BindingSource.Query,
                 DefaultValue = string.Empty
             });

src/Grpc/JsonTranscoding/test/Microsoft.AspNetCore.Grpc.Swagger.Tests/Proto/xmldoc.proto

@@ -35,6 +35,12 @@ service XmlDoc {
       delete: "/v1/greeter/{name}"
     };
   }
+  // QueryGet!
+  rpc QueryGet (StringRequestWithDetail) returns (StringReply) {
+    option (google.api.http) = {
+      get: "/v1/greeter/query/{name}"
+    };
+  }
 }
 
 // StringRequest!

src/Grpc/JsonTranscoding/test/Microsoft.AspNetCore.Grpc.Swagger.Tests/XmlComments/XmlDocumentationIntegrationTests.cs

@@ -108,6 +108,29 @@ public void RequestDescription_Nested_ProtoFieldDocs()
         Assert.Equal("Detail field!", path.Operations[OperationType.Post].RequestBody.Description);
     }
 
+    [Fact]
+    public void Parameters_QueryParameters_ProtoFieldDocs()
+    {
+        // Arrange & Act
+        var swagger = OpenApiTestHelpers.GetOpenApiDocument<XmlDocService>(_testOutputHelper);
+
+        // Assert
+        var path = swagger.Paths["/v1/greeter/query/{name}"];
+        Assert.Collection(path.Operations[OperationType.Get].Parameters,
+            p =>
+            {
+                Assert.Equal(ParameterLocation.Path, p.In);
+                Assert.Equal("name", p.Name);
+                Assert.Equal("Name field!", p.Description);
+            },
+            p =>
+            {
+                Assert.Equal(ParameterLocation.Query, p.In);
+                Assert.Equal("detail.age", p.Name);
+                Assert.Equal("Age field!", p.Description);
+            });
+    }
+
     [Fact]
     public void Message_UseProtoDocs()
     {