Fix incorrect Swagger return type when using IResult (#34197)

When a POCO is wrapped in an IResult, an incorrect return type
is used to determine the default API response format, which results in
the response being mapped correctly. This then results in the metadata
specified by an [ProducesResponseType] attribute not being used.

Author: martincostello

src/Mvc/Mvc.ApiExplorer/src/EndpointMetadataApiDescriptionProvider.cs

@@ -265,7 +265,7 @@ private static void AddSupportedResponseTypes(
                     {
                         AddResponseContentTypes(apiResponseType.ApiResponseFormats, contentTypes);
                     }
-                    else if (CreateDefaultApiResponseFormat(responseType) is { } defaultResponseFormat)
+                    else if (CreateDefaultApiResponseFormat(apiResponseType.Type) is { } defaultResponseFormat)
                     {
                         apiResponseType.ApiResponseFormats.Add(defaultResponseFormat);
                     }

src/Mvc/Mvc.ApiExplorer/test/EndpointMetadataApiDescriptionProviderTest.cs

@@ -179,7 +179,7 @@ public void AddsResponseFormatFromMetadata()
         }
 
         [Fact]
-        public void AddsMultipleResponseFormatsFromMetadata()
+        public void AddsMultipleResponseFormatsFromMetadataWithPoco()
         {
             var apiDescription = GetApiDescription(
                 [ProducesResponseType(typeof(TimeSpan), StatusCodes.Status201Created)]
@@ -207,6 +207,34 @@ public void AddsMultipleResponseFormatsFromMetadata()
             Assert.Equal("application/json", badRequestResponseFormat.MediaType);
         }
 
+        [Fact]
+        public void AddsMultipleResponseFormatsFromMetadataWithIResult()
+        {
+            var apiDescription = GetApiDescription(
+                [ProducesResponseType(typeof(InferredJsonClass), StatusCodes.Status201Created)]
+                [ProducesResponseType(StatusCodes.Status400BadRequest)]
+                () => Results.Ok(new InferredJsonClass()));
+
+            Assert.Equal(2, apiDescription.SupportedResponseTypes.Count);
+
+            var createdResponseType = apiDescription.SupportedResponseTypes[0];
+
+            Assert.Equal(201, createdResponseType.StatusCode);
+            Assert.Equal(typeof(InferredJsonClass), createdResponseType.Type);
+            Assert.Equal(typeof(InferredJsonClass), createdResponseType.ModelMetadata.ModelType);
+
+            var createdResponseFormat = Assert.Single(createdResponseType.ApiResponseFormats);
+            Assert.Equal("application/json", createdResponseFormat.MediaType);
+
+            var badRequestResponseType = apiDescription.SupportedResponseTypes[1];
+
+            Assert.Equal(400, badRequestResponseType.StatusCode);
+            Assert.Equal(typeof(void), badRequestResponseType.Type);
+            Assert.Equal(typeof(void), badRequestResponseType.ModelMetadata.ModelType);
+
+            Assert.Empty(badRequestResponseType.ApiResponseFormats);
+        }
+
         [Fact]
         public void AddsFromRouteParameterAsPath()
         {

src/Mvc/Mvc.ApiExplorer/test/Microsoft.AspNetCore.Mvc.ApiExplorer.Test.csproj

@@ -6,6 +6,7 @@
   </PropertyGroup>
 
   <ItemGroup>
+    <Reference Include="Microsoft.AspNetCore.Http.Results" />
     <Reference Include="Microsoft.AspNetCore.Mvc.ApiExplorer" />
     <Reference Include="Microsoft.AspNetCore.Mvc.NewtonsoftJson" />
     <ProjectReference Include="..\..\shared\Mvc.Core.TestCommon\Microsoft.AspNetCore.Mvc.Core.TestCommon.csproj" />