Fixed the issue. Will be adding the tests as a separate commit. (#60096)

# Include typed result metadata in the action descriptors for MVC Controller actions

## Description

The endpoint metadata wasn't being captured in ActionModel during the ApplicationModel creation. This is addressed by the change in the DefaultApplicationModelProvider class. The metadata is now being extracted based on the return type of the action and then the selectors associated with the action are populated with that metadata, as that's what is being used later on for populating the ActionDescriptor's EndpointMetadata.

Fixes #44988

src/Mvc/Mvc.Core/src/ApplicationModels/DefaultApplicationModelProvider.cs

@@ -4,6 +4,7 @@
 using System.Linq;
 using System.Reflection;
 using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Http.Metadata;
 using Microsoft.AspNetCore.Mvc.ActionConstraints;
 using Microsoft.AspNetCore.Mvc.ApiExplorer;
 using Microsoft.AspNetCore.Mvc.Filters;
@@ -349,9 +350,41 @@ internal PropertyModel CreatePropertyModel(PropertyInfo propertyInfo)
         applicableAttributes.AddRange(routeAttributes);
         AddRange(actionModel.Selectors, CreateSelectors(applicableAttributes));
 
+        AddReturnTypeMetadata(actionModel.Selectors, methodInfo);
+
         return actionModel;
     }
 
+    internal static void AddReturnTypeMetadata(IList<SelectorModel> selectors, MethodInfo methodInfo)
+    {
+        // Get metadata from return type
+        var returnType = methodInfo.ReturnType;
+        if (CoercedAwaitableInfo.IsTypeAwaitable(returnType, out var coercedAwaitableInfo))
+        {
+            returnType = coercedAwaitableInfo.AwaitableInfo.ResultType;
+        }
+
+        if (returnType is not null && typeof(IEndpointMetadataProvider).IsAssignableFrom(returnType))
+        {
+            // Return type implements IEndpointMetadataProvider
+            var builder = new InertEndpointBuilder();
+            var invokeArgs = new object[2];
+            invokeArgs[0] = methodInfo;
+            invokeArgs[1] = builder;
+            EndpointMetadataPopulator.PopulateMetadataForEndpointMethod.MakeGenericMethod(returnType).Invoke(null, invokeArgs);
+
+            // The metadata is added to the builder's metadata collection.
+            // We need to populate the selectors with that metadata.
+            foreach (var metadata in builder.Metadata)
+            {
+                foreach (var selector in selectors)
+                {
+                    selector.EndpointMetadata.Add(metadata);
+                }
+            }
+        }
+    }
+
     private string CanonicalizeActionName(string actionName)
     {
         const string Suffix = "Async";

src/Mvc/Mvc.Core/src/Microsoft.AspNetCore.Mvc.Core.WarningSuppressions.xml

@@ -37,6 +37,12 @@
       <property name="Scope">member</property>
       <property name="Target">M:Microsoft.AspNetCore.Mvc.AcceptedAtRouteResult.#ctor(System.String,System.Object,System.Object)</property>
     </attribute>
+    <attribute fullname="System.Diagnostics.CodeAnalysis.UnconditionalSuppressMessageAttribute">
+      <argument>ILLink</argument>
+      <argument>IL2026</argument>
+      <property name="Scope">member</property>
+      <property name="Target">M:Microsoft.AspNetCore.Mvc.ApplicationModels.DefaultApplicationModelProvider.AddReturnTypeMetadata(System.Collections.Generic.IList{Microsoft.AspNetCore.Mvc.ApplicationModels.SelectorModel},System.Reflection.MethodInfo)</property>
+    </attribute>
     <attribute fullname="System.Diagnostics.CodeAnalysis.UnconditionalSuppressMessageAttribute">
       <argument>ILLink</argument>
       <argument>IL2026</argument>
@@ -517,6 +523,12 @@
       <property name="Scope">member</property>
       <property name="Target">M:Microsoft.AspNetCore.Mvc.ApplicationParts.ProvideApplicationPartFactoryAttribute.GetFactoryType</property>
     </attribute>
+    <attribute fullname="System.Diagnostics.CodeAnalysis.UnconditionalSuppressMessageAttribute">
+      <argument>ILLink</argument>
+      <argument>IL2060</argument>
+      <property name="Scope">member</property>
+      <property name="Target">M:Microsoft.AspNetCore.Mvc.ApplicationModels.DefaultApplicationModelProvider.AddReturnTypeMetadata(System.Collections.Generic.IList{Microsoft.AspNetCore.Mvc.ApplicationModels.SelectorModel},System.Reflection.MethodInfo)</property>
+    </attribute>
     <attribute fullname="System.Diagnostics.CodeAnalysis.UnconditionalSuppressMessageAttribute">
       <argument>ILLink</argument>
       <argument>IL2060</argument>
@@ -637,6 +649,12 @@
       <property name="Scope">member</property>
       <property name="Target">M:Microsoft.AspNetCore.Mvc.ModelBinding.Metadata.DefaultBindingMetadataProvider.GetBoundConstructor(System.Type)</property>
     </attribute>
+    <attribute fullname="System.Diagnostics.CodeAnalysis.UnconditionalSuppressMessageAttribute">
+      <argument>ILLink</argument>
+      <argument>IL2072</argument>
+      <property name="Scope">member</property>
+      <property name="Target">M:Microsoft.AspNetCore.Mvc.ApplicationModels.DefaultApplicationModelProvider.AddReturnTypeMetadata(System.Collections.Generic.IList{Microsoft.AspNetCore.Mvc.ApplicationModels.SelectorModel},System.Reflection.MethodInfo)</property>
+    </attribute>
     <attribute fullname="System.Diagnostics.CodeAnalysis.UnconditionalSuppressMessageAttribute">
       <argument>ILLink</argument>
       <argument>IL2072</argument>

src/Mvc/Mvc.Core/src/Routing/ActionEndpointFactory.cs

@@ -543,12 +543,4 @@ private static RequestDelegate CreateRequestDelegate()
             return invoker!.InvokeAsync();
         };
     }
-
-    private sealed class InertEndpointBuilder : EndpointBuilder
-    {
-        public override Endpoint Build()
-        {
-            return new Endpoint(RequestDelegate, new EndpointMetadataCollection(Metadata), DisplayName);
-        }
-    }
 }

src/Mvc/Mvc.Core/src/Routing/InertEndpointBuilder.cs

@@ -0,0 +1,15 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Http;
+
+namespace Microsoft.AspNetCore.Mvc.Routing;
+
+internal sealed class InertEndpointBuilder : EndpointBuilder
+{
+    public override Endpoint Build()
+    {
+        return new Endpoint(RequestDelegate, new EndpointMetadataCollection(Metadata), DisplayName);
+    }
+}

src/Mvc/Mvc.Core/test/ApplicationModels/DefaultApplicationModelProviderTest.cs

@@ -1243,6 +1243,45 @@ public void CreateActionModel_InheritedAttributeRoutesOverridden()
         Assert.Contains(selectorModel.AttributeRouteModel.Attribute, action.Attributes);
     }
 
+    [Fact]
+    public void CreateActionModel_PopulatesReturnTypeEndpointMetadata() {
+        // Arrange
+        var builder = new TestApplicationModelProvider();
+        var typeInfo = typeof(TypedResultsReturningActionsController).GetTypeInfo();
+        var actionName = nameof(TypedResultsReturningActionsController.Get);
+
+        // Act
+        var action = builder.CreateActionModel(typeInfo, typeInfo.AsType().GetMethod(actionName));
+
+        // Assert
+        Assert.NotNull(action.Selectors);
+        Assert.All(action.Selectors, selector =>
+        {
+            Assert.NotNull(selector.EndpointMetadata);
+            Assert.Contains(selector.EndpointMetadata, m => m is ProducesResponseTypeMetadata);
+        });
+        var metadata = action.Selectors[0].EndpointMetadata.OfType<ProducesResponseTypeMetadata>().Single();
+        Assert.Equal(200, metadata.StatusCode);
+    }
+
+    [Fact]
+    public void AddReturnTypeMetadata_ExtractsMetadataFromReturnType()
+    {
+        // Arrange
+        var selector = new SelectorModel();
+        var selectors = new List<SelectorModel> { selector };
+        var actionMethod = typeof(TypedResultsReturningActionsController).GetMethod(nameof(TypedResultsReturningActionsController.Get));
+
+        // Act
+        DefaultApplicationModelProvider.AddReturnTypeMetadata(selectors, actionMethod);
+
+        // Assert
+        Assert.NotNull(selector.EndpointMetadata);
+        Assert.Single(selector.EndpointMetadata);
+        Assert.IsType<ProducesResponseTypeMetadata>(selector.EndpointMetadata.Single()); 
+        Assert.Equal(200, ((ProducesResponseTypeMetadata)selector.EndpointMetadata[0]).StatusCode);
+    }
+
     [Fact]
     public void ControllerDispose_ExplicitlyImplemented_IDisposableMethods_AreTreatedAs_NonActions()
     {
@@ -1711,6 +1750,16 @@ public void Details() { }
         public void List() { }
     }
 
+    private class TypedResultsReturningActionsController : Controller
+    {
+        [HttpGet]
+        public Http.HttpResults.Ok<Foo> Get() => TypedResults.Ok<Foo>(new Foo { Info = "Hello" });
+    }
+
+    public class Foo {
+        public required string Info { get; set; }
+    }
+
     private class CustomHttpMethodsAttribute : Attribute, IActionHttpMethodProvider
     {
         private readonly string[] _methods;

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

@@ -12,6 +12,7 @@
   <ItemGroup>
     <Reference Include="FSharp.Core" />
     <Reference Include="Microsoft.AspNetCore.Mvc.NewtonsoftJson" />
+    <Reference Include="Microsoft.AspNetCore.Http.Results" />
     <ProjectReference Include="..\..\shared\Mvc.Core.TestCommon\Microsoft.AspNetCore.Mvc.Core.TestCommon.csproj" />
     <ProjectReference Include="..\..\shared\Mvc.TestDiagnosticListener\Microsoft.AspNetCore.Mvc.TestDiagnosticListener.csproj" />
 

src/Mvc/test/Mvc.FunctionalTests/ApiExplorerTest.cs

@@ -11,6 +11,11 @@
 using Microsoft.Extensions.Logging;
 using System.Reflection;
 using Xunit.Abstractions;
+using Microsoft.AspNetCore.Mvc.ApplicationModels;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.AspNetCore.Mvc.ApiExplorer;
+using Microsoft.AspNetCore.Http.HttpResults;
+using Microsoft.AspNetCore.Http;
 
 namespace Microsoft.AspNetCore.Mvc.FunctionalTests;
 
@@ -1565,6 +1570,26 @@ public async Task ApiExplorer_LogsInvokedDescriptionProvidersOnStartup()
         Assert.Contains(TestSink.Writes, w => w.Message.Equals("Executing API description provider 'JsonPatchOperationsArrayProvider' from assembly Microsoft.AspNetCore.Mvc.NewtonsoftJson v42.42.42.42.", StringComparison.Ordinal));
     }
 
+    [Fact]
+    public void ApiExplorer_BuildsMetadataForActionWithTypedResult()
+    {
+        var apiDescCollectionProvider = Factory.Server.Services.GetService<IApiDescriptionGroupCollectionProvider>();
+        var testGroupName = nameof(ApiExplorerWithTypedResultController).Replace("Controller", string.Empty);
+        var group = apiDescCollectionProvider.ApiDescriptionGroups.Items.Where(i => i.GroupName == testGroupName).SingleOrDefault();
+        Assert.NotNull(group);
+        var apiDescription = Assert.Single<ApiDescription>(group.Items);
+
+        var responseType = Assert.Single(apiDescription.SupportedResponseTypes);
+        Assert.Equal(StatusCodes.Status200OK, responseType.StatusCode);
+        Assert.Equal(typeof(Product), responseType.Type);
+
+        Assert.NotNull(apiDescription.ActionDescriptor.EndpointMetadata);
+        var producesResponseTypeMetadata = apiDescription.ActionDescriptor.EndpointMetadata.OfType<ProducesResponseTypeMetadata>().SingleOrDefault();
+        Assert.NotNull(producesResponseTypeMetadata);
+        Assert.Equal(StatusCodes.Status200OK, producesResponseTypeMetadata.StatusCode);
+        Assert.Equal(typeof(Product), producesResponseTypeMetadata.Type);
+    }
+
     private IEnumerable<string> GetSortedMediaTypes(ApiExplorerResponseType apiResponseType)
     {
         return apiResponseType.ResponseFormats

src/Mvc/test/WebSites/ApiExplorerWebSite/ApiExplorerWebSite.csproj

@@ -7,6 +7,7 @@
   <ItemGroup>
     <Reference Include="Microsoft.AspNetCore.Mvc" />
     <Reference Include="Microsoft.AspNetCore.Mvc.Formatters.Xml" />
+    <Reference Include="Microsoft.AspNetCore.Http.Results" />
     <Reference Include="Microsoft.AspNetCore.Mvc.NewtonsoftJson" />
 
     <Reference Include="Microsoft.AspNetCore.Server.IISIntegration" />

src/Mvc/test/WebSites/ApiExplorerWebSite/Controllers/ApiExplorerWithTypedResultController.cs

@@ -0,0 +1,14 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Microsoft.AspNetCore.Http.HttpResults;
+using Microsoft.AspNetCore.Mvc;
+
+namespace ApiExplorerWebSite;
+
+[Route("ApiExplorerWithTypedResult/[Action]")]
+public class ApiExplorerWithTypedResultController : Controller
+{
+    [HttpGet]
+    public Ok<Product> GetProduct() => TypedResults.Ok(new Product { Name = "Test product" });
+}

src/OpenApi/sample/Controllers/TestController.cs

@@ -3,6 +3,7 @@
 
 using System.ComponentModel.DataAnnotations;
 using System.Diagnostics.CodeAnalysis;
+using Microsoft.AspNetCore.Http.HttpResults;
 using Microsoft.AspNetCore.Mvc;
 
 [ApiController]
@@ -17,6 +18,13 @@ public string GetByIdAndName(RouteParamsContainer paramsContainer)
         return paramsContainer.Id + "_" + paramsContainer.Name;
     }
 
+    [HttpGet]
+    [Route("/gettypedresult")]
+    public Ok<MvcTodo> GetTypedResult()
+    {
+        return TypedResults.Ok(new MvcTodo("Title", "Description", true));
+    }
+
     [HttpPost]
     [Route("/forms")]
     public IActionResult PostForm([FromForm] MvcTodo todo)

src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Integration/snapshots/OpenApiDocumentIntegrationTests.VerifyOpenApiDocument_documentName=controllers.verified.txt

@@ -54,6 +54,25 @@
         }
       }
     },
+    "/gettypedresult": {
+      "get": {
+        "tags": [
+          "Test"
+        ],
+        "responses": {
+          "200": {
+            "description": "OK",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/MvcTodo"
+                }
+              }
+            }
+          }
+        }
+      }
+    },
     "/forms": {
       "post": {
         "tags": [
@@ -88,6 +107,29 @@
       }
     }
   },
+  "components": {
+    "schemas": {
+      "MvcTodo": {
+        "required": [
+          "title",
+          "description",
+          "isCompleted"
+        ],
+        "type": "object",
+        "properties": {
+          "title": {
+            "type": "string"
+          },
+          "description": {
+            "type": "string"
+          },
+          "isCompleted": {
+            "type": "boolean"
+          }
+        }
+      }
+    }
+  },
   "tags": [
     {
       "name": "Test"

src/Shared/EndpointMetadataPopulator.cs

@@ -16,7 +16,7 @@ namespace Microsoft.AspNetCore.Http;
 internal static class EndpointMetadataPopulator
 {
     private static readonly MethodInfo PopulateMetadataForParameterMethod = typeof(EndpointMetadataPopulator).GetMethod(nameof(PopulateMetadataForParameter), BindingFlags.NonPublic | BindingFlags.Static)!;
-    private static readonly MethodInfo PopulateMetadataForEndpointMethod = typeof(EndpointMetadataPopulator).GetMethod(nameof(PopulateMetadataForEndpoint), BindingFlags.NonPublic | BindingFlags.Static)!;
+    internal static readonly MethodInfo PopulateMetadataForEndpointMethod = typeof(EndpointMetadataPopulator).GetMethod(nameof(PopulateMetadataForEndpoint), BindingFlags.NonPublic | BindingFlags.Static)!;
 
     public static void PopulateMetadata(MethodInfo methodInfo, EndpointBuilder builder, IEnumerable<ParameterInfo>? parameters = null)
     {