Fixed the issue

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)
     {