Add mapping service for action results

This allows the use of custom 'envelope' types like ActionResult<> with
a corresponding API Explorer implementation.

Basically this PR services to decouple a bunch of infrastructure from
ActionResult<>.

src/Microsoft.AspNetCore.Mvc.ApiExplorer/DefaultApiDescriptionProvider.cs

@@ -9,6 +9,7 @@ using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Mvc.Abstractions;
 using Microsoft.AspNetCore.Mvc.Controllers;
 using Microsoft.AspNetCore.Mvc.Formatters;
+using Microsoft.AspNetCore.Mvc.Infrastructure;
 using Microsoft.AspNetCore.Mvc.Internal;
 using Microsoft.AspNetCore.Mvc.ModelBinding;
 using Microsoft.AspNetCore.Routing;
@@ -25,6 +26,7 @@ namespace Microsoft.AspNetCore.Mvc.ApiExplorer
     public class DefaultApiDescriptionProvider : IApiDescriptionProvider
     {
         private readonly MvcOptions _mvcOptions;
+        private readonly IActionResultTypeMapper _mapper;
         private readonly IInlineConstraintResolver _constraintResolver;
         private readonly IModelMetadataProvider _modelMetadataProvider;
 
@@ -35,6 +37,7 @@ namespace Microsoft.AspNetCore.Mvc.ApiExplorer
         /// <param name="constraintResolver">The <see cref="IInlineConstraintResolver"/> used for resolving inline
         /// constraints.</param>
         /// <param name="modelMetadataProvider">The <see cref="IModelMetadataProvider"/>.</param>
+        [Obsolete("This constructor is obsolete and will be removed in a future release.")]
         public DefaultApiDescriptionProvider(
             IOptions<MvcOptions> optionsAccessor,
             IInlineConstraintResolver constraintResolver,
@@ -45,6 +48,26 @@ namespace Microsoft.AspNetCore.Mvc.ApiExplorer
             _modelMetadataProvider = modelMetadataProvider;
         }
 
+        /// <summary>
+        /// Creates a new instance of <see cref="DefaultApiDescriptionProvider"/>.
+        /// </summary>
+        /// <param name="optionsAccessor">The accessor for <see cref="MvcOptions"/>.</param>
+        /// <param name="constraintResolver">The <see cref="IInlineConstraintResolver"/> used for resolving inline
+        /// constraints.</param>
+        /// <param name="modelMetadataProvider">The <see cref="IModelMetadataProvider"/>.</param>
+        /// <param name="mapper"> The <see cref="IActionResultTypeMapper"/>.</param>
+        public DefaultApiDescriptionProvider(
+            IOptions<MvcOptions> optionsAccessor,
+            IInlineConstraintResolver constraintResolver,
+            IModelMetadataProvider modelMetadataProvider,
+            IActionResultTypeMapper mapper)
+        {
+            _mvcOptions = optionsAccessor.Value;
+            _constraintResolver = constraintResolver;
+            _modelMetadataProvider = modelMetadataProvider;
+            _mapper = mapper;
+        }
+
         /// <inheritdoc />
         public int Order => -1000;
 
@@ -481,12 +504,14 @@ namespace Microsoft.AspNetCore.Mvc.ApiExplorer
             {
                 return typeof(void);
             }
-
+            
             // Unwrap the type if it's a Task<T>. The Task (non-generic) case was already handled.
-            var unwrappedType = UnwrapGenericType(declaredReturnType, typeof(Task<>));
+            Type unwrappedType = declaredReturnType;
-
+            if (declaredReturnType.IsGenericType && 
-            // Unwrap the type if it's ActionResult<T> or Task<ActionResult<T>>.
+                declaredReturnType.GetGenericTypeDefinition() == typeof(Task<>))
-            unwrappedType = UnwrapGenericType(unwrappedType, typeof(ActionResult<>));
+            {
+                unwrappedType = declaredReturnType.GetGenericArguments()[0];
+            }
 
             // If the method is declared to return IActionResult or a derived class, that information
             // isn't valuable to the formatter.
@@ -494,16 +519,11 @@ namespace Microsoft.AspNetCore.Mvc.ApiExplorer
             {
                 return null;
             }
-            else
-            {
-                return unwrappedType;
-            }
 
-            Type UnwrapGenericType(Type type, Type queryType)
+            // If we get here, the type should be a user-defined data type or an envelope type
-            {
+            // like ActionResult<T>. The mapper service will unwrap envelopes.
-                var genericType = ClosedGenericMatcher.ExtractGenericInterface(type, queryType);
+            unwrappedType = _mapper.GetResultDataType(unwrappedType);
-                return genericType?.GenericTypeArguments[0] ?? type;
+            return unwrappedType;
-            }
         }
 
         private Type GetRuntimeReturnType(Type declaredReturnType)

src/Microsoft.AspNetCore.Mvc.Core/DependencyInjection/MvcCoreServiceCollectionExtensions.cs

@@ -202,6 +202,7 @@ namespace Microsoft.Extensions.DependencyInjection
             services.TryAddSingleton<ControllerActionInvokerCache>();
             services.TryAddEnumerable(
                 ServiceDescriptor.Singleton<IFilterProvider, DefaultFilterProvider>());
+            services.TryAddSingleton<IActionResultTypeMapper, ActionResultTypeMapper>();
 
             //
             // Request body limit filters

src/Microsoft.AspNetCore.Mvc.Core/Infrastructure/IActionResultTypeMapper.cs

@@ -0,0 +1,48 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.Threading.Tasks;
+
+namespace Microsoft.AspNetCore.Mvc.Infrastructure
+{
+    /// <summary>
+    /// Provides a mapping from the return value of an action to an <see cref="IActionResult"/>
+    /// for request processing.
+    /// </summary>
+    /// <remarks>
+    /// The default implementation of this service handles the conversion of 
+    /// <see cref="ActionResult{TValue}"/> to an <see cref="IActionResult"/> during request
+    /// processing as well as the mapping of <see cref="ActionResult{TValue}"/> to <c>TValue</c>
+    /// during API Explorer processing.
+    /// </remarks>
+    public interface IActionResultTypeMapper
+    {
+        /// <summary>
+        /// Gets the result data type that corresponds to <paramref name="returnType"/>. This
+        /// method will not be called for actions that return <c>void</c> or an <see cref="IActionResult"/>
+        /// type.
+        /// </summary>
+        /// <param name="returnType">The declared return type of an action.</param>
+        /// <returns>A <see cref="Type"/> that represents the response data.</returns>
+        /// <remarks>
+        /// Prior to calling this method, the infrastructure will unwrap <see cref="Task{TResult}"/> or
+        /// other task-like types.
+        /// </remarks>
+        Type GetResultDataType(Type returnType);
+
+        /// <summary>
+        /// Converts the result of an action to an <see cref="IActionResult"/> for response processing.
+        /// This method will be not be called when a method returns <c>void</c> or an
+        /// <see cref="IActionResult"/> value.
+        /// </summary>
+        /// <param name="value">The action return value. May be <c>null</c>.</param>
+        /// <param name="returnType">The declared return type.</param>
+        /// <returns>An <see cref="IActionResult"/> for response processing.</returns>
+        /// <remarks>
+        /// Prior to calling this method, the infrastructure will unwrap <see cref="Task{TResult}"/> or
+        /// other task-like types.
+        /// </remarks>
+        IActionResult Convert(object value, Type returnType);
+    }
+}

src/Microsoft.AspNetCore.Mvc.Core/Internal/ActionMethodExecutor.cs

@@ -27,7 +27,11 @@ namespace Microsoft.AspNetCore.Mvc.Internal
             new AwaitableObjectResultExecutor(),
         };
 
-        public abstract ValueTask<IActionResult> Execute(ObjectMethodExecutor executor, object controller, object[] arguments);
+        public abstract ValueTask<IActionResult> Execute(
+            IActionResultTypeMapper mapper,
+            ObjectMethodExecutor executor,
+            object controller,
+            object[] arguments);
 
         protected abstract bool CanExecute(ObjectMethodExecutor executor);
 
@@ -48,7 +52,11 @@ namespace Microsoft.AspNetCore.Mvc.Internal
         // void LogMessage(..)
         private class VoidResultExecutor : ActionMethodExecutor
         {
-            public override ValueTask<IActionResult> Execute(ObjectMethodExecutor executor, object controller, object[] arguments)
+            public override ValueTask<IActionResult> Execute(
+                IActionResultTypeMapper mapper,
+                ObjectMethodExecutor executor,
+                object controller,
+                object[] arguments)
             {
                 executor.Execute(controller, arguments);
                 return new ValueTask<IActionResult>(new EmptyResult());
@@ -62,7 +70,11 @@ namespace Microsoft.AspNetCore.Mvc.Internal
         // CreatedAtResult Put(..)
         private class SyncActionResultExecutor : ActionMethodExecutor
         {
-            public override ValueTask<IActionResult> Execute(ObjectMethodExecutor executor, object controller, object[] arguments)
+            public override ValueTask<IActionResult> Execute(
+                IActionResultTypeMapper mapper,
+                ObjectMethodExecutor executor,
+                object controller,
+                object[] arguments)
             {
                 var actionResult = (IActionResult)executor.Execute(controller, arguments);
                 EnsureActionResultNotNull(executor, actionResult);
@@ -78,11 +90,15 @@ namespace Microsoft.AspNetCore.Mvc.Internal
         // object Index(..)
         private class SyncObjectResultExecutor : ActionMethodExecutor
         {
-            public override ValueTask<IActionResult> Execute(ObjectMethodExecutor executor, object controller, object[] arguments)
+            public override ValueTask<IActionResult> Execute(
+                IActionResultTypeMapper mapper,
+                ObjectMethodExecutor executor,
+                object controller,
+                object[] arguments)
             {
                 // Sync method returning arbitrary object
                 var returnValue = executor.Execute(controller, arguments);
-                var actionResult = ConvertToActionResult(returnValue, executor.MethodReturnType);
+                var actionResult = ConvertToActionResult(mapper, returnValue, executor.MethodReturnType);
                 return new ValueTask<IActionResult>(actionResult);
             }
 
@@ -93,7 +109,11 @@ namespace Microsoft.AspNetCore.Mvc.Internal
         // Task SaveState(..)
         private class TaskResultExecutor : ActionMethodExecutor
         {
-            public override async ValueTask<IActionResult> Execute(ObjectMethodExecutor executor, object controller, object[] arguments)
+            public override async ValueTask<IActionResult> Execute(
+                IActionResultTypeMapper mapper,
+                ObjectMethodExecutor executor,
+                object controller,
+                object[] arguments)
             {
                 await (Task)executor.Execute(controller, arguments);
                 return new EmptyResult();
@@ -106,7 +126,11 @@ namespace Microsoft.AspNetCore.Mvc.Internal
         // Custom task-like type with no return value.
         private class AwaitableResultExecutor : ActionMethodExecutor
         {
-            public override async ValueTask<IActionResult> Execute(ObjectMethodExecutor executor, object controller, object[] arguments)
+            public override async ValueTask<IActionResult> Execute(
+                IActionResultTypeMapper mapper,
+                ObjectMethodExecutor executor,
+                object controller,
+                object[] arguments)
             {
                 await executor.ExecuteAsync(controller, arguments);
                 return new EmptyResult();
@@ -122,7 +146,11 @@ namespace Microsoft.AspNetCore.Mvc.Internal
         // Task<IActionResult> Post(..)
         private class TaskOfIActionResultExecutor : ActionMethodExecutor
         {
-            public override async ValueTask<IActionResult> Execute(ObjectMethodExecutor executor, object controller, object[] arguments)
+            public override async ValueTask<IActionResult> Execute(
+                IActionResultTypeMapper mapper,
+                ObjectMethodExecutor executor,
+                object controller,
+                object[] arguments)
             {
                 // Async method returning Task<IActionResult>
                 // Avoid extra allocations by calling Execute rather than ExecuteAsync and casting to Task<IActionResult>.
@@ -141,7 +169,11 @@ namespace Microsoft.AspNetCore.Mvc.Internal
         // ValueTask<ViewResult> GetViewsAsync(..)
         private class TaskOfActionResultExecutor : ActionMethodExecutor
         {
-            public override async ValueTask<IActionResult> Execute(ObjectMethodExecutor executor, object controller, object[] arguments)
+            public override async ValueTask<IActionResult> Execute(
+                IActionResultTypeMapper mapper,
+                ObjectMethodExecutor executor,
+                object controller,
+                object[] arguments)
             {
                 // Async method returning awaitable-of-IActionResult (e.g., Task<ViewResult>)
                 // We have to use ExecuteAsync because we don't know the awaitable's type at compile time.
@@ -161,11 +193,15 @@ namespace Microsoft.AspNetCore.Mvc.Internal
         // Task<Customer> GetCustomerAsync(..)
         private class AwaitableObjectResultExecutor : ActionMethodExecutor
         {
-            public override async ValueTask<IActionResult> Execute(ObjectMethodExecutor executor, object controller, object[] arguments)
+            public override async ValueTask<IActionResult> Execute(
+                IActionResultTypeMapper mapper,
+                ObjectMethodExecutor executor,
+                object controller,
+                object[] arguments)
             {
                 // Async method returning awaitable-of-nonvoid
                 var returnValue = await executor.ExecuteAsync(controller, arguments);
-                var actionResult = ConvertToActionResult(returnValue, executor.MethodReturnType);
+                var actionResult = ConvertToActionResult(mapper, returnValue, executor.MethodReturnType);
                 return actionResult;
             }
 
@@ -176,30 +212,14 @@ namespace Microsoft.AspNetCore.Mvc.Internal
         {
             if (actionResult == null)
             {
-                throw new InvalidOperationException(
+                var type = executor.AsyncResultType ?? executor.MethodReturnType;
-                    Resources.FormatActionResult_ActionReturnValueCannotBeNull(executor.AsyncResultType ?? executor.MethodReturnType));
+                throw new InvalidOperationException(Resources.FormatActionResult_ActionReturnValueCannotBeNull(type));
             }
         }
 
-        private static IActionResult ConvertToActionResult(object returnValue, Type declaredType)
+        private IActionResult ConvertToActionResult(IActionResultTypeMapper mapper, object returnValue, Type declaredType)
         {
-            IActionResult result;
+            var result = (returnValue as IActionResult) ?? mapper.Convert(returnValue, declaredType);
-            switch (returnValue)
-            {
-                case IActionResult actionResult:
-                    result = actionResult;
-                    break;
-                case IConvertToActionResult convertToActionResult:
-                    result = convertToActionResult.Convert();
-                    break;
-                default:
-                    result = new ObjectResult(returnValue)
-                    {
-                        DeclaredType = declaredType,
-                    };
-                    break;
-            }
-
             if (result == null)
             {
                 throw new InvalidOperationException(Resources.FormatActionResult_ActionReturnValueCannotBeNull(declaredType));

src/Microsoft.AspNetCore.Mvc.Core/Internal/ActionResultTypeMapper.cs

@@ -0,0 +1,45 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using Microsoft.AspNetCore.Mvc.Infrastructure;
+
+namespace Microsoft.AspNetCore.Mvc.Internal
+{
+    public class ActionResultTypeMapper : IActionResultTypeMapper
+    {
+        public Type GetResultDataType(Type returnType)
+        {
+            if (returnType == null)
+            {
+                throw new ArgumentNullException(nameof(returnType));
+            }
+
+            if (returnType.IsGenericType && 
+                returnType.GetGenericTypeDefinition() == typeof(ActionResult<>))
+            {
+                return returnType.GetGenericArguments()[0];
+            }
+
+            return returnType;
+        }
+
+        public IActionResult Convert(object value, Type returnType)
+        {
+            if (returnType == null)
+            {
+                throw new ArgumentNullException(nameof(returnType));
+            }
+
+            if (value is IConvertToActionResult converter)
+            {
+                return converter.Convert();
+            }
+
+            return new ObjectResult(value)
+            {
+                DeclaredType = returnType,
+            };
+        }
+    }
+}

src/Microsoft.AspNetCore.Mvc.Core/Internal/ControllerActionInvoker.cs

@@ -28,10 +28,11 @@ namespace Microsoft.AspNetCore.Mvc.Internal
         internal ControllerActionInvoker(
             ILogger logger,
             DiagnosticSource diagnosticSource,
+            IActionResultTypeMapper mapper,
             ControllerContext controllerContext,
             ControllerActionInvokerCacheEntry cacheEntry,
             IFilterMetadata[] filters)
-            : base(diagnosticSource, logger, controllerContext, filters, controllerContext.ValueProviderFactories)
+            : base(diagnosticSource, logger, mapper, controllerContext, filters, controllerContext.ValueProviderFactories)
         {
             if (cacheEntry == null)
             {
@@ -347,7 +348,7 @@ namespace Microsoft.AspNetCore.Mvc.Internal
                     controller);
                 logger.ActionMethodExecuting(controllerContext, orderedArguments);
                 var stopwatch = ValueStopwatch.StartNew();
-                var actionResultValueTask = actionMethodExecutor.Execute(objectMethodExecutor, controller, orderedArguments);
+                var actionResultValueTask = actionMethodExecutor.Execute(_mapper, objectMethodExecutor, controller, orderedArguments);
                 if (actionResultValueTask.IsCompletedSuccessfully)
                 {
                     result = actionResultValueTask.Result;
@@ -370,18 +371,6 @@ namespace Microsoft.AspNetCore.Mvc.Internal
             }
         }
 
-        private static bool IsResultIActionResult(ObjectMethodExecutor executor)
-        {
-            var resultType = executor.AsyncResultType ?? executor.MethodReturnType;
-            return typeof(IActionResult).IsAssignableFrom(resultType);
-        }
-
-        private bool IsConvertibleToActionResult(ObjectMethodExecutor executor)
-        {
-            var resultType = executor.AsyncResultType ?? executor.MethodReturnType;
-            return typeof(IConvertToActionResult).IsAssignableFrom(resultType);
-        }
-
         /// <remarks><see cref="ResourceInvoker.InvokeFilterPipelineAsync"/> for details on what the
         /// variables in this method represent.</remarks>
         protected override async Task InvokeInnerFilterAsync()

src/Microsoft.AspNetCore.Mvc.Core/Internal/ControllerActionInvokerProvider.cs

@@ -7,6 +7,7 @@ using System.Diagnostics;
 using System.Linq;
 using Microsoft.AspNetCore.Mvc.Abstractions;
 using Microsoft.AspNetCore.Mvc.Controllers;
+using Microsoft.AspNetCore.Mvc.Infrastructure;
 using Microsoft.AspNetCore.Mvc.ModelBinding;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
@@ -20,18 +21,21 @@ namespace Microsoft.AspNetCore.Mvc.Internal
         private readonly int _maxModelValidationErrors;
         private readonly ILogger _logger;
         private readonly DiagnosticSource _diagnosticSource;
+        private readonly IActionResultTypeMapper _mapper;
 
         public ControllerActionInvokerProvider(
             ControllerActionInvokerCache controllerActionInvokerCache,
             IOptions<MvcOptions> optionsAccessor,
             ILoggerFactory loggerFactory,
-            DiagnosticSource diagnosticSource)
+            DiagnosticSource diagnosticSource,
+            IActionResultTypeMapper mapper)
         {
             _controllerActionInvokerCache = controllerActionInvokerCache;
             _valueProviderFactories = optionsAccessor.Value.ValueProviderFactories.ToArray();
             _maxModelValidationErrors = optionsAccessor.Value.MaxModelValidationErrors;
             _logger = loggerFactory.CreateLogger<ControllerActionInvoker>();
             _diagnosticSource = diagnosticSource;
+            _mapper = mapper;
         }
 
         public int Order => -1000;
@@ -56,6 +60,7 @@ namespace Microsoft.AspNetCore.Mvc.Internal
                 var invoker = new ControllerActionInvoker(
                     _logger,
                     _diagnosticSource,
+                    _mapper,
                     controllerContext,
                     cacheResult.cacheEntry,
                     cacheResult.filters);

src/Microsoft.AspNetCore.Mvc.Core/Internal/ResourceInvoker.cs

@@ -8,6 +8,7 @@ using System.Runtime.ExceptionServices;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Mvc.Core;
 using Microsoft.AspNetCore.Mvc.Filters;
+using Microsoft.AspNetCore.Mvc.Infrastructure;
 using Microsoft.AspNetCore.Mvc.ModelBinding;
 using Microsoft.Extensions.Internal;
 using Microsoft.Extensions.Logging;
@@ -18,6 +19,7 @@ namespace Microsoft.AspNetCore.Mvc.Internal
     {
         protected readonly DiagnosticSource _diagnosticSource;
         protected readonly ILogger _logger;
+        protected readonly IActionResultTypeMapper _mapper;
         protected readonly ActionContext _actionContext;
         protected readonly IFilterMetadata[] _filters;
         protected readonly IList<IValueProviderFactory> _valueProviderFactories;
@@ -38,12 +40,14 @@ namespace Microsoft.AspNetCore.Mvc.Internal
         public ResourceInvoker(
             DiagnosticSource diagnosticSource,
             ILogger logger,
+            IActionResultTypeMapper mapper,
             ActionContext actionContext,
             IFilterMetadata[] filters,
             IList<IValueProviderFactory> valueProviderFactories)
         {
             _diagnosticSource = diagnosticSource ?? throw new ArgumentNullException(nameof(diagnosticSource));
             _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+            _mapper = mapper ?? throw new ArgumentNullException(nameof(mapper));
             _actionContext = actionContext ?? throw new ArgumentNullException(nameof(actionContext));
 
             _filters = filters ?? throw new ArgumentNullException(nameof(filters));

src/Microsoft.AspNetCore.Mvc.RazorPages/Internal/PageActionInvoker.cs

@@ -9,6 +9,7 @@ using System.Runtime.ExceptionServices;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Mvc.Abstractions;
 using Microsoft.AspNetCore.Mvc.Filters;
+using Microsoft.AspNetCore.Mvc.Infrastructure;
 using Microsoft.AspNetCore.Mvc.Internal;
 using Microsoft.AspNetCore.Mvc.ModelBinding;
 using Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure;
@@ -43,6 +44,7 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
             IPageHandlerMethodSelector handlerMethodSelector,
             DiagnosticSource diagnosticSource,
             ILogger logger,
+            IActionResultTypeMapper mapper,
             PageContext pageContext,
             IFilterMetadata[] filterMetadata,
             PageActionInvokerCacheEntry cacheEntry,
@@ -52,6 +54,7 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
             : base(
                   diagnosticSource,
                   logger,
+                  mapper,
                   pageContext,
                   filterMetadata,
                   pageContext.ValueProviderFactories)

src/Microsoft.AspNetCore.Mvc.RazorPages/Internal/PageActionInvokerProvider.cs

@@ -42,6 +42,7 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
         private readonly RazorProjectFileSystem _razorFileSystem;
         private readonly DiagnosticSource _diagnosticSource;
         private readonly ILogger<PageActionInvoker> _logger;
+        private readonly IActionResultTypeMapper _mapper;
         private volatile InnerCache _currentCache;
 
         public PageActionInvokerProvider(
@@ -60,7 +61,8 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
             IPageHandlerMethodSelector selector,
             RazorProjectFileSystem razorFileSystem,
             DiagnosticSource diagnosticSource,
-            ILoggerFactory loggerFactory)
+            ILoggerFactory loggerFactory,
+            IActionResultTypeMapper mapper)
         {
             _loader = loader;
             _pageFactoryProvider = pageFactoryProvider;
@@ -79,6 +81,7 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
             _razorFileSystem = razorFileSystem;
             _diagnosticSource = diagnosticSource;
             _logger = loggerFactory.CreateLogger<PageActionInvoker>();
+            _mapper = mapper;
         }
 
         public int Order { get; } = -1000;
@@ -158,6 +161,7 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
                 _selector,
                 _diagnosticSource,
                 _logger,
+                _mapper,
                 pageContext,
                 filters,
                 cacheEntry,

test/Microsoft.AspNetCore.Mvc.ApiExplorer.Test/DefaultApiDescriptionProviderTest.cs

@@ -1449,7 +1449,8 @@ namespace Microsoft.AspNetCore.Mvc.Description
             var provider = new DefaultApiDescriptionProvider(
                 optionsAccessor,
                 constraintResolver.Object,
-                modelMetadataProvider);
+                modelMetadataProvider,
+                new ActionResultTypeMapper());
 
             provider.OnProvidersExecuting(context);
             provider.OnProvidersExecuted(context);

test/Microsoft.AspNetCore.Mvc.Core.Test/Internal/ActionMethodExecutorTest.cs

@@ -17,12 +17,13 @@ namespace Microsoft.AspNetCore.Mvc.Core.Internal
         public void ActionMethodExecutor_ExecutesVoidActions()
         {
             // Arrange
+            var mapper = new ActionResultTypeMapper();
             var controller = new TestController();
             var objectMethodExecutor = GetExecutor(nameof(TestController.VoidAction));
             var actionMethodExecutor = ActionMethodExecutor.GetExecutor(objectMethodExecutor);
 
             // Act
-            var valueTask = actionMethodExecutor.Execute(objectMethodExecutor, controller, Array.Empty<object>());
+            var valueTask = actionMethodExecutor.Execute(mapper, objectMethodExecutor, controller, Array.Empty<object>());
 
             // Assert
             Assert.True(controller.Executed);
@@ -33,12 +34,13 @@ namespace Microsoft.AspNetCore.Mvc.Core.Internal
         public void ActionMethodExecutor_ExecutesActionsReturningIActionResult()
         {
             // Arrange
+            var mapper = new ActionResultTypeMapper();
             var controller = new TestController();
             var objectMethodExecutor = GetExecutor(nameof(TestController.ReturnIActionResult));
             var actionMethodExecutor = ActionMethodExecutor.GetExecutor(objectMethodExecutor);
 
             // Act
-            var valueTask = actionMethodExecutor.Execute(objectMethodExecutor, controller, Array.Empty<object>());
+            var valueTask = actionMethodExecutor.Execute(mapper, objectMethodExecutor, controller, Array.Empty<object>());
 
             // Assert
             Assert.True(valueTask.IsCompleted);
@@ -49,12 +51,13 @@ namespace Microsoft.AspNetCore.Mvc.Core.Internal
         public void ActionMethodExecutor_ExecutesActionsReturningSubTypeOfActionResult()
         {
             // Arrange
+            var mapper = new ActionResultTypeMapper();
             var controller = new TestController();
             var objectMethodExecutor = GetExecutor(nameof(TestController.ReturnsIActionResultSubType));
             var actionMethodExecutor = ActionMethodExecutor.GetExecutor(objectMethodExecutor);
 
             // Act
-            var valueTask = actionMethodExecutor.Execute(objectMethodExecutor, controller, Array.Empty<object>());
+            var valueTask = actionMethodExecutor.Execute(mapper, objectMethodExecutor, controller, Array.Empty<object>());
 
             // Assert
             Assert.IsType<PartialViewResult>(valueTask.Result);
@@ -64,12 +67,13 @@ namespace Microsoft.AspNetCore.Mvc.Core.Internal
         public void ActionMethodExecutor_ExecutesActionsReturningActionResultOfT()
         {
             // Arrange
+            var mapper = new ActionResultTypeMapper();
             var controller = new TestController();
             var objectMethodExecutor = GetExecutor(nameof(TestController.ReturnsActionResultOfT));
             var actionMethodExecutor = ActionMethodExecutor.GetExecutor(objectMethodExecutor);
 
             // Act
-            var valueTask = actionMethodExecutor.Execute(objectMethodExecutor, controller, Array.Empty<object>());
+            var valueTask = actionMethodExecutor.Execute(mapper, objectMethodExecutor, controller, Array.Empty<object>());
 
             // Assert
             var result = Assert.IsType<ObjectResult>(valueTask.Result);
@@ -81,12 +85,13 @@ namespace Microsoft.AspNetCore.Mvc.Core.Internal
         public void ActionMethodExecutor_ExecutesActionsReturningModelAsModel()
         {
             // Arrange
+            var mapper = new ActionResultTypeMapper();
             var controller = new TestController();
             var objectMethodExecutor = GetExecutor(nameof(TestController.ReturnsModelAsModel));
             var actionMethodExecutor = ActionMethodExecutor.GetExecutor(objectMethodExecutor);
 
             // Act
-            var valueTask = actionMethodExecutor.Execute(objectMethodExecutor, controller, Array.Empty<object>());
+            var valueTask = actionMethodExecutor.Execute(mapper, objectMethodExecutor, controller, Array.Empty<object>());
 
             // Assert
             var result = Assert.IsType<ObjectResult>(valueTask.Result);
@@ -98,12 +103,13 @@ namespace Microsoft.AspNetCore.Mvc.Core.Internal
         public void ActionMethodExecutor_ExecutesActionsReturningModelAsObject()
         {
             // Arrange
+            var mapper = new ActionResultTypeMapper();
             var controller = new TestController();
             var objectMethodExecutor = GetExecutor(nameof(TestController.ReturnModelAsObject));
             var actionMethodExecutor = ActionMethodExecutor.GetExecutor(objectMethodExecutor);
 
             // Act
-            var valueTask = actionMethodExecutor.Execute(objectMethodExecutor, controller, Array.Empty<object>());
+            var valueTask = actionMethodExecutor.Execute(mapper, objectMethodExecutor, controller, Array.Empty<object>());
 
             // Assert
             var result = Assert.IsType<ObjectResult>(valueTask.Result);
@@ -115,12 +121,13 @@ namespace Microsoft.AspNetCore.Mvc.Core.Internal
         public void ActionMethodExecutor_ExecutesActionsReturningActionResultAsObject()
         {
             // Arrange
+            var mapper = new ActionResultTypeMapper();
             var controller = new TestController();
             var objectMethodExecutor = GetExecutor(nameof(TestController.ReturnsIActionResultSubType));
             var actionMethodExecutor = ActionMethodExecutor.GetExecutor(objectMethodExecutor);
 
             // Act
-            var valueTask = actionMethodExecutor.Execute(objectMethodExecutor, controller, Array.Empty<object>());
+            var valueTask = actionMethodExecutor.Execute(mapper, objectMethodExecutor, controller, Array.Empty<object>());
 
             // Assert
             Assert.IsType<PartialViewResult>(valueTask.Result);
@@ -130,12 +137,13 @@ namespace Microsoft.AspNetCore.Mvc.Core.Internal
         public void ActionMethodExecutor_ExecutesActionsReturnTask()
         {
             // Arrange
+            var mapper = new ActionResultTypeMapper();
             var controller = new TestController();
             var objectMethodExecutor = GetExecutor(nameof(TestController.ReturnsTask));
             var actionMethodExecutor = ActionMethodExecutor.GetExecutor(objectMethodExecutor);
 
             // Act
-            var valueTask = actionMethodExecutor.Execute(objectMethodExecutor, controller, Array.Empty<object>());
+            var valueTask = actionMethodExecutor.Execute(mapper, objectMethodExecutor, controller, Array.Empty<object>());
 
             // Assert
             Assert.True(controller.Executed);
@@ -146,12 +154,13 @@ namespace Microsoft.AspNetCore.Mvc.Core.Internal
         public void ActionMethodExecutorExecutesActionsAsynchronouslyReturningIActionResult()
         {
             // Arrange
+            var mapper = new ActionResultTypeMapper();
             var controller = new TestController();
             var objectMethodExecutor = GetExecutor(nameof(TestController.ReturnIActionResultAsync));
             var actionMethodExecutor = ActionMethodExecutor.GetExecutor(objectMethodExecutor);
 
             // Act
-            var valueTask = actionMethodExecutor.Execute(objectMethodExecutor, controller, Array.Empty<object>());
+            var valueTask = actionMethodExecutor.Execute(mapper, objectMethodExecutor, controller, Array.Empty<object>());
 
             // Assert
             Assert.IsType<ViewResult>(valueTask.Result);
@@ -161,12 +170,13 @@ namespace Microsoft.AspNetCore.Mvc.Core.Internal
         public async Task ActionMethodExecutor_ExecutesActionsAsynchronouslyReturningActionResultSubType()
         {
             // Arrange
+            var mapper = new ActionResultTypeMapper();
             var controller = new TestController();
             var objectMethodExecutor = GetExecutor(nameof(TestController.ReturnIActionResultAsync));
             var actionMethodExecutor = ActionMethodExecutor.GetExecutor(objectMethodExecutor);
 
             // Act
-            var valueTask = actionMethodExecutor.Execute(objectMethodExecutor, controller, Array.Empty<object>());
+            var valueTask = actionMethodExecutor.Execute(mapper, objectMethodExecutor, controller, Array.Empty<object>());
 
             // Assert
             await valueTask;
@@ -177,12 +187,13 @@ namespace Microsoft.AspNetCore.Mvc.Core.Internal
         public void ActionMethodExecutor_ExecutesActionsAsynchronouslyReturningModel()
         {
             // Arrange
+            var mapper = new ActionResultTypeMapper();
             var controller = new TestController();
             var objectMethodExecutor = GetExecutor(nameof(TestController.ReturnsModelAsModelAsync));
             var actionMethodExecutor = ActionMethodExecutor.GetExecutor(objectMethodExecutor);
 
             // Act
-            var valueTask = actionMethodExecutor.Execute(objectMethodExecutor, controller, Array.Empty<object>());
+            var valueTask = actionMethodExecutor.Execute(mapper, objectMethodExecutor, controller, Array.Empty<object>());
 
             // Assert
             var result = Assert.IsType<ObjectResult>(valueTask.Result);
@@ -194,12 +205,13 @@ namespace Microsoft.AspNetCore.Mvc.Core.Internal
         public void ActionMethodExecutor_ExecutesActionsAsynchronouslyReturningModelAsObject()
         {
             // Arrange
+            var mapper = new ActionResultTypeMapper();
             var controller = new TestController();
             var objectMethodExecutor = GetExecutor(nameof(TestController.ReturnsModelAsObjectAsync));
             var actionMethodExecutor = ActionMethodExecutor.GetExecutor(objectMethodExecutor);
 
             // Act
-            var valueTask = actionMethodExecutor.Execute(objectMethodExecutor, controller, Array.Empty<object>());
+            var valueTask = actionMethodExecutor.Execute(mapper, objectMethodExecutor, controller, Array.Empty<object>());
 
             // Assert
             var result = Assert.IsType<ObjectResult>(valueTask.Result);
@@ -211,12 +223,13 @@ namespace Microsoft.AspNetCore.Mvc.Core.Internal
         public void ActionMethodExecutor_ExecutesActionsAsynchronouslyReturningIActionResultAsObject()
         {
             // Arrange
+            var mapper = new ActionResultTypeMapper();
             var controller = new TestController();
             var objectMethodExecutor = GetExecutor(nameof(TestController.ReturnIActionResultAsObjectAsync));
             var actionMethodExecutor = ActionMethodExecutor.GetExecutor(objectMethodExecutor);
 
             // Act
-            var valueTask = actionMethodExecutor.Execute(objectMethodExecutor, controller, Array.Empty<object>());
+            var valueTask = actionMethodExecutor.Execute(mapper, objectMethodExecutor, controller, Array.Empty<object>());
 
             // Assert
             Assert.IsType<OkResult>(valueTask.Result);
@@ -226,12 +239,13 @@ namespace Microsoft.AspNetCore.Mvc.Core.Internal
         public void ActionMethodExecutor_ExecutesActionsAsynchronouslyReturningActionResultOfT()
         {
             // Arrange
+            var mapper = new ActionResultTypeMapper();
             var controller = new TestController();
             var objectMethodExecutor = GetExecutor(nameof(TestController.ReturnActionResultOFTAsync));
             var actionMethodExecutor = ActionMethodExecutor.GetExecutor(objectMethodExecutor);
 
             // Act
-            var valueTask = actionMethodExecutor.Execute(objectMethodExecutor, controller, Array.Empty<object>());
+            var valueTask = actionMethodExecutor.Execute(mapper, objectMethodExecutor, controller, Array.Empty<object>());
 
             // Assert
             var result = Assert.IsType<ObjectResult>(valueTask.Result);
@@ -243,13 +257,14 @@ namespace Microsoft.AspNetCore.Mvc.Core.Internal
         public void ActionMethodExecutor_ThrowsIfIConvertFromIActionResult_ReturnsNull()
         {
             // Arrange
+            var mapper = new ActionResultTypeMapper();
             var controller = new TestController();
             var objectMethodExecutor = GetExecutor(nameof(TestController.ReturnsCustomConvertibleFromIActionResult));
             var actionMethodExecutor = ActionMethodExecutor.GetExecutor(objectMethodExecutor);
 
             // Act & Assert
             var ex = Assert.Throws<InvalidOperationException>(
-                () => actionMethodExecutor.Execute(objectMethodExecutor, controller, Array.Empty<object>()));
+                () => actionMethodExecutor.Execute(mapper, objectMethodExecutor, controller, Array.Empty<object>()));
 
             Assert.Equal($"Cannot return null from an action method with a return type of '{typeof(CustomConvertibleFromAction)}'.", ex.Message);
         }

test/Microsoft.AspNetCore.Mvc.Core.Test/Internal/ActionResultTypeMapperTest.cs

@@ -0,0 +1,75 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using Microsoft.AspNetCore.Mvc.Infrastructure;
+using Moq;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Mvc.Internal
+{
+    public class ActionResultTypeMapperTest
+    {
+        [Fact]
+        public void Convert_WithIConvertToActionResult_DelegatesToInterface()
+        {
+            // Arrange
+            var mapper = new ActionResultTypeMapper();
+
+            var expected = new EmptyResult();
+            var returnValue = Mock.Of<IConvertToActionResult>(r => r.Convert() == expected);
+
+            // Act
+            var result = mapper.Convert(returnValue, typeof(string));
+
+            // Assert
+            Assert.Same(expected, result);
+        }
+
+        [Fact]
+        public void Convert_WithRegularType_CreatesObjectResult()
+        {
+            // Arrange
+            var mapper = new ActionResultTypeMapper();
+
+            var returnValue = "hello";
+
+            // Act
+            var result = mapper.Convert(returnValue, typeof(string));
+
+            // Assert
+            var objectResult = Assert.IsType<ObjectResult>(result);
+            Assert.Same(returnValue, objectResult.Value);
+            Assert.Equal(typeof(string), objectResult.DeclaredType);
+        }
+
+        [Fact]
+        public void GetResultDataType_WithActionResultOfT_UnwrapsType()
+        {
+            // Arrange
+            var mapper = new ActionResultTypeMapper();
+
+            var returnType = typeof(ActionResult<string>);
+
+            // Act
+            var result = mapper.GetResultDataType(returnType);
+
+            // Assert
+            Assert.Equal(typeof(string), result);
+        }
+
+        [Fact]
+        public void GetResultDataType_WithRegularType_ReturnsType()
+        {
+            // Arrange
+            var mapper = new ActionResultTypeMapper();
+
+            var returnType = typeof(string);
+
+            // Act
+            var result = mapper.GetResultDataType(returnType);
+
+            // Assert
+            Assert.Equal(typeof(string), result);
+        }
+    }
+}

test/Microsoft.AspNetCore.Mvc.Core.Test/Internal/ControllerActionInvokerTest.cs

@@ -1345,6 +1345,7 @@ namespace Microsoft.AspNetCore.Mvc.Internal
             var invoker = new ControllerActionInvoker(
                 new NullLoggerFactory().CreateLogger<ControllerActionInvoker>(),
                 new DiagnosticListener("Microsoft.AspNetCore"),
+                new ActionResultTypeMapper(),
                 controllerContext,
                 cacheEntry,
                 new IFilterMetadata[0]);
@@ -1624,6 +1625,7 @@ namespace Microsoft.AspNetCore.Mvc.Internal
             var invoker = new ControllerActionInvoker(
                 logger,
                 diagnosticSource,
+                new ActionResultTypeMapper(),
                 controllerContext,
                 cacheEntry,
                 filters);

test/Microsoft.AspNetCore.Mvc.Core.Test/Internal/MiddlewareFilterTest.cs

@@ -14,6 +14,7 @@ using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Mvc.Abstractions;
 using Microsoft.AspNetCore.Mvc.Controllers;
 using Microsoft.AspNetCore.Mvc.Filters;
+using Microsoft.AspNetCore.Mvc.Infrastructure;
 using Microsoft.AspNetCore.Mvc.ModelBinding;
 using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
 using Microsoft.AspNetCore.Routing;
@@ -285,6 +286,7 @@ namespace Microsoft.AspNetCore.Mvc.Internal
                 new MockControllerFactory(controller ?? this),
                 new NullLoggerFactory().CreateLogger<ControllerActionInvoker>(),
                 diagnosticSource,
+                new ActionResultTypeMapper(),
                 actionContext,
                 new List<IValueProviderFactory>(),
                 maxAllowedErrorsInModelState: 200);
@@ -389,12 +391,14 @@ namespace Microsoft.AspNetCore.Mvc.Internal
                 MockControllerFactory controllerFactory,
                 ILogger logger,
                 DiagnosticSource diagnosticSource,
+                IActionResultTypeMapper mapper,
                 ActionContext actionContext,
                 IReadOnlyList<IValueProviderFactory> valueProviderFactories,
                 int maxAllowedErrorsInModelState)
                 : base(
                       logger,
                       diagnosticSource,
+                      mapper,
                       CreatControllerContext(actionContext, valueProviderFactories, maxAllowedErrorsInModelState),
                       CreateCacheEntry((ControllerActionDescriptor)actionContext.ActionDescriptor, controllerFactory),
                       filters)

test/Microsoft.AspNetCore.Mvc.RazorPages.Test/Internal/PageActionInvokerProviderTest.cs

@@ -10,6 +10,7 @@ using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Mvc.Abstractions;
 using Microsoft.AspNetCore.Mvc.Filters;
 using Microsoft.AspNetCore.Mvc.Infrastructure;
+using Microsoft.AspNetCore.Mvc.Internal;
 using Microsoft.AspNetCore.Mvc.ModelBinding;
 using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
 using Microsoft.AspNetCore.Mvc.Razor;
@@ -515,7 +516,8 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
                 Mock.Of<IPageHandlerMethodSelector>(),
                 fileSystem,
                 new DiagnosticListener("Microsoft.AspNetCore"),
-                NullLoggerFactory.Instance);
+                NullLoggerFactory.Instance,
+                new ActionResultTypeMapper());
         }
 
         private IActionDescriptorCollectionProvider CreateActionDescriptorCollection(PageActionDescriptor descriptor)

test/Microsoft.AspNetCore.Mvc.RazorPages.Test/Internal/PageActionInvokerTest.cs

@@ -1217,6 +1217,7 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
                 selector.Object,
                 diagnosticListener ?? new DiagnosticListener("Microsoft.AspNetCore"),
                 logger ?? NullLogger.Instance,
+                new ActionResultTypeMapper(),
                 pageContext,
                 filters ?? Array.Empty<IFilterMetadata>(),
                 cacheEntry,