Make AddControllersAsServices not overwrite existing IControllerTypeProvider

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

@@ -26,7 +26,14 @@ namespace Microsoft.AspNetCore.Mvc.Internal
                 throw new ArgumentNullException(nameof(types));
             }
 
-            var controllerTypeProvider = new StaticControllerTypeProvider();
+            StaticControllerTypeProvider controllerTypeProvider = null;
+
+            controllerTypeProvider = services
+                .Where(s => s.ServiceType == typeof(IControllerTypeProvider))
+                .Select(s => s.ImplementationInstance)
+                .OfType<StaticControllerTypeProvider>()
+                .FirstOrDefault()
+                ?? new StaticControllerTypeProvider();
 
             foreach (var type in types)
             {

test/Microsoft.AspNetCore.Mvc.Core.Test/Internal/ControllerAsServicesTest.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.Collections.Generic;
+using System.Linq;
+using Microsoft.AspNetCore.Mvc.Controllers;
+using Microsoft.Extensions.DependencyInjection;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Mvc.Internal
+{
+    public class ControllerAsServicesTest
+    {
+        [Fact]
+        public void AddControllerAsServices_MultipleCalls_RetainsPreviouslyAddedTypes()
+        {
+            // Arrange
+            var services = new ServiceCollection();
+
+            // Act 1
+            ControllersAsServices.AddControllersAsServices(services, new Type[] { typeof(ControllerOne) });
+
+            // Assert 1
+            var serviceDescriptor = Assert.Single(services, s => s.ServiceType == typeof(IControllerTypeProvider));
+            var controllerTypeProvider = Assert.IsType<StaticControllerTypeProvider>(serviceDescriptor.ImplementationInstance);
+            var expectedControllerType = Assert.Single(controllerTypeProvider.ControllerTypes);
+
+            // Act 2
+            ControllersAsServices.AddControllersAsServices(services, new Type[] { typeof(ControllerTwo) });
+
+            // Assert 2
+            serviceDescriptor = Assert.Single(services, s => s.ServiceType == typeof(IControllerTypeProvider));
+            controllerTypeProvider = Assert.IsType<StaticControllerTypeProvider>(serviceDescriptor.ImplementationInstance);
+            Assert.Equal(2, controllerTypeProvider.ControllerTypes.Count);
+            Assert.Same(expectedControllerType, controllerTypeProvider.ControllerTypes[0]);
+            Assert.Same(typeof(ControllerTwo), controllerTypeProvider.ControllerTypes[1]);
+        }
+
+        private class ControllerOne
+        {
+        }
+
+        private class ControllerTwo
+        {
+        }
+    }
+}

test/Microsoft.AspNetCore.Mvc.FunctionalTests/ControllerFromServicesTests.cs

@@ -104,5 +104,18 @@ namespace Microsoft.AspNetCore.Mvc.FunctionalTests
             // Assert
             Assert.Equal(HttpStatusCode.NotFound, response.StatusCode);
         }
+
+        [Fact]
+        public async Task AddControllersAsServices_MultipleCalls_DoesNotReplacePreviousProvider()
+        {
+            // Arrange
+            var expected = "1";
+
+            // Act
+            var response = await Client.GetStringAsync("http://localhost/another/");
+
+            // Assert
+            Assert.Equal(expected, response);
+        }
     }
 }

test/WebSites/ControllersFromServicesWebSite/AnotherController.cs

@@ -0,0 +1,17 @@
+// 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;
+
+namespace ControllersFromServicesWebSite
+{
+    [Route("/[controller]")]
+    public class AnotherController : Controller
+    {
+        [HttpGet]
+        public int Get()
+        {
+            return 1;
+        }
+    }
+}

test/WebSites/ControllersFromServicesWebSite/Startup.cs

@@ -17,6 +17,7 @@ namespace ControllersFromServicesWebSite
         {
             services
                 .AddMvc()
+                .AddControllersAsServices(typeof(AnotherController))
                 .AddControllersAsServices(new[]
                 {
                     typeof(TimeScheduleController).GetTypeInfo().Assembly