Add KestrelServerOptionsSetup to IServiceCollection in UseKestrel() (#755)

- Previously, KestrelServerOptionsSetup was only added to IServiceCollection in UseKestrel(options)
- Required to ensure that options.ApplicationServices is available after calling UseKestrel()

src/Microsoft.AspNetCore.Server.Kestrel/WebHostBuilderKestrelExtensions.cs

@@ -23,7 +23,11 @@ namespace Microsoft.AspNetCore.Hosting
         /// </returns>
         public static IWebHostBuilder UseKestrel(this IWebHostBuilder hostBuilder)
         {
-            return hostBuilder.ConfigureServices(services => services.AddSingleton<IServer, KestrelServer>());
+            return hostBuilder.ConfigureServices(services =>
+            {
+                services.AddTransient<IConfigureOptions<KestrelServerOptions>, KestrelServerOptionsSetup>();
+                services.AddSingleton<IServer, KestrelServer>();
+            });
         }
 
         /// <summary>
@@ -42,7 +46,6 @@ namespace Microsoft.AspNetCore.Hosting
         {
             hostBuilder.ConfigureServices(services =>
             {
-                services.AddTransient<IConfigureOptions<KestrelServerOptions>, KestrelServerOptionsSetup>();
                 services.Configure(options);
             });
 

test/Microsoft.AspNetCore.Server.KestrelTests/WebHostBuilderKestrelExtensionsTests.cs

@@ -0,0 +1,35 @@
+// 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.Hosting;
+using Microsoft.AspNetCore.Server.Kestrel;
+using Microsoft.Extensions.DependencyInjection;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Server.KestrelTests
+{
+    public class WebHostBuilderKestrelExtensionsTests
+    {
+        [Fact]
+        public void ApplicationServicesNotNullAfterUseKestrelWithoutOptions()
+        {
+            // Arrange
+            var hostBuilder = new WebHostBuilder()
+                .UseKestrel()
+                .Configure(app => { });
+
+            hostBuilder.ConfigureServices(services =>
+            {
+                services.Configure<KestrelServerOptions>(options =>
+                {
+                    // Assert
+                    Assert.NotNull(options.ApplicationServices);
+                });
+            });
+
+            // Act
+            var host = hostBuilder.Build();
+        }
+    }
+}