Remove the DeveloperExceptionPage middleware from WebHost.CreateDefaultBuilder:

- The templates still have it explicitly and it's best to have middleware added by the app directly

src/Microsoft.AspNetCore/WebHost.cs

@@ -188,7 +188,6 @@ namespace Microsoft.AspNetCore
                 })
                 .ConfigureServices(services =>
                 {
-                    services.AddSingleton<IStartupFilter, WebHostStartupFilter>();
                     services.AddTransient<IConfigureOptions<KestrelServerOptions>, KestrelServerOptionsSetup>();
                 });
 

src/Microsoft.AspNetCore/WebHostStartupFilter.cs

@@ -1,26 +0,0 @@
-// 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.Builder;
-using Microsoft.AspNetCore.Hosting;
-using Microsoft.Extensions.DependencyInjection;
-
-namespace Microsoft.AspNetCore
-{
-    internal class WebHostStartupFilter : IStartupFilter
-    {
-        public Action<IApplicationBuilder> Configure(Action<IApplicationBuilder> next)
-        {
-            return app =>
-            {
-                var env = app.ApplicationServices.GetService<IHostingEnvironment>();
-                if (env.IsDevelopment())
-                {
-                    app.UseDeveloperExceptionPage();
-                }
-                next(app);
-            };
-        }
-    }
-}

test/Microsoft.AspNetCore.FunctionalTests/WebHostFunctionalTests.cs

@@ -54,10 +54,8 @@ namespace Microsoft.AspNetCore.Tests
             await ExecuteTestApp(applicationName, async (deploymentResult, logger) =>
             {
                 var response = await RetryHelper.RetryRequest(() => deploymentResult.HttpClient.GetAsync(string.Empty), logger, deploymentResult.HostShutdownToken);
-                var errorResponse = await RetryHelper.RetryRequest(() => deploymentResult.HttpClient.GetAsync("/error"), logger, deploymentResult.HostShutdownToken);
 
                 var responseText = await response.Content.ReadAsStringAsync();
-                var errorResponseText = await errorResponse.Content.ReadAsStringAsync();
                 try
                 {
                     // Assert server is Kestrel
@@ -65,9 +63,6 @@ namespace Microsoft.AspNetCore.Tests
 
                     // The application name will be sent in response when all asserts succeed in the test app.
                     Assert.Equal(applicationName, responseText);
-
-                    // Assert UseDeveloperExceptionPage is called in WebHostStartupFilter.
-                    Assert.Contains("An unhandled exception occurred while processing the request.", errorResponseText);
                 }
                 catch (XunitException)
                 {

test/TestSites/CreateDefaultBuilderApp/Program.cs

@@ -30,10 +30,6 @@ namespace CreateDefaultBuilderApp
                 })
                 .Configure(app =>
                 {
-                    app.Map("/error", subApp =>
-                    {
-                        subApp.Run(context => throw new Exception());
-                    });
                     app.Run(context =>
                     {
                         return context.Response.WriteAsync(responseMessage);