Add extension to configure capture startup errors setting which defau…

src/Microsoft.AspNet.Hosting/WebApplicationBuilderExtensions.cs

@@ -13,6 +13,11 @@ public static class WebApplicationBuilderExtensions
     {
         private static readonly string ServerUrlsSeparator = ";";
 
+        public static IWebApplicationBuilder UseCaptureStartupErrors(this IWebApplicationBuilder applicationBuilder, bool captureStartupError)
+        {
+            return applicationBuilder.UseSetting(WebApplicationDefaults.CaptureStartupErrorsKey, captureStartupError ? "true" : "false");
+        }
+
         public static IWebApplicationBuilder UseStartup<TStartup>(this IWebApplicationBuilder applicationBuilder) where TStartup : class
         {
             return applicationBuilder.UseStartup(typeof(TStartup));

src/Microsoft.AspNet.Hosting/WebApplicationConfiguration.cs

@@ -1,4 +1,8 @@
-using Microsoft.Extensions.Configuration;
+// 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.Collections.Generic;
+using Microsoft.Extensions.Configuration;
 
 namespace Microsoft.AspNet.Hosting
 {
@@ -11,9 +15,15 @@ public static IConfiguration GetDefault()
 
         public static IConfiguration GetDefault(string[] args)
         {
+            var defaultSettings = new Dictionary<string, string>
+            {
+                { WebApplicationDefaults.CaptureStartupErrorsKey, "true" }
+            };
+
             // We are adding all environment variables first and then adding the ASPNET_ ones
             // with the prefix removed to unify with the command line and config file formats
             var configBuilder = new ConfigurationBuilder()
+                .AddInMemoryCollection(defaultSettings)
                 .AddJsonFile(WebApplicationDefaults.HostingJsonFile, optional: true)
                 .AddEnvironmentVariables()
                 .AddEnvironmentVariables(prefix: WebApplicationDefaults.EnvironmentVariablesPrefix);

test/Microsoft.AspNet.Hosting.Tests/WebApplicationBuilderTests.cs

@@ -123,6 +123,29 @@ public async Task StartupConfigureThrows_Fallback()
             }
         }
 
+        [Fact]
+        public void CaptureStartupErrorsByDefault()
+        {
+            var applicationBuilder = new WebApplicationBuilder()
+                .UseServer(new TestServer())
+                .UseStartup<StartupBoom>();
+
+            // This should not throw
+            applicationBuilder.Build();
+        }
+
+        [Fact]
+        public void UseCaptureStartupErrorsHonored()
+        {
+            var applicationBuilder = new WebApplicationBuilder()
+                .UseCaptureStartupErrors(false)
+                .UseServer(new TestServer())
+                .UseStartup<StartupBoom>();
+
+            var exception = Assert.Throws<InvalidOperationException>(() => applicationBuilder.Build());
+            Assert.Equal("A public method named 'ConfigureProduction' or 'Configure' could not be found in the 'Microsoft.AspNet.Hosting.Fakes.StartupBoom' type.", exception.Message);
+        }
+
         [Fact]
         public void UseEnvironmentIsNotOverriden()
         {

test/Microsoft.AspNet.Hosting.Tests/WebApplicationConfigurationsTests.cs

@@ -10,6 +10,14 @@ namespace Microsoft.AspNet.Hosting.Tests
 {
     public class WebApplicationConfigurationTests
     {
+        [Fact]
+        public void DefaultCapturesStartupErrors()
+        {
+            var config = new WebApplicationOptions(WebApplicationConfiguration.GetDefault());
+
+            Assert.True(config.CaptureStartupErrors);
+        }
+
         [Fact]
         public void ReadsParametersCorrectly()
         {