From 0b14bc135badce4d39f0c90432e3120b63212ae8 Mon Sep 17 00:00:00 2001
From: Victor Hurdugaci <victor.hurdugaci@microsoft.com>
Date: Wed, 28 Oct 2015 12:12:37 -0700
Subject: [PATCH] Show type load exception on the startup error page

---
 .../Startup/StartupExceptionPage.cs           | 15 +++++++++++
 .../Fakes/StartupThrowTypeLoadException.cs    | 25 +++++++++++++++++++
 .../WebHostBuilderTests.cs                    | 12 +++++++++
 3 files changed, 52 insertions(+)
 create mode 100644 test/Microsoft.AspNet.Hosting.Tests/Fakes/StartupThrowTypeLoadException.cs

diff --git a/src/Microsoft.AspNet.Hosting/Startup/StartupExceptionPage.cs b/src/Microsoft.AspNet.Hosting/Startup/StartupExceptionPage.cs
index adc9656f89..8e15772526 100644
--- a/src/Microsoft.AspNet.Hosting/Startup/StartupExceptionPage.cs
+++ b/src/Microsoft.AspNet.Hosting/Startup/StartupExceptionPage.cs
@@ -508,6 +508,21 @@ namespace Microsoft.AspNet.Hosting.Startup
 
         private static IEnumerable<Exception> FlattenAndReverseExceptionTree(Exception ex)
         {
+            // ReflectionTypeLoadException is special because the details are in 
+            // a the LoaderExceptions property
+            var typeLoadException = ex as ReflectionTypeLoadException;
+            if (typeLoadException != null)
+            {
+                var typeLoadExceptions = new List<Exception>();
+                foreach (Exception loadException in typeLoadException.LoaderExceptions)
+                {
+                    typeLoadExceptions.AddRange(FlattenAndReverseExceptionTree(loadException));
+                }
+
+                typeLoadExceptions.Add(ex);
+                return typeLoadExceptions;
+            }
+
             var list = new List<Exception>();
             while (ex != null)
             {
diff --git a/test/Microsoft.AspNet.Hosting.Tests/Fakes/StartupThrowTypeLoadException.cs b/test/Microsoft.AspNet.Hosting.Tests/Fakes/StartupThrowTypeLoadException.cs
new file mode 100644
index 0000000000..fdfbc6a24e
--- /dev/null
+++ b/test/Microsoft.AspNet.Hosting.Tests/Fakes/StartupThrowTypeLoadException.cs
@@ -0,0 +1,25 @@
+// 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.IO;
+using System.Reflection;
+
+namespace Microsoft.AspNet.Hosting.Fakes
+{
+    public class StartupThrowTypeLoadException
+    {
+        public StartupThrowTypeLoadException()
+        {
+            // For this exception, the error page should contain details of the LoaderExceptions 
+            throw new ReflectionTypeLoadException(
+                classes: new Type[] { GetType() },
+                exceptions: new Exception[] { new FileNotFoundException("Message from the LoaderException") },
+                message: "This should not be in the output");
+        }
+
+        public void Configure()
+        {
+        }
+    }
+}
\ No newline at end of file
diff --git a/test/Microsoft.AspNet.Hosting.Tests/WebHostBuilderTests.cs b/test/Microsoft.AspNet.Hosting.Tests/WebHostBuilderTests.cs
index b8aa7c6e6c..988194f0a3 100644
--- a/test/Microsoft.AspNet.Hosting.Tests/WebHostBuilderTests.cs
+++ b/test/Microsoft.AspNet.Hosting.Tests/WebHostBuilderTests.cs
@@ -74,6 +74,18 @@ namespace Microsoft.AspNet.Hosting
             }
         }
 
+        [Fact]
+        public async Task StartupCtorThrows_TypeLoadException()
+        {
+            var builder = CreateWebHostBuilder();
+            var serverFactory = new TestServerFactory();
+            var engine = builder.UseServer(serverFactory).UseStartup<StartupThrowTypeLoadException>().Build();
+            using (engine.Start())
+            {
+                await AssertResponseContains(serverFactory.Application, "Message from the LoaderException</span>");
+            }
+        }
+
         [Fact]
         public async Task IApplicationLifetimeRegisteredEvenWhenStartupCtorThrows_Fallback()
         {