Throw when ConfigureServices has wrong signature

src/Microsoft.AspNet.Hosting/Internal/HostingUtilities.cs

@@ -13,7 +13,7 @@ namespace Microsoft.AspNet.Hosting.Internal
         internal static Tuple<string, string> SplitTypeName(string identifier)
         {
             string typeName = null;
-            string assemblyName = identifier.Trim();
+            var assemblyName = identifier.Trim();
             var parts = identifier.Split(new[] { ',' }, 2);
             if (parts.Length == 2)
             {

src/Microsoft.AspNet.Hosting/Internal/RequestServicesContainer.cs

@@ -39,7 +39,6 @@ namespace Microsoft.AspNet.Hosting.Internal
         private IServiceProvider PriorRequestServices { get; set; }
         private IServiceScope Scope { get; set; }
 
-
         // CONSIDER: this could be an extension method on HttpContext instead
         public static RequestServicesContainer EnsureRequestServices(HttpContext httpContext, IServiceProvider services)
         {

src/Microsoft.AspNet.Hosting/Program.cs

@@ -3,6 +3,8 @@
 
 using System;
 using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
 using Microsoft.AspNet.Hosting.Internal;
 using Microsoft.Framework.ConfigurationModel;
 using Microsoft.Framework.DependencyInjection;

src/Microsoft.AspNet.Hosting/Server/ServerLoader.cs

@@ -26,8 +26,8 @@ namespace Microsoft.AspNet.Hosting.Server
             }
 
             var nameParts = HostingUtilities.SplitTypeName(serverFactoryIdentifier);
-            string typeName = nameParts.Item1;
-            string assemblyName = nameParts.Item2;
+            var typeName = nameParts.Item1;
+            var assemblyName = nameParts.Item2;
 
             var assembly = Assembly.Load(new AssemblyName(assemblyName));
             if (assembly == null)

src/Microsoft.AspNet.Hosting/Startup/ConfigureDelegate.cs

@@ -20,10 +20,7 @@ namespace Microsoft.AspNet.Hosting.Startup
 
         public MethodInfo MethodInfo { get; }
 
-        public Action<IApplicationBuilder> Build(object instance)
-        {
-            return builder => Invoke(instance, builder);
-        }
+        public Action<IApplicationBuilder> Build(object instance) => builder => Invoke(instance, builder);
 
         private void Invoke(object instance, IApplicationBuilder builder)
         {

src/Microsoft.AspNet.Hosting/Startup/ConfigureServicesDelegate.cs

@@ -2,8 +2,10 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Linq;
 using System.Reflection;
 using Microsoft.Framework.DependencyInjection;
+using Microsoft.Framework.Internal;
 
 namespace Microsoft.AspNet.Hosting.Startup
 {
@@ -11,32 +13,33 @@ namespace Microsoft.AspNet.Hosting.Startup
 
     public class ConfigureServicesBuilder
     {
-        public ConfigureServicesBuilder(MethodInfo configureServices)
+        public ConfigureServicesBuilder([NotNull] MethodInfo configureServices)
         {
+            // Only support IServiceCollection parameters
+            var parameters = configureServices.GetParameters();
+            if (parameters.Length > 1 ||
+                parameters.Any(p => p.ParameterType != typeof(IServiceCollection)))
+            {
+                throw new InvalidOperationException("ConfigureServices can take at most a single IServiceCollection parameter.");
+            }
+
             MethodInfo = configureServices;
         }
 
         public MethodInfo MethodInfo { get; }
 
-        public ConfigureServicesDelegate Build(object instance)
-        {
-            return services => Invoke(instance, services);
-        }
+        public ConfigureServicesDelegate Build(object instance) => services => Invoke(instance, services);
 
-        private IServiceProvider Invoke(object instance, IServiceCollection exportServices)
+        private IServiceProvider Invoke(object instance, [NotNull] IServiceCollection exportServices)
         {
-            var parameterInfos = MethodInfo.GetParameters();
-            var parameters = new object[parameterInfos.Length];
-            for (var index = 0; index != parameterInfos.Length; ++index)
+            var parameters = new object[MethodInfo.GetParameters().Length];
+
+            // Ctor ensures we have at most one IServiceCollection parameter
+            if (parameters.Length > 0)
             {
-                var parameterInfo = parameterInfos[index];
-                if (exportServices != null && parameterInfo.ParameterType == typeof(IServiceCollection))
-                {
-                    parameters[index] = exportServices;
-                }
+                parameters[0] = exportServices;
             }
 
-            // REVIEW: We null ref if exportServices is null, cuz it should not be null
             return MethodInfo.Invoke(instance, parameters) as IServiceProvider ?? exportServices.BuildServiceProvider();
         }
     }

test/Microsoft.AspNet.Hosting.Tests/Fakes/Startup.cs

@@ -82,7 +82,7 @@ namespace Microsoft.AspNet.Hosting.Fakes
             return services.BuildServiceProvider();
         }
 
-        public IServiceProvider ConfigureProviderArgsServices(IApplicationBuilder me)
+        public IServiceProvider ConfigureProviderArgsServices()
         {
             var services = new ServiceCollection().AddOptions();
             services.Configure<FakeOptions>(o =>

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

@@ -323,6 +323,23 @@ namespace Microsoft.AspNet.Hosting
             }
         }
 
+        [Fact]
+        public void HostingEngine_ThrowsForBadConfigureServiceSignature()
+        {
+            var engine = CreateBuilder()
+                .UseServer(this)
+                .UseStartup<BadConfigureServicesStartup>()
+                .Build();
+            var ex = Assert.Throws<InvalidOperationException>(() => engine.Start());
+            Assert.True(ex.Message.Contains("ConfigureServices"));
+        }
+
+        public class BadConfigureServicesStartup
+        {
+            public void ConfigureServices(IServiceCollection services, int gunk) { }
+            public void Configure(IApplicationBuilder app) { }
+        }
+
         private IHostingEngine CreateHostingEngine(RequestDelegate requestDelegate)
         {
             var applicationBuilder = new Mock<IApplicationBuilder>();