Clean up doc comments and add a test

src/Microsoft.AspNetCore.Hosting.Abstractions/HostingAbstractionsWebHostBuilderExtensions.cs

@@ -4,7 +4,6 @@
 using System;
 using System.Linq;
 using System.Threading;
-using System.Threading.Tasks;
 using Microsoft.AspNetCore.Hosting.Server;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
@@ -58,8 +57,8 @@ public static IWebHostBuilder UseStartup(this IWebHostBuilder hostBuilder, strin
 
 
             return hostBuilder
-                    .UseSetting(WebHostDefaults.ApplicationKey, startupAssemblyName)
-                    .UseSetting(WebHostDefaults.StartupAssemblyKey, startupAssemblyName);
+                .UseSetting(WebHostDefaults.ApplicationKey, startupAssemblyName)
+                .UseSetting(WebHostDefaults.StartupAssemblyKey, startupAssemblyName);
         }
 
         /// <summary>

src/Microsoft.AspNetCore.Hosting.Abstractions/IWebHostBuilder.cs

@@ -27,13 +27,15 @@ public interface IWebHostBuilder
         /// </summary>
         IWebHost Build();
 
-        // TODO: update these doc comments to indicate what may be null during configuration.
-
         /// <summary>
         /// Adds a delegate for configuring the <see cref="IConfigurationBuilder"/> that will construct an <see cref="IConfiguration"/>.
         /// </summary>
         /// <param name="configureDelegate">The delegate for configuring the <see cref="IConfigurationBuilder" /> that will be used to construct an <see cref="IConfiguration" />.</param>
         /// <returns>The <see cref="IWebHostBuilder"/>.</returns>
+        /// <remarks>
+        /// The <see cref="IConfiguration"/> and <see cref="ILoggerFactory"/> on the <see cref="WebHostBuilderContext"/> are uninitialized at this stage.
+        /// The <see cref="IConfigurationBuilder"/> is pre-populated with the settings of the <see cref="IWebHostBuilder"/>.
+        /// </remarks>
         IWebHostBuilder ConfigureAppConfiguration(Action<WebHostBuilderContext, IConfigurationBuilder> configureDelegate);
 
         /// <summary>
@@ -47,20 +49,29 @@ public interface IWebHostBuilder
         /// Adds a delegate for configuring the provided <see cref="ILoggerFactory"/>. This may be called multiple times.
         /// </summary>
         /// <param name="configureLogging">The delegate that configures the <see cref="ILoggerFactory"/>.</param>
+        /// <typeparam name="T">
+        /// The type of <see cref="ILoggerFactory"/> to configure.
+        /// The delegate will not execute if the type provided does not match the <see cref="ILoggerFactory"/> used by the <see cref="IWebHostBuilder"/>
+        /// </typeparam>
         /// <returns>The <see cref="IWebHostBuilder"/>.</returns>
+        /// <remarks>
+        /// The <see cref="ILoggerFactory"/> on the <see cref="WebHostBuilderContext"/> is uninitialized at this stage.
+        /// </remarks>
         IWebHostBuilder ConfigureLogging<T>(Action<WebHostBuilderContext, T> configureLogging) where T : ILoggerFactory;
 
         /// <summary>
-        /// Specify the delegate that is used to configure the services of the web application.
+        /// Adds a delegate for configuring additional services for the host or web application. This may be called
+        /// multiple times.
         /// </summary>
-        /// <param name="configureServices">The delegate that configures the <see cref="IServiceCollection"/>.</param>
+        /// <param name="configureServices">A delegate for configuring the <see cref="IServiceCollection"/>.</param>
         /// <returns>The <see cref="IWebHostBuilder"/>.</returns>
         IWebHostBuilder ConfigureServices(Action<IServiceCollection> configureServices);
 
         /// <summary>
-        /// Specify the delegate that is used to configure the services of the web application.
+        /// Adds a delegate for configuring additional services for the host or web application. This may be called
+        /// multiple times.
         /// </summary>
-        /// <param name="configureServices">The delegate that configures the <see cref="IServiceCollection"/>.</param>
+        /// <param name="configureServices">A delegate for configuring the <see cref="IServiceCollection"/>.</param>
         /// <returns>The <see cref="IWebHostBuilder"/>.</returns>
         IWebHostBuilder ConfigureServices(Action<WebHostBuilderContext, IServiceCollection> configureServices);
 
@@ -92,6 +103,9 @@ public interface IWebHostBuilder
         /// </summary>
         /// <param name="createLoggerFactory">The delegate that constructs an <see cref="IConfigurationBuilder" /></param>
         /// <returns>The <see cref="IWebHostBuilder"/>.</returns>
+        /// <remarks>
+        /// The <see cref="ILoggerFactory"/> on the <see cref="WebHostBuilderContext"/> is uninitialized at this stage.
+        /// </remarks>
         IWebHostBuilder UseLoggerFactory(Func<WebHostBuilderContext, ILoggerFactory> createLoggerFactory);
     }
 }

src/Microsoft.AspNetCore.Hosting/WebHostBuilder.cs

@@ -32,7 +32,8 @@ public class WebHostBuilder : IWebHostBuilder
         private WebHostOptions _options;
         private bool _webHostBuilt;
         private Func<WebHostBuilderContext, ILoggerFactory> _createLoggerFactoryDelegate;
-        private List<Action<WebHostBuilderContext, IConfigurationBuilder>> _configureConfigurationBuilderDelegates;
+        private List<Action<WebHostBuilderContext, IConfigurationBuilder>> _configureAppConfigurationBuilderDelegates;
+
         public WebHostBuilderContext Context { get; }
 
         /// <summary>
@@ -43,7 +44,7 @@ public WebHostBuilder()
             _hostingEnvironment = new HostingEnvironment();
             _configureServicesDelegates = new List<Action<WebHostBuilderContext, IServiceCollection>>();
             _configureLoggingDelegates = new List<Action<WebHostBuilderContext, ILoggerFactory>>();
-            _configureConfigurationBuilderDelegates = new List<Action<WebHostBuilderContext, IConfigurationBuilder>>();
+            _configureAppConfigurationBuilderDelegates = new List<Action<WebHostBuilderContext, IConfigurationBuilder>>();
 
             _config = new ConfigurationBuilder()
                 .AddEnvironmentVariables(prefix: "ASPNETCORE_")
@@ -111,6 +112,9 @@ public IWebHostBuilder UseLoggerFactory(ILoggerFactory loggerFactory)
         /// </summary>
         /// <param name="createLoggerFactory">The delegate that constructs an <see cref="IConfigurationBuilder" /></param>
         /// <returns>The <see cref="IWebHostBuilder"/>.</returns>
+        /// <remarks>
+        /// The <see cref="ILoggerFactory"/> on the <see cref="WebHostBuilderContext"/> is uninitialized at this stage.
+        /// </remarks>
         public IWebHostBuilder UseLoggerFactory(Func<WebHostBuilderContext, ILoggerFactory> createLoggerFactory)
         {
             if (createLoggerFactory == null)
@@ -175,7 +179,14 @@ public IWebHostBuilder ConfigureLogging(Action<ILoggerFactory> configureLogging)
         /// Adds a delegate for configuring the provided <see cref="ILoggerFactory"/>. This may be called multiple times.
         /// </summary>
         /// <param name="configureLogging">The delegate that configures the <see cref="ILoggerFactory"/>.</param>
+        /// <typeparam name="T">
+        /// The type of <see cref="ILoggerFactory"/> to configure.
+        /// The delegate will not execute if the type provided does not match the <see cref="ILoggerFactory"/> used by the <see cref="IWebHostBuilder"/>
+        /// </typeparam>
         /// <returns>The <see cref="IWebHostBuilder"/>.</returns>
+        /// <remarks>
+        /// The <see cref="ILoggerFactory"/> on the <see cref="WebHostBuilderContext"/> is uninitialized at this stage.
+        /// </remarks>
         public IWebHostBuilder ConfigureLogging<T>(Action<WebHostBuilderContext, T> configureLogging) where T : ILoggerFactory
         {
             if (configureLogging == null)
@@ -198,14 +209,18 @@ public IWebHostBuilder ConfigureLogging<T>(Action<WebHostBuilderContext, T> conf
         /// </summary>
         /// <param name="configureDelegate">The delegate for configuring the <see cref="IConfigurationBuilder" /> that will be used to construct an <see cref="IConfiguration" />.</param>
         /// <returns>The <see cref="IWebHostBuilder"/>.</returns>
+        /// <remarks>
+        /// The <see cref="IConfiguration"/> and <see cref="ILoggerFactory"/> on the <see cref="WebHostBuilderContext"/> are uninitialized at this stage.
+        /// The <see cref="IConfigurationBuilder"/> is pre-populated with the settings of the <see cref="IWebHostBuilder"/>.
+        /// </remarks>
         public IWebHostBuilder ConfigureAppConfiguration(Action<WebHostBuilderContext, IConfigurationBuilder> configureDelegate)
         {
             if (configureDelegate == null)
             {
                 throw new ArgumentNullException(nameof(configureDelegate));
             }
 
-            _configureConfigurationBuilderDelegates.Add(configureDelegate);
+            _configureAppConfigurationBuilderDelegates.Add(configureDelegate);
             return this;
         }
 
@@ -270,14 +285,15 @@ private IServiceCollection BuildCommonServices(out AggregateException hostingSta
 
             var services = new ServiceCollection();
             services.AddSingleton(_hostingEnvironment);
+            services.AddSingleton(Context);
 
             var builder = new ConfigurationBuilder()
                 .SetBasePath(_hostingEnvironment.ContentRootPath)
                 .AddInMemoryCollection(_config.AsEnumerable());
 
-            foreach (var configureConfiguration in _configureConfigurationBuilderDelegates)
+            foreach (var configureAppConfiguration in _configureAppConfigurationBuilderDelegates)
             {
-                configureConfiguration(Context, builder);
+                configureAppConfiguration(Context, builder);
             }
 
             var configuration = builder.Build();
@@ -322,7 +338,6 @@ private IServiceCollection BuildCommonServices(out AggregateException hostingSta
                 }
             }
 
-            // Kept for back-compat, will remove once ConfigureLogging is removed.
             foreach (var configureLogging in _configureLoggingDelegates)
             {
                 configureLogging(Context, loggerFactory);

src/Microsoft.AspNetCore.Hosting/WebHostBuilderExtensions.cs

@@ -104,7 +104,7 @@ public static IWebHostBuilder UseDefaultServiceProvider(this IWebHostBuilder hos
         /// <returns>The <see cref="IWebHostBuilder"/>.</returns>
         public static IWebHostBuilder ConfigureLogging(this IWebHostBuilder hostBuilder, Action<WebHostBuilderContext, LoggerFactory> configureLogging)
         {
-            return hostBuilder.ConfigureLogging<LoggerFactory>(configureLogging);
+            return hostBuilder.ConfigureLogging(configureLogging);
         }
 
         /// <summary>