Add the ability to set the IApplicationEnvironment.ApplicationBasePath

- Added UseApplicationBasePath which sets the base path (used for views
and static files)

samples/SampleStartups/StartupFullControl.cs

@@ -1,4 +1,5 @@
 using System;
+using System.IO;
 using Microsoft.AspNet.Builder;
 using Microsoft.AspNet.Hosting;
 using Microsoft.Extensions.DependencyInjection;
@@ -14,6 +15,7 @@ namespace SampleStartups
         {
             var application = new WebApplicationBuilder()
                 .UseServerFactory("Microsoft.AspNet.Server.Kestrel") // Set the server manually
+                .UseApplicationBasePath(Directory.GetCurrentDirectory()) // Override the application base with the current directory
                 .UseEnvironment("Development")
                 .UseWebRoot("public")
                 .ConfigureLogging(loggerFactory =>

src/Microsoft.AspNet.Hosting/WebApplicationBuilder.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Diagnostics;
+using System.Runtime.Versioning;
 using Microsoft.AspNet.Builder;
 using Microsoft.AspNet.Hosting.Builder;
 using Microsoft.AspNet.Hosting.Internal;
@@ -29,6 +30,7 @@ namespace Microsoft.AspNet.Hosting
         private Action<IServiceCollection> _configureServices;
         private string _environmentName;
         private string _webRoot;
+        private string _applicationBasePath;
 
         // Only one of these should be set
         private StartupMethods _startup;
@@ -52,6 +54,12 @@ namespace Microsoft.AspNet.Hosting
             return this;
         }
 
+        public WebApplicationBuilder UseApplicationBasePath(string applicationBasePath)
+        {
+            _applicationBasePath = applicationBasePath;
+            return this;
+        }
+
         public WebApplicationBuilder UseEnvironment(string environment)
         {
             if (environment == null)
@@ -216,11 +224,18 @@ namespace Microsoft.AspNet.Hosting
             services.AddTransient<IStartupFilter, AutoRequestServicesStartupFilter>();
 
             var defaultPlatformServices = PlatformServices.Default;
+
             if (defaultPlatformServices != null)
             {
                 if (defaultPlatformServices.Application != null)
                 {
-                    services.TryAddSingleton(defaultPlatformServices.Application);
+                    var appEnv = defaultPlatformServices.Application;
+                    if (!string.IsNullOrEmpty(_applicationBasePath))
+                    {
+                        appEnv = new WrappedApplicationEnvironment(_applicationBasePath, appEnv);
+                    }
+
+                    services.TryAddSingleton(appEnv);
                 }
 
                 if (defaultPlatformServices.Runtime != null)
@@ -236,5 +251,24 @@ namespace Microsoft.AspNet.Hosting
 
             return services;
         }
+
+        private class WrappedApplicationEnvironment : IApplicationEnvironment
+        {
+            public WrappedApplicationEnvironment(string applicationBasePath, IApplicationEnvironment env)
+            {
+                ApplicationBasePath = applicationBasePath;
+                ApplicationName = env.ApplicationName;
+                ApplicationVersion = env.ApplicationVersion;
+                RuntimeFramework = env.RuntimeFramework;
+            }
+
+            public string ApplicationBasePath { get; }
+
+            public string ApplicationName { get; }
+
+            public string ApplicationVersion { get; }
+
+            public FrameworkName RuntimeFramework { get; }
+        }
     }
 }

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

@@ -13,6 +13,7 @@ using Microsoft.AspNet.Http.Features;
 using Microsoft.AspNet.Http.Internal;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.PlatformAbstractions;
 using Xunit;
 
 namespace Microsoft.AspNet.Hosting
@@ -137,6 +138,27 @@ namespace Microsoft.AspNet.Hosting
             Assert.Equal(expected, application.Services.GetService<IHostingEnvironment>().EnvironmentName);
         }
 
+        [Fact]
+        public void UseBasePathConfiguresBasePath()
+        {
+            var vals = new Dictionary<string, string>
+            {
+                { "ENV", "Dev" },
+            };
+            var builder = new ConfigurationBuilder()
+                .AddInMemoryCollection(vals);
+            var config = builder.Build();
+
+            var application = new WebApplicationBuilder()
+                .UseConfiguration(config)
+                .UseApplicationBasePath("/foo/bar")
+                .UseServer(new TestServer())
+                .UseStartup("Microsoft.AspNet.Hosting.Tests")
+                .Build();
+
+            Assert.Equal("/foo/bar", application.Services.GetService<IApplicationEnvironment>().ApplicationBasePath);
+        }
+
         private WebApplicationBuilder CreateWebApplicationBuilder()
         {
             var vals = new Dictionary<string, string>