Make "builder.Services" reflect the final state of the ServiceCollection

src/DefaultBuilder/src/WebApplicationBuilder.cs

@@ -205,6 +205,16 @@ private void ConfigureWebHost(IWebHostBuilder genericWebHostBuilder)
                 {
                     services.Add(s);
                 }
+
+                // Add any services to the user visible service collection so that they are observable
+                // just in case users capture the Services property. Orchard does this to get a "blueprint"
+                // of the service collection. The order needs to be preserved here so we clear the original
+                // collection and add all of the services in order.
+                Services.Clear();
+                foreach (var s in services)
+                {
+                    Services.Add(s);
+                }
             });
 
             genericWebHostBuilder.Configure(ConfigureApplication);

src/DefaultBuilder/test/Microsoft.AspNetCore.Tests/WebApplicationTests.cs

@@ -269,6 +269,52 @@ public void WebApplicationCreate_RegistersRouting()
             Assert.NotNull(linkGenerator);
         }
 
+        [Fact]
+        public void WebApplication_CanResolveDefaultServicesFromServiceCollection()
+        {
+            var builder = WebApplication.CreateBuilder();
+
+            // Add the service collection to the service collection
+            builder.Services.AddSingleton(builder.Services);
+
+            var app = builder.Build();
+
+            var env0 = app.Services.GetRequiredService<IHostEnvironment>();
+
+            var env1 = app.Services.GetRequiredService<IServiceCollection>().BuildServiceProvider().GetRequiredService<IHostEnvironment>();
+
+            Assert.Equal(env0.ApplicationName, env1.ApplicationName);
+            Assert.Equal(env0.EnvironmentName, env1.EnvironmentName);
+            Assert.Equal(env0.ContentRootPath, env1.ContentRootPath);
+        }
+
+        [Fact]
+        public void WebApplication_CanResolveDefaultServicesFromServiceCollectionInCorrectOrder()
+        {
+            var builder = WebApplication.CreateBuilder();
+
+            // Add the service collection to the service collection
+            builder.Services.AddSingleton(builder.Services);
+
+            // We're overriding the default IHostLifetime so that we can test the order in which it's resolved.
+            // This should override the default IHostLifetime.
+            builder.Services.AddSingleton<IHostLifetime, CustomHostLifetime>();
+
+            var app = builder.Build();
+
+            var hostLifetime0 = app.Services.GetRequiredService<IHostLifetime>();
+            var childServiceProvider = app.Services.GetRequiredService<IServiceCollection>().BuildServiceProvider();
+            var hostLifetime1 = childServiceProvider.GetRequiredService<IHostLifetime>();
+
+            var hostLifetimes0 = app.Services.GetServices<IHostLifetime>().ToArray();
+            var hostLifetimes1 = childServiceProvider.GetServices<IHostLifetime>().ToArray();
+
+            Assert.IsType<CustomHostLifetime>(hostLifetime0);
+            Assert.IsType<CustomHostLifetime>(hostLifetime1);
+
+            Assert.Equal(hostLifetimes1.Length, hostLifetimes0.Length);
+        }
+
         [Fact]
         public void WebApplicationCreate_RegistersEventSourceLogger()
         {
@@ -328,6 +374,19 @@ public void WebApplicationBuilder_CanSetWebRootPaths(bool useSetter)
             Assert.Equal(fullWebRootPath, app.Environment.WebRootPath);
         }
 
+        private class CustomHostLifetime : IHostLifetime
+        {
+            public Task StopAsync(CancellationToken cancellationToken)
+            {
+                throw new NotImplementedException();
+            }
+
+            public Task WaitForStartAsync(CancellationToken cancellationToken)
+            {
+                throw new NotImplementedException();
+            }
+        }
+
         private class TestEventListener : EventListener
         {
             private volatile bool _disposed;