Host: fix Cancellation not aborting Start in some cases (#113442)

Author: mus65

src/libraries/Microsoft.Extensions.Hosting/src/Internal/Host.cs

@@ -338,6 +338,10 @@ private static async Task ForeachService<T>(
                         {
                             exceptions.AddRange(task.Exception.InnerExceptions); // Log exception from async method.
                         }
+                        else if (task.IsCanceled)
+                        {
+                            exceptions.Add(new TaskCanceledException(task));
+                        }
                     }
                     else
                     {

src/libraries/Microsoft.Extensions.Hosting/tests/UnitTests/Internal/HostTests.cs

@@ -1453,6 +1453,23 @@ public async Task HostedServiceFactoryExceptionGetsLogged()
             Assert.Equal("HostedServiceStartupFaulted", events[0].EventId.Name);
         }
 
+        [Fact]
+        public async Task HostConcurrentCancelledStartAsyncAbortsStart()
+        {
+            using CancellationTokenSource cancellationTokenSource = new();
+            StartAsyncCancelledService service = new(cancellationTokenSource);
+
+            using IHost host = CreateBuilder()
+                .ConfigureServices((hostContext, services) =>
+                {
+                    services.Configure<HostOptions>(o => o.ServicesStartConcurrently = true);
+                    services.AddHostedService(sp => service);
+                })
+                .Build();
+
+            await Assert.ThrowsAsync<TaskCanceledException>(() => host.StartAsync(cancellationTokenSource.Token));
+        }
+
         /// <summary>
         /// Tests that when a BackgroundService is canceled when stopping the host,
         /// no error is logged.
@@ -1698,6 +1715,17 @@ private class BackgroundServiceDoesNotCallBase : BackgroundService
             public override Task StopAsync(CancellationToken cancellationToken) => Task.CompletedTask;
         }
 
+        private class StartAsyncCancelledService(CancellationTokenSource cancellationTokenSource) : IHostedService
+        {
+            public Task StartAsync(CancellationToken cancellationToken)
+            {
+                cancellationTokenSource.Cancel();
+                return Task.FromCanceled(cancellationToken);
+            }
+
+            public Task StopAsync(CancellationToken cancellationToken) => Task.CompletedTask;
+        }
+
         private class SlowStartService : IHostedService
         {
             public async Task StartAsync(CancellationToken cancellationToken)