Support Ctrl+C handling

src/System.CommandLine/Builder/CommandLineBuilder.cs

@@ -61,7 +61,8 @@ internal void AddMiddleware(
 
         internal static class MiddlewareOrder
         {
-            public const int ExceptionHandler = int.MinValue;
+            public const int UnloadHandler = int.MinValue;
+            public const int ExceptionHandler = UnloadHandler + 100;
             public const int Configuration = ExceptionHandler + 100;
             public const int Preprocessing = Configuration + 100;
             public const int AfterPreprocessing = Preprocessing + 100;

src/System.CommandLine/IConsole.cs

@@ -37,5 +37,7 @@ public interface IConsole : IDisposable
         bool IsVirtualTerminal { get; }
 
         void TryEnableVirtualTerminal();
+
+        event ConsoleCancelEventHandler CancelKeyPress;
     }
 }

src/System.CommandLine/Invocation/Binder.cs

@@ -4,6 +4,7 @@
 using System.Collections.Generic;
 using System.Linq;
 using System.Reflection;
+using System.Threading;
 
 namespace System.CommandLine.Invocation
 {
@@ -33,6 +34,10 @@ public static object[] GetMethodArguments(
                 {
                     arguments.Add(context.Console);
                 }
+                else if (parameterInfo.ParameterType == typeof(CancellationToken))
+                {
+                    arguments.Add(context.Canceled);
+                }
                 else
                 {
                     var argument = context.ParseResult

src/System.CommandLine/Invocation/InvocationContext.cs

@@ -1,11 +1,14 @@
 // Copyright (c) .NET Foundation and contributors. All rights reserved.
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
+using System.Threading;
+
 namespace System.CommandLine.Invocation
 {
     public sealed class InvocationContext : IDisposable
     {
         private readonly IDisposable _onDispose;
+        private readonly CancellationTokenSource _cts = new CancellationTokenSource();
 
         public InvocationContext(
             ParseResult parseResult,
@@ -36,6 +39,10 @@ public InvocationContext(
 
         public IInvocationResult InvocationResult { get; set; }
 
+        public CancellationToken Canceled => _cts.Token;
+
+        public void Cancel() => _cts.Cancel();
+
         public void Dispose()
         {
             _onDispose?.Dispose();

src/System.CommandLine/Invocation/InvocationExtensions.cs

@@ -6,14 +6,65 @@
 using System.IO;
 using System.Linq;
 using System.Reflection;
+using System.Runtime.Loader;
 using System.Text;
+using System.Threading;
 using System.Threading.Tasks;
 using static System.Environment;
 
 namespace System.CommandLine.Invocation
 {
     public static class InvocationExtensions
     {
+        public static CommandLineBuilder CancelOnCancelKey(this CommandLineBuilder builder)
+        {
+            builder.AddMiddleware(async (context, next) =>
+            {
+                ConsoleCancelEventHandler handler = (_, args) =>
+                {
+                    args.Cancel = true;
+                    context.Cancel();
+                };
+                try
+                {
+                    context.Console.CancelKeyPress += handler;
+                    await next(context);
+                }
+                finally
+                {
+                    context.Console.CancelKeyPress -= handler;
+                }
+            }, CommandLineBuilder.MiddlewareOrder.Configuration);
+
+            return builder;
+        }
+
+        public static CommandLineBuilder CancelOnUnload(this CommandLineBuilder builder)
+        {
+            builder.AddMiddleware(async (context, next) =>
+            {
+                var mre = new ManualResetEventSlim(initialState: false);
+                Action<AssemblyLoadContext> handler = _ =>
+                {
+                    context.Cancel();
+                    mre.Wait();
+                    Environment.ExitCode = context.ResultCode;
+                };
+                try
+                {
+                    AssemblyLoadContext.Default.Unloading += handler;
+                    await next(context);
+                }
+                finally
+                {
+                    AssemblyLoadContext.Default.Unloading -= handler;
+                    mre.Set();
+                }
+            }, CommandLineBuilder.MiddlewareOrder.UnloadHandler);
+
+            return builder;
+        }
+
         public static CommandLineBuilder UseMiddleware(
             this CommandLineBuilder builder,
             InvocationMiddleware middleware)

src/System.CommandLine/Invocation/SystemConsole.cs

@@ -103,6 +103,12 @@ public void Dispose()
             GC.SuppressFinalize(this);
         }
 
+        public event ConsoleCancelEventHandler CancelKeyPress
+        {
+            add => Console.CancelKeyPress += value;
+            remove => Console.CancelKeyPress -= value;
+        }
+
         ~SystemConsole()
         {
             ResetConsole();

src/System.CommandLine/System.CommandLine.csproj

@@ -13,6 +13,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.CSharp" Version="4.4.1" />
+    <PackageReference Include="System.Runtime.Loader" Version="4.3.0" />
   </ItemGroup>
 
 </Project>