fix #2634: Add SetAction for Task<int>

Author: petterh

src/System.CommandLine.ApiCompatibility.Tests/ApiCompatibilityApprovalTests.System_CommandLine_api_is_not_changed.approved.txt

@@ -55,6 +55,7 @@
     public System.Void SetAction(System.Func<ParseResult,System.Int32> action)
     public System.Void SetAction(System.Func<ParseResult,System.Threading.CancellationToken,System.Threading.Tasks.Task> action)
     public System.Void SetAction(System.Func<ParseResult,System.Threading.Tasks.Task> action)
+    public System.Void SetAction(System.Func<ParseResult,System.Threading.Tasks.Task<System.Int32>> action)
     public System.Void SetAction(System.Func<ParseResult,System.Threading.CancellationToken,System.Threading.Tasks.Task<System.Int32>> action)
   public static class CompletionSourceExtensions
     public static System.Void Add(this System.Collections.Generic.List<System.Func<System.CommandLine.Completions.CompletionContext,System.Collections.Generic.IEnumerable<System.CommandLine.Completions.CompletionItem>>> completionSources, System.Func<System.CommandLine.Completions.CompletionContext,System.Collections.Generic.IEnumerable<System.String>> completionsDelegate)

src/System.CommandLine.Tests/Invocation/InvocationTests.cs

@@ -160,6 +160,16 @@ public async Task Anonymous_RootCommand_Task_returning_Action_can_set_custom_res
             (await rootCommand.Parse("").InvokeAsync()).Should().Be(123);
         }
 
+        [Fact]
+        public async Task Anonymous_RootCommand_Task_int_returning_Action_can_set_custom_result_code_via_InvokeAsync()
+        {
+            var rootCommand = new RootCommand();
+
+            rootCommand.SetAction(_ => Task.FromResult(123));
+
+            (await rootCommand.Parse("").InvokeAsync()).Should().Be(123);
+        }
+
         [Fact]
         public void Anonymous_RootCommand_int_returning_Action_can_set_custom_result_code_via_Invoke()
         {

src/System.CommandLine/Command.cs

@@ -166,13 +166,36 @@ public void SetAction(Func<ParseResult, Task> action)
                 throw new ArgumentNullException(nameof(action));
             }
 
-            Action = new AnonymousAsynchronousCommandLineAction(async (context, cancellationToken) =>
+            Action = new AnonymousAsynchronousCommandLineAction(async (context, _) =>
             {
                 await action(context);
                 return 0;
             });
         }
 
+        /// <summary>
+        /// Sets an asynchronous action to be run when the command is invoked.
+        /// </summary>
+        /// <remarks>
+        /// When possible, prefer using the <see cref="SetAction(Func{ParseResult, CancellationToken, Task{int}})"/> overload
+        /// and passing the <see cref="CancellationToken"/> parameter to the async method(s) called by the action.
+        /// </remarks>
+        // Hide from intellisense, it's public to avoid the compiler choosing a sync overload
+        // for an async action (and fire and forget issue described in https://github.com/dotnet/command-line-api/issues/2562).
+        [EditorBrowsable(EditorBrowsableState.Never)]
+        public void SetAction(Func<ParseResult, Task<int>> action)
+        {
+            if (action is null)
+            {
+                throw new ArgumentNullException(nameof(action));
+            }
+
+            Action = new AnonymousAsynchronousCommandLineAction(async (context, _) =>
+            {
+                return await action(context);
+            });
+        }
+
         /// <summary>
         /// Sets an asynchronous action when the command is invoked.
         /// </summary>