no error for missing subcommand when HelpOption is present

Author: jonsequitur

src/System.CommandLine.Tests/UseHelpTests.cs

@@ -5,6 +5,7 @@
 using System.CommandLine.Invocation;
 using System.CommandLine.IO;
 using System.CommandLine.Parsing;
+using System.IO;
 using System.Threading.Tasks;
 using FluentAssertions;
 using Xunit;
@@ -109,12 +110,12 @@ public void There_are_no_parse_errors_when_help_is_invoked_on_root_command()
         [Fact]
         public void There_are_no_parse_errors_when_help_is_invoked_on_subcommand()
         {
-            var command = new RootCommand
+            var root = new RootCommand
             {
                 new Command("subcommand")
             };
 
-            var parser = new CommandLineBuilder(command)
+            var parser = new CommandLineBuilder(root)
                          .UseHelp()
                          .Build();
 
@@ -125,6 +126,23 @@ public void There_are_no_parse_errors_when_help_is_invoked_on_subcommand()
                   .BeEmpty();
         }
 
+        [Fact]
+        public void There_are_no_parse_errors_when_help_is_invoked_on_a_command_with_subcommands()
+        {
+            var root = new RootCommand
+            {
+                new Command("subcommand")
+            };
+
+            var parser = new CommandLineBuilder(root)
+                         .UseHelp()
+                         .Build();
+
+            var result = parser.Parse("-h");
+
+            result.Errors.Should().BeEmpty();
+        }
+
         [Theory]
         [InlineData("-h")]
         [InlineData("inner -h")]

src/System.CommandLine/Builder/CommandLineBuilderExtensions.cs

@@ -1,7 +1,6 @@
 // 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.Collections.Generic;
 using System.CommandLine.Binding;
 using System.CommandLine.Help;
 using System.CommandLine.Invocation;
@@ -268,9 +267,7 @@ void Default(Exception exception, InvocationContext context)
 
         public static CommandLineBuilder UseHelp(this CommandLineBuilder builder)
         {
-            var helpOption = new HelpOption();
-
-            return builder.UseHelp(helpOption);
+            return builder.UseHelp(new HelpOption());
         }
 
         internal static CommandLineBuilder UseHelp(
@@ -296,41 +293,6 @@ internal static CommandLineBuilder UseHelp(
             return builder;
         }
 
-        private class HelpOption : Option
-        {
-            public HelpOption() : base(new[]
-            {
-                "-h",
-                "/h",
-                "--help",
-                "-?",
-                "/?"
-            }, "Show help and usage information")
-            {
-            }
-
-            public override Argument Argument
-            {
-                get => Argument.None;
-                set => throw new NotSupportedException();
-            }
-
-            protected bool Equals(HelpOption other)
-            {
-                return other != null;
-            }
-
-            public override bool Equals(object obj)
-            {
-                return obj is HelpOption;
-            }
-
-            public override int GetHashCode()
-            {
-                return typeof(HelpOption).GetHashCode();
-            }
-        }
-
         public static TBuilder UseHelpBuilder<TBuilder>(this TBuilder builder, Func<BindingContext, IHelpBuilder> getHelpBuilder)
             where TBuilder : CommandLineBuilder
         {

src/System.CommandLine/Help/HelpOption.cs

@@ -0,0 +1,40 @@
+// 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.
+
+namespace System.CommandLine.Help
+{
+    internal class HelpOption : Option
+    {
+        public HelpOption() : base(new[]
+        {
+            "-h",
+            "/h",
+            "--help",
+            "-?",
+            "/?"
+        }, "Show help and usage information")
+        {
+        }
+
+        public override Argument Argument
+        {
+            get => Argument.None;
+            set => throw new NotSupportedException();
+        }
+
+        protected bool Equals(HelpOption other)
+        {
+            return other != null;
+        }
+
+        public override bool Equals(object obj)
+        {
+            return obj is HelpOption;
+        }
+
+        public override int GetHashCode()
+        {
+            return typeof(HelpOption).GetHashCode();
+        }
+    }
+}

src/System.CommandLine/Parsing/ParseResultVisitor.cs

@@ -3,6 +3,7 @@
 
 using System.Collections.Generic;
 using System.CommandLine.Binding;
+using System.CommandLine.Help;
 using System.Linq;
 
 namespace System.CommandLine.Parsing
@@ -227,7 +228,8 @@ private void ValidateCommandHandler()
         {
             if (_innermostCommandResult.Command is Command cmd &&
                 cmd.Handler == null &&
-                cmd.Children.OfType<ICommand>().Any())
+                cmd.Children.OfType<ICommand>().Any() && 
+                !cmd.Options.OfType<HelpOption>().Any())
             {
                 _errors.Insert(0,
                                new ParseError(