let the users provide MaxWidth via HelpAction (#2635)

Author: adamsitnik

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

@@ -178,6 +178,7 @@ System.CommandLine.Completions
 System.CommandLine.Help
   public class HelpAction : System.CommandLine.Invocation.SynchronousCommandLineAction
     .ctor()
+    public System.Int32 MaxWidth { get; set; }
     public System.Int32 Invoke(System.CommandLine.ParseResult parseResult)
   public class HelpOption : System.CommandLine.Option
     .ctor()

src/System.CommandLine.Tests/HelpOptionTests.cs

@@ -230,6 +230,31 @@ public void The_users_can_print_help_output_of_a_subcommand()
         output.ToString().Should().NotContain(RootDescription);
     }
 
+    [Fact]
+    public void The_users_can_set_max_width()
+    {
+        string firstPart = new('a', count: 50);
+        string secondPart = new('b', count: 50);
+        string description = firstPart + secondPart;
+
+        RootCommand rootCommand = new(description);
+        rootCommand.Options.Clear();
+        rootCommand.Options.Add(new HelpOption()
+        {
+            Action = new HelpAction()
+            {
+                MaxWidth = 2 /* each line starts with two spaces */ + description.Length / 2
+            }
+        });
+        StringWriter output = new ();
+
+        rootCommand.Parse("--help").Invoke(new() { Output = output });
+
+        output.ToString().Should().NotContain(description);
+        output.ToString().Should().Contain($"  {firstPart}{Environment.NewLine}");
+        output.ToString().Should().Contain($"  {secondPart}{Environment.NewLine}");
+    }
+
     private sealed class CustomizedHelpAction : SynchronousCommandLineAction
     {
         internal const string CustomUsageText = "This is custom command usage example.";

src/System.CommandLine/Help/HelpAction.cs

@@ -8,13 +8,47 @@ namespace System.CommandLine.Help
     public sealed class HelpAction : SynchronousCommandLineAction
     {
         private HelpBuilder? _builder;
+        private int _maxWidth = -1;
+
+        /// <summary>
+        /// The maximum width in characters after which help output is wrapped.
+        /// </summary>
+        /// <remarks>It defaults to <see cref="Console.WindowWidth"/>.</remarks>
+        public int MaxWidth
+        { 
+            get
+            {
+                if (_maxWidth < 0)
+                {
+                    try
+                    {
+                        _maxWidth = Console.IsOutputRedirected ? int.MaxValue : Console.WindowWidth;
+                    }
+                    catch (Exception)
+                    {
+                        _maxWidth = int.MaxValue;
+                    }
+                }
+
+                return _maxWidth;
+            }
+            set
+            {
+                if (value <= 0)
+                {
+                    throw new ArgumentOutOfRangeException(nameof(value));
+                }
+
+                _maxWidth = value;
+            }
+        }
 
         /// <summary>
         /// Specifies an <see cref="Builder"/> to be used to format help output when help is requested.
         /// </summary>
         internal HelpBuilder Builder
         {
-            get => _builder ??= new HelpBuilder(Console.IsOutputRedirected ? int.MaxValue : Console.WindowWidth);
+            get => _builder ??= new HelpBuilder(MaxWidth);
             set => _builder = value ?? throw new ArgumentNullException(nameof(value));
         }
 
@@ -32,4 +66,4 @@ public override int Invoke(ParseResult parseResult)
             return 0;
         }
     }
-}                                                                                                                                                                                                         
+}