Do not dispose ParserSettings.HelpWriter in ParserSettings.Dispose (fix for #355)

src/CommandLine/ParserSettings.cs

@@ -92,6 +92,9 @@ public CultureInfo ParsingCulture
         /// Gets or sets the <see cref="System.IO.TextWriter"/> used for help method output.
         /// Setting this property to null, will disable help screen.
         /// </summary>
+        /// <remarks>
+        /// It is the caller's responsibility to dispose or close the <see cref="TextWriter"/>.
+        /// </remarks>
         public TextWriter HelpWriter
         {
             get { return helpWriter; }
@@ -165,11 +168,7 @@ private void Dispose(bool disposing)
 
             if (disposing)
             {
-                if (HelpWriter != null)
-                {
-                    helpWriter.Dispose();
-                    helpWriter = null;
-                }
+                // Do not dispose HelpWriter. It is the caller's responsibility.
 
                 disposed = true;
             }

tests/CommandLine.Tests/CommandLine.Tests.csproj

@@ -116,6 +116,7 @@
     <Compile Include="Unit\Infrastructure\FSharpOptionHelperTests.cs" />
     <Compile Include="Unit\Core\ReflectionExtensions.cs" />
     <Compile Include="Unit\ParserResultExtensionsTests.cs" />
+    <Compile Include="Unit\ParserSettingsTests.cs" />
     <Compile Include="Unit\ParserTests.cs" />
     <Compile Include="Unit\Text\HelpTextTests.cs" />
     <Compile Include="Unit\UnParserExtensionsTests.cs" />

tests/CommandLine.Tests/Unit/ParserSettingsTests.cs

@@ -0,0 +1,44 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using FluentAssertions;
+using Xunit;
+
+namespace CommandLine.Tests.Unit
+{
+    public class ParserSettingsTests
+    {
+        public class DisposeTrackingStringWriter : StringWriter
+        {
+            public DisposeTrackingStringWriter()
+            {
+                Disposed = false;
+            }
+
+            public bool Disposed { get; private set; }
+
+            protected override void Dispose(bool disposing)
+            {
+                Disposed = true;
+                base.Dispose(disposing);
+            }
+        }
+
+        [Fact]
+        public void Disposal_does_not_dispose_HelpWriter()
+        {
+            using (DisposeTrackingStringWriter textWriter = new DisposeTrackingStringWriter())
+            {
+                using (ParserSettings parserSettings = new ParserSettings())
+                {
+                    parserSettings.HelpWriter = textWriter;
+                }
+
+                textWriter.Disposed.Should().BeFalse("not disposed");
+            }
+        }
+    }
+}