Display appropriate separator when writing default enumerable values in HelpText

Fix commandlineparser#490

Author: gfs

Diff for: src/CommandLine/Text/HelpText.cs

@@ -971,8 +971,11 @@ specification is OptionSpecification optionSpecification &&
             if (addEnumValuesToHelpText && specification.EnumValues.Any())
                 optionHelpText += " Valid values: " + string.Join(", ", specification.EnumValues);
 
+            var separator = (specification is OptionSpecification optionSpecification && optionSpecification.Separator != '\0')
+                ? optionSpecification.Separator
+                : ' ';
             specification.DefaultValue.Do(
-                defaultValue => optionHelpText = "(Default: {0}) ".FormatInvariant(FormatDefaultValue(defaultValue)) + optionHelpText);
+                defaultValue => optionHelpText = "(Default: {0}) ".FormatInvariant(FormatDefaultValue(defaultValue, separator)) + optionHelpText);
 
             var optionGroupSpecification = GetOptionGroupSpecification();
 
@@ -1106,7 +1109,7 @@ private int GetMaxValueLength(ValueSpecification spec)
             return specLength;
         }
 
-        private static string FormatDefaultValue<T>(T value)
+        private static string FormatDefaultValue<T>(T value, char separator)
         {
             if (value is bool)
                 return value.ToStringLocal().ToLowerInvariant();
@@ -1122,7 +1125,7 @@ private static string FormatDefaultValue<T>(T value)
             foreach (var item in asEnumerable)
                 builder
                     .Append(item.ToStringLocal())
-                    .Append(" ");
+                    .Append(separator);
 
             return builder.Length > 0
                 ? builder.ToString(0, builder.Length - 1)

Diff for: tests/CommandLine.Tests/Fakes/Options_With_Default_Set_To_Sequence_With_Separator.cs

@@ -0,0 +1,18 @@
+// Copyright 2005-2015 Giacomo Stelluti Scala & Contributors. All rights reserved. See License.md in the project root for license information.
+
+using System.Collections.Generic;
+
+namespace CommandLine.Tests.Fakes
+{
+    class Options_With_Default_Set_To_Sequence_With_Separator
+    {
+        [Option('z', "strseq", Default = new[] { "a", "b", "c" }, Separator = ',')]
+        public IEnumerable<string> StringSequence { get; set; }
+
+        [Option('y', "intseq", Default = new[] { 1, 2, 3 }, Separator = ',')]
+        public IEnumerable<int> IntSequence { get; set; }
+
+        [Option('q', "dblseq", Default = new[] { 1.1, 2.2, 3.3 }, Separator = ',')]
+        public IEnumerable<int> DoubleSequence { get; set; }
+    }
+}

Diff for: tests/CommandLine.Tests/Unit/Text/HelpTextTests.cs

@@ -849,6 +849,33 @@ public void Options_should_be_separated_by_spaces()
 
             // Teardown
         }
+        
+        [Fact]
+        public void Options_should_be_separated_by_separator()
+        {
+            // Fixture setup
+            var handlers = new CultureInfo("en-US").MakeCultureHandlers();
+            var fakeResult =
+                new NotParsed<Options_With_Default_Set_To_Sequence_With_Separator>(
+                    typeof(Options_With_Default_Set_To_Sequence_With_Separator).ToTypeInfo(),
+                    Enumerable.Empty<Error>()
+                );
+
+            // Exercize system
+            handlers.ChangeCulture();
+            var helpText = HelpText.AutoBuild(fakeResult);
+            handlers.ResetCulture();
+
+            // Verify outcome
+            var text = helpText.ToString();
+            var lines = text.ToLines().TrimStringArray();
+            
+            lines[3].Should().Be("-z, --strseq    (Default: a,b,c)");
+            lines[5].Should().Be("-y, --intseq    (Default: 1,2,3)");
+            lines[7].Should().Be("-q, --dblseq    (Default: 1.1,2.2,3.3)");
+
+            // Teardown
+        }
 
         [Fact]
         public void Options_Should_Render_OptionGroup_In_Parenthesis_When_Available()