Fix issue #104 of nullable enum

src/CommandLine/Core/Specification.cs

@@ -4,6 +4,7 @@
 using System.Collections.Generic;
 using System.Linq;
 using System.Reflection;
+using CommandLine.Infrastructure;
 using CSharpx;
 
 namespace CommandLine.Core
@@ -115,9 +116,8 @@ public static Specification FromProperty(PropertyInfo property)
             if (oa.Count() == 1)
             {
                 var spec = OptionSpecification.FromAttribute(oa.Single(), property.PropertyType,
-                    property.PropertyType.GetTypeInfo().IsEnum
-                        ? Enum.GetNames(property.PropertyType)
-                        : Enumerable.Empty<string>());
+                    ReflectionHelper.GetNamesOfEnum(property.PropertyType)); 
+
                 if (spec.ShortName.Length == 0 && spec.LongName.Length == 0)
                 {
                     return spec.WithLongName(property.Name.ToLowerInvariant());

src/CommandLine/Infrastructure/ReflectionHelper.cs

@@ -45,10 +45,10 @@ public static Maybe<TAttribute> GetAttribute<TAttribute>()
             // Test support
             if (_overrides != null)
             {
-                return 
+                return
                     _overrides.ContainsKey(typeof(TAttribute)) ?
                         Maybe.Just((TAttribute)_overrides[typeof(TAttribute)]) :
-                        Maybe.Nothing< TAttribute>();
+                        Maybe.Nothing<TAttribute>();
             }
 
             var assembly = GetExecutingOrEntryAssembly();
@@ -84,7 +84,7 @@ public static bool IsFSharpOptionType(Type type)
 
         public static T CreateDefaultImmutableInstance<T>(Type[] constructorTypes)
         {
-            var t = typeof(T);            
+            var t = typeof(T);
             return (T)CreateDefaultImmutableInstance(t, constructorTypes);
         }
 
@@ -100,7 +100,17 @@ private static Assembly GetExecutingOrEntryAssembly()
         {
             //resolve issues of null EntryAssembly in Xunit Test #392,424,389
             //return Assembly.GetEntryAssembly();
-            return Assembly.GetEntryAssembly()??Assembly.GetCallingAssembly();
+            return Assembly.GetEntryAssembly() ?? Assembly.GetCallingAssembly();
+        }
+
+       public static IEnumerable<string> GetNamesOfEnum(Type t)
+        {
+            if (t.IsEnum)
+                return Enum.GetNames(t);
+            Type u = Nullable.GetUnderlyingType(t);
+            if (u != null && u.IsEnum)
+                return Enum.GetNames(u);
+            return Enumerable.Empty<string>();
         }
     }
-}
+}

tests/CommandLine.Tests/Fakes/Options_With_Nullable_Enum_Having_HelpText.cs

@@ -0,0 +1,13 @@
+// Copyright 2005-2015 Giacomo Stelluti Scala & Contributors. All rights reserved. See License.md in the project root for license information.
+
+namespace CommandLine.Tests.Fakes
+{
+    class Options_With_Nullable_Enum_Having_HelpText
+    {
+        [Option(HelpText = "Define a string value here.")]
+        public string StringValue { get; set; }
+
+        [Option(HelpText="Define a enum value here.")]
+        public Shapes? Shape { get; set; }
+    }
+}

tests/CommandLine.Tests/Unit/Issue104Tests.cs

@@ -0,0 +1,68 @@
+using System.Linq;
+using CommandLine.Tests.Fakes;
+using CommandLine.Text;
+using FluentAssertions;
+using Xunit;
+using Xunit.Abstractions;
+
+//Issue #104
+//When outputting HelpText, the code will correctly list valid values for enum type options. However, if the option is a nullable enum type, then it will not list the valid values.
+
+namespace CommandLine.Tests.Unit
+{
+    public class Issue104Tests
+    {
+
+        [Fact]
+        public void Create_instance_with_enum_options_enabled_and_nullable_enum()
+        {
+            // Fixture setup
+            // Exercize system 
+            var sut = new HelpText { AddDashesToOption = true, AddEnumValuesToHelpText = true, MaximumDisplayWidth = 80 }
+                .AddPreOptionsLine("pre-options")
+                .AddOptions(new NotParsed<Options_With_Nullable_Enum_Having_HelpText>(TypeInfo.Create(typeof(Options_With_Enum_Having_HelpText)), Enumerable.Empty<Error>()))
+                .AddPostOptionsLine("post-options");
+
+            // Verify outcome
+
+            var lines = sut.ToString().ToNotEmptyLines().TrimStringArray();
+            lines[0].Should().BeEquivalentTo("pre-options");
+            lines[1].Should().BeEquivalentTo("--stringvalue    Define a string value here.");
+            lines[2].Should().BeEquivalentTo("--shape          Define a enum value here. Valid values: Circle, Square,");
+            lines[3].Should().BeEquivalentTo("Triangle");
+            lines[4].Should().BeEquivalentTo("--help           Display this help screen.");
+            lines[5].Should().BeEquivalentTo("--version        Display version information.");
+            lines[6].Should().BeEquivalentTo("post-options");
+            // Teardown
+        }
+
+        [Fact]
+        public void Help_with_enum_options_enabled_and_nullable_enum()
+        {
+            // Fixture setup
+            // Exercize system 
+            var args = "--help".Split();
+            var sut = new Parser(config => config.HelpWriter = null);
+            var parserResult = sut.ParseArguments<Options_With_Nullable_Enum_Having_HelpText>(args);
+            HelpText helpText = null;
+            parserResult.WithNotParsed(errors =>
+            {
+                // Use custom help text to ensure valid enum values are displayed
+                helpText = HelpText.AutoBuild(parserResult);
+                helpText.AddEnumValuesToHelpText = true;
+                helpText.AddOptions(parserResult);
+            });
+
+            // Verify outcome
+
+            var lines = helpText.ToString().ToNotEmptyLines().TrimStringArray();
+            lines[2].Should().BeEquivalentTo("--stringvalue    Define a string value here.");
+            lines[3].Should().BeEquivalentTo("--shape          Define a enum value here. Valid values: Circle, Square,");
+            lines[4].Should().BeEquivalentTo("Triangle");
+            lines[5].Should().BeEquivalentTo("--help           Display this help screen.");
+            lines[6].Should().BeEquivalentTo("--version        Display version information.");
+            // Teardown
+        }
+    }
+
+}