Add help text on error

Author: hadzhiyski

src/CommandLine/Core/SpecificationPropertyRules.cs

@@ -1,9 +1,10 @@
 // Copyright 2005-2015 Giacomo Stelluti Scala & Contributors. All rights reserved. See License.md in the project root for license information.
 
+using CSharpx;
+
 using System;
 using System.Collections.Generic;
 using System.Linq;
-using CSharpx;
 
 namespace CommandLine.Core
 {
@@ -46,7 +47,7 @@ group o by o.Option.Group.GetValueOrDefault(null) into g
 
                 if (errorGroups.Any())
                 {
-                    return errorGroups.Select(gr => new MissingGroupOptionError(gr.Key));
+                    return errorGroups.Select(gr => new MissingGroupOptionError(gr.Key, gr.Select(g => new NameInfo(g.Option.ShortName, g.Option.LongName))));
                 }
 
                 return Enumerable.Empty<Error>();

src/CommandLine/Error.cs

@@ -1,6 +1,7 @@
 // Copyright 2005-2015 Giacomo Stelluti Scala & Contributors. All rights reserved. See License.md in the project root for license information.
 
 using System;
+using System.Collections.Generic;
 
 namespace CommandLine
 {
@@ -69,7 +70,11 @@ public enum ErrorType
         /// <summary>
         /// Value of <see cref="CommandLine.InvalidAttributeConfigurationError"/> type.
         /// </summary>
-        InvalidAttributeConfigurationError
+        InvalidAttributeConfigurationError,
+        /// <summary>
+        /// Value of <see cref="CommandLine.MissingGroupOptionError"/> type.
+        /// </summary>
+        MissingGroupOptionError
 
     }
 
@@ -532,16 +537,23 @@ public sealed class MissingGroupOptionError : Error
         public const string ErrorMessage = "At least one option in a group must have value.";
 
         private readonly string group;
+        private readonly IEnumerable<NameInfo> names;
 
-        internal MissingGroupOptionError(string group)
-            : base(ErrorType.HelpRequestedError, true)
+        internal MissingGroupOptionError(string group, IEnumerable<NameInfo> names)
+            : base(ErrorType.MissingGroupOptionError)
         {
             this.group = group;
+            this.names = names;
         }
 
         public string Group
         {
             get { return group; }
         }
+
+        public IEnumerable<NameInfo> Names
+        {
+            get { return names; }
+        }
     }
 }

src/CommandLine/Text/SentenceBuilder.cs

@@ -1,10 +1,11 @@
 // Copyright 2005-2015 Giacomo Stelluti Scala & Contributors. All rights reserved. See License.md in the project root for license information.
 
+using CommandLine.Infrastructure;
+
 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
-using CommandLine.Infrastructure;
 
 namespace CommandLine.Text
 {
@@ -41,7 +42,7 @@ public static SentenceBuilder Create()
         /// <summary>
         /// Gets a delegate that returns usage text block heading text.
         /// </summary>
-        public abstract Func<string> UsageHeadingText { get; } 
+        public abstract Func<string> UsageHeadingText { get; }
 
         /// <summary>
         /// Get a delegate that returns the help text of help command.
@@ -53,7 +54,7 @@ public static SentenceBuilder Create()
         /// Get a delegate that returns the help text of vesion command.
         /// The delegates must accept a boolean that is equal <value>true</value> for options; otherwise <value>false</value> for verbs.
         /// </summary>
-        public abstract Func<bool, string> VersionCommandText { get; } 
+        public abstract Func<bool, string> VersionCommandText { get; }
 
         /// <summary>
         /// Gets a delegate that handles singular error formatting.
@@ -67,7 +68,7 @@ public static SentenceBuilder Create()
         /// </summary>
         public abstract Func<IEnumerable<MutuallyExclusiveSetError>, string> FormatMutuallyExclusiveSetErrors { get; }
 
-        private class DefaultSentenceBuilder : SentenceBuilder 
+        private class DefaultSentenceBuilder : SentenceBuilder
         {
             public override Func<string> RequiredWord
             {
@@ -140,6 +141,13 @@ public override Func<Error, string> FormatError
                                 case ErrorType.SetValueExceptionError:
                                     var setValueError = (SetValueExceptionError)error;
                                     return "Error setting value to option '".JoinTo(setValueError.NameInfo.NameText, "': ", setValueError.Exception.Message);
+                                case ErrorType.MissingGroupOptionError:
+                                    var missingGroupOptionError = (MissingGroupOptionError)error;
+                                    return "At least one option from group '".JoinTo(
+                                        missingGroupOptionError.Group,
+                                        "' (",
+                                        string.Join(", ", missingGroupOptionError.Names.Select(n => n.NameText)),
+                                        ") is required.");
                             }
                             throw new InvalidOperationException();
                         };
@@ -153,8 +161,8 @@ public override Func<IEnumerable<MutuallyExclusiveSetError>, string> FormatMutua
                     return errors =>
                     {
                         var bySet = from e in errors
-                                group e by e.SetName into g
-                                select new { SetName = g.Key, Errors = g.ToList() };
+                                    group e by e.SetName into g
+                                    select new { SetName = g.Key, Errors = g.ToList() };
 
                         var msgs = bySet.Select(
                             set =>
@@ -169,7 +177,7 @@ group e by e.SetName into g
                                     (from x in
                                          (from s in bySet where !s.SetName.Equals(set.SetName) from e in s.Errors select e)
                                         .Distinct()
-                                    select "'".JoinTo(x.NameInfo.NameText, "', ")).ToArray());
+                                     select "'".JoinTo(x.NameInfo.NameText, "', ")).ToArray());
 
                                 return
                                     new StringBuilder("Option")