Add prefer trailing commas code-style option

src/VisualStudio/CSharp/Impl/EditorConfigSettings/DataProvider/CodeStyle/CSharpCodeStyleSettingsProvider.cs

@@ -151,6 +151,7 @@ private IEnumerable<CodeStyleSetting> GetExpressionCodeStyleOptions(AnalyzerConf
             yield return CodeStyleSetting.Create(CSharpCodeStyleOptions.PreferRangeOperator, description: ServicesVSResources.Prefer_range_operator, editorConfigOptions, visualStudioOptions, updaterService, FileName);
             yield return CodeStyleSetting.Create(CSharpCodeStyleOptions.ImplicitObjectCreationWhenTypeIsApparent, description: CSharpVSResources.Prefer_implicit_object_creation_when_type_is_apparent, editorConfigOptions, visualStudioOptions, updaterService, FileName);
             yield return CodeStyleSetting.Create(CSharpCodeStyleOptions.PreferTupleSwap, description: ServicesVSResources.Prefer_tuple_swap, editorConfigOptions, visualStudioOptions, updaterService, FileName);
+            yield return CodeStyleSetting.Create(CSharpCodeStyleOptions.PreferTrailingCommas, description: ServicesVSResources.Prefer_trailing_commas, editorConfigOptions, visualStudioOptions, updaterService, FileName);
         }
 
         private IEnumerable<CodeStyleSetting> GetPatternMatchingCodeStyleOptions(AnalyzerConfigOptions editorConfigOptions, OptionSet visualStudioOptions, OptionUpdater updaterService)

src/VisualStudio/CSharp/Impl/Options/AutomationObject/AutomationObject.Style.cs

@@ -422,5 +422,11 @@ public string Style_NamespaceDeclarations
             get { return GetXmlOption(CSharpCodeStyleOptions.NamespaceDeclarations); }
             set { SetXmlOption(CSharpCodeStyleOptions.NamespaceDeclarations, value); }
         }
+
+        public string Style_PreferTrailingCommas
+        {
+            get { return GetXmlOption(CSharpCodeStyleOptions.PreferTrailingCommas); }
+            set { SetXmlOption(CSharpCodeStyleOptions.PreferTrailingCommas, value); }
+        }
     }
 }

src/VisualStudio/CSharp/Impl/Options/Formatting/StyleViewModel.cs

@@ -1118,6 +1118,26 @@ void M2(string[] args)
 //]
     }}
 }}
+";
+
+        private static readonly string s_preferTrailingCommas = $@"
+//[
+    // {ServicesVSResources.Prefer_colon}
+    enum E
+    {{
+        A,
+        B,
+    }}
+//]
+//[
+    // {ServicesVSResources.Over_colon}
+    enum E
+    {{
+        A,
+        B,
+    }}
+//]
+}}
 ";
 
         private static readonly string s_preferIsNullOverReferenceEquals = $@"
@@ -2138,6 +2158,8 @@ internal StyleViewModel(OptionStore optionStore, IServiceProvider serviceProvide
 
             CodeStyleItems.Add(new BooleanCodeStyleOptionViewModel(CSharpCodeStyleOptions.PreferTupleSwap, ServicesVSResources.Prefer_tuple_swap, s_preferTupleSwap, s_preferTupleSwap, this, optionStore, expressionPreferencesGroupTitle));
 
+            CodeStyleItems.Add(new BooleanCodeStyleOptionViewModel(CSharpCodeStyleOptions.PreferTrailingCommas, ServicesVSResources.Prefer_trailing_commas, s_preferTrailingCommas, s_preferTrailingCommas, this, optionStore, expressionPreferencesGroupTitle));
+
             AddExpressionBodyOptions(optionStore, expressionPreferencesGroupTitle);
             AddUnusedValueOptions(optionStore, expressionPreferencesGroupTitle);
 

src/VisualStudio/Core/Def/ServicesVSResources.resx

@@ -1903,4 +1903,7 @@ Additional information: {1}</value>
   <data name="Prefer_method_group_conversion" xml:space="preserve">
     <value>Prefer method group conversion</value>
   </data>
+  <data name="Prefer_trailing_commas" xml:space="preserve">
+    <value>Prefer trailing commas</value>
+  </data>
 </root>

src/Workspaces/CSharp/Portable/CodeGeneration/EnumMemberGenerator.cs

@@ -7,6 +7,7 @@
 using System.Linq;
 using System.Threading;
 using Microsoft.CodeAnalysis.CodeGeneration;
+using Microsoft.CodeAnalysis.CSharp.CodeStyle;
 using Microsoft.CodeAnalysis.CSharp.Extensions;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.Shared.Utilities;
@@ -25,22 +26,19 @@ internal static EnumDeclarationSyntax AddEnumMemberTo(EnumDeclarationSyntax dest
 
             var member = GenerateEnumMemberDeclaration(enumMember, destination, options, cancellationToken);
 
-            if (members.Count == 0)
-            {
-                members.Add(member);
-            }
-            else if (members.LastOrDefault().Kind() == SyntaxKind.CommaToken)
-            {
-                members.Add(member);
-                members.Add(SyntaxFactory.Token(SyntaxKind.CommaToken));
-            }
-            else
+            if (members.Count > 0 && !members[^1].IsKind(SyntaxKind.CommaToken))
             {
                 var lastMember = members.Last();
                 var trailingTrivia = lastMember.GetTrailingTrivia();
                 members[members.Count - 1] = lastMember.WithTrailingTrivia();
                 members.Add(SyntaxFactory.Token(SyntaxKind.CommaToken).WithTrailingTrivia(trailingTrivia));
-                members.Add(member);
+            }
+
+            members.Add(member);
+
+            if (options.Preferences.Options.GetOption(CSharpCodeStyleOptions.PreferTrailingCommas).Value)
+            {
+                members.Add(SyntaxFactory.Token(SyntaxKind.CommaToken));
             }
 
             return destination.EnsureOpenAndCloseBraceTokens()

src/Workspaces/SharedUtilitiesAndExtensions/Compiler/CSharp/CodeStyle/CSharpCodeStyleOptions.cs

@@ -345,6 +345,12 @@ private static Option2<CodeStyleOption2<NamespaceDeclarationPreference>> CreateN
             "csharp_style_prefer_method_group_conversion",
             "TextEditor.CSharp.Specific.PreferMethodGroupConversion");
 
+        public static readonly Option2<CodeStyleOption2<bool>> PreferTrailingCommas = CreateOption(
+            CSharpCodeStyleOptionGroups.ExpressionLevelPreferences, nameof(PreferTrailingCommas),
+            defaultValue: s_trueWithSuggestionEnforcement,
+            "csharp_style_prefer_trailing_commas",
+            $"TextEditor.CSharp.Specific.{nameof(PreferTrailingCommas)}");
+
 #if false
 
         public static readonly Option2<CodeStyleOption2<bool>> VarElsewhere = CreateOption(