Add user option to control new feature.

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

@@ -249,6 +249,27 @@ public C(string s)
 //]
     }
 }
+";
+
+        private static readonly string s_preferCoalesceExpression = @"
+using System;
+
+class C
+{
+    private string s;
+
+    public C(string s)
+    {
+//[
+        // Prefer:
+        var v = x ?? y;
+
+        // Over:
+        var v = x != null ? x : y; // and
+        var v = x == null ? y : x;
+//]
+    }
+}
 ";
 
         private static readonly string s_preferConditionalDelegateCall = @"
@@ -598,6 +619,7 @@ internal StyleViewModel(OptionSet optionSet, IServiceProvider serviceProvider) :
             // Null preferences.
             CodeStyleItems.Add(new SimpleCodeStyleOptionViewModel(CodeStyleOptions.PreferThrowExpression, CSharpVSResources.Prefer_throw_expression, s_preferThrowExpression, s_preferThrowExpression, this, optionSet, nullCheckingGroupTitle));
             CodeStyleItems.Add(new SimpleCodeStyleOptionViewModel(CSharpCodeStyleOptions.PreferConditionalDelegateCall, CSharpVSResources.Prefer_conditional_delegate_call, s_preferConditionalDelegateCall, s_preferConditionalDelegateCall, this, optionSet, nullCheckingGroupTitle));
+            CodeStyleItems.Add(new SimpleCodeStyleOptionViewModel(CodeStyleOptions.PreferCoalesceExpression, ServicesVSResources.Prefer_coalesce_expression, s_preferCoalesceExpression, s_preferCoalesceExpression, this, optionSet, nullCheckingGroupTitle));
         }
     }
 }
\ No newline at end of file

src/VisualStudio/Core/Def/ServicesVSResources.Designer.cs

@@ -1365,6 +1365,15 @@ internal class ServicesVSResources {
             }
         }
         
+        /// <summary>
+        ///   Looks up a localized string similar to Prefer coalesce expression.
+        /// </summary>
+        internal static string Prefer_coalesce_expression {
+            get {
+                return ResourceManager.GetString("Prefer_coalesce_expression", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Looks up a localized string similar to Prefer framework type.
         /// </summary>

src/VisualStudio/Core/Def/ServicesVSResources.resx

@@ -804,4 +804,7 @@ Additional information: {1}</value>
   <data name="This_item_cannot_be_deleted_because_it_is_used_by_an_existing_Naming_Rule" xml:space="preserve">
     <value>This item cannot be deleted because it is used by an existing Naming Rule.</value>
   </data>
+  <data name="Prefer_coalesce_expression" xml:space="preserve">
+    <value>Prefer coalesce expression</value>
+  </data>
 </root>
\ No newline at end of file