Extract helper for generating local names.

src/Features/Core/Portable/ConvertForToForEach/AbstractConvertForToForEachCodeRefactoringProvider.cs

@@ -307,7 +307,8 @@ bool IterationVariableIsUsedForMoreThanCollectionIndex(SyntaxNode current)
 
             if (foreachIdentifier.RawKind == 0)
             {
-                foreachIdentifier = generator.Identifier("v").WithAdditionalAnnotations(RenameAnnotation.Create());
+                foreachIdentifier = semanticFacts.GenerateUniqueName(semanticModel, forStatement, "v", cancellationToken)
+                                                 .WithAdditionalAnnotations(RenameAnnotation.Create());
             }
 
             var foreachIdentifierName = generator.IdentifierName(foreachIdentifier).WithoutTrivia().WithoutAnnotations();

src/Features/Core/Portable/IntroduceVariable/AbstractIntroduceVariableService.cs

@@ -221,20 +221,13 @@ private CodeAction CreateAction(State state, bool allOccurrences, bool isConstan
             SyntaxNode container,
             CancellationToken cancellationToken)
         {
-            var syntaxFacts = document.Document.GetLanguageService<ISyntaxFactsService>();
-            var semanticFacts = document.Document.GetLanguageService<ISemanticFactsService>();
-
             var semanticModel = document.SemanticModel;
-            var existingSymbols = semanticModel.GetExistingSymbols(container, cancellationToken);
 
+            var semanticFacts = document.Document.GetLanguageService<ISemanticFactsService>();
             var baseName = semanticFacts.GenerateNameForExpression(
                 semanticModel, expression, capitalize: isConstant, cancellationToken: cancellationToken);
-            var reservedNames = semanticModel.LookupSymbols(expression.SpanStart)
-                                             .Select(s => s.Name)
-                                             .Concat(existingSymbols.Select(s => s.Name));
 
-            return syntaxFacts.ToIdentifierToken(
-                NameGenerator.EnsureUniqueness(baseName, reservedNames, syntaxFacts.IsCaseSensitive));
+            return semanticFacts.GenerateUniqueName(semanticModel, container, baseName, cancellationToken);
         }
 
         protected ISet<TExpressionSyntax> FindMatches(

src/Workspaces/CSharp/Portable/LanguageServices/CSharpSemanticFactsService.cs

@@ -8,6 +8,7 @@
 using Microsoft.CodeAnalysis.CSharp.Extensions;
 using Microsoft.CodeAnalysis.CSharp.Extensions.ContextQuery;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Host;
 using Microsoft.CodeAnalysis.LanguageServices;
 using Microsoft.CodeAnalysis.PooledObjects;
 using Microsoft.CodeAnalysis.Shared.Extensions;
@@ -15,10 +16,12 @@
 
 namespace Microsoft.CodeAnalysis.CSharp
 {
-    internal class CSharpSemanticFactsService : ISemanticFactsService
+    internal class CSharpSemanticFactsService : AbstractSemanticFactsService, ISemanticFactsService
     {
         internal static readonly CSharpSemanticFactsService Instance = new CSharpSemanticFactsService();
 
+        protected override ISyntaxFactsService SyntaxFactsService => CSharpSyntaxFactsService.Instance;
+
         private CSharpSemanticFactsService()
         {
         }

src/Workspaces/Core/Portable/LanguageServices/SemanticsFactsService/ISemanticFactsService.cs

@@ -2,8 +2,11 @@
 
 using System.Collections.Generic;
 using System.Collections.Immutable;
+using System.Linq;
 using System.Threading;
 using Microsoft.CodeAnalysis.Host;
+using Microsoft.CodeAnalysis.Shared.Extensions;
+using Microsoft.CodeAnalysis.Shared.Utilities;
 
 namespace Microsoft.CodeAnalysis.LanguageServices
 {
@@ -101,5 +104,28 @@ internal interface ISemanticFactsService : ILanguageService
         IEnumerable<ISymbol> GetDeclaredSymbols(SemanticModel semanticModel, SyntaxNode memberDeclaration, CancellationToken cancellationToken);
 
         SymbolInfo GetSymbolInfo(SemanticModel semanticModel, SyntaxNode node, SyntaxToken token, CancellationToken cancellationToken);
+
+        SyntaxToken GenerateUniqueName(SemanticModel semanticModel, SyntaxNode location, string baseName, CancellationToken cancellationToken);
+    }
+
+    internal abstract class AbstractSemanticFactsService
+    {
+        protected abstract ISyntaxFactsService SyntaxFactsService { get; }
+
+        public SyntaxToken GenerateUniqueName(SemanticModel semanticModel, SyntaxNode location, string baseName, CancellationToken cancellationToken)
+        {
+            var syntaxFacts = this.SyntaxFactsService;
+
+            var container = location.AncestorsAndSelf().FirstOrDefault(
+                a => syntaxFacts.IsExecutableBlock(a) || syntaxFacts.IsMethodBody(a)) ?? location;
+            var existingSymbols = semanticModel.GetExistingSymbols(container, cancellationToken);
+
+            var reservedNames = semanticModel.LookupSymbols(container.SpanStart)
+                                             .Select(s => s.Name)
+                                             .Concat(existingSymbols.Select(s => s.Name));
+
+            return syntaxFacts.ToIdentifierToken(
+                NameGenerator.EnsureUniqueness(baseName, reservedNames, syntaxFacts.IsCaseSensitive));
+        }
     }
 }

src/Workspaces/VisualBasic/Portable/LanguageServices/VisualBasicSemanticFactsService.vb

@@ -21,10 +21,13 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
     End Class
 
     Friend Class VisualBasicSemanticFactsService
+        Inherits AbstractSemanticFactsService
         Implements ISemanticFactsService
 
         Public Shared ReadOnly Instance As New VisualBasicSemanticFactsService()
 
+        Protected Overrides ReadOnly Property SyntaxFactsService As ISyntaxFactsService = VisualBasicSyntaxFactsService.Instance
+
         Private Sub New()
         End Sub
 
@@ -294,5 +297,9 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
         Public Function GetSymbolInfo(semanticModel As SemanticModel, node As SyntaxNode, token As SyntaxToken, cancellationToken As CancellationToken) As SymbolInfo Implements ISemanticFactsService.GetSymbolInfo
             Return semanticModel.GetSymbolInfo(node, cancellationToken)
         End Function
+
+        Private Function ISemanticFactsService_GenerateUniqueName(semanticModel As SemanticModel, location As SyntaxNode, baseName As String, cancellationToken As CancellationToken) As SyntaxToken Implements ISemanticFactsService.GenerateUniqueName
+            Return MyBase.GenerateUniqueName(semanticModel, location, baseName, cancellationToken)
+        End Function
     End Class
 End Namespace