Breaking out refactoring helpers into core api vs service

src/Workspaces/SharedUtilitiesAndExtensions/Compiler/CSharp/CSharpCompilerExtensions.projitems

@@ -97,6 +97,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Services\Precedence\AbstractCSharpPrecedenceService.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Services\Precedence\CSharpPatternPrecedenceService.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Services\Precedence\CSharpExpressionPrecedenceService.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Services\RefactoringHelpers\CSharpRefactoringHelpers.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Services\SelectedMembers\CSharpSelectedMembers.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Services\SemanticFacts\CSharpSemanticFacts.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Services\SyntaxFacts\CSharpAccessibilityFacts.cs" />

src/Workspaces/SharedUtilitiesAndExtensions/Compiler/CSharp/Services/RefactoringHelpers/CSharpRefactoringHelpers.cs

@@ -0,0 +1,113 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
+using System.Linq;
+using Microsoft.CodeAnalysis.CodeRefactorings;
+using Microsoft.CodeAnalysis.CSharp.Extensions;
+using Microsoft.CodeAnalysis.CSharp.LanguageService;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.LanguageService;
+using Microsoft.CodeAnalysis.Shared.Extensions;
+using Microsoft.CodeAnalysis.Text;
+using Roslyn.Utilities;
+
+namespace Microsoft.CodeAnalysis.CSharp.CodeRefactorings;
+
+internal sealed class CSharpRefactoringHelpers : AbstractRefactoringHelpers<ExpressionSyntax, ArgumentSyntax, ExpressionStatementSyntax>
+{
+    public static readonly CSharpRefactoringHelpers Instance = new();
+
+    private CSharpRefactoringHelpers()
+    {
+    }
+
+    protected override IHeaderFacts HeaderFacts => CSharpHeaderFacts.Instance;
+    protected override ISyntaxFacts SyntaxFacts => CSharpSyntaxFacts.Instance;
+
+    public override bool IsBetweenTypeMembers(SourceText sourceText, SyntaxNode root, int position, [NotNullWhen(true)] out SyntaxNode? typeDeclaration)
+    {
+        var token = root.FindToken(position);
+        var typeDecl = token.GetAncestor<TypeDeclarationSyntax>();
+        typeDeclaration = typeDecl;
+
+        if (typeDecl == null)
+            return false;
+
+        RoslynDebug.AssertNotNull(typeDeclaration);
+        if (position < typeDecl.OpenBraceToken.Span.End ||
+            position > typeDecl.CloseBraceToken.Span.Start)
+        {
+            return false;
+        }
+
+        var line = sourceText.Lines.GetLineFromPosition(position);
+        if (!line.IsEmptyOrWhitespace())
+            return false;
+
+        var member = typeDecl.Members.FirstOrDefault(d => d.FullSpan.Contains(position));
+        if (member == null)
+        {
+            // There are no members, or we're after the last member.
+            return true;
+        }
+        else
+        {
+            // We're within a member.  Make sure we're in the leading whitespace of
+            // the member.
+            if (position < member.SpanStart)
+            {
+                foreach (var trivia in member.GetLeadingTrivia())
+                {
+                    if (!trivia.IsWhitespaceOrEndOfLine())
+                        return false;
+
+                    if (trivia.FullSpan.Contains(position))
+                        return true;
+                }
+            }
+        }
+
+        return false;
+    }
+
+    protected override IEnumerable<SyntaxNode> ExtractNodesSimple(SyntaxNode? node, ISyntaxFacts syntaxFacts)
+    {
+        if (node == null)
+        {
+            yield break;
+        }
+
+        foreach (var extractedNode in base.ExtractNodesSimple(node, syntaxFacts))
+        {
+            yield return extractedNode;
+        }
+
+        // `var a = b;`
+        // -> `var a = b`;
+        if (node is LocalDeclarationStatementSyntax localDeclaration)
+        {
+            yield return localDeclaration.Declaration;
+        }
+
+        // var `a = b`;
+        if (node is VariableDeclaratorSyntax declarator)
+        {
+            var declaration = declarator.Parent;
+            if (declaration?.Parent is LocalDeclarationStatementSyntax localDeclarationStatement)
+            {
+                var variables = syntaxFacts.GetVariablesOfLocalDeclarationStatement(localDeclarationStatement);
+                if (variables.Count == 1)
+                {
+                    // -> `var a = b`;
+                    yield return declaration;
+
+                    // -> `var a = b;`
+                    yield return localDeclarationStatement;
+                }
+            }
+        }
+    }
+}

src/Workspaces/SharedUtilitiesAndExtensions/Compiler/Core/CompilerExtensions.projitems

@@ -367,6 +367,8 @@
     <Compile Include="$(MSBuildThisFileDirectory)Options\OptionKey2.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Options\Option2.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Options\PerLanguageOption2.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)services\refactoringhelpers\AbstractRefactoringHelpers.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)services\refactoringhelpers\IRefactoringHelpers.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Services\SelectedMembers\AbstractSelectedMembers.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Services\SemanticFacts\ForEachSymbols.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Services\SemanticFacts\ISemanticFactsExtensions.cs" />
@@ -548,5 +550,6 @@
     <Folder Include="$(MSBuildThisFileDirectory)Extensions\Compiler\" />
     <Folder Include="$(MSBuildThisFileDirectory)Hashing\" />
     <Folder Include="$(MSBuildThisFileDirectory)Services\FileBannerFacts\" />
+    <Folder Include="$(MSBuildThisFileDirectory)Services\RefactoringHelpers\" />
   </ItemGroup>
 </Project>