Make it clearer when 'move declaration' might change semantics (#76331)

Author: CyrusNajmabadi

src/Analyzers/Core/CodeFixes/RemoveUnusedParametersAndValues/AbstractRemoveUnusedValuesCodeFixProvider.cs

@@ -10,7 +10,6 @@
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis;
-using Microsoft.CodeAnalysis.CodeActions;
 using Microsoft.CodeAnalysis.CodeFixes;
 using Microsoft.CodeAnalysis.CodeStyle;
 using Microsoft.CodeAnalysis.Diagnostics;
@@ -866,8 +865,13 @@ private async Task<SyntaxNode> AdjustLocalDeclarationsAsync(
             }
             else if (declStatement.HasAnnotation(s_newLocalDeclarationStatementAnnotation))
             {
-                // Otherwise, move the declaration closer to the first reference if possible.
-                if (await moveDeclarationService.CanMoveDeclarationNearReferenceAsync(document, declStatement, cancellationToken).ConfigureAwait(false))
+                // Otherwise, move the declaration closer to the first reference if possible.  Note: because the initial
+                // declaration value was unused (which is why we're removing/moving the local decl in the first place),
+                // there's no concern about changing the scope where the declaration now lives, which is why it's fine
+                // to ignore 'mayChangeSemantics' here.
+
+                var (canUse, mayChangeSemantics) = await moveDeclarationService.CanMoveDeclarationNearReferenceAsync(document, declStatement, cancellationToken).ConfigureAwait(false);
+                if (canUse)
                 {
                     document = await moveDeclarationService.MoveDeclarationNearReferenceAsync(document, declStatement, cancellationToken).ConfigureAwait(false);
                     await OnDocumentUpdatedAsync().ConfigureAwait(false);

src/Features/CSharp/Portable/MoveDeclarationNearReference/CSharpMoveDeclarationNearReferenceCodeRefactoringProvider.cs

@@ -2,8 +2,6 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-#nullable disable
-
 using System.Composition;
 using System.Diagnostics.CodeAnalysis;
 using Microsoft.CodeAnalysis.CodeRefactorings;
@@ -14,11 +12,7 @@ namespace Microsoft.CodeAnalysis.CSharp.MoveDeclarationNearReference;
 
 [ExportCodeRefactoringProvider(LanguageNames.CSharp, Name = PredefinedCodeRefactoringProviderNames.MoveDeclarationNearReference), Shared]
 [ExtensionOrder(After = PredefinedCodeRefactoringProviderNames.InlineTemporary)]
-internal class CSharpMoveDeclarationNearReferenceCodeRefactoringProvider : AbstractMoveDeclarationNearReferenceCodeRefactoringProvider<LocalDeclarationStatementSyntax>
-{
-    [ImportingConstructor]
-    [SuppressMessage("RoslynDiagnosticsReliability", "RS0033:Importing constructor should be [Obsolete]", Justification = "Used in test code: https://github.com/dotnet/roslyn/issues/42814")]
-    public CSharpMoveDeclarationNearReferenceCodeRefactoringProvider()
-    {
-    }
-}
+[method: ImportingConstructor]
+[method: SuppressMessage("RoslynDiagnosticsReliability", "RS0033:Importing constructor should be [Obsolete]", Justification = "Used in test code: https://github.com/dotnet/roslyn/issues/42814")]
+internal sealed class CSharpMoveDeclarationNearReferenceCodeRefactoringProvider()
+    : AbstractMoveDeclarationNearReferenceCodeRefactoringProvider<LocalDeclarationStatementSyntax>;

src/Features/CSharpTest/MoveDeclarationNearReference/MoveDeclarationNearReferenceTests.cs

@@ -653,7 +653,8 @@ void Main()
                     });
                 }
             }
-            """);
+            """,
+            title: FeaturesResources.Move_declaration_near_reference_may_change_semantics);
     }
 
     [Fact, WorkItem("http://vstfdevdiv:8080/DevDiv2/DevDiv/_workitems/edit/545435")]

src/Features/Core/Portable/FeaturesResources.resx

@@ -965,6 +965,9 @@ This version used in: {2}</value>
   <data name="Move_declaration_near_reference" xml:space="preserve">
     <value>Move declaration near reference</value>
   </data>
+  <data name="Move_declaration_near_reference_may_change_semantics" xml:space="preserve">
+    <value>Move declaration near reference (may change semantics)</value>
+  </data>
   <data name="Convert_to_full_property" xml:space="preserve">
     <value>Convert to full property</value>
   </data>

src/Features/Core/Portable/MoveDeclarationNearReference/AbstractMoveDeclarationNearReferenceCodeRefactoringProvider.cs

@@ -14,38 +14,32 @@ namespace Microsoft.CodeAnalysis.MoveDeclarationNearReference;
 
 internal abstract class AbstractMoveDeclarationNearReferenceCodeRefactoringProvider<TLocalDeclaration> : CodeRefactoringProvider where TLocalDeclaration : SyntaxNode
 {
-    [ImportingConstructor]
-    public AbstractMoveDeclarationNearReferenceCodeRefactoringProvider()
-    {
-    }
-
     public override async Task ComputeRefactoringsAsync(CodeRefactoringContext context)
     {
         var (document, _, cancellationToken) = context;
         var declaration = await context.TryGetRelevantNodeAsync<TLocalDeclaration>().ConfigureAwait(false);
         if (declaration == null)
-        {
             return;
-        }
 
         var syntaxFacts = document.GetRequiredLanguageService<ISyntaxFactsService>();
         var variables = syntaxFacts.GetVariablesOfLocalDeclarationStatement(declaration);
         if (variables.Count != 1)
-        {
             return;
-        }
 
         var service = document.GetRequiredLanguageService<IMoveDeclarationNearReferenceService>();
-        if (!await service.CanMoveDeclarationNearReferenceAsync(document, declaration, cancellationToken).ConfigureAwait(false))
-        {
+        var (canMove, mayChangeSemantics) = await service.CanMoveDeclarationNearReferenceAsync(document, declaration, cancellationToken).ConfigureAwait(false);
+        if (!canMove)
             return;
-        }
+
+        var (title, equivalenceKey) = mayChangeSemantics
+            ? (FeaturesResources.Move_declaration_near_reference_may_change_semantics, nameof(FeaturesResources.Move_declaration_near_reference_may_change_semantics))
+            : (FeaturesResources.Move_declaration_near_reference, nameof(FeaturesResources.Move_declaration_near_reference));
 
         context.RegisterRefactoring(
             CodeAction.Create(
-                FeaturesResources.Move_declaration_near_reference,
-                c => MoveDeclarationNearReferenceAsync(document, declaration, c),
-                nameof(FeaturesResources.Move_declaration_near_reference),
+                title,
+                cancellationToken => MoveDeclarationNearReferenceAsync(document, declaration, cancellationToken),
+                equivalenceKey,
                 CodeActionPriority.Low),
             declaration.Span);
     }