Add test for renaming to an existing file, and fix the bug that the test found

Author: davidwengier

src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/Refactoring/RenameEndpoint.cs

@@ -48,15 +48,16 @@ public void ApplyCapabilities(VSInternalServerCapabilities serverCapabilities, V
 
     protected override string CustomMessageTarget => CustomMessageNames.RazorRenameEndpointName;
 
-    protected override Task<WorkspaceEdit?> TryHandleAsync(RenameParams request, RazorRequestContext requestContext, DocumentPositionInfo positionInfo, CancellationToken cancellationToken)
+    protected override async Task<WorkspaceEdit?> TryHandleAsync(RenameParams request, RazorRequestContext requestContext, DocumentPositionInfo positionInfo, CancellationToken cancellationToken)
     {
         var documentContext = requestContext.DocumentContext;
         if (documentContext is null)
         {
-            return SpecializedTasks.Null<WorkspaceEdit>();
+            return null;
         }
 
-        return _renameService.TryGetRazorRenameEditsAsync(documentContext, positionInfo, request.NewName, _projectManager.GetQueryOperations(), cancellationToken);
+        var result = await _renameService.TryGetRazorRenameEditsAsync(documentContext, positionInfo, request.NewName, _projectManager.GetQueryOperations(), cancellationToken).ConfigureAwait(false);
+        return result.Edit;
     }
 
     protected override bool IsSupported()

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Rename/IRenameService.cs

@@ -10,10 +10,12 @@ namespace Microsoft.CodeAnalysis.Razor.Rename;
 
 internal interface IRenameService
 {
-    Task<WorkspaceEdit?> TryGetRazorRenameEditsAsync(
+    Task<RenameResult> TryGetRazorRenameEditsAsync(
         DocumentContext documentContext,
         DocumentPositionInfo positionInfo,
         string newName,
         ISolutionQueryOperations solutionQueryOperations,
         CancellationToken cancellationToken);
 }
+
+internal readonly record struct RenameResult(WorkspaceEdit? Edit, bool FallbackToCSharp = true);

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Rename/RenameService.cs

@@ -31,7 +31,7 @@ internal class RenameService(
     private readonly IFileSystem _fileSystem = fileSystem;
     private readonly LanguageServerFeatureOptions _languageServerFeatureOptions = languageServerFeatureOptions;
 
-    public async Task<WorkspaceEdit?> TryGetRazorRenameEditsAsync(
+    public async Task<RenameResult> TryGetRazorRenameEditsAsync(
         DocumentContext documentContext,
         DocumentPositionInfo positionInfo,
         string newName,
@@ -41,30 +41,32 @@ internal class RenameService(
         // We only support renaming of .razor components, not .cshtml tag helpers
         if (!documentContext.FileKind.IsComponent())
         {
-            return null;
+            return new(Edit: null);
         }
 
         var codeDocument = await documentContext.GetCodeDocumentAsync(cancellationToken).ConfigureAwait(false);
 
         var originTagHelpers = await GetOriginTagHelpersAsync(documentContext, positionInfo.HostDocumentIndex, cancellationToken).ConfigureAwait(false);
         if (originTagHelpers.IsDefaultOrEmpty)
         {
-            return null;
+            return new(Edit: null);
         }
 
         var originComponentDocumentSnapshot = await _componentSearchEngine
             .TryLocateComponentAsync(originTagHelpers.First(), solutionQueryOperations, cancellationToken)
             .ConfigureAwait(false);
         if (originComponentDocumentSnapshot is null)
         {
-            return null;
+            return new(Edit: null);
         }
 
         var originComponentDocumentFilePath = originComponentDocumentSnapshot.FilePath;
         var newPath = MakeNewPath(originComponentDocumentFilePath, newName);
         if (_fileSystem.FileExists(newPath))
         {
-            return null;
+            // We found a tag, but the new name would cause a conflict, so we can't proceed with the rename,
+            // even if C# might have worked.
+            return new(Edit: null, FallbackToCSharp: false);
         }
 
         using var _ = ListPool<SumType<TextDocumentEdit, CreateFile, RenameFile, DeleteFile>>.GetPooledObject(out var documentChanges);
@@ -88,10 +90,10 @@ internal class RenameService(
             }
         }
 
-        return new WorkspaceEdit
+        return new(new WorkspaceEdit
         {
             DocumentChanges = documentChanges.ToArray(),
-        };
+        });
     }
 
     private static ImmutableArray<IDocumentSnapshot> GetAllDocumentSnapshots(string filePath, ISolutionQueryOperations solutionQueryOperations)

src/Razor/src/Microsoft.CodeAnalysis.Remote.Razor/Rename/RemoteRenameService.cs

@@ -58,16 +58,21 @@ protected override IRemoteRenameService CreateService(in ServiceArgs args)
             .TryGetRazorRenameEditsAsync(context, positionInfo, newName, context.GetSolutionQueryOperations(), cancellationToken)
             .ConfigureAwait(false);
 
-        if (razorEdit is not null)
+        if (razorEdit.Edit is { } edit)
         {
-            return Results(razorEdit);
+            return Results(edit);
         }
 
         if (positionInfo.LanguageKind != CodeAnalysis.Razor.Protocol.RazorLanguageKind.CSharp)
         {
             return CallHtml;
         }
 
+        if (!razorEdit.FallbackToCSharp)
+        {
+            return NoFurtherHandling;
+        }
+
         var csharpEdit = await ExternalHandlers.Rename
             .GetRenameEditAsync(generatedDocument, positionInfo.Position.ToLinePosition(), newName, cancellationToken)
             .ConfigureAwait(false);

src/Razor/test/Microsoft.VisualStudioCode.RazorExtension.Test/Endpoints/Shared/CohostRenameEndpointTest.cs

@@ -316,6 +316,23 @@ public class HasJacketAttribute : Attribute
                     """)
            ]);
 
+    [Fact]
+    public Task Component_ExistingFile()
+     => VerifyRenamesAsync(
+         input: $"""
+                This is a Razor document.
+
+                <Comp$$onent />
+
+                The end.
+                """,
+         additionalFiles: [
+             (FilePath("Component.razor"), ""),
+             (FilePath("DifferentName.razor"), "")
+         ],
+         newName: "DifferentName",
+         expected: "");
+
     [Theory]
     [InlineData("$$Component")]
     [InlineData("Com$$ponent")]