Implement textDocument/prepareRename for better rename experience

src/Features/LanguageServer/Protocol/DefaultCapabilitiesProvider.cs

@@ -54,7 +54,10 @@ public ServerCapabilities GetCapabilities(ClientCapabilities clientCapabilities)
 
             capabilities.DefinitionProvider = true;
             capabilities.DocumentHighlightProvider = true;
-            capabilities.RenameProvider = true;
+            capabilities.RenameProvider = new RenameOptions
+            {
+                PrepareProvider = true,
+            };
             capabilities.ImplementationProvider = true;
             capabilities.CodeActionProvider = new CodeActionOptions { CodeActionKinds = [CodeActionKind.QuickFix, CodeActionKind.Refactor], ResolveProvider = true };
             capabilities.CompletionProvider = new VisualStudio.LanguageServer.Protocol.CompletionOptions

src/Features/LanguageServer/Protocol/Handler/Rename/PrepareRenameHandler.cs

@@ -0,0 +1,48 @@
+// 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;
+using System.Composition;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.CodeAnalysis.Host.Mef;
+using Microsoft.CodeAnalysis.Rename;
+using Microsoft.VisualStudio.LanguageServer.Protocol;
+using Roslyn.Utilities;
+
+namespace Microsoft.CodeAnalysis.LanguageServer.Handler;
+
+[ExportCSharpVisualBasicStatelessLspService(typeof(PrepareRenameHandler)), Shared]
+[Method(Methods.TextDocumentPrepareRenameName)]
+internal class PrepareRenameHandler : ILspServiceDocumentRequestHandler<PrepareRenameParams, DefaultBehaviorPrepareRename?>
+{
+    [ImportingConstructor]
+    [Obsolete(MefConstruction.ImportingConstructorMessage, error: true)]
+    public PrepareRenameHandler()
+    {
+    }
+
+    public bool MutatesSolutionState => false;
+    public bool RequiresLSPSolution => true;
+
+    public TextDocumentIdentifier GetTextDocumentIdentifier(PrepareRenameParams request) => request.TextDocument;
+
+    public async Task<DefaultBehaviorPrepareRename?> HandleRequestAsync(PrepareRenameParams request, RequestContext context, CancellationToken cancellationToken)
+    {
+        var document = context.Document;
+        Contract.ThrowIfNull(document);
+
+        var position = await document.GetPositionFromLinePositionAsync(ProtocolConversions.PositionToLinePosition(request.Position), cancellationToken).ConfigureAwait(false);
+
+        var symbolicRenameInfo = await SymbolicRenameInfo.GetRenameInfoAsync(
+            document, position, cancellationToken).ConfigureAwait(false);
+        if (symbolicRenameInfo.IsError)
+            return null;
+
+        return new DefaultBehaviorPrepareRename
+        {
+            DefaultBehavior = true,
+        };
+    }
+}

src/Features/LanguageServer/ProtocolUnitTests/Rename/PrepareRenameTests.cs

@@ -0,0 +1,68 @@
+// 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.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using Roslyn.Test.Utilities;
+using Xunit;
+using Xunit.Abstractions;
+using LSP = Microsoft.VisualStudio.LanguageServer.Protocol;
+
+namespace Microsoft.CodeAnalysis.LanguageServer.UnitTests.Rename
+{
+    public class PrepareRenameTests : AbstractLanguageServerProtocolTests
+    {
+        public PrepareRenameTests(ITestOutputHelper testOutputHelper) : base(testOutputHelper)
+        {
+        }
+
+        [Theory, CombinatorialData]
+        public async Task TestPrepareRenameValidLocationAsync(bool mutatingLspWorkspace)
+        {
+            var markup =
+@"class A
+{
+    void {|caret:|}M()
+    {
+    }
+}";
+            await using var testLspServer = await CreateTestLspServerAsync(markup, mutatingLspWorkspace);
+            var renameLocation = testLspServer.GetLocations("caret").First();
+
+            var results = await RunPrepareRenameAsync(testLspServer, CreatePrepareRenameParams(renameLocation));
+            Assert.True(results?.DefaultBehavior);
+        }
+
+        [Theory, CombinatorialData]
+        public async Task TestPrepareRenameInvalidLocationAsync(bool mutatingLspWorkspace)
+        {
+            var markup =
+@"class A
+{
+    // Cannot rename {|caret:|} inside a comment.
+    void M()
+    {
+    }
+}";
+            await using var testLspServer = await CreateTestLspServerAsync(markup, mutatingLspWorkspace);
+            var renameLocation = testLspServer.GetLocations("caret").First();
+
+            var results = await RunPrepareRenameAsync(testLspServer, CreatePrepareRenameParams(renameLocation));
+            Assert.Null(results);
+        }
+
+        private static LSP.PrepareRenameParams CreatePrepareRenameParams(LSP.Location location)
+            => new LSP.PrepareRenameParams()
+            {
+                Position = location.Range.Start,
+                TextDocument = CreateTextDocumentIdentifier(location.Uri)
+            };
+
+        private static async Task<LSP.DefaultBehaviorPrepareRename?> RunPrepareRenameAsync(TestLspServer testLspServer, LSP.PrepareRenameParams prepareRenameParams)
+        {
+            return await testLspServer.ExecuteRequestAsync<LSP.PrepareRenameParams, LSP.DefaultBehaviorPrepareRename?>(LSP.Methods.TextDocumentPrepareRenameName, prepareRenameParams, CancellationToken.None);
+        }
+    }
+}