Report telemetry event with LSP server capabilities

src/Features/LanguageServer/Protocol/Handler/ServerLifetime/InitializeHandler.cs

@@ -7,7 +7,9 @@
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis.Host.Mef;
+using Microsoft.CodeAnalysis.Internal.Log;
 using Microsoft.VisualStudio.LanguageServer.Protocol;
+using Newtonsoft.Json;
 
 namespace Microsoft.CodeAnalysis.LanguageServer.Handler;
 
@@ -41,6 +43,14 @@ public Task<InitializeResult> HandleRequestAsync(InitializeParams request, Reque
             var capabilitiesProvider = context.GetRequiredLspService<ICapabilitiesProvider>();
             var serverCapabilities = capabilitiesProvider.GetCapabilities(clientCapabilities);
 
+            // Record a telemetry event indicating what capabilities are being provided by the server.
+            // Useful for figuring out if a particular session is opted into an LSP feature.
+            Logger.Log(FunctionId.LSP_Initialize, KeyValueLogMessage.Create(m =>
+            {
+                m["serverKind"] = context.ServerKind.ToTelemetryString();
+                m["capabilities"] = JsonConvert.SerializeObject(serverCapabilities);
+            }));
+
             return Task.FromResult(new InitializeResult
             {
                 Capabilities = serverCapabilities,

src/Workspaces/SharedUtilitiesAndExtensions/Compiler/Core/Log/FunctionId.cs

@@ -589,5 +589,8 @@ internal enum FunctionId
 
         // 670-680 for newer rename ids
         Rename_TryApplyRename_WorkspaceChanged = 670,
+
+        // 680-690 LSP Initialization info ids.
+        LSP_Initialize = 680,
     }
 }