Now that we are using JsonConverters we can use that for VSClientCapabilities too

src/VisualStudio/Core/Def/Implementation/LanguageClient/InProcLanguageServer.cs

@@ -21,7 +21,6 @@
 using Microsoft.VisualStudio.LanguageServer.Client;
 using Microsoft.VisualStudio.LanguageServer.Protocol;
 using Microsoft.VisualStudio.Utilities.Internal;
-using Newtonsoft.Json.Linq;
 using Roslyn.Utilities;
 using StreamJsonRpc;
 using LSP = Microsoft.VisualStudio.LanguageServer.Protocol;
@@ -50,6 +49,7 @@ internal class InProcLanguageServer
 
             var jsonMessageFormatter = new JsonMessageFormatter();
             jsonMessageFormatter.JsonSerializer.Converters.Add(new VSExtensionConverter<TextDocumentIdentifier, VSTextDocumentIdentifier>());
+            jsonMessageFormatter.JsonSerializer.Converters.Add(new VSExtensionConverter<ClientCapabilities, VSClientCapabilities>());
 
             _jsonRpc = new JsonRpc(new HeaderDelimitedMessageHandler(outputStream, inputStream, jsonMessageFormatter));
             _jsonRpc.AddLocalRpcTarget(this);
@@ -67,15 +67,14 @@ internal class InProcLanguageServer
         /// and responding with the server capabilities.
         /// The specification assures that the initialize request is sent only once.
         /// </summary>
-        [JsonRpcMethod(Methods.InitializeName)]
-        public async Task<InitializeResult> InitializeAsync(JToken input, CancellationToken cancellationToken)
+        [JsonRpcMethod(Methods.InitializeName, UseSingleObjectParameterDeserialization = true)]
+        public async Task<InitializeResult> InitializeAsync(InitializeParams initializeParams, CancellationToken cancellationToken)
         {
-            // InitializeParams only references ClientCapabilities, but the VS LSP client
-            // sends additional VS specific capabilities, so directly deserialize them into the VSClientCapabilities
-            // to avoid losing them.
-            _clientCapabilities = input["capabilities"].ToObject<VSClientCapabilities>();
+            _clientCapabilities = (VSClientCapabilities)initializeParams.Capabilities;
+
             var serverCapabilities = await _protocol.ExecuteRequestAsync<InitializeParams, InitializeResult>(Methods.InitializeName,
-                _workspace.CurrentSolution, input.ToObject<InitializeParams>(), _clientCapabilities, _clientName, cancellationToken).ConfigureAwait(false);
+                _workspace.CurrentSolution, initializeParams, _clientCapabilities, _clientName, cancellationToken).ConfigureAwait(false);
+
             // Always support hover - if any LSP client for a content type advertises support,
             // then the liveshare provider is disabled.  So we must provide for both C# and razor
             // until https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1106064/ is fixed