All fixed

src/Draco.LanguageServer/Capabilities/DidDeleteFiles.cs

@@ -21,7 +21,7 @@ internal partial class DracoLanguageServer : IDidDeleteFiles
         }
     };
 
-    public async Task DidDeleteFilesAsync(DeleteFilesParams param, CancellationToken cancellationToken)
+    public async Task DidDeleteFilesAsync(DeleteFilesParams param)
     {
         foreach (var file in param.Files)
         {

src/Draco.LanguageServer/Capabilities/TextDocumentSync.cs

@@ -9,15 +9,15 @@ namespace Draco.LanguageServer;
 
 internal sealed partial class DracoLanguageServer : ITextDocumentSync
 {
-    public async Task TextDocumentDidOpenAsync(DidOpenTextDocumentParams param, CancellationToken cancellationToken)
+    public async Task TextDocumentDidOpenAsync(DidOpenTextDocumentParams param)
     {
         await this.PublishDiagnosticsAsync(param.TextDocument.Uri);
     }
 
-    public Task TextDocumentDidCloseAsync(DidCloseTextDocumentParams param, CancellationToken cancellationToken) =>
+    public Task TextDocumentDidCloseAsync(DidCloseTextDocumentParams param) =>
         Task.CompletedTask;
 
-    public async Task TextDocumentDidChangeAsync(DidChangeTextDocumentParams param, CancellationToken cancellationToken)
+    public async Task TextDocumentDidChangeAsync(DidChangeTextDocumentParams param)
     {
         var uri = param.TextDocument.Uri;
         var change = param.ContentChanges.First();

src/Draco.LanguageServer/Program.cs

@@ -45,8 +45,6 @@ internal static async Task Main(string[] args)
 
     internal static async Task RunServerAsync(bool stdioFlag)
     {
-        await Task.Delay(10000);
-
         var transportKind = GetTransportKind(stdioFlag);
         var transportStream = BuildTransportStream(transportKind);
 

src/Draco.Lsp/Server/LanguageClientProxy.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Concurrent;
+using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
 using System.Reflection;
@@ -41,11 +42,32 @@ internal class LanguageClientProxy : DispatchProxy
     private object? ProxyRpc(MethodInfo method, object?[] arguments)
     {
         var handler = this.handlers.GetOrAdd(method, m => new(m, this));
-        var args = handler.SupportsCancellation ? arguments[..^1] : arguments;
 
         if (handler.IsRequest)
         {
-            // It's a request
+            // Build up args
+            var args = new List<object?>();
+            // Method name
+            args.Add(handler.MethodName);
+            // Parameter
+            if (handler.AcceptsParams)
+            {
+                args.Add(arguments[0]);
+            }
+            else
+            {
+                args.Add(null);
+            }
+            // CT
+            if (handler.SupportsCancellation)
+            {
+                args.Add(arguments[1]!);
+            }
+            else
+            {
+                args.Add(CancellationToken.None);
+            }
+
             // Extract return type
             var returnType = method.ReturnType;
 
@@ -54,17 +76,14 @@ internal class LanguageClientProxy : DispatchProxy
                 returnType = returnType.GetGenericArguments()[0];
             }
 
-            // TODO: cancellation token
-            var ct = CancellationToken.None;
-
             return SendRequestMethod
                 .MakeGenericMethod(returnType)
-                .Invoke(this.Connection, new[] { handler.MethodName, args.SingleOrDefault(), ct });
+                .Invoke(this.Connection, args.ToArray());
         }
         else
         {
             // It's a notification
-            return this.Connection.SendNotificationAsync(handler.MethodName, args.SingleOrDefault());
+            return this.Connection.SendNotificationAsync(handler.MethodName, arguments.SingleOrDefault());
         }
     }
 }

src/Draco.Lsp/Server/LanguageServerConnection.cs

@@ -32,7 +32,12 @@ private LspMessageAdapter()
         Id = id,
         Params = @params,
     };
-    public static LspMessage CreateCancelRequest(int id) => throw new NotImplementedException();
+    public static LspMessage CreateCancelRequest(int id) => CreateNotification(
+        "$/cancelRequest",
+        JsonSerializer.SerializeToElement(new CancelParams
+        {
+            Id = id,
+        }));
     public static LspMessage CreateOkResponse(object id, JsonElement okResult) => new ResponseMessage
     {
         Jsonrpc = "2.0",
@@ -43,7 +48,7 @@ private LspMessageAdapter()
     {
         Jsonrpc = "2.0",
         Id = ToId(id),
-        Error = (ResponseError)errorResult,
+        Error = errorResult,
     };
     public static LspMessage CreateNotification(string method, JsonElement @params) => new NotificationMessage
     {

src/Draco.Lsp/Server/LanguageServerMethodHandler.cs

@@ -103,19 +103,12 @@ public LanguageServerMethodHandler(MethodInfo handlerMethod, object? target)
         this.DeclaredReturnType = returnType;
     }
 
-    public Task InvokeNotification(object?[] args)
-    {
-        Debug.WriteLine($"InvokeNotification {this.MethodName} START");
-        var result = (Task)this.handlerMethod.Invoke(this.target, args.ToArray())!;
-        Debug.WriteLine($"InvokeNotification {this.MethodName} END");
-        return result;
-    }
+    public Task InvokeNotification(object?[] args) =>
+        (Task)this.handlerMethod.Invoke(this.target, args.ToArray())!;
 
     public async Task<object?> InvokeRequest(object?[] args)
     {
-        Debug.WriteLine($"InvokeRequest {this.MethodName} START");
         var task = (Task)this.handlerMethod.Invoke(this.target, args.ToArray())!;
-        Debug.WriteLine($"InvokeRequest {this.MethodName} END");
         await task;
 
         if (this.DeclaredReturnType == typeof(Task))
@@ -124,9 +117,7 @@ public Task InvokeNotification(object?[] args)
         }
         else
         {
-            Debug.WriteLine($"EEEE {this.MethodName} START");
             var getResult = (MethodInfo)task.GetType().GetMemberWithSameMetadataDefinitionAs(taskGetResult);
-            Debug.WriteLine($"EEEE {this.MethodName} END");
             return getResult.Invoke(task, null);
         }
     }

src/Draco.Lsp/Server/TextDocument/ITextDocumentDidChange.cs

@@ -12,5 +12,5 @@ public interface ITextDocumentDidChange
     public TextDocumentChangeRegistrationOptions DidChangeRegistrationOptions { get; }
 
     [Notification("textDocument/didChange", Mutating = true)]
-    public Task TextDocumentDidChangeAsync(DidChangeTextDocumentParams param, CancellationToken cancellationToken);
+    public Task TextDocumentDidChangeAsync(DidChangeTextDocumentParams param);
 }

src/Draco.Lsp/Server/TextDocument/ITextDocumentDidClose.cs

@@ -12,5 +12,5 @@ public interface ITextDocumentDidClose
     public TextDocumentRegistrationOptions DidCloseRegistrationOptions { get; }
 
     [Notification("textDocument/didClose", Mutating = true)]
-    public Task TextDocumentDidCloseAsync(DidCloseTextDocumentParams param, CancellationToken cancellationToken);
+    public Task TextDocumentDidCloseAsync(DidCloseTextDocumentParams param);
 }

src/Draco.Lsp/Server/TextDocument/ITextDocumentDidOpen.cs

@@ -12,5 +12,5 @@ public interface ITextDocumentDidOpen
     public TextDocumentRegistrationOptions DidOpenRegistrationOptions { get; }
 
     [Notification("textDocument/didOpen", Mutating = true)]
-    public Task TextDocumentDidOpenAsync(DidOpenTextDocumentParams param, CancellationToken cancellationToken);
+    public Task TextDocumentDidOpenAsync(DidOpenTextDocumentParams param);
 }

src/Draco.Lsp/Server/Workspace/IDidDeleteFiles.cs

@@ -11,6 +11,6 @@ public interface IDidDeleteFiles
     [RegistrationOptions("workspace/didDeleteFiles")]
     public FileOperationRegistrationOptions DidDeleteFileRegistrationOptions { get; }
 
-    [Notification("workspace/didDeleteFiles")]
-    public Task DidDeleteFilesAsync(DeleteFilesParams param, CancellationToken cancellationToken);
+    [Notification("workspace/didDeleteFiles", Mutating = true)]
+    public Task DidDeleteFilesAsync(DeleteFilesParams param);
 }