feat(vscode): Add an option to trace LSP messages (#17)

* feat(vscode): Add an option to trace LSP messages

* chore: Some minor LSP handling improvementa

* fix(vscode): Fix tracing not working because of incorrect extension ID

* fix: Fix LSP errors being interpreted as results

Author: armsnyder

internal/lsp/server.go

@@ -82,13 +82,7 @@ func (s *Server) Serve() error {
 }
 
 func (s *Server) processMessage(payload []byte) bool {
-	// https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#requestMessage
-	var request struct {
-		ID     json.RawMessage `json:"id"`
-		Method string          `json:"method"`
-		Params json.RawMessage `json:"params"`
-	}
-
+	var request RequestMessage
 	if err := json.Unmarshal(payload, &request); err != nil {
 		slog.Error("Bad request", "error", err)
 		return true
@@ -117,27 +111,35 @@ func (s *Server) processMessage(payload []byte) bool {
 		logger.Debug("Received request", "params", string(request.Params))
 	}
 
-	response, err := s.handleRequest(request.Method, request.Params)
-	if err != nil {
+	result, err := s.handleRequest(request.Method, request.Params)
+	if err == nil {
+		err = s.writeMessage(&ResponseMessage{
+			JSONRPC: "2.0",
+			ID:      request.ID,
+			Result:  result,
+		})
+	} else {
 		logger.Error("Error handling request", "error", err)
 		var asResponseError *ResponseError
-		if errors.As(err, &asResponseError) {
-			response = asResponseError
-		} else {
-			response = &ResponseError{
+		if !errors.As(err, &asResponseError) {
+			asResponseError = &ResponseError{
 				Code:    CodeInternalError,
 				Message: err.Error(),
 			}
 		}
+		err = s.writeMessage(&ErrorResponseMessage{
+			JSONRPC: "2.0",
+			ID:      request.ID,
+			Error:   asResponseError,
+		})
 	}
 
-	if err := s.write(request.ID, response); err != nil {
-		logger.Error("Write error", "error", err)
-		return true
+	if err != nil {
+		logger.Error("Failed to write response", "error", err)
 	}
 
 	if debugEnabled {
-		logger.Debug("Sent response", "response", fmt.Sprintf("%#v", response))
+		logger.Debug("Sent response", "response", fmt.Sprintf("%#v", result))
 	}
 
 	return true
@@ -176,7 +178,7 @@ func (s *Server) handleNotification(method string, paramsRaw json.RawMessage) er
 	switch method {
 	case "initialized":
 
-	case "cancelRequest":
+	case "$/cancelRequest":
 		// TODO(asnyder): Handle cancelRequest and make everything
 		// async.
 
@@ -264,23 +266,24 @@ func parseParams(paramsRaw json.RawMessage, result any) error {
 	return nil
 }
 
-func (s *Server) write(requestID json.RawMessage, result any) error {
-	// https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#responseMessage
-	message := struct {
-		JSONRPC string          `json:"jsonrpc"`
-		ID      json.RawMessage `json:"id"`
-		Result  any             `json:"result"`
-	}{JSONRPC: "2.0", ID: requestID, Result: result}
-
+func (s *Server) writeMessage(message Message) error {
 	data, err := json.Marshal(message)
 	if err != nil {
-		return fmt.Errorf("invalid response: %w", err)
+		return fmt.Errorf("marshal response: %w", err)
 	}
 
+	if err := s.writeRaw(data); err != nil {
+		return fmt.Errorf("write response: %w", err)
+	}
+
+	return nil
+}
+
+func (s *Server) writeRaw(data []byte) error {
 	if s.Stdout == nil {
 		s.Stdout = os.Stdout
 	}
 
-	_, err = s.Stdout.Write(append([]byte("Content-Length: "+strconv.Itoa(len(data))+"\r\nContent-Type: application/vscode-jsonrpc; charset=utf-8\r\n\r\n"), data...))
+	_, err := s.Stdout.Write(append([]byte("Content-Length: "+strconv.Itoa(len(data))+"\r\nContent-Type: application/vscode-jsonrpc; charset=utf-8\r\n\r\n"), data...))
 	return err
 }

internal/lsp/types.go

@@ -22,7 +22,10 @@
 
 package lsp
 
-import "fmt"
+import (
+	"encoding/json"
+	"fmt"
+)
 
 // https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#clientCapabilities
 type ClientCapabilities struct{}
@@ -62,6 +65,49 @@ type ServerInfo struct {
 	Version string `json:"version"`
 }
 
+// Message satisfies the LSP message interface.
+// https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#abstractMessage
+type Message interface {
+	message()
+}
+
+// https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#requestMessage
+type RequestMessage struct {
+	JSONRPC string          `json:"jsonrpc"`
+	ID      json.RawMessage `json:"id"`
+	Method  string          `json:"method"`
+	Params  json.RawMessage `json:"params"`
+}
+
+func (r *RequestMessage) message() {}
+
+// https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#notificationMessage
+type NotificationMessage struct {
+	JSONRPC string          `json:"jsonrpc"`
+	Method  string          `json:"method"`
+	Params  json.RawMessage `json:"params,omitempty"`
+}
+
+func (n *NotificationMessage) message() {}
+
+// https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#responseMessage
+type ResponseMessage struct {
+	JSONRPC string          `json:"jsonrpc"`
+	ID      json.RawMessage `json:"id"`
+	Result  any             `json:"result"`
+}
+
+func (r *ResponseMessage) message() {}
+
+// https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#responseMessage
+type ErrorResponseMessage struct {
+	JSONRPC string          `json:"jsonrpc"`
+	ID      json.RawMessage `json:"id"`
+	Error   *ResponseError  `json:"error"`
+}
+
+func (e *ErrorResponseMessage) message() {}
+
 // https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#responseError
 type ResponseError struct {
 	Code          ErrorCode `json:"code"`

vscode-extension/package.json

@@ -70,6 +70,23 @@
     "lsp"
   ],
   "contributes": {
+    "configuration": {
+      "type": "object",
+      "title": "GDShader Language Server Configuration",
+      "properties": {
+        "gdshader.trace.server": {
+          "type": "string",
+          "scope": "window",
+          "default": "off",
+          "enum": [
+            "off",
+            "messages",
+            "verbose"
+          ],
+          "description": "Enables tracing of the underlying LSP requests and responses. This results in highly verbose logs (especially the document sync messages) and is not recommended for use outside development and troubleshooting contexts."
+        }
+      }
+    },
     "languages": [
       {
         "id": "gdshader",

vscode-extension/src/extension.js

@@ -78,10 +78,11 @@ async function activate(context) {
         fileEvents: vscode.workspace.createFileSystemWatcher("**/.clientrc"),
       },
       outputChannel: logger(),
+      traceOutputChannel: logger(),
     };
 
     const client = new LanguageClient(
-      "gdshaderLanguageServer",
+      "gdshader",
       "GDShader Language Server",
       serverOptions,
       clientOptions,