Allow plugins to modify server response messages (#1992)

plugin/core/sessions.py

@@ -875,6 +875,17 @@ def on_pre_send_notification_async(self, notification: Notification) -> None:
         """
         pass
 
+    def on_server_response_async(self, method: str, response: Response) -> None:
+        """
+        Notifies about a response message that has been received from the language server.
+        Only successful responses are passed to this method.
+
+        :param    method:    The method of the request.
+        :param    response:  The response object to the request. The response.result field can be modified by the
+                             plugin, before it gets further handled by the LSP package.
+        """
+        pass
+
     def on_open_uri_async(self, uri: DocumentUri, callback: Callable[[str, str, str], None]) -> bool:
         """
         Called when a language server reports to open an URI. If you know how to handle this URI, then return True and
@@ -1898,10 +1909,12 @@ def deduce_payload(
                 return res
         elif "id" in payload:
             response_id = int(payload["id"])
-            handler, result, is_error = self.response_handler(response_id, payload)
-            response_tuple = (handler, result, None, None, None)
+            handler, method, result, is_error = self.response_handler(response_id, payload)
             self._logger.incoming_response(response_id, result, is_error)
-            return response_tuple
+            response = Response(response_id, result)
+            if self._plugin and not is_error:
+                self._plugin.on_server_response_async(method, response)  # type: ignore
+            return handler, response.result, None, None, None
         else:
             debug("Unknown payload type: ", payload)
         return (None, None, None, None, None)
@@ -1925,21 +1938,25 @@ def on_payload(self, payload: Dict[str, Any]) -> None:
             except Exception as err:
                 exception_log("Error handling {}".format(typestr), err)
 
-    def response_handler(self, response_id: int, response: Dict[str, Any]) -> Tuple[Optional[Callable], Any, bool]:
+    def response_handler(
+        self,
+        response_id: int,
+        response: Dict[str, Any]
+    ) -> Tuple[Optional[Callable], Optional[str], Any, bool]:
         request, handler, error_handler = self._response_handlers.pop(response_id, (None, None, None))
         if not request:
             error = {"code": ErrorCode.InvalidParams, "message": "unknown response ID {}".format(response_id)}
-            return (print_to_status_bar, error, True)
+            return (print_to_status_bar, None, error, True)
         self._invoke_views(request, "on_request_finished_async", response_id)
         if "result" in response and "error" not in response:
-            return (handler, response["result"], False)
+            return (handler, request.method, response["result"], False)
         if not error_handler:
             error_handler = print_to_status_bar
         if "result" not in response and "error" in response:
             error = response["error"]
         else:
             error = {"code": ErrorCode.InvalidParams, "message": "invalid response payload"}
-        return (error_handler, error, True)
+        return (error_handler, request.method, error, True)
 
     def _get_handler(self, method: str) -> Optional[Callable]:
         return getattr(self, method2attr(method), None)