LanguageHandler with custom Notification class

plugin.py

from LSP.plugin.core.handlers import LanguageHandler
from LSP.plugin.core.settings import ClientConfig
from LSP.plugin.core.rpc import Notification

import os


class LspClangRcppPlugin(LanguageHandler):
    name = "clangd-rcpp"

    def __init__(self):
        self._config = ClientConfig(
            name=self.name,
            binary_args=["clangd"],
            tcp_port=None,
            scopes=["source.c", "source.c++", "source.objc", "source.objc++"],
            syntaxes=[
                "Packages/C++/C.sublime-syntax",
                "Packages/C++/C++.sublime-syntax",
                "Packages/Objective-C/Objective-C.sublime-syntax",
                "Packages/Objective-C/Objective-C++.sublime-syntax"
                "Packages/RIDE/Rcpp.sublime-syntax"
            ],
            languageId='c++',
            enabled=True,
            init_options=dict(),
            settings=dict(),
            env=dict()
        )

    @property
    def config(self):
        return self._config

    def on_start(self, window):
        return True

    def on_initialized(self, client):
        class ClangNotification(Notification):

            @classmethod
            def didOpen(cls, params: dict):
                if os.path.isfile(os.path.join(client.project_path, "DESCRIPTION")):
                    params["metadata"] = {"extraFlags": ["-I/usr/local/opt/r/include"]}
                return cls("textDocument/didOpen", params)

        client.notification_class = ClangNotification