langchain/document_loaders/googledrive.py/GoogleDriveLoader/_fetch_files_recursive
class GoogleDriveLoader:    def _fetch_files_recursive(
        self, service: Any, folder_id: str
    ) -> List[Dict[str, Union[str, List[str]]]]:
        """Fetch all files and subfolders recursively."""
        results = (
            service.files()
            .list(
                q=f"'{folder_id}' in parents",
                pageSize=1000,
                includeItemsFromAllDrives=True,
                supportsAllDrives=True,
                fields="nextPageToken, files(id, name, mimeType, parents, trashed)",
            )
            .execute()
        )
        files = results.get("files", [])
        returns = []
        for file in files:
            if file["mimeType"] == "application/vnd.google-apps.folder":
                if self.recursive:
                    returns.extend(self._fetch_files_recursive(service, file["id"]))
            else:
                returns.append(file)

        return returns