Comment 2 for bug 418931

It does reflect a real bug, and it's a bit comical:

    def _get_tags_bytes(self):
        medium = self._client._medium
        if medium._is_remote_before((1, 13)):
            return self._vfs_get_tags_bytes()
        try:
            response = self._call('Branch.get_tags_bytes', self._remote_path())
        except errors.UnknownSmartMethod:
            medium._remember_remote_is_before((1, 13))
            return self._vfs_get_tags_bytes()
        return response[0]

    def _vfs_set_tags_bytes(self, bytes):
        self._ensure_real()
        return self._real_branch._set_tags_bytes(bytes)

    def _set_tags_bytes(self, bytes):
        medium = self._client._medium
        if medium._is_remote_before((1, 18)):
            self._vfs_set_tags_bytes(bytes)
        try:
            args = (
                self._remote_path(), self._lock_token, self._repo_lock_token)
            response = self._call_with_body_bytes(
                'Branch.set_tags_bytes', args, bytes)
        except errors.UnknownSmartMethod:
            medium._remember_remote_is_before((1, 18))
            self._vfs_set_tags_bytes(bytes)

If the server doesn't support it, we do it over vfs and then try again by rpc.

So it's good the assertion caught this, but I also think it's a bit bad there's repeated code to do:

  if server older than X:
     do old method
  else:
    try it
    except not supported:
      server_is_older_than X