'Service we are extending either has a value for \'file\' set, which we
need to obtain a full path too or we are extending from a service
defined in our own file.'

def get_extended_config_path(self, extends_options):

    filename = self.service_config.filename
    validate_extends_file_path(self.service_config.name, extends_options, filename)
    if (u'file' in extends_options):
        return expand_path(self.working_dir, extends_options[u'file'])
    return filename
