这就是我最终使用的

/**
 * check if the path is writable. To make the check .
 *
 * @param string $path
 * @return boolean
 */
public static function is_writable( $path ) {
    global $wp_filesystem;
    include_once ABSPATH . \'wp-admin/includes/file.php\';
    // If for some reason the include doesn\'t work as expected just return false.
    if( ! function_exists( \'WP_Filesystem\' ) ) {
        return false;
    }
    $writable = WP_Filesystem( false, $path );
    // We consider the directory as writable if it uses the direct transport,
    // otherwise credentials would be needed
    return $writable && $wp_filesystem->method === \'direct\';
}