protected function writeAliasFile($filename, $contents)
{
if (is_readable($filename) && $contents !== file_get_contents($filename)) {
$backupName = dirname($filename) . '/' . str_replace('.php', '.bak.php', basename($filename));
$this->fs->rename($filename, $backupName, true);
}
$this->fs->dumpFile($filename, $contents);
}