Symfony\Installer\SelfUpdateCommand::checkNewVersionIsValid PHP Метод

    private function checkNewVersionIsValid()
    {
        // creating a Phar instance for an existing file is not allowed
        // when the Phar extension is in readonly mode
        if (!ini_get('phar.readonly')) {
            // test the phar validity
            $phar = new \Phar($this->newInstallerFile);
            // free the variable to unlock the file
            unset($phar);
        }
        return $this;
    }