/**
  * Returns the XHPAST version.
  *
  * @return string
  */
 public static function getVersion()
 {
     if (self::$version === null) {
         $bin = self::getPath();
         if (Filesystem::pathExists($bin)) {
             list($err, $stdout) = exec_manual('%s --version', $bin);
             if (!$err) {
                 self::$version = trim($stdout);
             }
         }
     }
     return self::$version;
 }