Flarum\Asset\CompilerInterface::addFile PHP Method

    public function addFile($file);

 /**
  * @param string $file
  */
 public function addFile($file)
 {
     $ext = pathinfo($file, PATHINFO_EXTENSION);
     switch ($ext) {
         case 'js':
             $this->js->addFile($file);
             break;
         case 'css':
         case 'less':
             $this->less->addFile($file);
             break;
         default:
             throw new DomainException('Unsupported asset type: ' . $ext);
     }
 }