protected function canEvaluateFunction($function)
 {
     if (!$this->getViewer()->getPHID()) {
         return false;
     }
     return parent::canEvaluateFunction($function);
 }
 protected function canEvaluateFunction($function)
 {
     foreach ($this->getUsableDatasources() as $source) {
         if ($source->canEvaluateFunction($function)) {
             return true;
         }
     }
     return parent::canEvaluateFunction($function);
 }