code: private function getAllDirectiveArgNodes(Directive $directive, $argName)
      {
          $argNodes      = [];
          $directiveNode = $directive->astNode;
          if ($directiveNode && $directiveNode->arguments) {
              foreach ($directiveNode->arguments as $node) {
                  if ($node->name->value !== $argName) {
                      continue;
                  }
  
                  $argNodes[] = $node;
              }
          }
  
          return $argNodes;
      }
docs: @param string $argName
  
  @return InputValueDefinitionNode[]