Flarum\Core\User::cannot PHP Method

    public function cannot($ability, $arguments = [])
    {
        return !$this->can($ability, $arguments);
    }

 /**
  * @param User $actor
  * @param Builder $query
  */
 public function find(User $actor, Builder $query)
 {
     if ($actor->cannot('viewDiscussions')) {
         $query->whereRaw('FALSE');
     } elseif (!$actor->hasPermission('discussion.hide')) {
         $query->where(function ($query) use($actor) {
             $query->whereNull('discussions.hide_time')->where('comments_count', '>', 0)->orWhere('start_user_id', $actor->id);
             $this->events->fire(new ScopeHiddenDiscussionVisibility($query, $actor, 'discussion.hide'));
         });
     }
 }