Flarum\Core\User::can PHP Method

    public function can($ability, $arguments = [])
    {
        return static::$gate->forUser($this)->allows($ability, $arguments);
    }

 /**
  * @param User $actor
  * @param string $ability
  * @param Post $post
  * @return bool|null
  */
 public function after(User $actor, $ability, Post $post)
 {
     if ($actor->can($ability . 'Posts', $post->discussion)) {
         return true;
     }
 }