Flarum\Core\Discussion::refreshLastPost PHP Method

    public function refreshLastPost()
    {
        if ($lastPost = $this->comments()->latest('time')->first()) {
            $this->setLastPost($lastPost);
        }
        return $this;
    }

 /**
  * Refreshes count and last Post for the discussion.
  *
  * @param Discussion $discussion
  */
 protected function refreshDiscussion(Discussion $discussion)
 {
     $discussion->refreshLastPost();
     $discussion->refreshCommentsCount();
     $discussion->refreshParticipantsCount();
     // Persist the new statistics.
     $discussion->save();
     return Discussion::find($discussion->id);
 }