Flarum\Core\User::isAdmin PHP Method

    public function isAdmin()
    {
        return $this->groups->contains(Group::ADMINISTRATOR_ID);
    }

 /**
  * Scope a query to only include records that are visible to a user.
  *
  * @param Builder $query
  * @param User $user
  * @return Builder
  */
 protected function scopeVisibleTo(Builder $query, User $user = null)
 {
     if ($user !== null && !$user->isAdmin()) {
         $query->whereIsHidden(0);
     }
     return $query;
 }