没有插件的自定义帖子类型的Wordpress搜索

function create_custom_post_type() {
    register_post_type('custom_post',
        array(
            'labels' => array(
                'name' => __('Custom Posts'),
                'singular_name' => __('Custom Post')
            ),
            'public' => true,
            'has_archive' => true,
            'rewrite' => array('slug' => 'custom-posts'),
        )
    );
}
add_action('init', 'create_custom_post_type');

function custom_search_filter($query) {
    if ($query->is_search && !is_admin()) {
        $query->set('post_type', array('post', 'custom_post'));
    }
}
add_action('pre_get_posts', 'custom_search_filter');

function custom_search_form($form) {
    $form = '<form role="search" method="get" id="searchform" action="' . home_url('/') . '" >
   <div><label class="screen-reader-text" for="s">' . __('Search for:') . '</label>
    <input type="text" value="' . get_search_query() . '" name="s" id="s" />
    <input type="hidden" name="post_type" value="any" />
    <input type="submit" id="searchsubmit" value="'. esc_attr__('Search') .'" />
    </div>
    </form>';
    return $form;
}
add_filter('get_search_form', 'custom_search_form');