// 页面链接添加html后缀
add_action('init', 'html_page_permalink', -1);
function html_page_permalink() {
    global $wp_rewrite;
    if ( !strpos($wp_rewrite->get_page_permastruct(), '.html')){
        $wp_rewrite->page_structure = $wp_rewrite->page_structure . '.html';
    }
}