WordPress: Add 'menu-item-parent' to menu lis that contain submenus #WordPress #snippet

menu-item-parent-class.php

/**
 * Set our new walker only if a menu is assigned,
 * and a child theme hasn't modified it to one level deep
 */
 function fstop_nav_menu_args( $args ) {
    if ( 1 !== $args[ 'depth' ] && has_nav_menu( 'main-nav' ) ) {
        $args[ 'walker' ] = new FStop_Page_Navigation_Walker;
    }
    return $args;
}
add_filter( 'wp_nav_menu_args', 'fstop_nav_menu_args' );

/**
 * Add CSS class to menus for submenu indicator
	 * via http://kwight.ca/blog/adding-a-sub-menu-indicator-to-parent-menu-items/
	 */

class FStop_Page_Navigation_Walker extends Walker_Nav_Menu {
    function display_element( $element, &$children_elements, $max_depth, $depth=0, $args, &$output ) {
        $id_field = $this->db_fields['id'];
        if ( !empty( $children_elements[ $element->$id_field ] ) ) {
            $element->classes[] = 'menu-item-parent';
        }
        Walker_Nav_Menu::display_element( $element, $children_elements, $max_depth, $depth, $args, $output );
    }
}