Add "parent" class to menu items with sub-menus

[Looimaster]

Currently there is no way to indicate that a menu has sub-menu (by inserting an arrow pointing downwards next to parent menu item) without custom menu walker or filters that will add 'parent' class to menu items that have sub-menus.

It would be great if that could become a default class in WordPress.

function add_parent_css( $classes, $item ) {
    global $dd_children;
    if( $dd_children ) {
        $classes[] = 'parent';
    }
    return $classes;
}
add_filter( 'nav_menu_css_class', 'add_parent_css', 10, 2 );

[Looimaster]

And here's the rest of the walker (can't update my original suggestion):

class custom_walker extends Walker_Nav_Menu {
  function display_element($element, &$children_elements, $max_depth, $depth=0, $args, &$output){
    $GLOBALS['dd_children'] = (isset($children_elements[$element->ID]))? 1:0;
    parent::display_element($element, $children_elements, $max_depth, $depth, $args, $output);
  }
  [...]
}

The reason I'm asking this is because plugins such as WPML add 'language switcher' as menu item and they ignore custom walker. Instead of chasing plugin authors and dropping them suggestions this could be a default feature of WordPress.

[SergeyBiryukov]

#14687, #20191