Menu walker: how to tell if a sub menu contains submenus?

Question

I can extend the Walker_Nav_Menu class, but after taking a look to it, it seems there’s no way to know when an sub-menu will contain other sub-menu, because there’s no data available about its children

You may want to look again mate.

The Walker::display_element(…) method take the “List of elements to continue traversing” (understand children list) as second parameter : array $children_elements

If you do a

var_dump($children_elements);

You will see every entry of your menu.
In order to know if an entry got children, you can check if $children_elements[$id] is empty, with $id beeing the id of the element in question :

$this->has_children = ! empty( $children_elements[ $id ] );

So you could check for each entry of your menu if it has children, and if yes, check if any children have children of his own :

<?php
/**
* menu_walker
*
* @since 1.0.0
* @package My Theme WordPress
*/

if ( ! class_exists( 'MyThemeWP_Top_Menu_Walker' ) ) {
class MyThemeWP_Top_Menu_Walker extends Walker_Nav_Menu {

  /**
  * Find menu elements with children containing children and give them the super-parent-class class
  * Then call the default display_element method
  */
  public  function display_element( $element, &$children_elements, $max_depth, $depth=0, $args, &$output ){
    if ( ! $element ) {
      return;
    }

    $id_field = $this->db_fields['id'];
    $id = $element->$id_field; 

    //var_dump($children_elements[ $id ]); // List the children elements of the element with $id

    $this->has_children = ! empty( $children_elements[ $id ] );
    if ( isset( $args[0] ) && is_array( $args[0] ) ) {
      $args[0]['has_children'] = $this->has_children; // Back-compat.
    }

    // If this element have children
    if ( ! empty( $children_elements[$id] ) //&& ( $depth == 0 ) // Remove this comment to apply the super-parent-class only to root elements
    //|| $element->category_post != '' && $element->object == 'category'
    ) {

      // var_dump($children_elements[$id]);

      // Loop through it's children
      foreach ($children_elements[$id] as &$child_element) {
        //var_dump($child_element->ID);
        //var_dump(! empty( $children_elements[$child_element->ID] ));

        // If this child has children of it's own, add super-parent-class to it's parent
        if ( ! empty( $children_elements[$child_element->ID] ) ){
          $element->classes[] = 'super-parent-class';
        }
      }
    }

    // Call default method from virtual parent class
    parent::display_element( $element, $children_elements, $max_depth, $depth, $args, $output );
    }

  } // class MyThemeWP_Top_Menu_Walker END
}
?>

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