class.Walker_Nav_Menu_Edit_Roles_4.7.php

<?php
/**
 * Custom Walker for Nav Menu Editor
 * Add wp_nav_menu_item_custom_fields hook
 * Hat tip to @kucrut and Menu Icons for the preg_replace() idea
 * means I no longer have to translate core strings
 *
 * @package Nav Menu Roles
 * @since 1.8.6
 * @uses Walker_Nav_Menu_Edit
 */
class Walker_Nav_Menu_Edit_Roles extends Walker_Nav_Menu_Edit {

    /**
     * Start the element output.
     *
     * @see Walker_Nav_Menu::start_el()
     *
     * @param string $output Passed by reference. Used to append additional content.
     * @param object $item   Menu item data object.
     * @param int    $depth  Depth of menu item. Used for padding.
     * @param array  $args   Not used.
     * @param int    $id     Not used.
     */
    public function start_el( &$output, $item, $depth = 0, $args = array(), $id = 0 ) {
        $item_output = '';
        $output .= parent::start_el( $item_output, $item, $depth, $args, $id );
        $output .= preg_replace(
            // NOTE: Check this regex on major WP version updates!
            '/(?=<fieldset[^>]+class="[^"]*field-move)/',
            $this->get_custom_fields( $item, $depth, $args ),
            $item_output
        );
    }


    /**
     * Get custom fields
     *
     * @access protected
     * @since 0.1.0
     * @uses do_action() Calls 'menu_item_custom_fields' hook
     *
     * @param object $item  Menu item data object.
     * @param int    $depth  Depth of menu item. Used for padding.
     * @param array  $args  Menu item args.
     * @param int    $id    Nav menu ID.
     *
     * @return string Form fields
     */
    protected function get_custom_fields( $item, $depth, $args = array(), $id = 0 ) {
        ob_start();
        $item_id = intval( $item->ID );
        /**
         * Get menu item custom fields from plugins/themes
         *
         * @since 0.1.0
         *
         * @param int    $item_id post ID of menu
         * @param object $item  Menu item data object.
         * @param int    $depth  Depth of menu item. Used for padding.
         * @param array  $args  Menu item args.
         *
         * @return string Custom fields
         */
        do_action( 'wp_nav_menu_item_custom_fields', $item_id, $item, $depth, $args );
        return ob_get_clean();
    }
} // Walker_Nav_Menu_Edit