Show WooCommerce basket total in wp_nav_menu item

class-theme-wc-walker.php

<?php
/**
 * A walker class for specific navigation menus in your theme, where you'd like to be
 * able to show your WooCommerce basket total
 *
 * @package YOUR_THEME
 * @since 1.0.0
 */
if (!class_exists('Theme_WC_Nav_Menu')) {
    class Theme_WC_Nav_Menu extends Walker_Nav_Menu {
        public function start_el( &$output, $item, $depth = 0, $args = array(), $id = 0 ) {
            parent::start_el($output, $item, $depth, $args, $id);

            if (in_array('wc-basket-total', $item->classes) && function_exists('WC')) {
                $output = str_replace('%n',
                    sprintf('<span class="total">%s</span>', WC()->cart->get_cart_contents_count()),
                $output);
            }
        }
    }
}

instructions.txt

You'll need to create a copy of the class-theme-wc-walker.php file in
your theme, and then include it in your functions.php file.

For this to work, we're targetting a specific class on a menu item in your
menu. So on the item where you want to show the basket total, you'll need
to add a class of "wc-basket-total"

As well as that, you'll also need to add "%n" wherever you want the total
to show up in the string. Aside from that, there's not much else to do.
But here's an exampe, just in case:

  My basket (%n)
  
..which, assuming the basket has 4 items in it, would render in your front-
end markup as:

  My basket (<span class="total">4</span>)

Feel free to fork and change the code above.

usage.php

<?php
    wp_nav_menu([
        'theme_location' => 'YOUR_MENU_NAME',
        'walker'         => new Theme_WC_Nav_Menu
    ]);