WordPress Dirty Active Menu

functions.php

<?php 

add_filter( 'nav_menu_css_class', 'add_parent_url_menu_class', 10, 2 );

function add_parent_url_menu_class( $classes = array(), $item = false ) {
   
    // Get current URL
    $current_url = current_url();
    
    // Get homepage URL
    $homepage_url = trailingslashit(get_bloginfo('url'));
    
    // Exclude 404 and homepage
    if(is_404() || $item->url == $homepage_url) return $classes;
        if (strstr( $current_url, $item->url)) {
            
            // Add the 'parent_url' class
            $classes[] = 'parent_url';
        }
    return $classes;
}

function current_url() {
    
    // Protocol
    $url =  'http://';
    $url .= $_SERVER['SERVER_NAME'];
    
    // Port
    $url .= ('80' == $_SERVER['SERVER_PORT']) ? '' : ':' . $_SERVER['SERVER_PORT'];
    $url .= $_SERVER['REQUEST_URI'];

    return trailingslashit($url);
}