WooCommerce: Display In-Stock Products First

index.php

<?php
/**
 * WooCommerce: Display In-Stock Products First
 * https://www.linkedin.com/posts/activity-7254955257355456515-ypfV
 *
 * This code snippet reorders products in WooCommerce to show 
 * in-stock items first, followed by out-of-stock items. It uses 
 * the 'posts_clauses' filter to modify the default product query.
 * 
 * Usage:
 * - Add the code to your theme's 'functions.php' file or create
 *   a custom plugin to implement it.
 * - The code checks if the query is on a product archive page and
 *   modifies the query to prioritize in-stock products, ensuring
 *   better visibility for customers.
 * 
 * Developed by: amirhp-com
 * Website: https://amirhp.com
 *
 * Disclaimer:
 * - Use this code at your own risk. The developer is not responsible 
 *   for any issues, errors, or malfunctions that may occur as a result 
 *   of using this code. Always test in a development environment first.
 */

add_filter("posts_clauses", "reorder_products_in_stock_first", 10, 2);
function reorder_products_in_stock_first($clauses, $query) {
    if (is_admin() || !$query->is_main_query() || !$query->is_post_type_archive('product') && !$query->is_tax('product_cat') ) {return $clauses;}
    global $wpdb;
    $clauses['join'] .= " LEFT JOIN {$wpdb->postmeta} AS pm_stock ON {$wpdb->posts}.ID = pm_stock.post_id AND pm_stock.meta_key = '_stock_status' ";
    $clauses['orderby'] = " pm_stock.meta_value ASC, " . $clauses['orderby'];
    return $clauses;
}