Orders products by stock, putting out-of-stock ones to the end of the list

functions.php

// Orders products by stock, putting out-of-stock ones to the end of the shop and category archives
add_filter( 'posts_clauses', 'order_by_stock_status' );
function order_by_stock_status( $args ) {
	global $wpdb;

	$join_suffix = $args['join'];

	if ( is_woocommerce() && !is_admin() ) {
		$args['join']    = " LEFT JOIN {$wpdb->wc_product_meta_lookup} wc_product_meta_lookup ON $wpdb->posts.ID = wc_product_meta_lookup.product_id " . $join_suffix;
		$args['orderby'] = ' wc_product_meta_lookup.stock_status ASC, wc_product_meta_lookup.product_id DESC ';
	}

	return $args;
}