WooCommerce Display out of stock variable products as unavailable

functions.php

/**
 * Disable out of stock variations
 * https://github.com/woocommerce/woocommerce/blob/826af31e1e3b6e8e5fc3c1004cc517c5c5ec25b1/includes/class-wc-product-variation.php
 * @return Boolean
 * Description: unset WooCommerce billing & shipping address_1 field in checkout in favor for 2 new custom fields street and houseno
 * Author: Code Agency
 * Author URI: https://codeagency.be
 */

function codeagency_variation_is_active( $active, $variation ) {
	if( ! $variation->is_in_stock() ) {
		return false;
	}
	return $active;
}
add_filter( 'woocommerce_variation_is_active', 'codeagency_variation_is_active', 10, 2 );