WooCommerce: Allow free shipping when certain product is in cart

wc-allow-free-shipping-when-certain-product-in-cart

add_filter( 'woocommerce_shipping_free_shipping_is_available', 'prefix_is_available_for_certain_products', 10, 3 );
/**
 * @param bool                      $is_available
 * @param array                     $package Shipping package.
 * @param WC_Shipping_Free_Shipping $shipping_class
 *
 * @return bool
 */
function prefix_is_available_for_certain_products( $is_available, $package, $shipping_class ) {

	// Bail, if already allowed
	if ( $is_available ) {
		return $is_available;
	}

	// Add your product IDs
	$product_map = array(
		50,
		47,
		44
	);

	foreach ( $package['contents'] as $hash => $data ) {
		$id = 0 < $data['variation_id'] ? $data['variation_id'] : $data['product_id'];

		if ( in_array( $id, $product_map ) ) {
			return true;
		}
	}

	return $is_available;
}