Handling WC Notices about co-cart HOT 3 CLOSED

// takes a diff of WC notices before and after operation
function notice_sandwich($f) {
	$old = WC()->session->get( 'wc_notices', array() );
	$f();
	$new = WC()->session->get( 'wc_notices', array() );

	// remove new notices from notice queue
	wc_set_notices($old);

	return woocommerce_notices_diff($old, $new);
}

function woocommerce_notices_diff($old, $new) {
	$diff = [];
	if(isset($old['error'])) {
		$diff['error'] = array_slice($new['error'], count($old['error']));
	} elseif(isset($new['error'])) {
		$diff['error'] = $new['error'];
	}
	if(isset($old['success'])) {
		$diff['success'] = array_slice($new['success'], count($old['success']));
	} elseif(isset($new['success'])) {
		$diff['success'] = $new['success'];
	}
	return $diff;
}

$coupon_code = wc_clean( $data['coupon_code'] );

$notices = notice_sandwich(function() use($coupon_code) { 
	WC()->cart->apply_coupon($coupon_code);
});