override checkout index controller

Question

I would like to override only one line in checkout/index/index controller.

do I need to use preference or plugin or observer?

if (!$this->_customerSession->isLoggedIn() && !$checkoutHelper->isAllowedGuestCheckout($quote)) {

            $this->messageManager->addErrorMessage(__('Guest checkout is disabled.'));

            return $this->resultRedirectFactory->create()->setPath('checkout/cart');

        }

to

if (!$this->_customerSession->isLoggedIn() && !$checkoutHelper->isAllowedGuestCheckout($quote)) {

            $this->messageManager->addErrorMessage(__('Guest checkout is disabled.'));

            return $this->resultRedirectFactory->create()->setPath('customer/account/login');

        }

Answer 1

You can use preference like this in your custom module:

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
 <preference for=Magento\Checkout\Controller\Index\Index" 
             type="Vendor\Module\Controller\Index\Index" />
</config>

Answer 2

You have to use the Preference to override the controller.