Why is overriding a block function causing template errors?

Question

Simply put, I'm trying to load order information on the Onepage Checkout Success page. I have a module set up, these files are under app/code/Tainted/Checkout:

registration.php (standard)

etc/di.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../../../../../lib/internal/Magento/Framework/ObjectManager/etc/config.xsd">
    <preference for="Magento\Checkout\Block\Onepage\Success" type="Tainted\Checkout\Block\Onepage\Success" />
</config>

etc/module.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
    <module name="Tainted_Checkout" setup_version="0.0.1"/>
</config>

Finally, Block/Onepage/Success.php:

<?php
namespace Tainted\Checkout\Block\Onepage;

class Success extends \Magento\Checkout\Block\Onepage\Success
{
    /**
     * Prepares block data
     *
     * @return void
     */
    protected function prepareBlockData()
    {
        $order = $this->_checkoutSession->getLastRealOrder();

        $this->addData(
            [
                'is_order_visible' => $this->isVisible($order),
                'view_order_url' => $this->getUrl(
                    'sales/order/view/',
                    ['order_id' => $order->getEntityId()]
                ),
                'print_url' => $this->getUrl(
                    'sales/order/print',
                    ['order_id' => $order->getEntityId()]
                ),
                'can_print_order' => $this->isVisible($order),
                'can_view_order'  => $this->canViewOrder($order),
                'order_id'  => $order->getIncrementId(),
                'grand_total' => $order->getGrandTotal(),
                'delivery_method' => $order->getAddressShippingMethod(),
                'items' => $order->getAllItems()
            ]
        );
    }
}

The prepareBlockData function is copied from the original class and I've added a few extra lines to it to pass more data to the frontend template. E.g. grand total.

However, when I checkout the success page is missing the success.phtml template and the only errors I can find appear in the system.log as follows:

[2017-04-27 16:17:41] main.CRITICAL: Invalid template file: 'button.phtml' in module: 'Tainted_Checkout' block's name: 'checkout.success.print.button' [] []
[2017-04-27 16:17:41] main.CRITICAL: Invalid template file: 'success.phtml' in module: 'Tainted_Checkout' block's name: 'checkout.success' [] []

I haven't touched those templates yet but that error reads as though they're missing, not broken anyway. I've tried copying them in to app/design/frontend/Tainted/theme/Magento_Checkout/templates and I've copied the checkout_onepage_success.xml file in to the layout folder but that hasn't helped either.

It feels like I'm trying to do something very simple (in Magento 2 terms) but I can't see where I've gone wrong. Any help would be greatly appreciated.

Answer 1

The templates are being referenced like template="button.phtml" in checkout_onepage_success.xml so you need to add

protected function _construct()
{
    $this->setModuleName('Magento_Checkout');
    parent::_construct();
}

to your block to tell magento where to look for those templates, otherwise it looks in the current module.

Usually templates are referenced with the module name, e.i. Some_Module::template.phtml, in which case you wouldn't have to do this.

Answer 2

Try this:

If you don't already have a default.xml file in your module, create it at view/frontend/layout/default.xml. Then add the following handle at the top, right after the <page> tag:

<update handle="checkout_onepage_success"/>

That will pull in the layout xml for the base module into your module. To be explicitly clear about that process, here's the full code:

<?xml version="1.0"?>
<page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
    <update handle="checkout_onepage_success"/>
</page>

This should pull in the XML into your module. I haven't tried it but give it a go and let me know if that works.