Workaround for broken mail context in Shopware

app_services.xml

<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="http://symfony.com/schema/dic/services http://symfony.com/schema/dic/services/services-1.0.xsd">

    <!-- Add some generic project services here -->
    <services>
        <service id="App\EventListener\FixBackendMailModule">
            <tag name="shopware.event_subscriber"/>
            <argument type="service" id="models"/>
        </service>

        <service id="App\EventListener\TemplateMailFactory">
            <tag name="shopware.event_subscriber"/>
        </service>
    </services>
</container>

app_src_Components_TemplateMail.php

<?php declare(strict_types=1);

namespace App\Components;

use Doctrine\DBAL\Types\ConversionException;
use Enlight_Components_Mail;
use Shopware\Components\Model\ModelManager;
use Shopware\Models\Mail\Mail;
use Shopware_Components_StringCompiler;
use Shopware_Components_TemplateMail;

class TemplateMail extends Shopware_Components_TemplateMail
{
    /**
     * @var Shopware_Components_TemplateMail
     */
    private $templateMail;

    public function __construct(Shopware_Components_TemplateMail $templateMail)
    {
        $this->templateMail = $templateMail;
    }

    public function createMail($mailModel, $context = [], $shop = null, $overrideConfig = [])
    {
        try {
            return $this->templateMail->createMail($mailModel, $context, $shop, $overrideConfig);
        } catch (ConversionException $exception) {
            $this->resetMailContext((string) $mailModel);

            return $this->templateMail->createMail($mailModel, $context, $shop, $overrideConfig);
        }
    }

    public function setModelManager(ModelManager $modelManager)
    {
        return call_user_func_array([$this->templateMail, __FUNCTION__], func_get_args());
    }

    public function getModelManager()
    {
        return call_user_func_array([$this->templateMail, __FUNCTION__], func_get_args());
    }

    public function setShop($shop)
    {
        return call_user_func_array([$this->templateMail, __FUNCTION__], func_get_args());
    }

    public function getShop()
    {
        return call_user_func_array([$this->templateMail, __FUNCTION__], func_get_args());
    }

    public function getTranslationReader()
    {
        return call_user_func_array([$this->templateMail, __FUNCTION__], func_get_args());
    }

    public function setTranslationReader($translationReader)
    {
        return call_user_func_array([$this->templateMail, __FUNCTION__], func_get_args());
    }

    public function setStringCompiler(Shopware_Components_StringCompiler $stringCompiler)
    {
        return call_user_func_array([$this->templateMail, __FUNCTION__], func_get_args());
    }

    public function getStringCompiler()
    {
        return call_user_func_array([$this->templateMail, __FUNCTION__], func_get_args());
    }

    public function loadValues(Enlight_Components_Mail $mail, Mail $mailModel, $overrideConfig = [])
    {
        return call_user_func_array([$this->templateMail, __FUNCTION__], func_get_args());
    }

    private function resetMailContext(string $mailModel): void
    {
        $this->templateMail->getModelManager()->getConnection()->update('s_core_config_mails', [
            'context' => null,
        ], [
            'name' => $mailModel,
        ]);
    }
}

app_src_EventListener_FixBackendMailModule.php

<?php declare(strict_types=1);

namespace App\EventListener;

use Doctrine\DBAL\Types\ConversionException;
use Doctrine\ORM\OptimisticLockException;
use Doctrine\ORM\ORMException;
use Doctrine\ORM\TransactionRequiredException;
use Enlight\Event\SubscriberInterface;
use PDO;
use Shopware\Components\Model\ModelManager;
use Shopware\Models\Mail\Mail;

class FixBackendMailModule implements SubscriberInterface
{
    /**
     * @var ModelManager
     */
    private $modelManager;

    public function __construct(ModelManager $modelManager)
    {
        $this->modelManager = $modelManager;
    }

    public static function getSubscribedEvents()
    {
        return [
            'Enlight_Controller_Action_Backend_Mail_getMails' => 'fix',
        ];
    }

    public function fix()
    {
        try {
            $this->modelManager->getRepository(Mail::class)->findAll();
        } catch (ConversionException $exception) {
            $mailIds = $this->getMailIds();

            foreach ($mailIds as $mailId) {
                try {
                    $this->modelManager->find(Mail::class, (int) $mailId);
                } catch (ConversionException $exception) {
                    $this->resetMailContext((int) $mailId);
                } catch (OptimisticLockException | TransactionRequiredException | ORMException $exception) {
                    continue;
                }
            }
        }
    }

    private function getMailIds(): array
    {
        return (array) $this->modelManager->getConnection()->createQueryBuilder()
            ->select('id')
            ->from('s_core_config_mails')
            ->execute()
            ->fetchAll(PDO::FETCH_COLUMN)
        ;
    }

    private function resetMailContext(int $id)
    {
        $this->modelManager->getConnection()->update('s_core_config_mails', [
            'context' => null,
        ], [
            'id' => $id,
        ]);
    }
}

app_src_EventListener_TemplateMailFactory.php

<?php declare(strict_types=1);

namespace App\EventListener;

use App\Components\TemplateMail;
use Enlight\Event\SubscriberInterface;
use Enlight_Event_EventArgs;
use Shopware\Components\DependencyInjection\Container;

class TemplateMailFactory implements SubscriberInterface
{
    public static function getSubscribedEvents()
    {
        return [
            'Enlight_Bootstrap_AfterInitResource_templatemail' => 'factory',
        ];
    }

    public function factory(Enlight_Event_EventArgs $args)
    {
        /** @var Container $container */
        $container = $args->getSubject();

        $service = $container->get('templatemail');

        $container->set('templatemail', new TemplateMail($service));
    }
}