Let a Symfony bundle configure their own Doctrine EnumTypes via the PrependExtensionInterface

AppExtension.php

<?php

namespace AppBundle\DependencyInjection;

use Symfony\Component\DependencyInjection\ContainerBuilder;
use Symfony\Component\DependencyInjection\Extension\PrependExtensionInterface;
use Symfony\Component\HttpKernel\DependencyInjection\Extension;

class AppExtension extends Extension implements PrependExtensionInterface
{

    /**
     * @inheritdoc
     */
    public function load(array $config, ContainerBuilder $container)
    {
        // Do nothing, we only care about the prepend functionality (for this demo)
    }

    /**
     * @inheritdoc
     */
    public function prepend(ContainerBuilder $container)
    {
        $container->prependExtensionConfig('doctrine', [
            'dbal' => [
                'types' => [
                    'BookFormatType' => 'AppBundle\DBAL\Types\BookFormatType',
                    // ... all of our bundle's Enums
                ]
            ]
        ]);
    }
}