ConfigSubscriber.php

<?php

namespace Drupal\config;

use Drupal\Core\Config\ConfigEvents;
use Drupal\Core\Config\ConfigImporterEvent;
use Drupal\Core\Config\ConfigImportValidateEventSubscriberBase;

/**
 * Config subscriber.
 */
class ConfigSubscriber extends ConfigImportValidateEventSubscriberBase {
    
    /**
     * Checks that the Configuration module is not being uninstalled.
     *
     * @param \Drupal\Core\Config\ConfigImporterEvent $event
     *   The config import event.
     */
    public function onConfigImporterValidate(ConfigImporterEvent $event) {
        // Make sure config syncs performed via the Config UI don't break, but
        // don't worry about syncs initiated via the command line.
        if (PHP_SAPI === 'cli') {
            return;
        }
        $importer = $event->getConfigImporter();
        $core_extension = $importer->getStorageComparer()
            ->getSourceStorage()
            ->read('core.extension');
        if (!isset($core_extension['module']['config'])) {
            $importer->logError($this->t('Can not uninstall the Configuration module as part of a configuration synchronization through the user interface.'));
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public static function getSubscribedEvents() : array {
        $events[ConfigEvents::IMPORT_VALIDATE][] = [
            'onConfigImporterValidate',
            20,
        ];
        return $events;
    }

}