Issue #3253649: Validate update_fetch_with_http_fallback setting

src/Validator/SettingsValidator.php

+<?php
+
+namespace Drupal\automatic_updates\Validator;
+
+use Drupal\automatic_updates\Event\ReadinessCheckEvent;
+use Drupal\automatic_updates\Updater;
+use Drupal\Core\Site\Settings;
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+use Drupal\Core\StringTranslation\TranslationInterface;
+use Drupal\package_manager\Event\PreCreateEvent;
+use Drupal\package_manager\Event\PreOperationStageEvent;
+use Symfony\Component\EventDispatcher\EventSubscriberInterface;
+
+class SettingsValidator implements EventSubscriberInterface {
+
+  use StringTranslationTrait;
+
+  /**
+   * Constructs a SettingsValidator object.
+   *
+   * @param \Drupal\Core\StringTranslation\TranslationInterface $translation
+   *   The string translation service.
+   */
+  public function __construct(TranslationInterface $translation) {
+    $this->setStringTranslation($translation);
+  }
+
+  /**
+   * Validates site settings before an update starts.
+   *
+   * @param \Drupal\package_manager\Event\PreOperationStageEvent $event
+   *   The event object.
+   */
+  public function checkSettings(PreOperationStageEvent $event): void {
+    if ($event->getStage() instanceof Updater && Settings::get('update_fetch_with_http_fallback')) {
+      $event->addError([
+        $this->t('The <code>update_fetch_with_http_fallback</code> setting must be disabled for automatic updates.'),
+      ]);
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getSubscribedEvents() {
+    return [
+      ReadinessCheckEvent::class => 'checkSettings',
+      PreCreateEvent::class => 'checkSettings',
+    ];
+  }
+
+}

[Ted Bowman]

don't we need class comment for core standards to pass?