Issue #2350939: Implement a generic revision UI

core/lib/Drupal/Core/Entity/Controller/EntityRevisionViewController.php

+<?php
+
+namespace Drupal\Core\Entity\Controller;
+
+use Drupal\Core\Datetime\DateFormatterInterface;
+use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
+use Drupal\Core\Entity\EntityRepositoryInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Entity\RevisionableInterface;
+use Drupal\Core\Entity\RevisionLogInterface;
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Drupal\Core\StringTranslation\TranslationInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Defines a controller to view an entity revision.
+ */
+class EntityRevisionViewController implements ContainerInjectionInterface {
+
+  use StringTranslationTrait;
+
+  /**
+   * Creates a new EntityRevisionViewController.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entityTypeManager
+   *   The entity type manager.
+   * @param \Drupal\Core\Entity\EntityRepositoryInterface $entityRepository
+   *   The entity repository.
+   * @param \Drupal\Core\Datetime\DateFormatterInterface $dateFormatter
+   *   The date formatter.
+   * @param \Drupal\Core\StringTranslation\TranslationInterface $translation
+   *   The string translation manager.
+   */
+  public function __construct(
+    protected EntityTypeManagerInterface $entityTypeManager,
+    protected EntityRepositoryInterface $entityRepository,
+    protected DateFormatterInterface $dateFormatter,
+    TranslationInterface $translation,
+  ) {
+    $this->setStringTranslation($translation);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('entity_type.manager'),
+      $container->get('entity.repository'),
+      $container->get('date.formatter'),
+      $container->get('string_translation'),
+    );
+  }
+
+  /**
+   * Provides a page to render a single entity revision.
+   *
+   * @param \Drupal\Core\Entity\RevisionableInterface $_entity_revision
+   *   The Entity to be rendered. Note this variable is named $_entity_revision
+   *   rather than $entity to prevent collisions with other named placeholders
+   *   in the route.
+   * @param string $view_mode
+   *   (optional) The view mode that should be used to display the entity.
+   *   Defaults to 'full'.
+   *
+   * @return array
+   *   A render array.
+   */
+  public function __invoke(RevisionableInterface $_entity_revision, string $view_mode = 'full'): array {
+    $entityTypeId = $_entity_revision->getEntityTypeId();
+
+    $page = $this->entityTypeManager
+      ->getViewBuilder($entityTypeId)
+      ->view($_entity_revision, $view_mode);
+
+    $page['#entity_type'] = $entityTypeId;
+    $page['#' . $entityTypeId] = $_entity_revision;
+    return $page;
+  }
+
+  /**
+   * Provides a title callback for a revision of an entity.
+   *
+   * @param \Drupal\Core\Entity\RevisionableInterface $_entity_revision
+   *   The revisionable entity, passed in directly from request attributes.
+   *
+   * @return \Drupal\Core\StringTranslation\TranslatableMarkup
+   *   The title for the entity revision view page.
+   */
+  public function title(RevisionableInterface $_entity_revision): TranslatableMarkup {
+    $revision = $this->entityRepository->getTranslationFromContext($_entity_revision);
+    $titleArgs = ['%title' => $revision->label()];
+    if (!$revision instanceof RevisionLogInterface) {
+      return $this->t('Revision of %title', $titleArgs);
+    }
+
+    $titleArgs['%date'] = $this->dateFormatter->format($revision->getRevisionCreationTime());
+    return $this->t('Revision of %title from %date', $titleArgs);
+  }
+
+}