ViewModeAccessCheck.php

<?php

/**
 * @file
 * Contains \Drupal\field_ui\Access\ViewModeAccessCheck.
 */
namespace Drupal\field_ui\Access;

use Drupal\Core\Access\AccessCheckInterface;
use Symfony\Component\Routing\Route;
use Symfony\Component\HttpFoundation\Request;

/**
 * Allows access to routes to be controlled by an '_access' boolean parameter.
 */
class ViewModeAccessCheck implements AccessCheckInterface {

  /**
   * {@inheritdoc}
   */
  public function applies(Route $route) {
    return array_key_exists('_field_ui_view_mode_access', $route
      ->getRequirements());
  }

  /**
   * {@inheritdoc}
   */
  public function access(Route $route, Request $request) {
    if ($entity_type = $request->attributes
      ->get('entity_type')) {
      $bundle = $request->attributes
        ->get('bundle');
      $view_mode = $request->attributes
        ->get('view_mode');
      $view_mode_settings = field_view_mode_settings($entity_type, $bundle);
      $visibility = $view_mode == 'default' || !empty($view_mode_settings[$view_mode]['status']);
      if ($visibility) {
        $permission = $route
          ->getRequirement('_field_ui_view_mode_access');
        return user_access($permission);
      }
    }
  }

}