class ExtensionExistsConstraintValidator

class ExtensionExistsConstraintValidator extends ConstraintValidator implements ContainerInjectionInterface {
  
  /**
   * The module handler service.
   *
   * @var \Drupal\Core\Extension\ModuleHandlerInterface
   */
  protected ModuleHandlerInterface $moduleHandler;
  
  /**
   * The theme handler service.
   *
   * @var \Drupal\Core\Extension\ThemeHandlerInterface
   */
  protected ThemeHandlerInterface $themeHandler;
  
  /**
   * Constructs a ExtensionExistsConstraintValidator object.
   *
   * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
   *   The module handler service.
   * @param \Drupal\Core\Extension\ThemeHandlerInterface $theme_handler
   *   The theme handler service.
   */
  public function __construct(ModuleHandlerInterface $module_handler, ThemeHandlerInterface $theme_handler) {
    $this->moduleHandler = $module_handler;
    $this->themeHandler = $theme_handler;
  }
  
  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container) {
    return new static($container->get('module_handler'), $container->get('theme_handler'));
  }
  
  /**
   * {@inheritdoc}
   */
  public function validate(mixed $extension_name, Constraint $constraint) {
    $variables = [
      '@name' => $extension_name,
    ];
    switch ($constraint->type) {
      case 'module':
        // This constraint may be used to validate nullable (optional) values.
        if ($extension_name === NULL) {
          return;
        }
        // Some plugins are shipped in `core/lib`, which corresponds to the
        // special `core` extension name.
        // For example: \Drupal\Core\Menu\Plugin\Block\LocalActionsBlock.
        if ($extension_name === 'core') {
          return;
        }
        if (!$this->moduleHandler
          ->moduleExists($extension_name)) {
          $this->context
            ->addViolation($constraint->moduleMessage, $variables);
        }
        break;

      case 'theme':
        // This constraint may be used to validate nullable (optional) values.
        if ($extension_name === NULL) {
          return;
        }
        if (!$this->themeHandler
          ->themeExists($extension_name)) {
          $this->context
            ->addViolation($constraint->themeMessage, $variables);
        }
        break;

      default:
        throw new \InvalidArgumentException("Unknown extension type: '{$constraint->type}'");
    }
  }

}