ViewsExposedForm::validateForm

public ViewsExposedForm::validateForm(array &$form, FormStateInterface $form_state)

public function validateForm(array &$form, FormStateInterface $form_state) {
  $view = $form_state->get('view');

  foreach (array('field', 'filter') as $type) {
    /** @var \Drupal\views\Plugin\views\ViewsHandlerInterface[] $handlers */
    $handlers = &$view->$type;
    foreach ($handlers as $key => $handler) {
      $handlers[$key]->validateExposed($form, $form_state);
    }
  }
  /** @var \Drupal\views\Plugin\views\exposed_form\ExposedFormPluginInterface $exposed_form_plugin */
  $exposed_form_plugin = $view->display_handler->getPlugin('exposed_form');
  $exposed_form_plugin->exposedFormValidate($form, $form_state);
}