WidgetBase::flagErrors

public WidgetBase::flagErrors(FieldItemListInterface $items, ConstraintViolationListInterface $violations, array $form, FormStateInterface $form_state)

public function flagErrors(FieldItemListInterface $items, ConstraintViolationListInterface $violations, array $form, FormStateInterface $form_state) {
  $field_name = $this->fieldDefinition->getName();

  $field_state = static::getWidgetState($form['#parents'], $field_name, $form_state);

  if ($violations->count()) {
    // Locate the correct element in the form.
    $element = NestedArray::getValue($form_state->getCompleteForm(), $field_state['array_parents']);

    // Do not report entity-level validation errors if Form API errors have
    // already been reported for the field.
    // @todo Field validation should not be run on fields with FAPI errors to
    //   begin with. See https://www.drupal.org/node/2070429.
    $element_path = implode('][', $element['#parents']);
    if ($reported_errors = $form_state->getErrors()) {
      foreach (array_keys($reported_errors) as $error_path) {
        if (strpos($error_path, $element_path) === 0) {
          return;
        }
      }
    }

    // Only set errors if the element is visible.
    if (Element::isVisibleElement($element)) {
      $handles_multiple = $this->handlesMultipleValues();

      $violations_by_delta = array();
      foreach ($violations as $violation) {
        // Separate violations by delta.
        $property_path = explode('.', $violation->getPropertyPath());
        $delta = array_shift($property_path);
        $violations_by_delta[$delta][] = $violation;
        $violation->arrayPropertyPath = $property_path;
      }

      /** @var \Symfony\Component\Validator\ConstraintViolationInterface[] $delta_violations */
      foreach ($violations_by_delta as $delta => $delta_violations) {
        // Pass violations to the main element:
        // - if this is a multiple-value widget,
        // - or if the violations are at the ItemList level.
        if ($handles_multiple || !is_numeric($delta)) {
          $delta_element = $element;
        }
        // Otherwise, pass errors by delta to the corresponding sub-element.
        else {
          $original_delta = $field_state['original_deltas'][$delta];
          $delta_element = $element[$original_delta];
        }
        foreach ($delta_violations as $violation) {
          // @todo: Pass $violation->arrayPropertyPath as property path.
          $error_element = $this->errorElement($delta_element, $violation, $form, $form_state);
          if ($error_element !== FALSE) {
            $form_state->setError($error_element, $violation->getMessage());
          }
        }
      }
    }
  }
}