Add support for compound fields like Name and Address fields

Updated the description to take into account how the https://www.drupal.org/project/address and https://www.drupal.org/project/name modules let site-builders manage which sub-fields are required.

Updated title to clarify that this isn't about cardinality, but fields types that include multiple fields--compound fields.

Original report

The original report proposed that all subfields should be marked optional when reproducing this issue. It then suggested that the field could be subsequently submitted as Published without the desired required fields. This makes sense because there was no field marked as required. ROP validation kicks in if the field is left completely empty.

For the Address field, this means that to not have selected a Country, it would not pass Require on Publish validation. And it correctly does not.

For the Name field, it does not even allow you to set all subfields as optional, at least Given or Family must be required:

If I were to fill in the Given and Family fields, and Select a Country, this is able to be saved as Published.

Gave this a shot.

/**
 * Implements hook_field_widget_complete_form_alter().
 */
function require_on_publish_field_widget_complete_form_alter(&$field_widget_complete_form, FormStateInterface $form_state, $context) {
  $field_config = $context['items']->getFieldDefinition();
  $field_name = $field_widget_complete_form['widget']['#field_name'];
  /** @var \Drupal\Core\Entity\EntityFormInterface $form_object */
  $form_object = $form_state->getFormObject();
  if ($form_object instanceof EntityFormInterface) {
    /** @var \Drupal\Core\Entity\ContentEntityInterface $entity */
    $entity = $form_object->getEntity();
    if (_require_on_publish_entity_is_publishable(get_class($entity))) {
      // $field = $entity->getFields()[$field_name];
      // $field_config = $field->getFieldDefinition();
      if (($field_config instanceof FieldConfigInterface)) {
        if ($field_config->getThirdPartySetting('require_on_publish', 'require_on_publish', FALSE)) {
          $place_breakpoint_here = 'Analyze the available Widget';
          // Loop the widget sub-fields and determine if they're required. Then,
          // treat each required subfield as if it were required on publish.
        }
      }
    }
  }
}

Tried similar attempts from preprocess hooks, like require_on_publish_preprocess_form_element(). The problem is that I cannot get a combination of render array and the entity context necessary to alter the render array to:

1. Determine the subfield's parent is required on publish.
2. Remove the required attribute.
3. Somehow implement the require_on_publish logic.

I am open to suggestions and willing to accept DMs in #slack.

Just had an idea, noting it here so I don't forget.

What if I tackle this from a new Constraint?

I was able to Disable HTML5 validation → to get around the Address module's required attribute. So, similar to Name, I am getting the required subfield validation.

Using the existing constraint, if I could just get it to run the AddressFormatConstraintValidator before RequireOnPublishValidator, I think I would then be able to alter the $this->context->getViolations.

Tried increasing the module weight with module_set_weight() to no avail.

A patch supporting the Name field.