Move original validation rule to field_validation_legacy module

After I move them to field_validation_legacy, to enable field_validation_legacy module, I get fatal errors:

Drupal\Component\Plugin\Exception\PluginNotFoundException: The "unique_field_validation_rule" plugin does not exist. Valid plugin IDs for Drupal\field_validation\FieldValidationRuleManager are: length_constraint_rule in Drupal\Core\Plugin\DefaultPluginManager->doGetDefinition() (line 53 of core\lib\Drupal\Component\Plugin\Discovery\DiscoveryTrait.php).

Which make it difficult to update. It seems Drupal core does not support enable a new module when there is PluginNotFoundException.

It is possible. after another test, I enable it.

Automatically closed - issue fixed for 2 weeks with no activity.

Upgrading from 8.x dev to 3.0.x dev causes the error described in #2 with no way out so the user is forced to downgrade back to 8.x - There is no obvious way for the average user to upgrade now to v3.

There is document for update:
https://www.drupal.org/docs/extending-drupal/contributed-modules/contrib... →