Remove unnecessary constraint from moderation state transition validation

This is a test (ignore)

I've had a look at this and found that:

Do we need the same constraint on both fields?

Nope, when the constraint is checked for the ContentModerationState entity, it fails the first check in the constraint:

    if (!$this->moderationInformation->isModeratedEntity($entity)) {
      return;
    }

Given the checks seem centered around the entity actually being moderated, it seems like it would be a lot of effort to make the constraint work with both entities for not much benefit, given the data stored in the field on the unsupported entity has already been validated.

- Is it even valid?

Looks like there is a test which tries to set invalid states (EntityStateChangeValidationTest) and the constraint is used there.

- Does it work since we changed to a computed field?

Yep, it looks like the constraint is checked for computed fields.

tl;dr, it can be removed from ContentModerationState, it's valid for the computed field with tests to prove it.

Wrong version.

Yeah, I'm stumped on what we would actually be testing with this removed, given it never did anything to begin with.

Personally I don't see the need for a test or to validate this stuff. updateOrCreateFromEntity is marked as internal, so I see this issue as removing some dead code.

Based on the save method interacting with the parent entity, I think this actually proves there isn't a way to trigger this without using an internal method. We could write a validator specifically for this entity, but personally I think it's extra code to maintain for not much benefit.

The title of this issue is way scarier than the patch in it.

Yeah this constraint is probably a copy&paste error...

  /**
   * {@inheritdoc}
   */
  public function validate($value, Constraint $constraint) {
    /** @var \Drupal\Core\Entity\EntityInterface $entity */
    $entity = $value->getEntity();

    // Ignore entities that are not subject to moderation anyway.
    if (!$this->moderationInformation->isModeratedEntity($entity)) {
      return;
    }

It is always going to just return cause you can't moderation and ContentModerationState content entity - fortunately because that would be beyond inception.

Committed and pushed 2a55d2d to 8.4.x and 6983b38 to 8.3.x. Thanks!