dependencySerializationTraitProperty.unsupportedPrivateProperty false positive for non-service properties

[travis-bradbury]

Bug report

dependencySerializationTraitProperty.unsupportedPrivateProperty reports an issue for properties that aren't relevant to DependencySerializationTrait. See #1024 for an example.

DependencySerializationTrait only looks at properties that are objects and services (by looking up the service ID from the value) https://git.drupalcode.org/project/drupal/-/blob/main/core/lib/Drupal/Core/DependencyInjection/DependencySerializationTrait.php#L39. A property that's a scalar value (eg, bool) is trivially serializable and is ignored by the trait, but it reported by dependencySerializationTraitProperty.unsupportedPrivateProperty.

Code snippet that reproduces the problem

Example 7c0932e.

[travis-bradbury]

In my code, there's a handful of places this happens. In one simple case I've rewritten it to avoid this, but another matches a pattern we have in core: entity forms with a property for the entity.

It looks like this:

final class FooConfirmForm extends FormBase implements ConfirmFormInterface {

    private ?Foo $foo;
}

FormBase uses DependencySerializationTrait, so we get the error. The same pattern is in core's ContentEntityForm:

class ContentEntityForm extends EntityForm implements ContentEntityFormInterface {

  /**
   * The entity being used by this form.
   *
   * @var \Drupal\Core\Entity\ContentEntityInterface|\Drupal\Core\Entity\RevisionLogInterface
   */
  protected $entity;

That won't trigger dependencySerializationTraitProperty.unsupportedPrivateProperty since it's protected, but it's essentially the same as what I'm doing in my forms. In both cases, the class uses DependencySerializationTrait and has properties that are not services.