SmartDateItemNormalizer::normalize() return type incompatible with TimestampItemNormalizer in Drupal 11.4+

Hello,
I've raised MR for this.
Kindly check and review it.

Thank you!

I'm concerned that this change will break any site running Drupal <11.4, which would be its own critical issue.

I don't love the idea of having to have a new version that would only support Drupal 11.4+. Are there alternatives we could consider?

@mandclu

With the help of AI

> The good news is that return types in PHP are covariant: an overriding/implementing method may declare a narrower return type than the interface it implements, but not a wider one. Since array is one of the members of the union array|string|int|float|bool|\ArrayObject|null, declaring your method as returning plain array is a valid covariant override of an interface that declares the wider union. So this single declaration satisfies both the new interface (: array) and the old one (: array|string|int|float|bool|\ArrayObject|NULL):

Thanks for that @dalin. I was able to load a patched version of Smart Date in Drupal 11.3 and didn't see any errors. That said, I didn't realize at the time that there is actually more required to trigger the error.

Also leaning into our robot overlords for advice:

The reason you likely can't reproduce it: the fatal error only fires when SmartDateItemNormalizer is actually autoloaded, which only happens during a serialization request. It won't appear on normal page loads. To reproduce it you need:

The serialization module enabled (it's the one that changed the parent class signature). JSON:API or REST module being enabled is the typical trigger.
A content type with a Smart Date field.
An actual serialization request against a node/entity with that field — e.g., a JSON:API GET: GET /jsonapi/node/article/<uuid> or a REST endpoint call.

If your local site doesn't use REST/JSON:API, or doesn't have the serialization module enabled, you'd never load the normalizer class and would never see the error.

I was ultimately able to reproduce the error by enabling JSON:API (and not before). Subsequently I was able to reproduce the error on the command line with (using a node with a Smart Date field):

ddev drush php-eval "\Drupal::service('serializer')->normalize(\Drupal\node\Entity\Node::load(1), 'application/json');"

This allowed me to confirm that the provided patch does, in fact resolve the fatal error. I feel like I should give contribution credit to Claude as well :P

Thanks for the work here. I will roll a new release with this fix.