CardinalityMediaLibraryWidget does not work with base field

Maybe I'm not following this... But here I go:

As far as I know, a media library field widget should only be available to fields of type media / entity reference.

I don't recall Drupal having base fields of type media / entity reference (Unless you create your own, of course).

Are you talking about this use case, specifically: Custom base fields of type media / entity reference?

Otherwise I cannot see how you would use a media library widget with a base field of a type other than media / entity reference.

Having said that, I haven't been able to reproduce the issue.

I would appreciate if you could provide more detailed instructions.

Okay, I'm sorry about the confusion.

I did a test in here and I can see that creating a custom base field on a custom entity is the use case you were referring to.

I can confirm that 1) I've been able to reproduce the error by following the instructions on the issue's description; 2) The patch on #3 by @stefan.korn did fix the error for me.

For other folks wanting to test this out, I suggest creating a custom content entity using drush gen content-entity and then using this sample field definition on your entity's baseFieldDefinitions() method:

      $fields['media_reference'] = BaseFieldDefinition::create('entity_reference')
      ->setLabel(t('Media Reference'))
      ->setDescription(t('Example field'))
      ->setSetting('target_type', 'media')
      ->setDisplayOptions('view', [
        'label' => 'above',
        'type' => 'entity_reference_label',
        'weight' => -4,
      ])
      ->setDisplayOptions('form', [
        'type' => 'media_library_widget',
        'weight' => -4,
        'settings' => [],
      ])
      ->setCardinality(3);

Hey,

I've re-rolled the patch in #3 to add back the type casting to the $cardinality variable.

This is needed to stop a failure in type comparison on line 473 of /core/modules/media_library/src/Plugin/Field/FieldWidget/MediaLibraryWidget.php.

Thanks

Luke