Define custom revision delete behavior for this module's field types.
This hook is invoked just before the data is deleted from field storage in field_attach_delete_revision(), and will only be called for fieldable types that are versioned.
\Drupal\Core\Entity\EntityInterface $entity: The entity for the operation.
$field: The field structure for the operation.
$instance: The instance structure for $field on $entity's bundle.
$langcode: The language associated with $items.
$items: $entity->{$field['field_name']}[$langcode], or an empty array if unset.
Note: this list is generated by pattern matching, so it may include some functions that are not actually implementations of this hook.
function hook_field_delete_revision(\Drupal\Core\Entity\EntityInterface $entity, $field, $instance, $langcode, &$items) {
foreach ($items as $delta => $item) {
// Decrement the file usage count by 1.
file_usage()
->delete(file_load($item['fid']), 'file', $entity
->entityType(), $entity
->id());
}
}