Call to undefined method Drupal\Core\TypedData\DataDefinition::getPropertyDefinitions()

getPropertyDefinition comes from \Drupal\Core\TypedData\ComplexDataDefinitionInterface and \Drupal\Core\TypedData\ComplexDataDefinitionBase which implements that method.

As far as I remember, all xero data type plugins should use a complex data definition, but I think that Drupal's Typed Data Manager will technically let a data type be instantiated with a different definition. My guess is that something happened during denormalization that caused the data type to be instantiated incorrectly.

In my case, this error is happening when trying to add a Xero Reference with the xero autocomplete widget to a Xero Item. It fails when trying to getProperties on the xero Detail Datatype.

It seems to be an issue in \Drupal\xero\TypedData\Definition\ItemDefiniton, where the class DataDefinition for

$info['PurchaseDetails'] = DataDefinition::create('xero_detail')->setLabel('Purchase Details');
$info['SalesDetails'] = DataDefinition::create('xero_detail')->setLabel('Sales Details');

should be:

$info['PurchaseDetails'] = DetailDefinition::create('xero_detail')->setLabel('Purchase Details');
$info['SalesDetails'] = DetailDefinition::create('xero_detail')->setLabel('Sales Details');

I've updated the MR

Thank you for finding the root cause. This looks good to me. I added a test to go through non-list properties that start with "xero" and assert the definition interface.

Merged.