Steps to reproduce the issue

Create a custom field «component»\src\Field\DatacenterField.php which loads has a helper method to get the options values from the database. Then create a form where the fueld is declared like this:

<field
  name="datacenters"
  type="supplierDatacenter"
  label="Main datacenter"
  validate="options"
  default="FR"
/>

Click 'save' and get an error...

Expected result

Serverside validation as the option is selected from the list of options provided and not somehow injected

Actual result

A message stating 'Invalid field: «field name»'.

System information (as much as possible)

The issue is somewhere in the OptionsRule.php as this is the rule supposed to validate the input. It seems the OptionsRule looks at the xml definition of the field, but this lacks the valid options.

Additional comments

Possibly server-side validation is not possible for custom list fields, but this is not very clear.