ECA "form field: set as required" does not work with a file upload field with cardinality > 1

Digging further, it appears that the problem is unrelated to ECA.

If we disable the ECA, and try to set `['#required'] = TRUE` in code, we get the same results:
- validation error is thrown for cardinality 1 or unlimited
- validation error is not thrown for cardinality > 1 (that is, 2, 3, or some other number)

Tested with the following code:

function mymodule_form_alter(&$form, $form_state, $form_id): void {
  if ($form_id == 'node_page_form') {
    $form_object = $form_state->getFormObject();
    $entity = $form_object->getEntity();
    foreach ($entity->getFieldDefinitions() as $field_name => $field_definition) {
      if ($field_definition->getName() == 'field_file') {
        // Set the field as required
        $form[$field_name]['widget'][0]['#required'] = TRUE;
      }
    }
  }
}

Moved the issue to the core issue queue.

Thank you to @tstoeckler and @rodrigoaguilera for your help at Drupal Dev Days Leuven.
Tests are now green, though perhaps more tests are needed.

Since the fix appears to be in the file module can test be moved there too

Thanks

Changes are made on on 11.x (our main development branch) first, and are then back ported as needed according to the Core change policies → .