Trying to edit a locked field in the UI throws a WSOD

"Edit the body field, and replace `body` in the URL with the layout field name: `layout_builder__layout`"

I am not sure to understand what is meaned there. Is it possible to have more details ?

Hi frederiko_,

Certainly!
Editing the "body"-field will lead you to a URL like:
/admin/structure/types/manage/page/fields/node.page.body

Replace the last part (the field's machine name, in this case 'body'), with the locked field's machine name, for example:
/admin/structure/types/manage/page/fields/node.page.layout_builder__layout

And it'll give you the WSOD.

The problem seems to be that in file core/modules/field_ui/field_ui.module,
The $form['field_storage']['subform'] doesn't seem to exist, in the function below.
I don't know what the correct solution would be.. I'd say the form still needs to be alterable, and we still need to trigger the alter hooks on the bottom.

/**
 * Implements hook_form_FORM_ID_alter() for field_config_edit_form.
 */
function field_ui_form_field_config_edit_form_alter(&$form, FormStateInterface $form_state) {
  if (!isset($form['field_storage']['subform'])) {
    return;
  }

  $field_config = $form_state->getFormObject()->getEntity();
  assert($field_config instanceof FieldConfigInterface);

  $form_id = 'field_storage_config_edit_form';
  $hook = 'form_' . $form_id;

  $field_storage_form = \Drupal::entityTypeManager()->getFormObject('field_storage_config', $form_state->getFormObject()->getOperation());
  $field_storage_form->setEntity($field_config->getFieldStorageDefinition());
  $subform_state = SubformState::createForSubform($form['field_storage']['subform'], $form, $form_state, $field_storage_form);

  \Drupal::moduleHandler()->alterDeprecated('Use hook_form_field_config_edit_form_alter() instead. See https://www.drupal.org/node/3386675.', $hook, $form['field_storage']['subform'], $subform_state, $form_id);
  \Drupal::theme()->alter($hook, $form['field_storage']['subform'], $subform_state, $form_id);
}

This needs to be fixed on 11.x (main) first.

I tried to work around this issue, and it seems to be resolved in Drupal 11.0.0 with fix 📌 Remove deprecated code from field_ui Fixed .

The function field_ui_form_field_config_edit_form_alter(), which caused an error, has been removed by fix #3442361, and now displays "The field Layout is locked and cannot be edited".

I have attached a screenshot of the operation check, so I would be happy if anyone could verify it.

For the tests