Config schema issues with extended DS layouts

MR created, let me know if you have a better idea on the approach.

This may need a change record so site owners are aware they need to define the schema for all their custom layouts.
E.g.: If ds_my_layout uses the main Drupal\ds\Plugin\DsLayout class, then we have to use.:

layout_plugin.settings.ds_my_layout:
  type: ds.layout_plugin.settings.default

Static patch for composer, if anyone needs it.

Sorry for the delay, patch idea is logical, never thought about that!

Will double test what happens with custom layouts on existing projects when the schema isn't defined. I wonder if hook_config_schema_info_alter could help here (never ever used that hook, but who knows !)

Oh indeed, that could simplify things a lot.
Maybe loading all DS layouts and setting the default type to ds.layout_plugin.settings.default

So it's not possible (yet) to dynamically add new schema definitions, see ✨ Allow adding dynamic configuration schema Needs work and ConfigSchemaAlterException. Bummer, otherwise the code underneath would solve a lot.

Can't think of any other approach at the moment which doesn't involve warning users that they need to define a schema for the custom layouts in a module or theme. Let me think and experiment a bit more. But even if we don't find another solution, committing this isn't probably that much of a problem as config will still be imported afaik and everything will still keep on working.

(merged 8.x-3.x with the fork, but no other changes yet)

/**
 * Implements hook_config_schema_info_alter().
 */
function ds_config_schema_info_alter(&$definitions) {
  // Bummer, this is not allowed!
  foreach (DS::getLayouts() as $layout_name => $layout) {
    if ($layout->getClass() == 'Drupal\ds\Plugin\DsLayout') {
      $definitions['layout_plugin.settings.' . $layout_name]['type'] = 'ds.layout_plugin.settings.default';
    }
  }
}

Ok tried the following:

2. Used layout_plugin.settings.ds.[%parent.id] in ds.entity_display.schema.yml
3. Defined layout_plugin.settings.ds.* to use ds.layout_plugin.settings.default - all layouts should pick this up normally

config inspector seems happy, let's hope the tests are too :)

Ok, tests are happy! It looks like this might be a good approach and we don't have to warn users to update the schema. We can create a change record though explaining the new feature instead, win-win!

I'm not missing something am I ? :)