Reverting an Overridden Config using Config Update Writes the Wrong Config into Config Storage

I rewrote the description of this issue because I wasn't 100% sure what the original description was alluding to and I just ran into this issue when reverting a config as part of an existing module that uses install-time config overrides.

I am not sure if a lot can be done inside the ICO module to handle this case better, since it doesn't impact how configuration files get discovered by Core. It appears that Core caches only a single path for each config, so solving this problem might require a custom InstallStorage implementation that changes the way that getAllFolders() builds its cache under the hood.

As a workaround, an update hook could write the desired configuration directly into configuration storage using a utility method like this:

/**
 * Import a config from an explicit file path into database storage.
 *
 * @param string $config_name
 *   The name of the config item to import from the config folder.
 * @param string $config_path
 *   The path to the config folder.
 *
 * @return bool
 *   TRUE on success, or FALSE if the config could not be installed.
 */
function my_module_import_single_config(string $config_name, string $config_path): bool {
  $source = new FileStorage($config_path);

  $config_storage = \Drupal::service('config.storage');
  assert($config_storage instanceof StorageInterface);

  return $config_storage->write($config_name, $source->read($config_name));
}

This is risky, since the config does NOT get validated. A safer version could look like this:

/**
 * Import a config from an explicit file path by its entity type and ID.
 *
 * @param string $config_path
 *   The path to the config folder.
 * @param string $entity_type
 *   The machine name of the configuration entity being imported.
 * @param string $id
 *   The ID of the configuration being imported.
 */
function my_module_import_single_config_safer(string $config_path, string $entity_type, string $id): void {
  $source = new FileStorage($config_path);

  try {
    $config_full_name = _arkayo_am_get_full_config_name($entity_type, $id);
    $config_storage   = \Drupal::entityTypeManager()->getStorage($entity_type);

    // _arkayo_am_get_full_config_name() should have thrown an exception on the
    // entity type by now if this assertion does not hold.
    assert($config_storage instanceof ConfigEntityStorageInterface);

    $config_data = $source->read($config_full_name);

    $entity = $config_storage->createFromStorageRecord($config_data);
    $entity->save();
  }
  catch (PluginNotFoundException | InvalidPluginDefinitionException $ex) {
    throw new InvalidArgumentException(
      sprintf(
        'Invalid configuration entity type ("%s"): %s',
        $entity_type,
        $ex->getMessage()
      )
    );
  }
  catch (EntityStorageException $ex) {
    throw new InvalidArgumentException(
      sprintf(
        'Failed to import configuration to "%s": %s',
        $config_full_name ?? sprintf('%s.%s', $entity_type, $id),
        $ex->getMessage()
      ));
  }
}