Issue #3232494 by bircher, NigelCunningham, alexpott: Optimise...

   *   The configuration storage to copy to.

   */

  protected static function replaceStorageContents(StorageInterface $source, StorageInterface &$target) {

    // Make sure there is no stale configuration in the target storage.

    foreach (array_merge([StorageInterface::DEFAULT_COLLECTION], $target->getAllCollectionNames()) as $collection) {

    // Remove all collections from the target which are not in the source.

    foreach (array_diff($target->getAllCollectionNames(), $source->getAllCollectionNames()) as $collection) {

      // We do this first so we don't have to loop over the added collections.

      $target->createCollection($collection)->deleteAll();

    }

    // Copy all the configuration from all the collections.

    foreach (array_merge([StorageInterface::DEFAULT_COLLECTION], $source->getAllCollectionNames()) as $collection) {

      $source_collection = $source->createCollection($collection);

      $target_collection = $target->createCollection($collection);

      foreach ($source_collection->listAll() as $name) {

      $names = $source_collection->listAll();

      // First we delete all the config which shouldn't be in the target.

      foreach (array_diff($target_collection->listAll(), $names) as $name) {

        $target_collection->delete($name);

      }

      // Then we loop over the config which needs to be there.

      foreach ($names as $name) {

        $data = $source_collection->read($name);

        if ($data !== FALSE) {

          if ($target_collection->read($name) !== $data) {

            // Update the target collection if the data is different.

            $target_collection->write($name, $data);

          }

        }

        else {

          $target_collection->delete($name);

          \Drupal::logger('config')->notice('Missing required data for configuration: %config', [

            '%config' => $name,

          ]);