field_config_import_steps_alter

field_config_import_steps_alter(&$sync_steps, ConfigImporter $config_importer)

function field_config_import_steps_alter(&$sync_steps, ConfigImporter $config_importer) {
  $field_storages = ConfigImporterFieldPurger::getFieldStoragesToPurge(
  $config_importer->getStorageComparer()->getSourceStorage()->read('core.extension'), 
  $config_importer->getStorageComparer()->getChangelist('delete')
  );
  if ($field_storages) {
    // Add a step to the beginning of the configuration synchronization process
    // to purge field data where the module that provides the field is being
    // uninstalled.
    array_unshift($sync_steps, array('\Drupal\field\ConfigImporterFieldPurger', 'process'));
  }
}