test1/public/drupal-8.3.1/core/modules/hal/hal.install

<?php

/**
 * @file
 * Update functions for the HAL module.
 */

/**
 * Move 'link_domain' from 'rest.settings' to 'hal.settings'.
 */
function hal_update_8301() {
  $config_factory = \Drupal::configFactory();

  // The default value for the 'link_domain' key is `~`, which is the YAML
  // equivalent of PHP's `NULL`. If the REST module is not installed, this is
  // the value we will store in 'hal.settings'.
  $link_domain = NULL;

  // But if the REST module was installed, we migrate its 'link_domain' setting,
  // because we are actually moving that setting from 'rest.settings' to
  // 'hal.settings'.
  $rest_settings = $config_factory->getEditable('rest.settings');
  if ($rest_settings->getRawData() !== []) {
    $link_domain = $rest_settings->get('link_domain');
    // Remove the 'link_domain' setting from 'rest.settings'.
    $rest_settings->clear('link_domain')
      ->save();
  }

  $hal_settings = $config_factory->getEditable('hal.settings');
  $hal_settings->set('link_domain', $link_domain);
  $hal_settings->save(TRUE);
}