D8_rplf/core/modules/config/config.install

<?php

/**
 * @file
 * Install, update and uninstall functions for the config module.
 */

/**
* Implements hook_requirements().
*/
function config_requirements($phase) {
  $requirements = [];
  try {
    $directory = config_get_config_directory(CONFIG_SYNC_DIRECTORY);
  }
  catch (\Exception $e) {
    // system_requirements() guarantees that the CONFIG_SYNC_DIRECTORY exists
    // as the config.storage.staging service relies on it.
    $directory = FALSE;
  }
  // Ensure the configuration sync directory is writable. This is only a warning
  // because only configuration import from a tarball requires the folder to be
  // web writable.
  if ($phase !== 'install' && !is_writable($directory)) {
    $requirements['config directory ' . CONFIG_SYNC_DIRECTORY] = [
      'title' => t('Configuration directory: %type', ['%type' => CONFIG_SYNC_DIRECTORY]),
      'description' => t('The directory %directory is not writable.', ['%directory' => $directory]),
      'severity' => REQUIREMENT_WARNING,
    ];
  }
  return $requirements;
}