private function loadConfig() {
    drush_log(dt('Loading config paths.'), 'debug');
    $config_paths = [$this->getSiteDir()];

    // Find directories to scan for environment config files.
    // system, 'home.drush', 'drupal', 'custom'
    foreach ($this->contexts as $context) {
      if ($files = _drush_config_file($context, 'env')) {
        if (is_array($files)) {
          foreach ($files as $file) {
            $config_paths[] = dirname($file);
          }
        }
        else {
          $config_paths[] = dirname($files);
        }
      }
    }

    // Remove any empty values.
    $config_paths = array_filter($config_paths);

    // Flip the config list for proper hierarchy.
    $this->configPaths = array_reverse($config_paths);
    drush_log(dt('Loaded config paths.'), 'debug');
  }