getRequiredKeys example

public function parse($filename) {
    if (!file_exists($filename)) {
      $parsed_info = [];
    }
    else {
      try {
        $parsed_info = Yaml::decode(file_get_contents($filename));
      }
      catch (InvalidDataTypeException $e) {
        throw new InfoParserException("Unable to parse $filename " . $e->getMessage());
      }
      $missing_keys = array_diff($this->getRequiredKeys(), array_keys($parsed_info));
      if (!empty($missing_keys)) {
        throw new InfoParserException('Missing required keys (' . implode(', ', $missing_keys) . ') in ' . $filename);
      }
      if (!isset($parsed_info['core_version_requirement'])) {
        if (str_starts_with($filename, 'core/') || str_starts_with($filename, $this->root . '/core/')) {
          // Core extensions do not need to specify core compatibility: they are           // by definition compatible so a sensible default is used. Core           // modules are allowed to provide these for testing purposes.           $parsed_info['core_version_requirement'] = \Drupal::VERSION;
        }
        elseif (isset($parsed_info['package']) && $parsed_info['package'] === 'Testing') {