class Rss

1. 9.x drupal/core/modules/views/lib/Drupal/views/Plugin/views/style/Rss.php \Drupal\views\Plugin\views\style\Rss
2. 9.x drupal/core/modules/node/lib/Drupal/node/Plugin/views/row/Rss.php \Drupal\node\Plugin\views\row\Rss
3. 9.x drupal/core/modules/comment/lib/Drupal/comment/Plugin/views/row/Rss.php \Drupal\comment\Plugin\views\row\Rss

class Rss extends RowPluginBase {
  var $base_table = 'comment';
  var $base_field = 'cid';
  protected function defineOptions() {
    $options = parent::defineOptions();
    $options['item_length'] = array(
      'default' => 'default',
    );
    $options['links'] = array(
      'default' => FALSE,
      'bool' => TRUE,
    );
    return $options;
  }
  public function buildOptionsForm(&$form, &$form_state) {
    parent::buildOptionsForm($form, $form_state);
    $form['item_length'] = array(
      '#type' => 'select',
      '#title' => t('Display type'),
      '#options' => $this
        ->options_form_summary_options(),
      '#default_value' => $this->options['item_length'],
    );
    $form['links'] = array(
      '#type' => 'checkbox',
      '#title' => t('Display links'),
      '#default_value' => $this->options['links'],
    );
  }
  function pre_render($result) {
    $cids = array();
    $nids = array();
    foreach ($result as $row) {
      $cids[] = $row->cid;
    }
    $this->comments = comment_load_multiple($cids);
    foreach ($this->comments as &$comment) {
      $comment->depth = count(explode('.', $comment->thread)) - 1;
      $nids[] = $comment->nid;
    }
    $this->nodes = node_load_multiple($nids);
  }

  /**
   * Return the main options, which are shown in the summary title
   *
   * @see views_plugin_row_node_rss::options_form_summary_options()
   * @todo: Maybe provide a views_plugin_row_rss_entity and reuse this method
   * in views_plugin_row_comment|node_rss.inc
   */
  function options_form_summary_options() {
    $entity_info = entity_get_info('node');
    $options = array();
    if (!empty($entity_info['view_modes'])) {
      foreach ($entity_info['view_modes'] as $mode => $settings) {
        $options[$mode] = $settings['label'];
      }
    }
    $options['title'] = t('Title only');
    $options['default'] = t('Use site default RSS settings');
    return $options;
  }
  function render($row) {
    global $base_url;
    $cid = $row->{$this->field_alias};
    if (!is_numeric($cid)) {
      return;
    }
    $item_length = $this->options['item_length'];
    if ($item_length == 'default') {
      $item_length = config('system.rss')
        ->get('items.view_mode');
    }

    // Load the specified comment and its associated node:
    $comment = $this->comments[$cid];
    if (empty($comment) || empty($this->nodes[$comment->nid])) {
      return;
    }
    $item_text = '';
    $uri = $comment
      ->uri();
    $comment->link = url($uri['path'], $uri['options'] + array(
      'absolute' => TRUE,
    ));
    $comment->rss_namespaces = array();
    $comment->rss_elements = array(
      array(
        'key' => 'pubDate',
        'value' => gmdate('r', $comment->created),
      ),
      array(
        'key' => 'dc:creator',
        'value' => $comment->name,
      ),
      array(
        'key' => 'guid',
        'value' => 'comment ' . $comment
          ->id() . ' at ' . $base_url,
        'attributes' => array(
          'isPermaLink' => 'false',
        ),
      ),
    );

    // The comment gets built and modules add to or modify
    // $comment->rss_elements and $comment->rss_namespaces.
    $build = comment_view($comment, $this->nodes[$comment->nid], 'rss');
    unset($build['#theme']);
    if (!empty($comment->rss_namespaces)) {
      $this->view->style_plugin->namespaces = array_merge($this->view->style_plugin->namespaces, $comment->rss_namespaces);
    }

    // Hide the links if desired.
    if (!$this->options['links']) {
      hide($build['links']);
    }
    if ($item_length != 'title') {

      // We render comment contents and force links to be last.
      $build['links']['#weight'] = 1000;
      $item_text .= drupal_render($build);
    }
    $item = new stdClass();
    $item->description = $item_text;
    $item->title = $comment
      ->label();
    $item->link = $comment->link;
    $item->elements = $comment->rss_elements;
    $item->cid = $comment
      ->id();
    return theme($this
      ->themeFunctions(), array(
      'view' => $this->view,
      'options' => $this->options,
      'row' => $item,
    ));
  }

}