class Rss

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

class Rss extends StylePluginBase {

  /**
   * Does the style plugin for itself support to add fields to it's output.
   *
   * @var bool
   */
  protected $usesRowPlugin = TRUE;
  public function attachTo($display_id, $path, $title) {
    $display = $this->view->displayHandlers
      ->get($display_id);
    $url_options = array();
    $input = $this->view
      ->getExposedInput();
    if ($input) {
      $url_options['query'] = $input;
    }
    $url_options['absolute'] = TRUE;
    $url = url($this->view
      ->getUrl(NULL, $path), $url_options);
    if ($display
      ->hasPath()) {
      if (empty($this->preview)) {
        drupal_add_feed($url, $title);
      }
    }
    else {
      if (empty($this->view->feed_icon)) {
        $this->view->feed_icon = '';
      }
      $feed_icon = array(
        '#theme' => 'feed_icon',
        '#url' => $url,
        '#title' => $title,
      );
      $this->view->feed_icon .= drupal_render($feed_icon);
      drupal_add_html_head_link(array(
        'rel' => 'alternate',
        'type' => 'application/rss+xml',
        'title' => $title,
        'href' => $url,
      ));
    }
  }
  protected function defineOptions() {
    $options = parent::defineOptions();
    $options['description'] = array(
      'default' => '',
      'translatable' => TRUE,
    );
    return $options;
  }
  public function buildOptionsForm(&$form, &$form_state) {
    parent::buildOptionsForm($form, $form_state);
    $form['description'] = array(
      '#type' => 'textfield',
      '#title' => t('RSS description'),
      '#default_value' => $this->options['description'],
      '#description' => t('This will appear in the RSS feed itself.'),
      '#maxlength' => 1024,
    );
  }

  /**
   * Return an array of additional XHTML elements to add to the channel.
   *
   * @return
   *   An array that can be passed to format_xml_elements().
   */
  protected function getChannelElements() {
    return array();
  }

  /**
   * Get RSS feed description.
   *
   * @return string
   *   The string containing the description with the tokens replaced.
   */
  public function getDescription() {
    $description = $this->options['description'];

    // Allow substitutions from the first row.
    $description = $this
      ->tokenizeValue($description, 0);
    return $description;
  }
  function render() {
    if (empty($this->view->rowPlugin)) {
      debug('Drupal\\views\\Plugin\\views\\style\\Rss: Missing row plugin');
      return;
    }
    $rows = '';

    // This will be filled in by the row plugin and is used later on in the
    // theming output.
    $this->namespaces = array(
      'xmlns:dc' => 'http://purl.org/dc/elements/1.1/',
    );

    // Fetch any additional elements for the channel and merge in their
    // namespaces.
    $this->channel_elements = $this
      ->getChannelElements();
    foreach ($this->channel_elements as $element) {
      if (isset($element['namespace'])) {
        $this->namespaces = array_merge($this->namespaces, $element['namespace']);
      }
    }
    foreach ($this->view->result as $row_index => $row) {
      $this->view->row_index = $row_index;
      $rows .= $this->view->rowPlugin
        ->render($row);
    }
    $output = theme($this
      ->themeFunctions(), array(
      'view' => $this->view,
      'options' => $this->options,
      'rows' => $rows,
    ));
    unset($this->view->row_index);
    return $output;
  }

}