class Url

class Url extends FieldPluginBase {
    
    /**
     * {@inheritdoc}
     */
    protected function defineOptions() {
        $options = parent::defineOptions();
        $options['display_as_link'] = [
            'default' => TRUE,
        ];
        return $options;
    }
    
    /**
     * Provide link to the page being visited.
     */
    public function buildOptionsForm(&$form, FormStateInterface $form_state) {
        $form['display_as_link'] = [
            '#title' => $this->t('Display as link'),
            '#type' => 'checkbox',
            '#default_value' => !empty($this->options['display_as_link']),
        ];
        parent::buildOptionsForm($form, $form_state);
    }
    
    /**
     * {@inheritdoc}
     */
    public function render(ResultRow $values) {
        $value = $this->getValue($values);
        if (!empty($this->options['display_as_link'])) {
            // @todo Views should expect and store a leading /. See:
            //   https://www.drupal.org/node/2423913
            return Link::fromTextAndUrl($this->sanitizeValue($value), CoreUrl::fromUserInput('/' . $value))
                ->toString();
        }
        else {
            return $this->sanitizeValue($value, 'url');
        }
    }

}