class DescriptionAwareFileFormatterBase

abstract class DescriptionAwareFileFormatterBase extends FileFormatterBase {
    
    /**
     * {@inheritdoc}
     */
    public static function defaultSettings() {
        $settings = parent::defaultSettings();
        $settings['use_description_as_link_text'] = TRUE;
        return $settings;
    }
    
    /**
     * {@inheritdoc}
     */
    public function settingsForm(array $form, FormStateInterface $form_state) {
        $form = parent::settingsForm($form, $form_state);
        $form['use_description_as_link_text'] = [
            '#title' => $this->t('Use description as link text'),
            '#description' => $this->t('Replace the file name by its description when available'),
            '#type' => 'checkbox',
            '#default_value' => $this->getSetting('use_description_as_link_text'),
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function settingsSummary() {
        $summary = parent::settingsSummary();
        if ($this->getSetting('use_description_as_link_text')) {
            $summary[] = $this->t('Use description as link text');
        }
        return $summary;
    }

}