class TestFieldWidget

class TestFieldWidget extends WidgetBase {
    
    /**
     * {@inheritdoc}
     */
    public static function defaultSettings() {
        return [
            'test_widget_setting' => 'dummy test string',
            'role' => 'anonymous',
            'role2' => 'anonymous',
        ] + parent::defaultSettings();
    }
    
    /**
     * {@inheritdoc}
     */
    public function settingsForm(array $form, FormStateInterface $form_state) {
        $element['test_widget_setting'] = [
            '#type' => 'textfield',
            '#title' => t('Field test field widget setting'),
            '#description' => t('A dummy form element to simulate field widget setting.'),
            '#default_value' => $this->getSetting('test_widget_setting'),
            '#required' => FALSE,
        ];
        return $element;
    }
    
    /**
     * {@inheritdoc}
     */
    public function settingsSummary() {
        $summary = [];
        $summary[] = t('@setting: @value', [
            '@setting' => 'test_widget_setting',
            '@value' => $this->getSetting('test_widget_setting'),
        ]);
        return $summary;
    }
    
    /**
     * {@inheritdoc}
     */
    public function formElement(FieldItemListInterface $items, $delta, array $element, array &$form, FormStateInterface $form_state) {
        $element += [
            '#type' => 'textfield',
            '#default_value' => isset($items[$delta]->value) ? $items[$delta]->value : '',
        ];
        return [
            'value' => $element,
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function errorElement(array $element, ConstraintViolationInterface $violation, array $form, FormStateInterface $form_state) {
        return $element['value'];
    }
    
    /**
     * {@inheritdoc}
     */
    public function calculateDependencies() {
        $dependencies = parent::calculateDependencies();
        foreach ([
            'role',
            'role2',
        ] as $setting) {
            if (!empty($role_id = $this->getSetting($setting))) {
                // Create a dependency on the role config entity referenced in settings.
                $dependencies['config'][] = "user.role.{$role_id}";
            }
        }
        return $dependencies;
    }
    
    /**
     * {@inheritdoc}
     */
    public function onDependencyRemoval(array $dependencies) {
        $changed = parent::onDependencyRemoval($dependencies);
        // Only the setting 'role' is resolved here. When the dependency related to
        // this setting is removed, is expected that the widget component will be
        // update accordingly in the display entity. The 'role2' setting is
        // deliberately left out from being updated. When the dependency
        // corresponding to this setting is removed, is expected that the widget
        // component will be disabled in the display entity.
        if (!empty($role_id = $this->getSetting('role'))) {
            if (!empty($dependencies['config']["user.role.{$role_id}"])) {
                $this->setSetting('role', 'anonymous');
                $changed = TRUE;
            }
        }
        return $changed;
    }

}