class FormTestFormStateValuesCleanForm

class FormTestFormStateValuesCleanForm extends FormBase {
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'form_test_form_state_clean_values_form';
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        // Build an example form containing multiple submit and button elements; not
        // only on the top-level.
        $form = [
            '#tree' => TRUE,
        ];
        $form['foo'] = [
            '#type' => 'submit',
            '#value' => t('Submit'),
        ];
        $form['bar'] = [
            '#type' => 'submit',
            '#value' => t('Submit'),
        ];
        $form['beer'] = [
            '#type' => 'value',
            '#value' => 1000,
        ];
        $form['baz']['foo'] = [
            '#type' => 'button',
            '#value' => t('Submit'),
        ];
        $form['baz']['baz'] = [
            '#type' => 'submit',
            '#value' => t('Submit'),
        ];
        $form['baz']['beer'] = [
            '#type' => 'value',
            '#value' => 2000,
        ];
        // Add an arbitrary element and manually set it to be cleaned.
        // Using $form_state->addCleanValueKey('wine'); didn't work here.
        $class = static::class;
        $form['wine'] = [
            '#type' => 'value',
            '#value' => 3000,
            '#process' => [
                [
                    $class,
                    'cleanValue',
                ],
            ],
        ];
        return $form;
    }
    
    /**
     * Helper function to clean a value on an element.
     */
    public static function cleanValue(&$element, FormStateInterface $form_state, &$complete_form) {
        $form_state->addCleanValueKey('wine');
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        $form_state->cleanValues();
        // This won't have a proper JSON header, but Drupal doesn't check for that
        // anyway so this is fine until it's replaced with a JsonResponse.
        print Json::encode($form_state->getValues());
        exit;
    }

}