class SearchPageAddForm

class SearchPageAddForm extends SearchPageFormBase {
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state, $search_plugin_id = NULL) {
        $this->entity
            ->setPlugin($search_plugin_id);
        $definition = $this->entity
            ->getPlugin()
            ->getPluginDefinition();
        $this->entity
            ->set('label', $definition['title']);
        return parent::buildForm($form, $form_state);
    }
    
    /**
     * {@inheritdoc}
     */
    protected function actions(array $form, FormStateInterface $form_state) {
        $actions = parent::actions($form, $form_state);
        $actions['submit']['#value'] = $this->t('Save');
        return $actions;
    }
    
    /**
     * {@inheritdoc}
     */
    public function save(array $form, FormStateInterface $form_state) {
        // If there is no default search page, make the added search the default.
        if (!$this->searchPageRepository
            ->getDefaultSearchPage()) {
            $this->searchPageRepository
                ->setDefaultSearchPage($this->entity);
        }
        parent::save($form, $form_state);
        $this->messenger()
            ->addStatus($this->t('The %label search page has been added.', [
            '%label' => $this->entity
                ->label(),
        ]));
    }

}