PluginFormBase.php

<?php

namespace Drupal\Core\Plugin;

use Drupal\Component\Plugin\PluginAwareInterface;
use Drupal\Component\Plugin\PluginInspectionInterface;
use Drupal\Core\Form\FormStateInterface;

/**
 * Provides a base class for plugin forms.
 *
 * Classes extending this can be in any namespace, but are commonly placed in
 * the 'PluginForm' namespace, such as \Drupal\module_name\PluginForm\ClassName.
 */
abstract class PluginFormBase implements PluginFormInterface, PluginAwareInterface {
    
    /**
     * The plugin this form is for.
     *
     * @var \Drupal\Component\Plugin\PluginInspectionInterface
     */
    protected $plugin;
    
    /**
     * {@inheritdoc}
     */
    public function setPlugin(PluginInspectionInterface $plugin) {
        $this->plugin = $plugin;
    }
    
    /**
     * {@inheritdoc}
     */
    public function validateConfigurationForm(array &$form, FormStateInterface $form_state) {
        // Validation is optional.
    }

}