class BlockBase

abstract class BlockBase extends PluginBase implements BlockPluginInterface, PluginWithFormsInterface, PreviewAwarePluginInterface, PreviewFallbackInterface, ContextAwarePluginInterface {
  use BlockPluginTrait {
    buildConfigurationForm as traitBuildConfigurationForm;
    submitConfigurationForm as traitSubmitConfigurationForm;
  }
  use ContextAwarePluginTrait;
  use ContextAwarePluginAssignmentTrait;
  
  /**
   * {@inheritdoc}
   */
  public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
    $form = $this->traitBuildConfigurationForm($form, $form_state);
    // Add context mapping UI form elements.
    $contexts = $form_state->getTemporaryValue('gathered_contexts') ?: [];
    $form['context_mapping'] = $this->addContextAssignmentElement($this, $contexts);
    return $form;
  }
  
  /**
   * {@inheritdoc}
   */
  public function submitConfigurationForm(array &$form, FormStateInterface $form_state) : void {
    if (!$form_state->getErrors() && $form_state->getValue('context_mapping')) {
      $this->configuration['context_mapping'] = $form_state->getValue('context_mapping');
    }
    $this->traitSubmitConfigurationForm($form, $form_state);
  }

}