ActionFormBase::form

public ActionFormBase::form(array $form, FormStateInterface $form_state)

public function form(array $form, FormStateInterface $form_state) {
  $form['label'] = array(
    '#type' => 'textfield',
    '#title' => $this->t('Label'),
    '#default_value' => $this->entity->label(),
    '#maxlength' => '255',
    '#description' => $this->t('A unique label for this advanced action. This label will be displayed in the interface of modules that integrate with actions.'),
  );

  $form['id'] = array(
    '#type' => 'machine_name',
    '#default_value' => $this->entity->id(),
    '#disabled' => !$this->entity->isNew(),
    '#maxlength' => 64,
    '#description' => $this->t('A unique name for this action. It must only contain lowercase letters, numbers and underscores.'),
    '#machine_name' => array(
      'exists' => array($this, 'exists'),
    ),
  );
  $form['plugin'] = array(
    '#type' => 'value',
    '#value' => $this->entity->get('plugin'),
  );
  $form['type'] = array(
    '#type' => 'value',
    '#value' => $this->entity->getType(),
  );

  if ($this->plugin instanceof PluginFormInterface) {
    $form += $this->plugin->buildConfigurationForm($form, $form_state);
  }

  return parent::form($form, $form_state);
}