ViewDuplicateForm::form

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

public function form(array $form, FormStateInterface $form_state) {
  parent::form($form, $form_state);

  $form['#title'] = $this->t('Duplicate of @label', array('@label' => $this->entity->label()));

  $form['label'] = array(
    '#type' => 'textfield',
    '#title' => $this->t('View name'),
    '#required' => TRUE,
    '#size' => 32,
    '#maxlength' => 255,
    '#default_value' => $this->t('Duplicate of @label', array('@label' => $this->entity->label())),
  );
  $form['id'] = array(
    '#type' => 'machine_name',
    '#maxlength' => 128,
    '#machine_name' => array(
      'exists' => '\Drupal\views\Views::getView',
      'source' => array('label'),
    ),
    '#default_value' => '',
    '#description' => $this->t('A unique machine-readable name for this View. It must only contain lowercase letters, numbers, and underscores.'),
  );

  return $form;
}