ShortcutSetForm::form

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

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

  $entity = $this->entity;
  $form['label'] = array(
    '#type' => 'textfield',
    '#title' => t('Set name'),
    '#description' => t('The new set is created by copying items from your default shortcut set.'),
    '#required' => TRUE,
    '#default_value' => $entity->label(),
  );
  $form['id'] = array(
    '#type' => 'machine_name',
    '#machine_name' => array(
      'exists' => '\Drupal\shortcut\Entity\ShortcutSet::load',
      'source' => array('label'),
      'replace_pattern' => '[^a-z0-9-]+',
      'replace' => '-',
    ),
    '#default_value' => $entity->id(),
    // This id could be used for menu name.
    '#maxlength' => 23,
  );

  $form['actions']['submit']['#value'] = t('Create new set');

  return $this->protectBundleIdElement($form);
}