NodeForm::form

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

public function form(array $form, FormStateInterface $form_state) {
  // Try to restore from temp store, this must be done before calling
  // parent::form().
  $uuid = $this->entity->uuid();
  $store = $this->tempStoreFactory->get('node_preview');

  // If the user is creating a new node, the UUID is passed in the request.
  if ($request_uuid = \Drupal::request()->query->get('uuid')) {
    $uuid = $request_uuid;
  }

  if ($preview = $store->get($uuid)) {
    /** @var $preview \Drupal\Core\Form\FormStateInterface */

    foreach ($preview->getValues() as $name => $value) {
      $form_state->setValue($name, $value);
    }

    // Rebuild the form.
    $form_state->setRebuild();
    $this->entity = $preview->getFormObject()->getEntity();
    $this->entity->in_preview = NULL;

    // Remove the stale temp store entry for existing nodes.
    if (!$this->entity->isNew()) {
      $store->delete($uuid);
    }

    $this->hasBeenPreviewed = TRUE;
  }

  /** @var \Drupal\node\NodeInterface $node */
  $node = $this->entity;

  if ($this->operation == 'edit') {
    $form['#title'] = $this->t('<em>Edit @type</em> @title', array('@type' => node_get_type_label($node), '@title' => $node->label()));
  }

  $current_user = $this->currentUser();

  // Changed must be sent to the client, for later overwrite error checking.
  $form['changed'] = array(
    '#type' => 'hidden',
    '#default_value' => $node->getChangedTime(),
  );

  $form['advanced'] = array(
    '#type' => 'vertical_tabs',
    '#attributes' => array('class' => array('entity-meta')),
    '#weight' => 99,
  );
  $form = parent::form($form, $form_state);

  // Add a revision_log field if the "Create new revision" option is checked,
  // or if the current user has the ability to check that option.
  $form['revision_information'] = array(
    '#type' => 'details',
    '#group' => 'advanced',
    '#title' => t('Revision information'),
    // Open by default when "Create new revision" is checked.
    '#open' => $node->isNewRevision(),
    '#attributes' => array(
      'class' => array('node-form-revision-information'),
    ),
    '#attached' => array(
      'library' => array('node/drupal.node'),
    ),
    '#weight' => 20,
    '#optional' => TRUE,
  );

  $form['revision'] = array(
    '#type' => 'checkbox',
    '#title' => t('Create new revision'),
    '#default_value' => $node->type->entity->isNewRevision(),
    '#access' => $current_user->hasPermission('administer nodes'),
    '#group' => 'revision_information',
  );

  $form['revision_log'] += array(
    '#states' => array(
      'visible' => array(
        ':input[name="revision"]' => array('checked' => TRUE),
      ),
    ),
    '#group' => 'revision_information',
  );

  // Node author information for administrators.
  $form['author'] = array(
    '#type' => 'details',
    '#title' => t('Authoring information'),
    '#group' => 'advanced',
    '#attributes' => array(
      'class' => array('node-form-author'),
    ),
    '#attached' => array(
      'library' => array('node/drupal.node'),
    ),
    '#weight' => 90,
    '#optional' => TRUE,
  );

  if (isset($form['uid'])) {
    $form['uid']['#group'] = 'author';
  }

  if (isset($form['created'])) {
    $form['created']['#group'] = 'author';
  }

  // Node options for administrators.
  $form['options'] = array(
    '#type' => 'details',
    '#title' => t('Promotion options'),
    '#group' => 'advanced',
    '#attributes' => array(
      'class' => array('node-form-options'),
    ),
    '#attached' => array(
      'library' => array('node/drupal.node'),
    ),
    '#weight' => 95,
    '#optional' => TRUE,
  );

  if (isset($form['promote'])) {
    $form['promote']['#group'] = 'options';
  }

  if (isset($form['sticky'])) {
    $form['sticky']['#group'] = 'options';
  }

  $form['#attached']['library'][] = 'node/form';

  $form['#entity_builders']['update_status'] = [$this, 'updateStatus'];

  return $form;
}