SiteConfigureForm::buildForm

public SiteConfigureForm::buildForm(array $form, FormStateInterface $form_state)

public function buildForm(array $form, FormStateInterface $form_state) {
  $form['#title'] = $this->t('Configure site');

  // Warn about settings.php permissions risk
  $settings_dir = $this->sitePath;
  $settings_file = $settings_dir . '/settings.php';
  // Check that $_POST is empty so we only show this message when the form is
  // first displayed, not on the next page after it is submitted. (We do not
  // want to repeat it multiple times because it is a general warning that is
  // not related to the rest of the installation process; it would also be
  // especially out of place on the last page of the installer, where it would
  // distract from the message that the Drupal installation has completed
  // successfully.)
  $post_params = $this->getRequest()->request->all();
  if (empty($post_params) && (!drupal_verify_install_file($this->root . '/' . $settings_file, FILE_EXIST | FILE_READABLE | FILE_NOT_WRITABLE) || !drupal_verify_install_file($this->root . '/' . $settings_dir, FILE_NOT_WRITABLE, 'dir'))) {
    drupal_set_message(t('All necessary changes to %dir and %file have been made, so you should remove write permissions to them now in order to avoid security risks. If you are unsure how to do so, consult the <a href=":handbook_url">online handbook</a>.', array('%dir' => $settings_dir, '%file' => $settings_file, ':handbook_url' => 'https://www.drupal.org/server-permissions')), 'warning');
  }

  $form['#attached']['library'][] = 'system/drupal.system';
  // Add JavaScript time zone detection.
  $form['#attached']['library'][] = 'core/drupal.timezone';
  // We add these strings as settings because JavaScript translation does not
  // work during installation.
  $form['#attached']['drupalSettings']['copyFieldValue']['edit-site-mail'] = ['edit-account-mail'];

  $form['site_information'] = array(
    '#type' => 'fieldgroup',
    '#title' => $this->t('Site information'),
  );
  $form['site_information']['site_name'] = array(
    '#type' => 'textfield',
    '#title' => $this->t('Site name'),
    '#required' => TRUE,
    '#weight' => -20,
  );
  $form['site_information']['site_mail'] = array(
    '#type' => 'email',
    '#title' => $this->t('Site email address'),
    '#default_value' => ini_get('sendmail_from'),
    '#description' => $this->t("Automated emails, such as registration information, will be sent from this address. Use an address ending in your site's domain to help prevent these emails from being flagged as spam."),
    '#required' => TRUE,
    '#weight' => -15,
  );

  $form['admin_account'] = array(
    '#type' => 'fieldgroup',
    '#title' => $this->t('Site maintenance account'),
  );
  $form['admin_account']['account']['name'] = array(
    '#type' => 'textfield',
    '#title' => $this->t('Username'),
    '#maxlength' => USERNAME_MAX_LENGTH,
    '#description' => $this->t("Several special characters are allowed, including space, period (.), hyphen (-), apostrophe ('), underscore (_), and the @ sign."),
    '#required' => TRUE,
    '#attributes' => array('class' => array('username')),
  );
  $form['admin_account']['account']['pass'] = array(
    '#type' => 'password_confirm',
    '#required' => TRUE,
    '#size' => 25,
  );
  $form['admin_account']['account']['#tree'] = TRUE;
  $form['admin_account']['account']['mail'] = array(
    '#type' => 'email',
    '#title' => $this->t('Email address'),
    '#required' => TRUE,
  );

  $form['regional_settings'] = array(
    '#type' => 'fieldgroup',
    '#title' => $this->t('Regional settings'),
  );
  $countries = $this->countryManager->getList();
  $form['regional_settings']['site_default_country'] = array(
    '#type' => 'select',
    '#title' => $this->t('Default country'),
    '#empty_value' => '',
    '#default_value' => $this->config('system.date')->get('country.default'),
    '#options' => $countries,
    '#description' => $this->t('Select the default country for the site.'),
    '#weight' => 0,
  );
  $form['regional_settings']['date_default_timezone'] = array(
    '#type' => 'select',
    '#title' => $this->t('Default time zone'),
    // Use system timezone if set, but avoid throwing a warning in PHP >=5.4
    '#default_value' => @date_default_timezone_get(),
    '#options' => system_time_zones(),
    '#description' => $this->t('By default, dates in this site will be displayed in the chosen time zone.'),
    '#weight' => 5,
    '#attributes' => array('class' => array('timezone-detect')),
  );

  $form['update_notifications'] = array(
    '#type' => 'fieldgroup',
    '#title' => $this->t('Update notifications'),
  );
  $form['update_notifications']['update_status_module'] = array(
    '#type' => 'checkboxes',
    '#title' => $this->t('Update notifications'),
    '#options' => array(
      1 => $this->t('Check for updates automatically'),
      2 => $this->t('Receive email notifications'),
    ),
    '#default_value' => array(1, 2),
    '#description' => $this->t('The system will notify you when updates and important security releases are available for installed components. Anonymous information about your site is sent to <a href=":drupal">Drupal.org</a>.', array(':drupal' => 'https://www.drupal.org')),
    '#weight' => 15,
  );
  $form['update_notifications']['update_status_module'][2] = array(
    '#states' => array(
      'visible' => array(
        'input[name="update_status_module[1]"]' => array('checked' => TRUE),
      ),
    ),
  );

  $form['actions'] = array('#type' => 'actions');
  $form['actions']['submit'] = array(
    '#type' => 'submit',
    '#value' => $this->t('Save and continue'),
    '#weight' => 15,
    '#button_type' => 'primary',
  );

  return $form;
}