username-1.0.x-dev/modules/username_displayname/username_displayname.module

<?php

/**
 * @file
 * Exposes global functionality for username on user form.
 */

use Drupal\Core\Form\FormStateInterface;

/**
 * Implements hook_username_display().
 *
 * Adds Display name options in username settings form.
 */
function username_displayname_username_display() {
  return [
    'name' => t('Use name fields configured in the display name field settings'),
  ];
}

/**
 * Implements hook_username_display_name_pattern_alter().
 *
 * Adds the default display name pattern on the username settings page.
 */
function username_displayname_username_display_name_pattern_alter(&$pattern, $account) {
  $pattern = '[user:user_name:first] [user:user_name:last]';
}

/**
 * Implements hook_form_FORM_ID_alter().
 *
 * Alters the user form to attach the username display name library.
 */
function username_displayname_form_user_form_alter(&$form, FormStateInterface $form_state) {
  // Attach the username display name library.
  $form['#attached']['library'][] = 'username_displayname/username_displayname';
}