form_mode_manager-8.x-1.x-dev/modules/form_mode_user_roles_assign/form_mode_user_roles_assign.module

<?php

/**
 * @file
 * Contains form_mode_user_roles_assign.module.
 */

use Drupal\Core\Form\FormStateInterface;
use Drupal\form_mode_user_roles_assign\FormAlter;

/**
 * Implements hook_form_alter().
 */
function form_mode_user_roles_assign_form_alter(array &$form, FormStateInterface $form_state, $form_id) {
  return \Drupal::service('class_resolver')
    ->getInstanceFromDefinition(FormAlter::class)
    ->formAlter($form, $form_state, $form_id);
}