CustomerGroupsOptionsProvider.php

<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
namespace Magento\CatalogRule\Model\Rule;

class CustomerGroupsOptionsProvider implements \Magento\Framework\Data\OptionSourceInterface
{
    /**
     * @var \Magento\Customer\Api\GroupRepositoryInterface
     */
    private $groupRepository;

    /**
     * @var \Magento\Framework\Api\SearchCriteriaBuilder
     */
    private $searchCriteriaBuilder;

    /**
     * @var \Magento\Framework\Convert\DataObject
     */
    private $objectConverter;

    /**
     * @param \Magento\Customer\Api\GroupRepositoryInterface $groupRepository
     * @param \Magento\Framework\Api\SearchCriteriaBuilder $searchCriteriaBuilder
     * @param \Magento\Framework\Convert\DataObject $objectConverter
     */
    public function __construct(
        \Magento\Customer\Api\GroupRepositoryInterface $groupRepository,
        \Magento\Framework\Api\SearchCriteriaBuilder $searchCriteriaBuilder,
        \Magento\Framework\Convert\DataObject $objectConverter
    ) {
        $this->groupRepository = $groupRepository;
        $this->searchCriteriaBuilder = $searchCriteriaBuilder;
        $this->objectConverter = $objectConverter;
    }

    /**
     * @return array
     */
    public function toOptionArray()
    {
        $customerGroups = $this->groupRepository->getList($this->searchCriteriaBuilder->create())->getItems();
        return $this->objectConverter->toOptionArray($customerGroups, 'id', 'code');
    }
}