HandlerInterface.php

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

use Magento\Framework\App\ResourceConnection\SourceProviderInterface;

/**
 * @api Implement custom Handler
 * @since 100.0.2
 */
interface HandlerInterface
{
    /**
     * Prepare SQL for field and add it to collection
     *
     * @param SourceProviderInterface $source
     * @param string $alias
     * @param array $fieldInfo
     * @return void
     */
    public function prepareSql(SourceProviderInterface $source, $alias, $fieldInfo);
}