Rule source on GitHub

DowngradeArrayFirstLastRector

Replace array_first() and array_last() with $array[array_key_first($array)] and $array[array_key_last($array)]

-echo array_first($array);
-echo array_last($array);
+echo $array[array_key_first($array)];
+echo $array[array_key_last($array)];

Configure your rector.php:

<?php

use Rector\Config\RectorConfig;
use Rector\DowngradePhp85\Rector\FuncCall\DowngradeArrayFirstLastRector;

return RectorConfig::configure()
    ->withRules([
        DowngradeArrayFirstLastRector::class,
    ]);