Rule source on GitHub

DowngradeArraySpreadRector

Replace array spread with array_merge function

 class SomeClass
 {
     public function run()
     {
         $parts = ['apple', 'pear'];
-        $fruits = ['banana', 'orange', ...$parts, 'watermelon'];
+        $fruits = array_merge(['banana', 'orange'], $parts, ['watermelon']);
     }

     public function runWithIterable()
     {
-        $fruits = ['banana', 'orange', ...new ArrayIterator(['durian', 'kiwi']), 'watermelon'];
+        $fruits = array_merge(
+            ['banana', 'orange'],
+            is_array(new ArrayIterator(['durian', 'kiwi'])) ?
+                new ArrayIterator(['durian', 'kiwi']) :
+                iterator_to_array(new ArrayIterator(['durian', 'kiwi'])),
+            ['watermelon']
+        );
     }
 }

Configure your rector.php:

<?php

use Rector\Config\RectorConfig;
use Rector\DowngradePhp74\Rector\Array_\DowngradeArraySpreadRector;

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