Hi,
I found this bug regarding the variable by reference:
<?php
namespace Devsense\Builtin;
class Test
{
public function toString(): string
{
return '';
}
}
/**
* @var Test[] $store
*/
$store = [];
array_walk($store, function(Test &$test) {
$test = $test->toString();
});

Could you check the type / tooltip for $test in the array_walk call?
toString is unknown because $test is a string instead of Test.
Thank you for you help.