Description

The following code:

<?php
function foobar(
    string|null $a = null,
    string $b
) {}

foobar(b: "x");

Resulted in this output:

Fatal error: Uncaught ArgumentCountError: foobar(): Argument #1 ($a) not passed

But I expected this error instead:

Deprecated: Optional parameter $a declared before required parameter $b is implicitly treated as a required parameter

To explain; $a does not end up being optional, and if you perform reflection on the property, it does not have a default-value. So PHP is silently ignoring the user-specified behavior. While it seems that PHP considers having optional properties in-front of required properties as invalid, it should at least issue a warning instead of silently changing expectations. If you put a string as default-value instead, it will emit the above depreciation notice.

PHP Version

PHP 8.2.7

Operating System

No response