UnusedParam false positive when param assigned by reference

[smaddock]

If a method parameter is used in the method as a reference (AKA alias, i.e., prefixing with an ampersand), Psalm marks that parameter as unused. Removing the ampersand removes the error.

https://psalm.dev/r/b46281057c

(Apologies if this is a duplicate, I searched several times and couldn't find this reported previously.)

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/b46281057c

<?php

final class MyClass
{
    private \stdClass $config;

    public function __construct(\stdClass $config) {
        $this->config = &$config;
    }
}

Psalm output (using commit 08afc45):

INFO: UnusedClass - 3:13 - Class MyClass is never used

INFO: UnusedParam - 7:43 - Param #1 is never referenced in this method

[jack-worman]

Object are always passed by reference. $this->config = &$config; is the exact same as $this->config = $config;

It saying the param is unused is a bug, but you can avoid it by not having redundant code.
Here is an example of this bug with non-redundant code: https://psalm.dev/r/578763b870