UndefinedDocblockClass for generic template

[simPod]

I'm getting

UndefinedDocblockClass - 9:23 - Docblock-defined class or interface O does not exist

<?php
 
class Output {
}

/** @template O of Output */
interface Format
{
    /** @psalm-return O */
    public static function output(string $contents) : Output;
}

This works just fine with phpstan. I went through docs and some internal stubs here and can't see what I'm doing wrong. Why psalm does not know O for @return when it's defined as a template? Thanks!

[muglug]

@simPod I removed the ability to use templated classes in static methods because it's easy to get things wrong – I created a feature request in PHPStan's repo here: phpstan/phpstan#2738, and here's a link to where I announced I was mentioned that I was breaking this feature in Psalm: phpstan/phpstan#2731 (comment)

[simPod]

Thanks for links! Can you briefly explain what does it's easy to get things wrong mean? I read those discussions and snippets but it's hard to spot the problem. Is it about methods not being pure? Thanks a lot.

[muglug]

No, it's about thinking that you have some sort of templated protections & inference on input, when in fact you don't. The author was intending for $a to be templated as Some<string> here: https://phpstan.org/r/16a98fd4-f85f-421d-bb21-cb4da6d08694

[simPod]

I see the issue but isn't there the same problem with calling it through dynamic context? https://phpstan.org/r/da30f478-a9fe-4e67-972d-351e1965b531
I kinda expect PHP not to give me any guarantees based on phpdocs :D

[simPod]

@muglug if you had a few seconds I'd be very curious on your view here. It doesn't "click" together to me now :( Thanks!

[muglug]

I think your example should now work in Psalm - after further consideration I reverted to the more-permissive behaviour.

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/56eabbc3e2

<?php
 
class Output {
}

/** @template O of Output */
interface Format
{
    /** @psalm-return O */
    public static function output(string $contents) : Output;
}

Psalm output (using commit 0f5b0fd):

No issues!