param-out not taken into account when using generics

[greg0ire]

Actual issue: #8891 (comment)

Psalm doesn't seem to realize that 42 is an integer here:

https://psalm.dev/r/654392acdb

It is suggesting to use param-out, which is confusing as I'm already using it.

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/654392acdb

<?php

/**
 * @template T of positive-int
 */
class X {
    /**
     * @param-out T $s
     */
    function addFoo(mixed &$s) : void {
    }
}

function f3($z) {
    $x = new X();
    $x->addFoo($z);
    /** @psalm-trace $z */
}

Psalm output (using commit ef02ded):

INFO: Trace - 17:0 - $z: int<1, max>|mixed

INFO: MissingParamType - 14:13 - Parameter $z has no provided type

INFO: MissingReturnType - 14:10 - Method f3 does not have a return type, expecting void

[weirdan]

The snippet seems outdated and does not illustrate the issue.

[greg0ire]

You're right, I made a copy-paste mistake when examining another issue 😅 Thanks for pointing that out! Here is what I meant to post: https://psalm.dev/r/e46c3120a6

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/e46c3120a6

<?php

/**
 * @template T of int
 */
class X {
    /**
     * @param-out T $s
     */
    function addFoo(string &$s): void {
        $s = 42;
    }
}

Psalm output (using commit ef02ded):

ERROR: ReferenceConstraintViolation - 10:29 - Variable $s is limited to values of type T:X as int because it is passed by reference, 42 type found. Use @param-out to specify a different output type

[weirdan]

While 42 is int, it's not necessarily T. E.g. when you have X<13>, T is 13, but you're outputting 42.

[greg0ire]

That makes sense I think, but then, does this also makes sense: https://psalm.dev/r/bb313a293d

There is no implementation here, so I think in this particular case Psalm should say nothing.

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/bb313a293d

<?php

/**
 * @template T of int
 */
abstract class X {
    /**
     * @param-out T $s
     */
    abstract function addFoo(string &$s): void;
}

Psalm output (using commit ef02ded):

ERROR: ReferenceConstraintViolation - 10:38 - Variable $s is limited to values of type T:X as int because it is passed by reference, string type found. Use @param-out to specify a different output type

[weirdan]

No, that doesn't make much sense to me (of course, it should be int &$s).

[greg0ire]

Should it? If the param enters the method as '42', and then is set to 42, then this should be correct, right (and is the purpose of param-out)?

Here is an example: https://github.com/doctrine/lexer/blob/2.0.x/tests/ConcreteLexer.php (not sure how realistic it is though, I known doctrine/orm doesn't do that kind of stuff).

[greg0ire]

Here is an example with just Psalm: https://psalm.dev/r/b7de7cfb93
And that same code running: https://3v4l.org/jUfG8

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/b7de7cfb93

<?php

/**
 * @template T of int
 */
abstract class X {
    /**
     * @param-out T $s
     */
    abstract function addFoo(string &$s): void;
}

/**
 * @extends X<int>
 */
class Y extends X
{
    public function addFoo(string &$s): void
    {
        $s = 42;
    }
}

Psalm output (using commit ef02ded):

ERROR: ReferenceConstraintViolation - 10:38 - Variable $s is limited to values of type T:X as int because it is passed by reference, string type found. Use @param-out to specify a different output type

ERROR: ReferenceConstraintViolation - 18:36 - Variable $s is limited to values of type string because it is passed by reference, 42 type found. Use @param-out to specify a different output type