False positive MixedPropertyFetch after instanceof $this

[kynx]

<?php

abstract class A
{
    public function __construct(private string $value)
    {
    }

    public function equals(mixed $other): bool
    {
        if (! $other instanceof $this) {
            return false;
        }

        return $this->value === $other->value;
    }
}

Results in:

ERROR: MixedPropertyFetch - src/A.php:15:33 - Cannot fetch property on mixed var $other (see https://psalm.dev/034)
        return $this->value === $other->value;

[psalm-github-bot]

Hey @kynx, can you reproduce the issue on https://psalm.dev? These will be used as phpunit tests when implementing the feature or fixing this bug.

[kynx]

https://psalm.dev/r/814236f6c7

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/814236f6c7

<?php

abstract class A
{
    public function __construct(private string $value)
    {
    }

    public function equals(mixed $other): bool
    {
        if (! $other instanceof $this) {
            return false;
        }

        return $this->value === $other->value;
    }
}

Psalm output (using commit c56f798):

INFO: MixedPropertyFetch - 15:33 - Cannot fetch property on mixed var $other

[orklah]

Note that replacing $this by static works if it's not inverted
https://psalm.dev/r/0afbd90e20

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/0afbd90e20

<?php

abstract class A
{
    public function __construct(private string $value)
    {
    }

    public function equals(mixed $other): bool
    {
        if ($other instanceof static) {
            /** @psalm-trace $other */;
            return false;
        }
		/** @psalm-trace $other */;
        return $this->value === $other->value;
    }
}

Psalm output (using commit c56f798):

INFO: Trace - 12:39 - $other: A&static

INFO: Trace - 15:29 - $other: mixed

INFO: MixedPropertyFetch - 16:33 - Cannot fetch property on mixed var $other