PropertyTypeCoercion when constructing WeakMap

[dvdoug]

When initialising an (appropriately annotated) property that is a WeakMap, Psalm complains about type coercion when calling the constructor. There cannot be any possibility of type coercion at that point, the newly constructed map is empty.

Reproducer: https://psalm.dev/r/b3a63077ef

Potentially a variation of #4055 ?

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/b3a63077ef

<?php

declare(strict_types=1);

use WeakMap;

class Foo
{
    /** @var WeakMap<SplFileObject, int> */
    protected WeakMap $bar;

    public function __construct()
    {
            $this->bar = new WeakMap();
    }
}

Psalm output (using commit 858be40):

ERROR: PropertyTypeCoercion - 14:26 - $this->bar expects 'WeakMap<SplFileObject, int>',  parent type 'WeakMap<object, mixed>' provided

[weirdan]

At this point this is well-known limitation of Psalm generics. To work around this you have to provide the type information missing at the generic construction point using @var: https://psalm.dev/r/a0a3590bcd

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/a0a3590bcd

<?php

declare(strict_types=1);

use WeakMap;

class Foo
{
    /** @var WeakMap<SplFileObject, int> */
    protected WeakMap $bar;

    public function __construct()
    {
        /** @var WeakMap<SplFileObject, int> */
        $this->bar = new WeakMap();
    }
}

Psalm output (using commit f79f857):

No issues!

[dvdoug]

Hi

You say "well-known" but I wasn't able to find anything in the docs when I looked or in the existing issues list. Is there a link where I can find out more?

[bwoebi]

Hey @weirdan,

I just encountered that same issue, is there any reason it cannot be initialized the same way than SplObjectStorage is, similarly to 346d475?

[danog]

I've started working on #10577 to fix this.