Narrow type in Collection::filter()

[whataboutpereira]

It would be great if Collection::filter() would also be able to narrow types.

class Group extends Node
    /**
     * @var Collection<int, Node>
     */
    #[ORM\OneToMany(targetEntity: Node::class, mappedBy: 'parent')]
    private Collection $children;

    /**
     * @return Collection<int, Group>
     */
    public function getGroups(): Collection
    {
        return $this->children
            ->filter(static fn (Node $node): bool => $node instanceof Group)
        ;
    }
}

Yields:

Method App\Entity\Group::getGroups() should return Doctrine\Common\Collections\Collection<int, App\Entity\Group>
but returns Doctrine\Common\Collections\Collection<int, App\Entity\Node>.

A workaround is to convert to an array.

    /**
     * @return array<int, Group>
     */
    public function getGroups(): array
    {
        return array_filter(
            $this->children->toArray(),
            static fn (Node $node): bool => $node instanceof Group
        );
    }

[VincentLanglet]

This is because of the ArrayFilterFunctionReturnTypeExtension

https://github.com/phpstan/phpstan-src/blob/ffe633714bfd19074feb4e7e9a673f2174be342d/src/Type/Php/ArrayFilterFunctionReturnTypeExtension.php#L13

Similar class should be implemented for Collection::filter, if you want to work on it @whataboutpereira

I assume you can rely on arrayFilterFunctionReturnTypeHelper, and then transform the type into a collection.

[ondrejmirtes]

I wouldn't use the helper, I'd just make a "virtual" FuncCall node to array_filter and call Scope::getType() with it.