False-positive ImpureMethodCall when calling method on an object that created inside of a pure method

[fluffycondor]

https://psalm.dev/r/0310c9c472

If I understand correctly, this code shouldn't yield an error. It blocks psalm/psalm-plugin-doctrine#125 now, so I'd like to know can I safely suppress it.

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/0310c9c472

<?php

class Collection {
    /** @psalm-mutation-free Returns a new collection, doesn't mutate the existing one */
	public function matching(Criteria $criteria): Collection
    {
    	return new Collection();
    }
}

class Criteria {
    private ?string $key = null;
    
    /** @psalm-external-mutation-free Mutates only its own state */
	public function orderBy(string $key): Criteria
    {
        $this->key = $key;
        return $this;
    }
}

/** @psalm-pure */
function foo(Collection $collection): Collection
{
    return $collection->matching((new Criteria())->orderBy('key'));
}

Psalm output (using commit 42462b8):

ERROR: ImpureMethodCall - 25:52 - Cannot call a non-mutation-free method Criteria::orderBy from a pure context

[AndrolGenhald]

Yeah, this can be safely suppressed, duplicate of #5615. As weirdan mentioned there, it seems cloning fixes this, so we need to make it so that creating a new object works the same way as cloning.

If you trick Psalm by creating and then cloning it works fine: https://psalm.dev/r/c75ed63c79

I think that issue will probably have to be fixed before merging that PR though, as I understand it the PR will cause everyone that uses Criteria::orderBy to have the false positive that they have to suppress, rather than just being a suppression in the plugin itself.

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/c75ed63c79

<?php

class Collection {
    /** @psalm-mutation-free Returns a new collection, doesn't mutate the existing one */
	public function matching(Criteria $criteria): Collection
    {
    	return new Collection();
    }
}

class Criteria {
    private ?string $key = null;
    
    /** @psalm-external-mutation-free Mutates only its own state */
	public function orderBy(string $key): Criteria
    {
        $this->key = $key;
        return $this;
    }
}

/** @psalm-pure */
function foo(Collection $collection): Collection
{
    $criteria = new Criteria();
    $criteria = clone $criteria;
    $criteria = $criteria->orderBy('key');
    return $collection->matching($criteria);
}

Psalm output (using commit 42462b8):

No issues!