assertCount with remembered values causing false positives

[janedbal]

Simplified reproducible example:

class AssertCountProblemTest extends TestCase
{

    /**
     * @var list<string>
     */
    private static array $database = [];

    public function testFoo(): void
    {
        self::assertCount(0, $this->getDataFromDatabase());

        self::editDataInDatabase();

        $newData = $this->getDataFromDatabase();
        self::assertCount(1, $newData); // error: Call to static method PHPUnit\Framework\Assert::assertCount() with 1 and array{} will always evaluate to false.
    }

    /**
     * @return list<string>
     */
    private function getDataFromDatabase(): array
    {
        return self::$database;
    }

    private static function editDataInDatabase(): void
    {
        self::$database[] = 'new data';
    }

}

This poped up while upgrading phpstan-phpunit from 1.3.15 to 1.4.0

[janedbal]

1.3.16 is the version where this breaks.

[Ciloe]

Same here at version 1.4.1.

I solved temporarly by creating a variable, and using it in the Count function :

// Before :
self::assertCount(1, $this->getDataFromDatabase());

// After :
$newData = $this->getDataFromDatabase();
self::assertCount(1, $newData);

[thePanz]

Just upgraded to PHPStan v2.11.1 and got this issue.
The same code worked fine with v2.10.7 (this was the previous version I had installed)

[ondrejmirtes]

@thePanz Your problem probably stems from a much smarter type narrowing when count() is involved. This isn't a bug but a feature. It's not specific to PHPUnit either.

You can either:

1. Mark the function as @phpstan-impure: https://phpstan.org/r/e621db72-ce3f-4833-a967-79c455f25542
2. or you can set rememberPossiblyImpureFunctionValues: false: https://phpstan.org/config-reference#rememberpossiblyimpurefunctionvalues

Detailed here: https://phpstan.org/blog/remembering-and-forgetting-returned-values

Also I talk about it for 10 minutes here: https://www.youtube.com/watch?v=AFjr3RlDOZQ&t=1728s

[ondrejmirtes]

As this isn't specific to PHPUnit either, @janedbal please re-report this in PHPStan: https://phpstan.org/r/b610c6cb-c572-49b1-a78c-1a1ad5bd9100

[janedbal]

Please re-report this in PHPStan: https://phpstan.org/r/b610c6cb-c572-49b1-a78c-1a1ad5bd9100

Does that actually make sense? It works when properly annotated. I believe the problem is more about DX. Nobody wants to mark all similar methods with @phpstan-impure.

[ondrejmirtes]

I'm not sure what you're suggesting. As I'm describing the recording of my talk, these defaults make sense to me. If you don't want to use @phpstan-impure, there's rememberPossiblyImpureFunctionValues: false.