function (Model $x) {} passed to Closure(object): void is not reported in level <=6

[mvorisek]

Bug report

Currently, with level 3 - 6, Closure(object) accepts Closure(X extends Cl), but Closure(Cl) does not. This is inconsistent as object is a weaker type.

With #8964 implemented, this issue should actually aim to not accept function (Model $x) {} into Closure(object): void property/param.

Code snippet that reproduces the problem

repro: https://3v4l.org/gIfXB (TypeErrorException)
https://phpstan.org/r/9e11c8b2-622b-4520-88c1-10ec04c86378 (no phpstan error for level <= 6)

Expected output

phpstan type error

[phpstan-bot]

@mvorisek After the latest push in 1.11.x, PHPStan now reports different result with your code snippet:

@@ @@
-25: Property UserAction::$enabled2 (bool|(Closure(Model): bool)) does not accept Closure(X): false.
+No errors

[ondrejmirtes]

Changed: phpstan/phpstan-src@eceb9f6

[ondrejmirtes]

Decided to revert the fix.

[mvorisek]

Allowing Closure(Cl) to accept Closure(X extends Cl) is on the other side quite dangerous as it leads to a TypeError.

Example:

class Cl {}
class X extends Cl {}

class Foo {
    /** @var \Closure(Cl): void */
    public $fx;

    public function run(): void {
        ($this->fx)(new Cl());
    }
}

$foo = new Foo();
$foo->fx = function (X $obj): void { var_dump($obj); };
$foo->run();

https://3v4l.org/ddhWL

Maybe this should be solved with something like type projection like in phpstan/phpdoc-parser#138 as "\Closure(xxx) is more or less generic Closure, only the syntax uses ( and not <".

So the clean way to allow Closure with subclass params acceptance should be like \Closure(object of Cl).

@jiripudil what do you think

---

real world example:

https://github.com/atk4/ui/blob/67cfdbd00d/src/Form/Control/Lookup.php#L57

the property must accept function (X $fx, array $arr) {} where X extends Model as X is needed to hind/typecheck the passed model, but the Control class cannot be made generic.

[ondrejmirtes]

This is correctly reported https://phpstan.org/r/94ae1e00-8bb6-47dd-aa9e-06fad4a45880

[mvorisek]

That is correct. But currently, phpdoc cannot be used to specify the Closure should accept class that is or extends Model as the 1st param. This issue is to allow such requirement properly documented better than object.

[jiripudil]

Type projections wouldn't help you, even if we implemented them for Closures; you'd need a covariant projection, but Closure/callable parameters are contravariant, as you've demonstrated. That's an impossible combination.

[mvorisek]

You are both right. With #8964 implemented... I have updated the issue title and the description.