Closure as a subset of callable

[nyamsprod]

I have an issue that I could reproduce with the following snippet.

https://phpstan.org/r/06e3c164-f67b-42b2-8e81-9178a6b0a358

Parameter #1 expects callable(array, int|string=): bool, Closure(array, int|string): true given.

Since all closures are subtype of callable why is PHPStan complaining ? 🤔

Parameter #2 $key of passed callable is required but the parameter of accepting callable is optional. It might be called without it.

If the parameter is optional why complains if the parameter is provided ? 🤔

[ondrejmirtes]

PHPStan is only complaining because of the reason it gives you:

Parameter #2 $key of passed callable is required but the parameter of accepting callable is optional. It might be called without it.

If you fix that it's okay to pass Closure into callable: https://phpstan.org/r/1e938868-d00d-4246-87d3-c8dcde692b96

The reason why Closure(array, int|string): true is not accepted into callable(array, int|string=): bool is because the callable might be called without the 2nd parameter.

If you call this callback without the 2nd parameter (which is okay based on the signature), PHP is going to crash: https://3v4l.org/lYvts

That's why PHPStan complains on line 16 and not line 9 in this example: https://phpstan.org/r/3e8f88d5-a483-4d67-b2b6-6d9208085b21