Make Option covariant

[devnix]

No description provided.

[ondrejmirtes]

I'd only merge this if the original was covariant as well: https://github.com/azjezz/psl/blob/next/src/Psl/Option/Option.php

Otherwise it's not safe.

[devnix]

It looks like it maybe shouldn't be covariant due to methods like or(), orElse(), compare() and equals().

There are cases that I'm unsure about how to handle, for example:

Parameter ...  of method Foo::__invoke() expects Psl\Option\Option<non-empty-list<Bar>>,
Psl\Option\Option<array{Bar}> given.

I'm not sure about if it's a problem that should be handled with call-site variance (expecting Psl\Option\Option<covariant non-empty-list<Bar>> or if native subtypes are treated as class/interface subtypes, at least in terms of variance and they should not.

I'm not sure at all about that last point, as I'm still understanding variance, but to me array{Bar} should be a valid param for non-empty-list<Bar>. Is this case related to phpstan/phpstan#6732 (comment)?

[ondrejmirtes]

Hard to judge without a code sample on phpstan.org/try

[devnix]

I'll close the pull request for now and open an issue with any specific example if I get an reproducer.