null coalesce inside is_string() on optional array key has issues

[JurgenvanF]

Bug report

Code snippet that reproduces the problem

https://phpstan.org/r/f0b56620-fd83-4fd4-9c03-9e85afdfa2c3

Expected output

No errors

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[herndlm]

quick question about this one that confused me - the core problem is the combination of
a) phpstan resolving string when accessing the potential unset $in['maybe'] https://phpstan.org/r/16baf67e-2c9b-4018-af1a-b8ebbf3a7200
in combination with
b) the typespecifier specifying string for $in['maybe'] via is_string($in['maybe'] ?? null) which is no new info and therefore leads to ImpossibleCheckTypeHelper returning true

I'm not entirely sure if this should/can be fixed in the type specifying code or somewhere else. my initial idea was to make the scope resolve such unsafe offsets "correctly" (e.g. string|null), but that is surely wrong, right? that would break many many things I suppose

[herndlm]

ok, I played around a bit and figured it out I think. of course changing how unsafe ArrayDimFetch expressions are resolved does not make sense. this should be fixable in the type specifier 😊

[ondrejmirtes]

Fixed by phpstan/phpstan-src#1793

[github-actions]

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