Coalesce operator with array access on mixed

[enumag]

Bug report

I'm not completely sure if this is bug or intended behavior but long story short I wanted a simple code to get a particular field from a json response and throw exception if it wasn't there or had unexpected type. I'd like to avoid needless complications to the code just to satisfy phpstan.

Code snippet that reproduces the problem

https://phpstan.org/r/f66c7736-6cc6-48a3-8a50-6bfdde596384

Expected output

I'd expect no errors since the ?? operator handles the case when the variable isn't an array. See https://3v4l.org/qEje7

[herndlm]

In general I'd say it needs to be narrowed-down to an array first before you try accessing offsets on the return value. But since the second arg is set to true and there are no further flags specified it should only ever return mixed[]|bool|null I think. And accessing the offset via null coalescing there should be fine as in https://3v4l.org/XHnIE

But PHPStan doesn't currently know the return type of json_decode and thinks it is mixed. Looks like a case where a type specifying extension would greatly help :)

[enumag]

json_decode can return string or int or float as well so mixed is fine here. It's just that whatever the type the coalesce operator is there to handle it as expected so any narrowing down would be dead code just to satisfy phpstan.

[herndlm]

Right yeah, I forgot that. I mean it could return a stdClass instance as well, given the second param is false, right? And then the null coalescing would fail apparently. So I think mixed in general is not fine in this case. If we add an extension and make phpstan aware your problem might be fixed though.
UPDATE: added a better example https://3v4l.org/1GDVr

[herndlm]

I just wanted to say that I'm interested in working on this, but there seems to be phpstan/phpstan-src#993 already. mixed is not further narrowed down there though. Maybe it makes sense to wait until that is merged.

[ondrejmirtes]

This is a level 9 issue. You should first make sure you're working with the type you want. There's little sense in accessing an array offset on something that isn't an array.

[ondrejmirtes]

mixed can be anything. Array acess on incompatible objects leads to fatal error even in ??: https://3v4l.org/jYnmB

[enumag]

@herndlm good points!

@ondrejmirtes True but the point is that it most likely is an array and I'm using ?? specifically to handle the case if it isn't. Incompatible object can't appear here since I used json_decode($json, true); - preventing any object to appear in the result. The code IS safe to run no matter what $json contains (technically I should add JSON_THROW_ON_ERROR but that's it).

[github-actions]

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