Complaining about isset on general `object` properties (as returned by the likes of `json_decode()`)

[dktapps]

Bug report

This requires enabling strict rules, although strict rules doesn't seem to be the problem directly.

I'm not sure if this is intended or not, but it wasn't reported as an error before 2.x.

When the specific type of object isn't known, checking for isset on object can be used to inform its shape, so reporting an error about this doesn't make any sense to me.

Code snippet that reproduces the problem

https://phpstan.org/r/8bf0e12b-3cc8-4b4b-a086-2c4d15d5a7a1

Expected output

No error should be reported

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[VincentLanglet]

One way to solve this would be to update the return type of json_decode from mixed to

int|float|string|bool|null|array|stdClass

But changing mixed to an union type always migrate some level 9 errors into level 7-8 ones...

Another might to update the return type to mixed ~ (object ~ stdclass)
But seems like nested substracted type are weird
https://phpstan.org/r/0850c2cb-3c81-4451-b2f6-b570d1d41a30