Bug report

array{a, b}|array{c, d} is improperly collapsed as array{a|c, b|d}

Code snippet that reproduces the problem

https://phpstan.org/r/2fe252ba-d874-4f42-9164-d5672993d555

Expected output

Line 10: No error
Line 30: Function do_foo() should return array(true, null)|array(null, true) but returns ....
Actually, something (else) weird seems to be going on in line 30 since the reported "actual" type doesn't seem to make any sense.