Bug report

I came to a conclusion that iterable<T> in PHPStan is declared to be contravariant in its parameter. This is wrong; it should be covariant in it instead.

Code snippet that reproduces the problem

https://phpstan.org/r/112368bd-0528-4d62-b3de-97e068c0e005

Expected output

This code fails at runtime (we attempt to call putStrLn with an int) but produces no errors during type-checking. The reason is that IProcessor must be contravariant in its parameter T, but PHPStan believes it is covariant in it. It seems that builtin type iterable<T> is mistakingly declared in PHPStan to be contravariant in T. This is wrong: its method current() returns T, and only covariant types can occur in that position. If you change iterable to \Iterator, \Generator, or array in the code, you’ll get a type error, which is the correct behaviour.