Track safe usage of 'unsafe' type parameters

[KotlinIsland]

Here's an idea, is it possible to track safe usage of type parameters in potentially unsafe positions?

class A(Generic[T_co]):
    def foo(self, t: T_co):
        print(t)

This code is perfectly safe (although a subtype could change that) and ideally should be allowed.

It would be super interesting to investigate the bounds of what's possible in terms of "safe variance"

[DetachHead]

is this related to the SafeVariance idea

[KotlinIsland]

Actually it's related to UnsafeVariance #209

[KotlinIsland]

Thinking about this a bit more, it might be a more refined form of SafeVariance, where the parameter is basically object.