Fix stray type error in fs.py

[stuhood]

[ci skip-rust-tests]

[stuhood]

Unclear why, but this is failing in an unrelated branch. I think that possibly due to undeclared dependencies, it only fails when run in particular ways? Not sure.

[Eric-Arellano]

Oof. I was hoping we wouldn't hit this. This was my exact fear with the thread yesterday at https://pantsbuild.slack.com/archives/CASMF8SJ1/p1593122804189300.

Indeed, this happens when you run on fs.py and internals:scheduler is not in the transitive closure. We have an undeclared dependency because of a dep cycle.

This PR will not fix things. Why? MyPy warns when you have unnecessary casts, so this cause errors when running lint ::, because internals:scheduler will now be in the closure and the import can be followed.

Instead, we need to do two things:

1. Remove the conditional imports from interactive_runner.py and fs.py for now. They will not work robustly with v2 MyPy. Replace them with the type hint Any.
2. Lean into your solution on dep cycles.

The takeaway is that Pants must support dep cycles for Python for MyPy to be usable in many codebases.

[stuhood]

2. Lean into your solution on dep cycles.

That is in fact the unrelated PR, heh. On it.

[Eric-Arellano]

Thanks. I would have expected you to need to remove from pants.engine.internals.scheduler import SchedulerSession, but if this passes, great.

[stuhood]

Thanks. I would have expected you to need to remove from pants.engine.internals.scheduler import SchedulerSession, but if this passes, great.

Yep: thank you. I read your comment more carefully the second time.