Mypy complaining about invalid types

[Strilanc]

Couldn't figure this out

cirq/google/engine/engine.py:171: error: Invalid type "cirq.study.study.Sweepable"
cirq/google/engine/engine.py:434: error: Invalid type "cirq.study.study.Sweepable"
cirq/google/sim/xmon_simulator.py:169: error: Invalid type "cirq.study.study.Sweepable"
cirq/google/sim/xmon_simulator.py:236: error: Invalid type "cirq.study.study.Sweepable"

[Strilanc]

Well, a couple hours later, I added this line to engine:

from cirq.study.study import Sweepable

And the type errors went away. I then removed the line, and the type errors stayed gone.

Quite frustrating. Worth knowing.

[Strilanc]

It just switched back to failing.

[Strilanc]

This is... literally impossible to debug. I delete some files, run mypy, it reports failures, I make a commit as a checkpoint, run a local check, run mypy again, and the failures are gone!

[Strilanc]

Doing nothing but run mypy can affect whether mypy reports failures.

$ bash continuous-integration/check-pull-request.sh --only=typecheck
[...]
cirq/google/engine/engine.py:172: error: Invalid type "cirq.study.study.Sweepable"
cirq/google/engine/engine.py:435: error: Invalid type "cirq.study.study.Sweepable"
cirq/google/sim/xmon_simulator.py:169: error: Invalid type "cirq.study.study.Sweepable"
cirq/google/sim/xmon_simulator.py:236: error: Invalid type "cirq.study.study.Sweepable"
[...]
('typecheck by maintainer', (False, '4 issues', None))


$ mypy --config-file=continuous-integration/mypy.ini .
[no failures]


$ bash continuous-integration/check-pull-request.sh --only=typecheck
[...]
('typecheck by maintainer', (True, 'Types look good!', None))

[Strilanc]

Okay, I've figured out the weird stateful thing. It's because I was accidentally copying .mypycache along with the source files when preparing the test environment. That's fixed now. Should go quicker.

[Strilanc]

When I run the exact same command as the one invoked by python, I get no results instead of some results. Maybe there's some kind of environment variable ruining everything...?

[Strilanc]

I managed to make a small repro and report it to mypy: python/mypy#5015