mypy cache bug in particular configuration of packages, files, and imports

[dzhlobo]

Bug Report

When I run mypy to type check my classes against protocols and the check passes it no longer fails after I introduce errors later until I clean cache.

To Reproduce

I made a demo with steps to reproduce in dockerized environment: https://github.com/dzhlobo/mypy-cache-issue-demo

Expected Behavior

mypy fails when I change protocol implementation and introduce an error.

Actual Behavior

mypy passes.

Your Environment

• Mypy version used: 1.4.1
• Python version used: 3.11.4

[ilevkivskyi]

@dzhlobo Can you still reproduce the issue with the current mypy master?

[ilevkivskyi]

In the meantime I found that I still can reproduce a variant of this, and I have a fix locally, will make a PR soon.