Disable mypy cache

[thopre]

Summary

Mypy crashes with "AssertionError: Cannot find module for UpdatedBase"
when analyzing lnt/server/db/migrations/upgrade_0_to_1.py with a
populated cache. This leads to a number of files not being analyzed by
mypy.

[danilaml]

Why does the cache cause this error in mypy? Is it a documented problem?

[thopre]

In D95033#2509413, @danilaml wrote:

Why does the cache cause this error in mypy? Is it a documented problem?

I think it might be a problem with the sqlalchemy stub/plugin. UpdatedBase is alias to the same call to declarative_base() as Base in the same file. I'm guessing that plugin does not inform Mypy of the dynamic nature of that function call or something like that. It's still early days for that plugin apparently but without using it we get some error that cannot be fixed due to that same declarative_base. I'll try to report the bug.

[cmatthews]

This SGTM. Can you add a note to revisit in a future version of mypy as well.

tox.ini

 [testenv:mypy]
 basepython = python3
 skip_install = true
 deps =
     mypy
     sqlalchemy-stubs
 commands =
     # No where close to passing yet, but nice to have.
-    - mypy --junit-xml=junit-{envname}.xml --py2 --ignore-missing-imports lnt
-    - mypy --junit-xml=junit-{envname}.xml --ignore-missing-imports lnt
+    - mypy --no-incremental --junit-xml=junit-{envname}.xml --py2 --ignore-missing-imports lnt
+    - mypy --no-incremental --junit-xml=junit-{envname}.xml --ignore-missing-imports lnt
 
 [testenv:flake8]
 skip_install = true
 deps =
     flake8
 
 commands =
     # Lets keep the clean files clean.