Run mypy in CI with dependencies' type annotations

[hukkin]

• Run mypy in an env that has dependencies and their typehints
  • Fix resulting mypy errors
• Add a few strictness flags for mypy
  • Fix resulting mypy errors

[sloria]

Won't this mean that mypy runs twice--once in pre-commit and once here?

[hukkin]

Yes it does. In pre-commit it doesn't have the typehints of dependencies' so the checks aren't as comprehensive. If you want, we can remove mypy from pre-commit. I left it because it can still be useful when making a git commit locally.

[sloria]

I'd be fine removing mypy from pre-commit. the lint job is already the slowest job in CI at the moment, and I'd hate to make it slower. Also, it's one less thing to manually sync between pre-commit-config.yaml and setup.py.

[sloria]

Also, maybe add a comment above this line explaining why we're running mypy outside of pre-commit

[hukkin]

Removed mypy from pre-commit and made the comment in tox.ini

[sloria]

Thanks. Will give this another look and release after work today or tomorrow.