Enable mypy in precommit

[hackaugusto]

• Adds mypy to the precommit
• Fixes some typing issues with code that should have been type checked
• Made the configuration for type checking opt-out instead of opt-in (the idea is that code in new modules should be typed by default)

[hackaugusto]

Notes:

• Mypy treats repeated module names as an error. Because of theses, the conftest.py files used to configure pytest results in errors. The fix is to run mypy on each module independently Suppress 'duplicate module named xx' errors? python/mypy#4008, because of this I'm not yet enabling mypy for the test code
• We support python >=3.7, user defined type guards were only introduced on python >=3.10, so for now the code has quite a few asserts for types

[jlprat]

Do you think it would be worth to add this to CONTRIBUTING.md so people know are aware of this?

[hackaugusto]

Do you think it would be worth to add this to CONTRIBUTING.md so people know are aware of this?

We do mention it, the problem was that mypy was not configured to run with pre-commit.

[hackaugusto]

Note: to enable mypy for the tests, something like this should be used:

  # `mypy tests` can't be run because mypy complains about the repeated conftest.py
  # https://github.com/python/mypy/issues/4008: current solution is to run mypy separately
  - repo: https://github.com/pre-commit/mirrors-mypy
    rev: v0.931
    hooks:
      - id: mypy
        name: Mypy Karapace
        pass_filenames: false
        args: ["--ignore-missing-imports", "--package", "karapace"]

      - id: mypy
        name: Mypy integration tests
        pass_filenames: false
        args: ["--ignore-missing-imports", "tests/integration"]

      - id: mypy
        name: Mypy unit tests
        pass_filenames: false
        args: ["--ignore-missing-imports", "tests/unit"]

[hackaugusto]

I did a quick look on how to model the JSON Schema using recursive types, but that is just not really feasible now for a few reasons:

• To represent dictionaries with non-homegenous value types we need TypedDict which is only >=3.8 (otherwise we would need to add the typing extensions as a dependency and that has other issues)
  • Even if we had TypedDict, it seems that it is a closed model (unknown keys are not allowed), whereas the JSON Schema object is an open model (additional keys are ignored)
• Recursion is not really supported by Mypy with type aliases, only with protocols, and as far as I can see those only works with classes, not dicts

[jongiddy]

Looks good, apart for one spelling error.