Ensure venv pre-commit hook

A pre-commit hook that ensures the Python virtual environment is activated.

Use case

You have your own .pre-commit-config.yaml configuration with specified repo: local hooks that run locally installed linters and code formatters, i.e. flake8, ruff, isort, mypy, etc.

-   repo: local
    hooks:
    -   id: mypy
        name: Type check (mypy)
        entry: mypy
        args: [--config-file, mypy.ini, app/, core/, main.py]
        types: [python]
        require_serial: true
        always_run: true
        language: system
        pass_filenames: false

You may want to ensure that the mypy executable used in the pre-commit hook is the one installed locally in your project's virtual environment, not the one taken from the global site-packages. You can use the ensure-venv hook to do this:

-   repo: https://github.com/diachkow/ensure-venv-pre-commit
    rev: v1.0.0
    hooks:
    -   id: ensure-venv

You must place this hook before any repo: local hooks that need to use the locally installed executable. The final configuration will look like this

# ... other non-local hooks ...
-   repo: https://github.com/diachkow/ensure-venv-pre-commit
    rev: v1.0.0
    hooks:
    -   id: ensure-venv
-   repo: local
    hooks:
    -   id: mypy
        name: Type check (mypy)
        entry: mypy
        args: [--config-file, mypy.ini, app/, core/, main.py]
        types: [python]
        require_serial: true
        always_run: true
        language: system
        pass_filenames: false
# ... other non-local hooks ...

If the virtual environment is not enabled, the pre-commit will fail fast at the ensure-venv step and will not run the mypy, giving you an error telling you to enable your virtual environment.