pre-commit additional_dependencies in a local repository

Question

I'm trying to introduce pre-commit to our project. The project lives in a monorepo, and we would like to have all our checks to live in that same repo as well. We have a flake8 plugin, and I'm trying to configure the flake8 to use that plugin, however I cannot figure out how to have pre-commit to install our plugin from the local repo.

I've added this to .pre-commit-config.yaml

repos:

  - repo: https://github.com/PyCQA/flake8
    rev: 5.0.4
    hooks:
      - id: flake8
        additional_dependencies:
          - ./my_flake8_plugin

But when I run pre-commit run --all I get this error:

An unexpected error has occurred: CalledProcessError: command: ('/Users/dtv/.cache/pre-commit/repo0620p39l/py_env-python3.10/bin/python', '-mpip', 'install', '.', './my_flake8_plugin')

I do realise that I could specify the absolute path to the plugin, but that will not work on CI or other developers' machines. I couldn't find anything about "variables" or "placeholders" in the doc (e.g. so one could write something like - $(PROJECT_DIR)/my_flake8_plugin.

Is there proper way of doing it apart from writing a separate pre-commit plugin?

Answer 1

pre-commit will never install from the repository under test -- only from the configuration file (otherwise caching is intractable)

your best bet is probably to either package your flake8 plugin and install from a package index server or to utilize flake8's local-plugins feature.

for example if your plugin lives in ./sub-dir and is at module.path:Plugin providing code ABC you might set:

[flake8:local-plugins]
extension =
   ABC = module.path:Plugin
paths = ./sub-dir

in your flake8 configuration

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disclaimer: I created pre-commit and I'm the current flake8 maintainer