Pre-commit flake8 with setup.cfg in subfolder - pre-commit-hook

Question

I use flake8 with a bunch of plugins (flake8-docstrings, flake8-isort, flake8-black). I have them all pre-installed into a venv.
My repo to be checked with pre-commit:
Root folder has two packages
Each has its own
pyproject.toml (configures black and isort)
setup.cfg (configures flake8 and pydocstyle)
├── foo
│   ├── pyproject.toml
│   ├── setup.cfg
│   └── (the package)
├── bar
│   ├── pyproject.toml
│   ├── setup.cfg
│   └── (the package)
└── venv
I want to invoke flake8 via pre-commit for the two packages.
Here's how I do it currently:
---
repos:
- repo: local
hooks:
- id: flake8-foo
name: Run flake8 in foo package
entry: bash -c "cd foo && flake8"
language: python
- id: flake8-bar
name: Run flake8 in bar package
entry: bash -c "cd bar && flake8"
language: python
When I run pre-commit run --all-files and there's an error in foo, it prints the same output many times:
./path/in/foo/to/file.py:49:1: D401 First line should be in imperative mood
./path/in/foo/to/file.py:49:1: D401 First line should be in imperative mood
./path/in/foo/to/file.py:49:1: D401 First line should be in imperative mood
./path/in/foo/to/file.py:49:1: D401 First line should be in imperative mood
./path/in/foo/to/file.py:49:1: D401 First line should be in imperative mood
./path/in/foo/to/file.py:49:1: D401 First line should be in imperative mood
./path/in/foo/to/file.py:49:1: D401 First line should be in imperative mood
./path/in/foo/to/file.py:49:1: D401 First line should be in imperative mood
./path/in/foo/to/file.py:49:1: D401 First line should be in imperative mood
./path/in/foo/to/file.py:49:1: D401 First line should be in imperative mood
./path/in/foo/to/file.py:49:1: D401 First line should be in imperative mood
Is there a better way to go about this?
No, I am not open to splitting up the packages into their own repos
How can I have the error message only print once?

Answer 1

pre-commit by design operates on files, it also is optimized to batch runs of linters against files into multiple processes
what's happening here is your configuration is running several invocations (~1 per processor) of bash -c "cd bar && flake8" file1 file2 file3 etc. etc.
fortunately there's a setting you can use to fix this for you:
pass_filenames: false
with that:
---
repos:
- repo: local
hooks:
- id: flake8-foo
name: Run flake8 in foo package
entry: bash -c "cd foo && flake8"
language: python
pass_filenames: false
files: ^foo/
types: [python]
- id: flake8-bar
name: Run flake8 in bar package
entry: bash -c "cd bar && flake8"
language: python
pass_filenames: false
files: ^bar/
types: [python]
that said, you're losing most of the benefits of the framework by going to a repo: local hook:
pre-commit isn't managing the installation of the tools (each of your developers has to install the tool separately and at a particular version)
any filename-based optimizations aren't happening
if you only change one file, you're currently linting your whole repository twice
during merge conflicts, pre-commit optimizes which files to run (not the whole repo)
and more
what I'd suggest instead for your monorepo setup is to still call flake8 in the normal way but utilize --config such that it works against your sub-repos:
repos:
- repo: https://gitlab.com/pycqa/flake8
rev: 3.8.4
hooks:
- id: flake8
name: flake8 ./foo/
alias: flake8-foo
files: ^foo/
args: [--config, foo/setup.cfg]
- id: flake8
name: flake8 ./bar/
alias: flake8-bar
files: ^bar/
args: [--config, bar/setup.cfg]
disclaimer: I'm the author of pre-commit and the current maintainer of flake8