README: Pants-Ruff Bug?

Introduction

This document describes a potential bug related to the import order in hello_ruff.py when using the ruff command and pants command to sort the order.

The Bug

When running the command below from src/python, the import order in hello_ruff.py changes as expected:

> ruff --config ../../ruff.toml . --fix

Before running the above command, the import order in hello_ruff.py is:

from hello_user import hello_user
from scipy.special import cbrt

After running the above command, the import order in hello_ruff.py becomes:

from scipy.special import cbrt

from hello_user import hello_user

However, when running the following command, scipy is treated as a first party import and the import order remains unchanged:

> pants fmt fix lint ::

As a result, the import order in hello_ruff.py remains as:

from hello_user import hello_user
from scipy.special import cbrt

Furthermore, if these two commands are run alternately, the import order will alternate between the two forms described above.

A workaround

The issue can be mitigated by adding the source root entries in pants.toml to ruff.toml. Something like

src = ["src/python"]

However, having to specify the source roots in two places is not desirable.