Request: supporting sub-configs (aka per-directory config)

[jamesbraza]

Is your feature request related to a problem? Please describe.

I like black's default of 88-char line length, except for docs/ renderings, where code blocks may be rendered via Sphinx with 79 char width. This leads to unnecessary scrolling left/right to see the last 9 chars.

It would be useful to enable black to have sub-configurations. This was requested in #1370, and was postponed into the future.

Describe the solution you'd like

Enabling subdirectories to have their own pyproject.toml, and black will accept overrides from that sub-pyproject.toml.

Describe alternatives you've considered

ruff is a project that adopted sub-configs through use of the extend keyword. It has been great, I have:

• One repo-wide config
• Two sub-configs: docs/ and tests/

This can be an example successful implementation of sub-configs.

Additional context

One counter argument is simplying invoking black once/config:

• Once for the repo root
• Once for the subdirectory with its special config

I think this complicates things (e.g. multiple make commands or multiple pre-commit hooks), though it is a valid workaround

[skrawcz]

+1 to this request -- I am running into the same issue with sphinx docs and want a different line length for that code.

[maanijou]

+1 for this.
We have also usecases where we have different types of modules and scripts and for some of them it makes sense to have a different config. For example, formatting for a utility library, compared to a pyspark code can be different and one might need to customize the formatting for different modules in the code

[luator]

+1. I just ran into the exact same use-case that for examples which are included in Sphinx documentation, a shorter line-length would be good.

[Jswig]

• 1 as well. I ran into this recently with Databricks, whose built-in formatter uses black with 88 line length, while the rest of our organization's codebase uses 100 lines