Possible to define a default/fallback config?

[BryceBeagle]

Hey all,

We're working on implementing a ruff framework in our monorepo where we have the following constraints

1. We have a central config file. Let's call it /config/ruff.toml
2. We have a bunch of python libraries scattered around our codebase.
   • It's important to note that the central config is not in a directory directly "above" the libraries, so the normal relative "config file discovery" doesn't apply
3. Some of these libraries will have their own ruff.toml(s)
   • They have extend = "/config/ruff.toml", and then either enable or disable a couple specific rules
4. Other libraries will not have their own ruff.tomls
5. Either way, /config/ruff.toml's rules should be the default for all code, unless otherwise overridden in a local ruff.toml

Some approaches we considered:

• Always providing --config=/config/ruff.toml
  • this doesn't work because then the local config files are completely ignored
• Using multiple --config flags and passing both the central and local configs
  • this doesn't work because using multiple --config flags is not supported
• Never providing --config with a file and instead using --config "extend = '/config/ruff.toml'"
  • this doesn't work because extend is explicitly blocked from being used with --config
• Only providing --config if the the library doesn't have any ruff.toml of it's own
  • this kinda works but falls apart if some subdirectories of the library have ruff.tomls, but not all.
  • If this is the case, some directories will not use any config, which is undesirable
• Force-overriding $XDG_CONFIG_HOME=/config so that the default config fallback described here would pick it as the default
  • This is gross and could potentially interfere with other things in our pipeline that rely on the env var/dirs crate
  • We also have developers on MacOS and hacking around $HOME/Library/Application Support too is even less tenable

The question is: is there a better way to do this without getting hacky?

[MichaReiser]

That's an interesting use case. I don't think there's currently a better way of doing what you want. How do other tools discover your configuration in /config/? Or is Ruff the only tool where you need this specific behavior?

[BryceBeagle]

How do other tools discover your configuration in /config/? Or is Ruff the only tool where you need this specific behavior?

Admittedly, at the moment, ruff is the only tool with this requirement. We're implementing some generic tooling for linting in the monorepo with Bazel (starting with ruff), and the idea was to have the config files live with the tooling.