Allow overwrite of config file, config directory and languages.toml

[Stupremee]

Describe your feature request

I'm currently packaging Helix into a nice NixOS module similar, but much better IMO, to the Neovim module in Home-Manager.
However, it's currently not possible to overwrite the Config file and other directories (except runtime directory), which doesn't work
well with NixOS as I will write the immutable config into the Nix store and Helix should use that one.

I suggest doing the following:

• Allow overwriting the path to the config file (via CLI or environment variable, like -u in Neovim)
  This will not change the config directory, so the languages.toml can still be found at ~/.config/helix/languages.toml
• Allow overwriting the path for the language config (this will just overwrite the path for the languages.toml configuration, nothing else)
• Allow overwriting the whole config directory which will change language config and config file location to the new path

I would be ready to open a PR because this is a very important feature for me!

[archseer]

home-manager should be able to write to the xdg config directory just fine though.

home-manager.users.<user>.xdg.configFile."helix/helix.config" etc

[Stupremee]

Yes, I know, but I'm not writing a home-manager module.

[archseer]

Neovim module in Home-Manager

Yeah okay, I was going off of this. Well, we lookup the xdg config directory to find the underlying location so you could set XDG_CONFIG_HOME to your desired location?

[Stupremee]

Yeah that was badly written 😅
It was meant in API ways so that you can configure Helix using Nix Language.

Oh that would work too I guess. I will try that. Thank you!

[the-mikedavis]

Let's close this out in favor of #1216 which is more focused towards the CLI switch for choosing a config file. #2135 should allow the remaining customization.