Update CONTRIBUTING.md with Nix developer shell instructions

[yvan-sraka]

This PR does not modify the cabal behavior. It only updates the CONTRIBUTING.md documentation with instructions on setting up a Nix developer shell. I believe this could help some newcomers get started more easily to contribute to the project.

Rendered

Checklist:

• Patches conform to the coding conventions.

[andreabedini]

See #8753

[andreabedini]

Summarising the discussion in the issue linked above. There is little appetite to have a nix setup in this repository.

This kind of things tend to get bit-rotten [^1] and they are trivial to maintain externally. Indeed all you are proposing here can be obtained with a one-liner:

$ nix-shell -p ghc -p cabal-install -p zlib.dev -p pkgconfig -p haskellPackages.fourmolu -p ghcid

Nevertheless (IIRC) the consensus was that it would ok to add such one liner (as a merge suggestion) to https://github.com/haskell/cabal/blob/master/CONTRIBUTING.md.

[^1] there's bunch of dockerfiles in the repo, does anybody use them?

I appreciate your contribution but I suggest closing this.

[Kleidukos]

@yvan-sraka Do you think it would be better to have a flake hosted somewhere else? I'm thinking about dependency pinning for instance, because fourmolu needs to be one exact version.

[yvan-sraka]

I've discarded my previous commit and updated the CONTRIBUTING.md. You can view the rendered changes here.

[yvan-sraka]

@yvan-sraka Do you think it would be better to have a flake hosted somewhere else? I'm thinking about dependency pinning for instance, because fourmolu needs to be one exact version.

I don't know, but it would be really easy to just copy this flake or that one in another repo, and then you can use e.g. nix develop github:yvan-sraka/cabal.nix to work with it (which is the approach of ghc.nix).

[Kleidukos]

@yvan-sraka I think I'd be in favour of pointing to your flake, especially if it means a better, more principled approach.

[yvan-sraka]

@yvan-sraka I think I'd be in favour of pointing to your flake, especially if it means a better, more principled approach.

I've updated the PR (and edited its description to align with the changes) :)