Update haskell packages to launch nix-shell in CONTRIBUTING.md

[taimoorzaeem]

Running the given command in CONTRIBUTING.md, raises the following errors:

$ nix-shell -p cabal-install ghc ghcid haskellPackages.fourmolu_0_12_0_0 pkgconfig zlib.dev

     error: attribute 'fourmolu_0_12_0_0' missing
     at «string»:1:137:
          1| {...}@args: with import <nixpkgs> args; (pkgs.runCommandCC or pkgs.runCommand) "shell" { buildInputs = [ (cabal-install) (ghc) (ghcid) (haskellPackages.fourmolu_0_12_0_0) (pkgconfig) (zlib.dev) ]; } ""
           |                                                                                                                                         ^
     Did you mean one of fourmolu_0_15_0_0 or fourmolu_0_16_2_0?
   
     error: 'pkgconfig' has been renamed to/replaced by 'pkg-config'

This seemed like a simple fix which is updating these packages with the new package names. Hence the PR. Please review and merge.

[ulysses4ever]

The pkg-config update is fine but fourmolu is not: our codebase depends on 0.12 and is known to be not well-formed w.r.t. 0.15. So, for a proper fix, you probably need to learn how to get an arbitrary version of a package from Hackage. I couldn't quickly google how to do that but I seem to remember that there was such a thing.

[taimoorzaeem]

Sorry, I couldn't help but think how would getting an arbitrary package from hackage is going to fix this? Could you elaborate further?

[geekosaur]

The Fourmolu versions in Nix won't work, as @ulysses4ever told you. You must install the older one somehow.

[taimoorzaeem]

@ulysses4ever What do you think about adding a shell.nix file to the project. This way we can specify that we want to install the 0_12_0_0 version as shown in an example here here?

[ulysses4ever]

There are varying opinions among the active Cabal maintainers towards how much nix-related stuff could be added to the Cabal repository. I'm (apparently) in minority supporting some lightweight nix instrumentation but provided there's a smoke test for that in our CI. Most of the devs, though, seem to reject anything Nix-related in the repo, see this thread for more context #8753 (I'm honestly stunned that any nix stuff was allowed in the CONTRIBUTING.md at all)

[geekosaur]

I think there's a difference between "here's some tips from Nix users on how to contribute if you use Nix", and providing (hence implying support, when we have none because none of us use Nix) Nix-related resources in our build tree (shell.nix, flake.nix, etc.).

xmonad has some Nix-related things in the tree, but they were accepted with the understanding that someone must support them or they will be jettisoned.

[ulysses4ever]

none of us use Nix

I maintain three local machines and one server that run NixOS. So, I very much use nix. I don't use nix for cabal development. Adding a shell.nix as suggested above would make my life a little easier (but not much). In return, I'm happy to oversee the proposed CI job. For something simple, along the lines of the SO referenced above, it will require very low maintenance, I think. But I agree that it's a different level of support requiring some discussion.

[ulysses4ever]

The simplest way forward for this particular issue may be to remove fourmolu from the -p altogether and maybe add a note that "these are not a complete list of dependencies, e.g. fourmolu-0.12.0.0 used by the Cabal project is not available in nixpkgs-unstable". I'm also not sure why pkg-config is there tbh (maybe when you don't have it, some tests won't be run?..).

We could also reference https://github.com/yvan-sraka/cabal.nix but it looks a little lonely (updated 9 months ago).
EDIT: this repo seems to be doing the same mistake with haskellPackages.fourmolu_0_12_0_0 and not pinning nixpkgs to a point when fourmolu-0.12.0.0 was still there. Unless, that is, you're using it via the flake.

[ulysses4ever]

Makes sense to me!

[Kleidukos]

@yvan-sraka Anything you can do on your cabal.nix setup?

[ulysses4ever]

@fgaz @Kleidukos you approved the PR that added the initial version of these nix-shell-related instructions for cabal development. Would you consider giving a review to this update for the instructions?

[geekosaur]

Not that I'm qualified to review Nix stuff.

[ulysses4ever]

I took the liberty to apply the label. If no updates come in two days, this will be auto-merged by the bot.

[ulysses4ever]

And thanks Brandon!

[Kleidukos]

We use fourmolu 0.14.0.0

[ulysses4ever]

I don't think so:

cabal/.github/workflows/format.yml

Line 15 in 72e5439

version: "0.12.0.0"

[Kleidukos]

Well-spotted, I was under a false impression.

[Kleidukos]

@taimoorzaeem nevermind then, apologies for the confusion!

We still run fourmolu 0.12