Add `pre-commit-hooks.nix` for codequality

[MangoIV]

I recently used pre-commit-hooks.nix quite often which makes it really easy to ensure codequality in a flake.

It provides very easy interface to code-quality tools like

• statix
• different nix formatters like nixpkgs-fmt or alejandra
• shellcheck

It provides

• a check that can be run automatically in the checks attribute
• a shellHook that runs all formatters and linters that have been selected upon each commit
• a pre-commit script which you can use to run your formatters and linters

Example:

inputs.pre-commit-hooks = {
  url = "github:cachix/pre-commit-hooks.nix";
  inputs.nixpkgs.follows = "nixpkgs";
  inputs.flake-utils.follows = "flake-utils";
};
outputs =
let 
  # -- snip util funs  -- 

  # configuration is trivial
  preCommitCheckFor = system:
    pre-commit-hooks.lib.${system}.run
      {
        src = ./.;

        settings = { };

        hooks = {
          cabal-fmt.enable = false;
          fourmolu.enable = false;
          hlint.enable = false;
          markdownlint.enable = false;
          nixpkgs-fmt.enable = true;
          shellcheck.enable = true;
          statix.enable = true;
          stylish-haskell.enable = true;
        };

        tools = {
          fourmolu = fourmoluFor system;
          hlint = hlintFor system;
        };
      };
in 
 {
    devShells = perSystem (system: {
      default =
        let
          pkgs = nixpkgsFor system;
        in
        pkgs.mkShell {
          # adds pre-commit tool and pre-commit hook 
          inherit (preCommitCheckFor system) shellHook;
        };
    });
    checks = perSystem (system:
      { formatCheck = preCommitCheckFor system; }
      # format check is for free
    );
 }; 

[michaelpj]

Sorry, what do you want to add this to? To the haskell.nix repo? or what?

[michaelpj]

Generally I'm :-1: on adding more stuff automatigally to haskell.nix projects. haskell.nix has way too much stuff in it already.

[MangoIV]

Sorry, what do you want to add this to? To the haskell.nix repo

Yes, for formatting and linting in the Haskell.nix repo.

[michaelpj]

I'd be fine with that. It would be superb to get most of our shell code shellcheck-ed, but I'm not sure if we can do that since it's mostly in string literals in nix code. Perhaps an argument for trying to pull it out into separate files.

[MangoIV]

yes, I agree, that would be nice, that would also make it easier to read.

pre-commit-hooks is also nice in regards to that it forces the developer/ contributor to make their formatting/ linting checks, like that there aren't any PRs whose checks don't pass because of formatting/ linting errors. I think that's a huge plus, I found that I (and another person that uses it and I asked about it) forget it more often than I would like to

[stale[bot]]

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