Nix HS Utils

Nix utility functions for Haskell flakes

Schema

Functions

High level

• mkLibs and mkRelLibs: convenience functions for adding packages built by callCabal2nix.
• mkDevTools: returns a list with:
  • formatters: cabal-fmt, fourmolu, nixpkgs-fmt/nixfmt, ormolu.
  • linters: hlint (with apply-refact).
  • haskell-language-server.
• mkHaskellPkg: Wrapper for developPackage. Returns either a development shell or a derivation, depending on the value of returnShellEnv. Uses mkDevTools by default.

Low level

• mkLib and mkRelLib: singular versions of mkLibs and mkRelLibs, respectively.
• mkBuildTools: function returning a list of cabal and zlib.

Apps

High level

• format: formats *.cabal, *.nix, and *.hs (ormolu or fourmolu).
• format-hs: formats *.hs (ormolu or fourmolu).
• format-yaml: formats *.yaml (prettier).
• lint: Runs hlint on *.hs.
• lint-refactor: Runs hlint on *.hs, refactoring suggestions.
• lint-yaml: Runs yamllint on ..

Low level

• mkShellApp: Makes an app via writeShellApplication.
• mkApp: Makes an app via a derivation.
• mergeApps: Merges multiple apps together.

Example usage

{
  description = "A flake for a haskell package";
  inputs = {
    nix-hs-utils.url = "github:tbidne/nix-hs-utils";
    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";

    # top-level libs buildable w/ callCabal2nix
    lib1.url = "github:user/lib1";
    lib2.url = "github:user/lib2";

    # multiple libs in subdirs e.g. libs/sublib1, libs/sublib2
    # also buildable w/ callCabal2nix
    libs.url = "github:user/libs";
  };
  outputs =
    inputs@{ nix-hs-utils
    , nixpkgs
    , self
    , ...
    }:
      let
        system = "x86_64-linux";
        pkgs = import nixpkgs {
          inherit system;
        };

        ghc-version = "ghc944";
        compiler = pkgs.haskell.packages."${ghc-version}".override {
          overrides = final: prev: {
            # some normal overrides
            ormolu = prev.ormolu_0_5_3_0;
          } # adding lib1 lib2 deps
            // nix-hs-utils.mkLibs inputs final [
              "lib1"
              "lib2"
          ] # adding libs' relative deps
            // nix-hs-utils.mkRelLibs inputs.libs final [
              "sublib1"
              "sublib2"
          ];
        };
        mkPkg = returnShellEnv:
          nix-hs-utils.mkHaskellPkg {
            inherit compiler pkgs returnShellEnv;
            name = "my-hs-pkg-name";
            root = ./.;
          };
    in
    {
      # builds exe/lib
      packages."${system}".default = mkPkg false;

      # dev shell w/ default build/dev tools
      devShells."${system}".default = mkPkg true;

      # formatting and linting
      apps = {
        format = nix-hs-utils.format {
          inherit compiler pkgs;
          # hsFmt = "fourmolu"; # defaults to ormolu
        };
        # Formats haskell files only
        format-hs = nix-hs-utils.format-hs {
          inherit compiler pkgs;
        };
        # Use find over fd. Probably want to explicitly pass in dirs
        # (findHsArgs) in this case.
        formatFind = nix-hs-utils.format {
          inherit compiler pkgs;
          findHsArgs = "app src test";
          fd = false;
        };
        lint = nix-hs-utils.lint {
          inherit compiler pkgs;
        };
        lint-refactor = nix-hs-utils.lint-refactor {
          inherit compiler pkgs;
        };
      };
    };
}

Tip

We can also merge multiple apps together, using the mkDrv argument (default true) and mergeApps:

let
  # mergeApps takes in a list of app AttrSet and merges them together into a
  # single app.
  format = nix-hs-utils.mergeApps {
    apps = [
      # setting 'mkDrv = false' means that instead of the derivation, we
      # will return the preliminary set.
      (nix-hs-utils.format ({ ... mkDrv = false; ... }))
      (nix-hs-utils.format-yaml ({ ... mkDrv = false; ... }))
    ];
  };