fmt.nix

{
  perSystem = {
    inputs',
    config,
    pkgs,
    ...
  }: {
    # provide the formatter for `nix fmt`
    formatter = config.treefmt.build.wrapper;

    # configure treefmt
    treefmt = {
      projectRootFile = "flake.nix";

      programs = {
        alejandra = {
          enable = true;
          package = inputs'.nyxpkgs.packages.alejandra-no-ads;
        };

        shellcheck.enable = true; # cannot be configured, errors on basic bash convention

        prettier = {
          enable = true;
          package = pkgs.prettierd;
          excludes = ["*.age"];
          settings = {
            editorconfig = true;
          };
        };

        shfmt = {
          enable = true;
          # https://flake.parts/options/treefmt-nix.html#opt-perSystem.treefmt.programs.shfmt.indent_size
          indent_size = 2; # set to 0 to use tabs
        };
      };
    };
  };
}