Packaging things in Nix

NixOS and Nix is notoriously underdocumented, and it frankly has no structure that lends itself to be nicely documented. (Maybe Flakes will provide some relief? I doubt it though.

Until that situation is better, here’s my own documentation on things:

Getting node modules into your env

Use pkgs.yarn2nix-moretea.mkYarnModules to generate a derivation that contains the packages you need through a lock file:

nodeModules = pkgs.yarn2nix-moretea.mkYarnModules {
    inherit version;
    pname = "${project-name}-js-deps";
    packageJSON = ./package.json;
    yarnLock = ./yarn.lock;
};

This will create a derivation that contains a node_modules folder with all the dependencies.

In this case, I wanted to have tailwind access to more packages. So, I had to add the nodeModules derivation to the NODE_PATH env variable.

Luckily, this is possible with the makeWrapper helper:

tailwind = pkgs.stdenv.mkDerivation {
    inherit version;
    pname = "${pname}-tailwindcss";

    nativeBuildInputs = [ pkgs.makeWrapper ];

    buildCommand = ''
        mkdir -p $out/bin
        makeWrapper ${pkgs.nodePackages.tailwindcss}/bin/tailwindcss $out/bin/tailwindcss \
            --prefix NODE_PATH ":" "${nodeModules}/node_modules"
    '';
};

This prefixed the NODE_PATH env variable with a path to the node_modules folder that we built earlier. This way, tailwind will find whatever we gave it.