flake-parts

flake-parts is a tool for generating a flake from other modularly prepared nix derivations. I wish documentation was a bit more elaborate, but by checking enough repositories it is possible to understand the basic usage.

The default structure for a simple package such as the one I generated for nixvim is

flake.nix
pkg.nix
config/default.nix

flake.nix

{
  description = "";
 
  
  inputs = {
    flake-parts.url = "github:hercules-ci/flake-parts";
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
  };
 
  outputs = inputs @ {flake-parts, ...}:
    flake-parts.lib.mkFlake {inherit inputs;} ({
      withSystem,
      flake-parts-lib,
      moduleWithSystem,
      ...
    }: {
      imports = [
        ./pkg.nix
      ];
      systems = ["x86_64-linux" "aarch64-darwin"];
      
      perSystem = {
        system,
        pkgs,
        self',
        lib,
        ...
      }: {
        formatter = pkgs.alejandra;
        devShells.default = pkgs.mkShell {
          nativeBuildInputs = [
            pkgs.alejandra
            self'.packages.<package_name>
          ];
        };
      };
    });
}

pkg.nix

This file is a function, where perSystem is a function that takes some inputs and returns the per-system flake outputs. In my repo, I set it so that package.default takes a config module to, somehow, generate the package.

{
  inputs,
  self,
  ...
}: {
  perSystem = {
    inputs',
    self',
    pkgs,
    system,
    ...
  }: {
    packages.default = ...;
 
    checks.test = ...;
  };
}