claude-code: Skill for Claude Code

Nix Best Practices

Flake Structure

Standard flake.nix structure:

{
  description = "Project description";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
    flake-utils.url = "github:numtide/flake-utils";
  };

  outputs = { self, nixpkgs, flake-utils }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        pkgs = import nixpkgs {
          inherit system;
        };
      in {
        devShells.default = pkgs.mkShell {
          buildInputs = with pkgs; [
            # packages here
          ];
        };
      });
}

Follows Pattern (Avoid Duplicate Nixpkgs)

When adding overlay inputs, use follows to share the parent nixpkgs and avoid downloading multiple versions:

inputs = {
  nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";

  # Overlay follows parent nixpkgs
  some-overlay.url = "github:owner/some-overlay";
  some-overlay.inputs.nixpkgs.follows = "nixpkgs";

  # Chain follows through intermediate inputs
  another-overlay.url = "github:owner/another-overlay";
  another-overlay.inputs.nixpkgs.follows = "some-overlay";
};

All inputs must be listed in outputs function even if not directly used:

outputs = { self, nixpkgs, some-overlay, another-overlay, ... }:

Applying Overlays

Overlays modify or add packages to nixpkgs:

let
  pkgs = import nixpkgs {
    inherit system;
    overlays = [
      overlay1.overlays.default
      overlay2.overlays.default
      # Inline overlay
      (final: prev: {
        myPackage = prev.myPackage.override { ... };
      })
    ];
  };
in

Handling Unfree Packages

Option 1: nixpkgs-unfree (Recommended for Teams)

Use numtide/nixpkgs-unfree for EULA-licensed packages without requiring user config:

inputs = {
  nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
  nixpkgs-unfree.url = "github:numtide/nixpkgs-unfree/nixos-unstable";
  nixpkgs-unfree.inputs.nixpkgs.follows = "nixpkgs";

  # Unfree overlay follows nixpkgs-unfree
  proprietary-tool.url = "github:owner/proprietary-tool-overlay";
  proprietary-tool.inputs.nixpkgs.follows = "nixpkgs-unfree";
};