---

name: nix description: Expert Nix development assistance. Use when working with Nix code, .nix files, flakes, NixOS configuration, or when user mentions Nix, flake-parts, nixpkgs.

Nix Development

Guidelines

• Use flake-parts when creating new flakes
• Format with nixpkgs-fmt after changes
• Use writeShellApplication for shell scripts (not writeShellScriptBin)
  • Automatically runs ShellCheck validation
  • Sets strict bash options (set -euo pipefail)
  • Fix ALL ShellCheck warnings without ignoring them
  • Add meta.description

Building with Nix

When running nix build:

• ALWAYS use --print-out-paths flag so final build path is printed
• NEVER run with timeout - allow command to finish completely
• If command doesn't finish OR final out path is not shown, consider it FAILED
• On failure, investigate logs without hallucinating - look at actual error messages

Home-Manager Module

When adding a home-manager module to a project:

1. Module: nix/modules/home-manager/<name>.nix - options & config with systemd (Linux) + launchd (Darwin)
2. Export: nix/modules/flake/<name>-module.nix - flake.homeManagerModules.<name> = ../home-manager/<name>.nix;
3. Example: nix/examples/home-manager/flake.nix - homeConfiguration + checks.runNixOSTest
4. CI: Add to vira.hs build.flakes: "./nix/examples/home-manager" { overrideInputs = [("<name>", ".")] }
5. Format: nixpkgs-fmt all .nix files