feat: add Nix flake for package distribution

[PJalv]

Summary

• Adds Nix flake for installing mex without requiring npx
• Enables direct integration into NixOS configurations

Features

• buildNpmPackage derivation for the CLI
• NixOS module for easy system integration (programs.mex.enable = true)
• Dev shell with Node.js 22
• Overlay for use in other flakes

Usage

NixOS Configuration

{
  inputs.mex.url = "github:PJalv/mex";
  
  outputs = { nixpkgs, mex, ... }: {
    nixosConfigurations.your-system = nixpkgs.lib.nixosSystem {
      modules = [
        mex.nixosModules.default
        { programs.mex.enable = true; }
      ];
    };
  };
}

Ad-hoc Usage

nix run github:PJalv/mex

Dev Shell

nix develop github:PJalv/mex

[theDakshJaitly]

Hey @PJalv, thanks for this — nice contribution for Nix users! A few things to address before merging:

Version mismatch

flake.nix:22 hardcodes version = "0.4.0" but package.json is currently at 0.3.2. This should match. Ideally it would be derived from package.json so it doesn't drift on every release, but at minimum it needs to be 0.3.2 right now.

npmDepsHash maintenance

flake.nix:25 — this hash will break any time package-lock.json changes. Could you add a comment above it noting that? Something like:

# Update this hash when package-lock.json changes:
# nix build 2>&1 | grep 'got:' | awk '{print $2}'
npmDepsHash = "sha256-...";

Just so future contributors know what to do when the build fails.

Add result to .gitignore

nix build creates a result symlink in the project root. Should add that to .gitignore so it doesn't get accidentally committed.

Minor note

The postInstall path ($out/lib/node_modules/promexeus/templates/) uses the npm package name promexeus — that's correct today, just flagging it as something that would need updating if the package name ever changes.

---

Everything else looks solid — platform coverage, the NixOS module, overlay, and dev shell all follow standard patterns. Nice work.

[PJalv]

Thanks for checking it out!
I will definitely be making sure the flake correctly reflects the current state of the package;
Already trying it out with my current AI workflow!

[theDakshJaitly]

All review feedback addressed — version aligned to 0.3.2, npmDepsHash comment added, result in .gitignore. Looks good, thanks @PJalv!