Agent Skills: Add Nix Packaging to Flake

Add Nix Packaging to Flake

Convert a devShell-only flake to a deployable package using bun2nix.

Prerequisites

• Existing flake.nix with devShell
• bun.lock file (run bun install first)
• Entry point file (e.g., src/main.ts or src/index.ts)

Steps

1. Detect project info:

   • pname/version from package.json
   • Entry point: check for src/main.ts, src/index.ts, or ask

2. Generate bun.nix:

   nix run github:nix-community/bun2nix
   

3. Replace flake.nix with packaging version:

   {
     description = "<project-name>";
   
     inputs = {
       nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
       flake-utils.url = "github:numtide/flake-utils";
       bun2nix = {
         url = "github:nix-community/bun2nix";
         inputs.nixpkgs.follows = "nixpkgs";
       };
     };
   
     outputs = {
       self,
       nixpkgs,
       flake-utils,
       bun2nix,
     }:
       flake-utils.lib.eachDefaultSystem (system: let
         pkgs = nixpkgs.legacyPackages.${system};
         bun2nix' = bun2nix.packages.${system}.default;
       in {
         packages.default = pkgs.stdenv.mkDerivation {
           pname = "<pname>";
           version = "<version>";
           src = ./.;
   
           nativeBuildInputs = [
             bun2nix'.hook
             pkgs.makeBinaryWrapper
           ];
   
           bunDeps = bun2nix'.fetchBunDeps {
             bunNix = ./bun.nix;
           };
   
           # Run with bun interpreter (not AOT compiled)
           dontUseBunBuild = true;
           dontUseBunCheck = true;
           dontUseBunInstall = true;
   
           installPhase = ''
             runHook preInstall
   
             mkdir -p $out/lib/<pname>
             cp -r . $out/lib/<pname>
   
             mkdir -p $out/bin
             makeBinaryWrapper ${pkgs.bun}/bin/bun $out/bin/<pname> \
               --add-flags "run $out/lib/<pname>/<entry-point>"
   
             runHook postInstall
           '';
         };
   
         devShells.default = pkgs.mkShell {
           buildInputs = with pkgs; [
             bun
             typescript
             lefthook
             bun2nix'
           ];
   
           shellHook = ''
             echo "<project-name> dev shell"
             echo "  bun2nix - Regenerate bun.nix after lockfile changes"
           '';
         };
       });
   }
   

4. Add to .gitignore (if not present):

   result
   

5. Test the build:

   nix build
   ./result/bin/<pname>
   

6. Summary: Note that bun2nix must be re-run after lockfile changes

Notes

• Uses bun interpreter at runtime (not AOT compilation) for better compatibility
• Add extra packages to devShell as needed
• For monorepos, adjust entry point path accordingly