Using a forked version of nixpkgs to test Sculpin

January 26th, 2026

I recently submitted a pull request to add Sculpin to the nixpkgs repository.

At the time of writing, it is awaiting review, but the CI pipeline checks pass.

I use Sculpin for a few personal websites, including the in-progress PHP South Wales website reboot, and wanted to test my new package and ensure it worked.

I was previously adding PHP and Composer to my shell via this flake.nix file:

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

  outputs =
    inputs:
    let
      system = "x86_64-linux";
      pkgs = import inputs.nixpkgs { inherit system; };

      inherit (pkgs) fetchFromGitHub lib;
    in
    {
      devShells.${system}.default = pkgs.mkShell {
        packages = with pkgs; [
          php
          phpPackages.composer

          (import ./sculpin.nix {
            inherit fetchFromGitHub lib php;
          })
        ];
      };
    };
}

I had a copy of my Sculpin derivation in sculpin.nix and was importing it as an additional package.

But with this flake.nix file, I can use my fork of nixpkgs that the branch that contains my Sculpin package and install it directly:

{
  inputs.nixpkgs.url = "github:opdavies/nixpkgs/add-sculpin";

  outputs =
    inputs:
    let
      system = "x86_64-linux";
      pkgs = import inputs.nixpkgs { inherit system; };
    in
    {
      devShells.${system}.default = pkgs.mkShell {
        packages = with pkgs; [ sculpin ];
      };
    };
}

Changing inputs.nixpkgs.url to my fork uses it as the nixpkgs repository instead of the official one, and now I can add sculpin as if it were already committed.