nix overlay example

overlays-default.nix

# .config/nixpkgs/overlays/default.nix
self: super:

let
  callPackage = super.lib.callPackageWith super;
in
{
  packer = super.callPackage ./pkgs/packer {};
}

overlays-pkgs-packer-default.nix

# .config/nixpkgs/overlays/pkgs/packer/default.nix
{ stdenv, buildGoPackage, fetchFromGitHub }:

buildGoPackage rec {
  name = "packer-${version}";
  version = "1.3.5";

  goPackagePath = "github.com/hashicorp/packer";

  subPackages = [ "." ];

  src = fetchFromGitHub {
    owner = "hashicorp";
    repo = "packer";
    rev = "v${version}";
    sha256 = "08anrc95nd5j4x4gia9rw151bdb99z72zgjdj8h0h9da177lqhbz";
  };

  meta = with stdenv.lib; {
    description = "A tool for creating identical machine images for multiple platforms from a single source configuration";
    homepage    = https://www.packer.io;
    license     = licenses.mpl20;
    platforms   = platforms.unix;
  };
}