rec {

  overlays = [

    (final: prev: {

      # rebase is a helper which takes all files/dirs under oldroot, and
      # creates a new derivation with those files/dirs copied under newroot
      # (where newroot is a relative path to the root of the derivation).
      rebase = name: oldroot: newroot: prev.stdenv.mkDerivation {
        name = name;
        inherit oldroot newroot;
        builder = builtins.toFile "builder.sh" ''
          source $stdenv/setup
          mkdir -p "$out"/"$newroot"
          cp -rL "$oldroot"/* "$out"/"$newroot"
        '';
      };

      # make buildGoModule default to static compilation
      buildGoModule = args: prev.buildGoModule ({
        doCheck = false;
        CGO_ENABLED=0;
        tags = [ "netgo" "timetzdata" ];
        ldflags = [ "-w" "-extldflags=-static" ];
      } // args);

    })

    (final: prev: {

      yq-go = prev.buildGoModule rec {

        pname = "yq-go";
        version = "4.21.1";

        src = prev.fetchFromGitHub {
          owner = "mikefarah";
          repo = "yq";
          rev = "v${version}";
          sha256 = "sha256-283xe7FVHYSsRl4cZD7WDzIW1gqNAFsNrWYJkthZheU=";
        };

        vendorSha256 = "sha256-F11FnDYJ59aKrdRXDPpKlhX52yQXdaN1sblSkVI2j9w=";
      };

      nebula = prev.buildGoModule rec {
        pname = "nebula";

        # If this changes, remember to change:
        # - the AppDir/etc/daemon.yml vpn.firewall docs
        # - the version imported in go-workspace
        version = "1.4.0";

        src = prev.fetchFromGitHub {
          owner = "slackhq";
          repo = pname;
          rev = "v${version}";
          sha256 = "lu2/rSB9cFD7VUiK+niuqCX9CI2x+k4Pi+U5yksETSU=";
        };

        vendorSha256 = "p1inJ9+NAb2d81cn+y+ofhxFz9ObUiLgj+9cACa6Jqg=";

        subPackages = [ "cmd/nebula" "cmd/nebula-cert" ];
      };

    })

  ];

  stableSrc = fetchTarball {
    name = "nixpkgs-22-05";
    url = "https://github.com/NixOS/nixpkgs/archive/2aec372cdcd4d73b94863611fea70e0884270fdc.tar.gz";
    sha256 = "1pbfhlh4v8l70p44gspsci3i6w0wk70vaisiawg3jhka2nxb8367";
  };

  stable = import stableSrc { inherit overlays; };
}