{ sources ? import ./sources.nix
, system ? builtins.currentSystem
, crossSystem ? null
, config ? {} }:

let
  # our own overlays:
  local-overlays = [
  ];

  globals =
    if builtins.pathExists ../globals.nix
    then [(import ../globals.nix)]
    else builtins.trace "globals.nix missing, please add symlink" [];

  # merge upstream sources with our own:
  upstream-overlays = [
      ( _: super: {

      sources = (super.sources or {}) // sources;
    })
  ];

  overlays =
    local-overlays ++
    globals ++
    upstream-overlays;
in
  import sources.nixpkgs {
    inherit overlays system crossSystem config;
  }