nix overlay setup

config-overlay.nix

{ config, pkgs, ... }:
let

  inherit (import <nixpkgs>{}) fetchgitPrivate;

  overlay = fetchgitPrivate {
    url = "...";
    rev = "...";
    sha256 = "...";
  };

in {

  nixpkgs.overlays = [ (import overlay) ];

  imports = [
    "${overlay}/modules/module-list.nix"
  ];

}

configuration.nix

{ config, pkgs, ... }:
{

  imports = [
    ...
    ./config/overlay.nix
    ...
  ];

  ...

}

overlay-default.nix

self: super:
let

  packageOverrides = py-self: py-super: let
    inherit (py-self) callPackage;
  in {
  
    some-package = callPackage ./packages/python/some-package { };
  
  };

in {

  python2 = super.python2.override { inherit packageOverrides; };
  python3 = super.python3.override { inherit packageOverrides; };

  some-program = self.callPackage ./packages/some-program { };

}

overlay-modules-module-list.nix

{

  imports = [
    ./some-service/default.nix
  ];

}