what i want

https://nixos.org/nixpkgs/manual/#sec-pkg-overrideAttrs documents overrideAttrs and it can be used with top-level/all-packages.nix.

so i want to be able to use overrideAttrs in my own nixpkgs overlay!

the code

rec {
  frontend = pkgs.callPackage "${nixcloud-frontend}/release.nix" {
    inherit nixcloud-editor;
  };

  AAA = frontend.overrideAttrs  (oldAttrs: rec {
    API_HOST="wss://";
  });

  helloWithDebug = pkgs.hello.overrideAttrs (oldAttrs: rec {
    separateDebugInfo = true;
  });

}

problem

but the problem is evaluating AAA won't work:

nix-build nixcloud-pkgs.nix -A AAA
error: attribute ‘overrideAttrs’ missing, at /home/joachim/Desktop/projects/nixcloud/nixcloud-webservices/nixcloud-pkgs.nix:17:9

in contrast, evaluating helloWithDebug works:

nix-build nixcloud-pkgs.nix -A helloWithDebug
these derivations will be built:
  /nix/store/x01q7lfqbwlj08iknph37jxh2bk3il68-hello-2.10.drv
these paths will be fetched (0.69 MiB download, 0.69 MiB unpacked):
  /nix/store/3x7dwzq014bblazs7kq20p9hyzz0qh8g-hello-2.10.tar.gz

hint

in nixpkgs i see:

lib/customisation.nix used in lib/default.nix for which i can't say where it is injected yet.

hacking nixpkgs

to see the stack i just added breaking code into lib/customisation.nix:

nix-build -I nixpkgs=../nixpkgs -A tests --show-trace                                                                 ~/Desktop/projects/nixos/nixpkgs
error: while evaluating anonymous function at /home/joachim/Desktop/projects/nixos/nixpkgs/pkgs/top-level/impure.nix:15:1, called from undefined position:
while evaluating anonymous function at /home/joachim/Desktop/projects/nixos/nixpkgs/pkgs/top-level/default.nix:20:1, called from /home/joachim/Desktop/projects/nixos/nixpkgs/pkgs/top-level/impure.nix:64:1:
while evaluating anonymous function at /home/joachim/Desktop/projects/nixos/nixpkgs/pkgs/stdenv/booter.nix:42:1, called from /home/joachim/Desktop/projects/nixos/nixpkgs/pkgs/top-level/default.nix:97:10:
while evaluating ‘dfold’ at /home/joachim/Desktop/projects/nixos/nixpkgs/pkgs/stdenv/booter.nix:60:27, called from /home/joachim/Desktop/projects/nixos/nixpkgs/pkgs/stdenv/booter.nix:104:4:
while evaluating ‘go’ at /home/joachim/Desktop/projects/nixos/nixpkgs/pkgs/stdenv/booter.nix:63:18, called from /home/joachim/Desktop/projects/nixos/nixpkgs/pkgs/stdenv/booter.nix:71:8:
while evaluating the file ‘/home/joachim/Desktop/projects/nixos/nixpkgs/lib/default.nix’:
syntax error, unexpected ID, expecting '.' or '=', at /home/joachim/Desktop/projects/nixos/nixpkgs/lib/customisation.nix:37:3