[Nix-dev] Building separate nixos/nixpkgs in the same nix build

[Rickard Nilsson]

Hi,

How do one go about building two NixOS systems in one build, when the two  
systems have separate nixos and nixpkgs sources from each other?

I've digged around a bit in nixos/default.nix and  
nixos/lib/eval-config.nix, and it seems the <nixpkgs> path is used in  
several places, and can't really be substituted by a nix expression. And I  
can't change the current NIX_PATH from within a nix expression, can I?

What I'm looking for is something like this:

{
   nixos1 = fetchgit { ... };
   nixpkgs1 = fetchgit { ... };
   nixos2 = /etc/system2/nixos;
   nixpkgs2 = /etc/system2/nixpkgs;

   system1 = (import nixos1 {
     configuration = /etc/system1/configuration.nix;
     nixpkgs = nixpkgs1;
   }).system;

   system2 = (import nixos2 {
     configuration = /etc/system2/configuration.nix;
     nixpkgs = nixpkgs2;
   }).system;
}

I've looked at Charon, but it seems all configurations and machines must  
use the same nixos and nixpkgs there?


Best regards,
   Rickard Nilsson