A plan or diff-current-to-next command would be useful to have.

We can get something pretty close already by combining colmena and nix-diff:

$ colmena build --on laptop
[INFO ] Using configuration: ./deployment.nix
[INFO ] Enumerating nodes...
[INFO ] Selected 1 out of 5 hosts.
       ✅ 11s All done!
laptop ✅ 10s Evaluated laptop
laptop ✅ 1s Built "/nix/store/r829pyjngqxmn7k1j9j39w3rcaarg2d1-nixos-system-laptop-21.11pre-git"

$ nix-diff --color always --character-oriented /var/run/current-system /nix/store/r829pyjngqxmn7k1j9j39w3rcaarg2d1-nixos-system-laptop-21.11pre-git | less -R

There are a few problems with the above:

• nix-diff is a separate package to install,
• the diff isn't great (the full diff contains the entirety of options.xml and is 26MB in size); that said, i think that if we diffed just a few specific things like system-path, that would be useful,
• the diff requires the previous system derivation to be available locally.

If you're interested in a feature like this, I'd be up for rewriting nix-diff as a rust library and trying to integrate it into colmena.

In reply to @winterqt:nixos.dev
yeah that seems to be broken 😅