In reply to @raitobezarius:matrix.org
I think blocking on evaluation is the least way to piss people off

yes. unfortunately, we only seem to have the infrastructure for doing that for the variant of outright removing the option ...

I guess the principled way of doing that would be to add a kind of system-level "check phase", where before system activation, something would check compatibility ....

feels like we could get started by replacing activation with something that runs the existing code through something like

[{action: "nixos.generation-symlink/set",
  target: "/nix/store/<system>"},
 {action: "nixos.legacy/activate-system",
  variant: "boot",
  target: "/nix/store/<system>"}]

In reply to @raitobezarius:matrix.org
anyone is welcome to work on that, but there's a lot of work involved into touching stc

and according to my reverse-engineered deployment script, these are the two necessary actions, to emulate nixos-rebuild:

  deploy-ssh-for = {
    type = "app";
    program = toString (pkgs.writeScript "deploy-ssh-for" ''
      #!${pkgs.stdenv.shell}
      set -eux
      configName=$1
      remote=root@$2
      action=$3
      shift 3
      if [ gc = "$action" ]
      then ssh -C $remote nix-collect-garbage "$@"
           exit 0
      fi
      configuration=$(nix build .#nixosConfigurations.$configName.config.system.build.toplevel --print-out-paths --no-link -L)
      nix-copy-closure $(if [ "''${1-}" != --direct ]; then echo --use-substitutes; fi) --gzip --to $remote $configuration
      if [ dry-run = "$action" ]
      then set +x
           echo "[dry-run] Would run these commands:"
           echo "    ssh -C $remote nix-env --profile /nix/var/nix/profiles/system --set $configuration"
           echo "    ssh -C $remote $configuration/bin/switch-to-configuration $action"
      else if [ build = "$action" ]
      then ssh -C $remote nix-env --profile /tmp/nixos-system --set $configuration
      else if [ boot = "$action" -o switch = "$action" ]
      then ssh -C $remote nix-env --profile /nix/var/nix/profiles/system --set $configuration
           ssh -C $remote $configuration/bin/switch-to-configuration $action
      else echo "Unknown action '$action'. Use one of: dry-run, boot, switch"
      fi fi fi
    '');
  };