Add upgrade-diff

modules/default.nix

@@ -49,6 +49,7 @@
     ./udmx.nix
     ./uefi.nix
     ./unfree.nix
+    ./upgrade-diff.nix
     ./wireshark.nix
     ./yubikey-gpg.nix
   ];

modules/upgrade-diff.nix

@@ -0,0 +1,14 @@
+# MIT Jörg Thalheim - https://github.com/Mic92/dotfiles/blob/c6cad4e57016945c4816c8ec6f0a94daaa0c3203/nixos/modules/upgrade-diff.nix
+{ config, pkgs, ... }:
+{
+  system.activationScripts.diff = {
+    supportsDryActivation = true;
+    text = ''
+      if [[ -e /run/current-system ]]; then
+        echo "--- diff to current-system"
+        ${pkgs.nvd}/bin/nvd --nix-bin-dir=${config.nix.package}/bin diff /run/current-system "$systemConfig"
+        echo "---"
+      fi
+    '';
+  };
+}