show configuration diffs

add formatting for nix and elixir

nixos/default.nix

@@ -39,7 +39,17 @@
   };
 
   environment = {
-    systemPackages = with pkgs; [ wget curl git btop ripgrep vim dogdns tree dig ];
+    systemPackages = with pkgs; [
+      wget
+      curl
+      git
+      btop
+      ripgrep
+      vim
+      dogdns
+      tree
+      dig
+    ];
     gnome.excludePackages = with pkgs; [
       gnome.totem
       gnome-tour
@@ -50,7 +60,15 @@
     ];
   };
 
-  system.stateVersion = "23.05";
+  system = {
+    stateVersion = "23.05";
+
+    activationScripts.diff = ''
+      if [[ -e  /run/current-system ]]; then
+        ${pkgs.nix}/bin/nix store diff-closures /run/current-system "$systemConfig"
+      fi
+    '';
+  };
 
   programs.ssh = {
     startAgent = true;