autorandr: deterministic and applies for LigthDM

os/default.nix

@@ -7,7 +7,7 @@
     ./boot
     ./ccc
     ./common.nix
-    ./desktop.nix
+    ./desktop
     ./dev
     ./diff
     disko.nixosModules.disko

os/desktop/autorandr.nix

@@ -0,0 +1,21 @@
+{ pkgs, lib, config, ... }:
+let
+  setupScript = "${pkgs.writeShellApplication {
+    name = "greeter-setup-script";
+    runtimeInputs = [ pkgs.autorandr ];
+    text = ''
+      autorandr --change
+    '';
+  }}/bin/greeter-setup-script";
+in
+{
+  config = {
+    services = {
+      autorandr.enable = true;
+      xserver.displayManager.lightdm.extraConfig = ''
+        [Seat:*]
+        display-setup-script = ${setupScript}
+      '';
+    };
+  };
+}

os/desktop/default.nix

@@ -45,4 +45,7 @@
     # So we can use gnome3 pinentry flavour
     services.dbus.packages = [ pkgs.gcr ];
   };
+  imports = [
+    ./autorandr.nix
+  ];
 }