Allow enabling spice

lib/config/custom-build-vm.nix

@@ -31,10 +31,26 @@ in {
           default = false;
         };
 
-        qemu.runInBackground = lib.mkOption {
+        qemu = {
+          runInBackground = lib.mkOption {
             type = lib.types.bool;
             default = false;
           };
+
+          spice = {
+            enable = lib.mkEnableOption "spice";
+
+            bindAddress = lib.mkOption {
+              type = lib.types.str;
+              default = "127.0.0.1";
+            };
+
+            port = lib.mkOption {
+              type = lib.types.port;
+              default = 5900;
+            };
+          };
+        };
       };
     };
   in {
@@ -54,6 +70,19 @@ in {
             virtualisation = {
               runAsRoot = lib.mkIf vmVariant.virtualisation.sharedHostKeys true;
 
+              qemu.options =
+                with {
+                  inherit (vmVariant.virtualisation.qemu) spice;
+                };
+                (
+                  lib.optional (spice.enable)
+                    ("-spice " + (
+                      lib.concatStringsSep "," [
+                        "addr=${lib.escapeShellArg spice.bindAddress}"
+                        "port=${toString spice.port}"
+                        "disable-ticketing=on"
+                      ])));
+
               sharedDirectories = lib.optionalAttrs (vmVariant.virtualisation.sharedHostKeys) {
                 hostKeys =
                 let