Create a script for prompting the device path

lib/modules/partition.nix

@@ -44,6 +44,12 @@
               else "/dev/${config.deviceName}";
           };
 
+          deviceScript = mkOption {
+            type = types.str;
+            description = "A command for loading the device path into the device variable";
+            internal = true;
+          };
+
           partitions = mkOption {
             type = types.attrsOf (types.nullOr partitionType);
             description = "The partitions of the disk.";
@@ -155,10 +161,7 @@
                 ''sudo sfdisk --part-type ${diskVar} ${toString partition.index} ${mkType partition.type}'')
               partitions);
         in {
-          script = ''
+          deviceScript = if osDisk && config.devicePath == null then ''
-            function partition() {
-              ${
-                if osDisk && config.devicePath == null then ''
               ${diskSelector}
             ''
             else ''
@@ -179,7 +182,11 @@
                   fallback;
                 fi
               '' else ""}
-                ''}
+            '';
+
+          script = ''
+            function partition() {
+              ${config.deviceScript}
 
               ${if (!config.wipe) then cleanup else ""}