start new dynamic apply function

modules/dynamicism/submodule.nix

@@ -1,8 +1,8 @@
 {
   name,
-  pkgs,
   lib,
   config,
+  host,
   ...
 }:
 let
@@ -19,6 +19,12 @@ let
   ;
   t = lib.types;
 
+  inherit (import ./lib.nix { inherit lib; })
+    recUpdateFoldl
+  ;
+
+  pkgs = host.pkgs;
+
   /** Either a list of strings, or a dotted string that will be split. */
   convenientAttrPath = t.coercedTo t.str (lib.splitString ".") (t.listOf t.str);
 
@@ -59,6 +65,14 @@ in
       default = lib.attrNames config.unitDropins;
     };
 
+    finalSettings = mkOption {
+      type = t.attrsOf t.raw;
+      internal = true;
+      default = recUpdateFoldl (optPath:
+        lib.setAttrByPath optPath (lib.getAttrFromPath optPath host.config)
+      ) config.source-options;
+    };
+
     configFile = mkOption {
       type = t.pathInStore;
       internal = true;