PoC part 2

modules/dynamicism/submodule.nix

@@ -1,5 +1,6 @@
 {
   name,
+  pkgs,
   lib,
   config,
   ...
@@ -13,10 +14,26 @@ let
     mkEnableOption
     literalExpression
   ;
+  inherit (lib.types)
+    mkOptionType
+  ;
   t = lib.types;
 
   /** Either a list of strings, or a dotted string that will be split. */
   convenientAttrPath = t.coercedTo t.str (lib.splitString ".") (t.listOf t.str);
+
+  executablePathInStore = mkOptionType {
+    name = "exepath";
+    description = "executable path in the Nix store";
+    descriptionClass = "noun";
+    merge = lib.mergeEqualOption;
+    functor = lib.defaultFunctor "exepath";
+    check = x: if lib.isDerivation x then (
+      x.meta.mainProgram or null != null
+    ) else (
+      lib.pathInStore.check x
+    );
+  };
 in
 {
   options = {
@@ -36,12 +53,46 @@ in
         A list of systemd unit names (including the suffix, e.g. `.service`) that need to be updated.
       '';
       example = literalExpression ''
-        "gotosocial.service"
+        [ "gotosocial.service" ]
       '';
+
+      default = lib.attrNames config.unitDropins;
+    };
+
+    configFile = mkOption {
+      type = t.pathInStore;
+      internal = true;
+    };
+
+    unitDropins = mkOption {
+      type = t.attrsOf t.pathInStore;
+      internal = true;
+    };
+
+    activate = mkOption {
+      type = executablePathInStore;
+      internal = true;
     };
   };
 
   config = mkIf config.enable {
-
+    activate = pkgs.writeShellApplication {
+      name = "dynamicism-for-${name}-activate";
+      runtimeInputs = [ pkgs.systemd ];
+      text = let
+        doEdits = config.unitDropins
+          |> lib.mapAttrsToList (service: dropin: ''
+            cat "${dropin}" | systemctl edit "${service}" --runtime --stdin
+          '');
+        doReloads = config.unitDropins
+        |> lib.mapAttrsToList (service: _: ''
+          systemctl reload-or-restart "${service}"
+        '');
+      in [
+        doEdits
+        doReloads
+      ] |> lib.concatLists
+      |> lib.concatStringsSep "\n";
+    };
   };
 }