Inventory/assertions: add seperate assertion layer

nixosModules/clanCore/default.nix

@@ -3,7 +3,7 @@
   imports = [
     ./backups.nix
     ./facts
-    ./inventory/interface.nix
+    ./inventory
     ./manual.nix
     ./meta/interface.nix
     ./metadata.nix

nixosModules/clanCore/inventory/default.nix

@@ -0,0 +1,6 @@
+{
+  imports = [
+    ./interface.nix
+    ./implementation.nix
+  ];
+}

nixosModules/clanCore/inventory/implementation.nix

@@ -0,0 +1,6 @@
+{ config, ... }:
+{
+  config.assertions = builtins.attrValues (
+    builtins.mapAttrs (_id: value: value // { inherit _id; }) config.clan.inventory.assertions
+  );
+}

nixosModules/clanCore/inventory/interface.nix

@@ -60,4 +60,21 @@ in
     '';
     type = lib.types.attrsOf (lib.types.attrsOf instanceOptions);
   };
+  options.clan.inventory.assertions = lib.mkOption {
+    default = { };
+    internal = true;
+    type = lib.types.attrsOf (
+      # TODO: use NixOS upstream type
+      lib.types.submodule {
+        options = {
+          assertion = lib.mkOption {
+            type = lib.types.bool;
+          };
+          message = lib.mkOption {
+            type = lib.types.str;
+          };
+        };
+      }
+    );
+  };
 }