feat: add stub home-manager module for systems without impermanence

flake.nix

@@ -34,6 +34,8 @@
           }
         ];
       };
+      # Stub module for home-manager on systems without impermanence
+      homeManagerModules.stub = import ./home-manager-stub.nix;
       nixosModule = self.nixosModules.impermanence;
       nixosModules.home-manager.impermanence = self.homeManagerModules.impermanence;
 

home-manager-stub.nix

@@ -0,0 +1,65 @@
+{ pkgs
+, config
+, lib
+, ...
+}:
+
+let
+  inherit (lib)
+    mkOption
+    types
+    catAttrs
+    any
+    hasInfix
+    attrValues
+    ;
+
+  inherit (types)
+    attrsOf
+    submodule
+    bool
+    ;
+
+  inherit (config) home;
+
+  cfg = config.home.persistence;
+
+  persistentStoragePaths = catAttrs "persistentStoragePath" (attrValues cfg);
+in
+{
+  options =
+    {
+      home.persistence = mkOption {
+        default = { };
+        type = attrsOf (
+          submodule (
+            { name, config, ... }:
+            import ./submodule-options.nix {
+              inherit pkgs lib name config;
+
+              user = home.username;
+              homeDir = home.homeDirectory;
+
+              # Home Manager doesn't seem to know about the user's group,
+              # so we default it to null here and fill it in in the NixOS
+              # module instead
+              group = null;
+            }
+          ));
+      };
+    };
+  config = {
+    assertions = [
+      {
+        assertion = !(any (hasInfix home.homeDirectory) persistentStoragePaths);
+        message = ''
+          home.persistence: persistentStoragePath contains home directory path!
+
+            The API has changed - the persistent storage path should no longer
+            contain the path to the user's home directory, as it will be added
+            automatically.
+        '';
+      }
+    ];
+  };
+}