modules.user: check that at least one of hashedPasswordFile or hashedPassword is set

modules/user/default.nix

@@ -114,6 +114,17 @@ inputs:
           (builtins.filter (user: hashedPasswordExist user) user.users));
       }
     )
+    # assert at least hashedPasswordFile or hashedPassword is set
+    {
+      assertions = builtins.map
+        (user:
+        {
+          assertion =
+            let u = inputs.config.users.users.${user}; in u.hashedPasswordFile != null || u.hashedPassword != null;
+          message = "User '${user}' must have either 'hashedPasswordFile' or 'hashedPassword' set.";
+        })
+        inputs.config.nixos.user.users;
+    }
     # setup root
     {
       users.users.root =