nixos-rebuild-ng: print out diffed closures

pkgs/by-name/ni/nixos-rebuild-ng/src/nixos_rebuild/nix.py

@@ -1,3 +1,4 @@
+import sys
 import json
 import logging
 import os
@@ -538,6 +539,11 @@ def list_generations(profile: Profile) -> list[GenerationJson]:
         )
 
 def diff_closures(current_config: Path, new_config: Path, target_host: Remote | None = None):
+    print(
+        f"<<< {current_config}"
+        f">>> {new_config}",
+        file=sys.stderr
+    )
     run_wrapper(
         [
             "nix",

pkgs/by-name/ni/nixos-rebuild-ng/src/nixos_rebuild/services.py

@@ -321,12 +321,12 @@ def build_and_activate_system(
             grouped_nix_args=grouped_nix_args,
         )
 
-    current_config = Path("/run/current-system")
+    current_config = Path("/run/current-system").readlink()
     if args.diff:
         if current_config.exists():
             nix.diff_closures(current_config=current_config, new_config=path_to_config, target_host=target_host)
         else:
-            logger.warn(f"missing '{str(current_config)}', skipping configuration diff...")
+            logger.warning(f"missing '{str(current_config)}', skipping configuration diff...")
 
     _activate_system(
         path_to_config=path_to_config,