WIP: tests.postgresql-autoupgrade: fix permission and state problems

nixos/services/postgresql/default.nix

@@ -212,7 +212,11 @@ in {
 
       flyingcircus.activationScripts = {
         postgresql-srv = lib.stringAfter [ "users" "groups" ] ''
+          # postgres data dirs are referenced in the unit as ReadWritePaths and
+          # already need to exist at unit start
+          install -d -o postgres /srv/postgresql
           install -d -o postgres /srv/postgresql/${cfg.majorVersion}
+          # keep around required postgres packages for upgrading
           install -d -o postgres /nix/var/nix/gcroots/per-user/postgres
         '';
       };

pkgs/fc/agent/fc/util/postgresql.py

@@ -359,6 +359,16 @@ def prepare_upgrade(
         collate=collate,
         ctype=ctype,
     )
+    if new_data_dir.exists() and len(list(new_data_dir.iterdir())) == 0:
+        # empty directories created at system activation time can be ignored,
+        # just let the upgrade process create a new one.
+        log.info(
+            "existing-empty-data-dir",
+            _replace_msg=(
+                f"New data dir {new_data_dir} is empty. Removing and recreating it."
+            ),
+        )
+        new_data_dir.rmdir()
     if new_data_dir.exists():
         check_new_data_dir(
             log,