Add upgrade path for postgresql

nixos/queen/configuration.nix

@@ -21,6 +21,7 @@
     ./mail-server.nix
     ./webmail.nix
     ./gotosocial.nix
+    ../upgrade/postgresql.nix
     #./akkoma.nix
   ];
 

nixos/upgrade/postgresql.nix

@@ -0,0 +1,36 @@
+{
+  config,
+  pkgs,
+  ...
+}: {
+  environment.systemPackages = [
+    (let
+      # XXX specify the postgresql package you'd like to upgrade to.
+      # Do not forget to list the extensions you need.
+      newPostgres = pkgs.postgresql_15.withPackages (pp: [
+        # pp.plv8
+      ]);
+    in
+      pkgs.writeScriptBin "upgrade-pg-cluster" ''
+        set -eux
+        # XXX it's perhaps advisable to stop all services that depend on postgresql
+        systemctl stop postgresql
+
+        export NEWDATA="/var/lib/postgresql/${newPostgres.psqlSchema}"
+
+        export NEWBIN="${newPostgres}/bin"
+
+        export OLDDATA="${config.services.postgresql.dataDir}"
+        export OLDBIN="${config.services.postgresql.package}/bin"
+
+        install -d -m 0700 -o postgres -g postgres "$NEWDATA"
+        cd "$NEWDATA"
+        sudo -u postgres $NEWBIN/initdb -D "$NEWDATA"
+
+        sudo -u postgres $NEWBIN/pg_upgrade \
+          --old-datadir "$OLDDATA" --new-datadir "$NEWDATA" \
+          --old-bindir $OLDBIN --new-bindir $NEWBIN \
+          "$@"
+      '')
+  ];
+}