nixos/rsyncd: fix ini format for global section (#385064)

According to the manpage the rsyncd.conf has a global section without a
module header. Settings for listening port or bind address must be put
there and will not work if defined in a global submodule (i.e. below a
"[global]" header).

This commit changes the ini format generator for the rsyncd service to
allow a global section in the config file without a submodule header.

Fixes #304293

Credits to @nydragon

* remove retrocompat, add incompat release notes

nixos/doc/manual/release-notes/rl-2505.section.md

@@ -443,6 +443,10 @@
 - `services.netbird.tunnels` was renamed to [`services.netbird.clients`](#opt-services.netbird.clients),
   hardened (using dedicated less-privileged users) and significantly extended.
 
+- `services.rsyncd.settings` now supports only two attributes `sections` and `globalSection`.
+  As a result, all sections previously defined under `services.rsyncd.settings` must now be put in `services.rsyncd.settings.sections`.
+  Global settings must now be placed in `services.rsyncd.settings.globalSection` instead of `services.rsyncd.settings.global`.
+
 <!-- To avoid merge conflicts, consider adding your item at an arbitrary place in the list instead. -->
 
 ## Other Notable Changes {#sec-release-25.05-notable-changes}

nixos/modules/services/network-filesystems/rsyncd.nix

@@ -6,7 +6,7 @@
 }:
 let
   cfg = config.services.rsyncd;
-  settingsFormat = pkgs.formats.ini { };
+  settingsFormat = pkgs.formats.iniWithGlobalSection { };
   configFile = settingsFormat.generate "rsyncd.conf" cfg.settings;
 in
 {
@@ -25,12 +25,14 @@ in
         inherit (settingsFormat) type;
         default = { };
         example = {
-          global = {
+          globalSection = {
             uid = "nobody";
             gid = "nobody";
             "use chroot" = true;
             "max connections" = 4;
+            address = "0.0.0.0";
           };
+          sections = {
             ftp = {
               path = "/var/ftp/./pub";
               comment = "whole ftp area";
@@ -45,6 +47,7 @@ in
               "secrets file" = "/etc/rsyncd.secrets";
             };
           };
+        };
         description = ''
           Configuration for rsyncd. See
           {manpage}`rsyncd.conf(5)`.
@@ -81,7 +84,7 @@ in
 
   config = lib.mkIf cfg.enable {
 
-    services.rsyncd.settings.global.port = toString cfg.port;
+    services.rsyncd.settings.globalSection.port = toString cfg.port;
 
     systemd =
       let

nixos/tests/rsyncd.nix

@@ -15,10 +15,11 @@ import ./make-test-python.nix (
               enable = true;
               inherit socketActivated;
               settings = {
-                global = {
+                globalSection = {
                   "reverse lookup" = false;
                   "forward lookup" = false;
                 };
+                sections = {
                   tmp = {
                     path = "/nix/store";
                     comment = "test module";
@@ -26,6 +27,7 @@ import ./make-test-python.nix (
                 };
               };
             };
+          };
       in
       {
         a = mkNode false;