rsyslogd & syslog-nd: fix broken module

nixos/modules/system/boot/systemd.nix

@@ -587,6 +587,14 @@ in
       '';
     };
 
+    services.journald.forwardToSyslog = mkOption {
+      default = (if config.services.rsyslogd.enable || config.services.syslog-ng.enable then true else false);
+      type = types.bool;
+      description = ''
+        Whether to forward log messages to syslog.
+      '';
+    };
+
     services.logind.extraConfig = mkOption {
       default = "";
       type = types.lines;
@@ -753,6 +761,9 @@ in
           ForwardToConsole=yes
           TTYPath=${config.services.journald.console}
         ''}
+        ${optionalString (config.services.journald.forwardToSyslog) ''
+          ForwardToSyslog=yes
+        ''}
         ${config.services.journald.extraConfig}
       '';
 

nixos/tests/rsyslogd.nix

@@ -0,0 +1,27 @@
+import ./make-test.nix ({ pkgs, lib, ... }:
+{
+  name = "rsyslogd";
+  meta.maintainers = [ lib.maintainers.aanderse ];
+
+  nodes = {
+    machine1 =
+      { config, pkgs, ... }:
+      { services.rsyslogd.enable = true;
+        services.journald.forwardToSyslog = false;
+      };
+
+    machine2 =
+      { config, pkgs, ... }:
+      { services.rsyslogd.enable = true;
+      };
+  };
+
+  # ensure rsyslogd is receiving messages from journald if and only if setup to do so
+  testScript = ''
+    $machine1->waitForUnit("default.target");
+    $machine1->fail("test -f /var/log/messages");
+
+    $machine2->waitForUnit("default.target");
+    $machine2->succeed("test -f /var/log/messages");
+  '';
+})