From ad586e6bebef46d3a2e61751b5e028dd261556b3 Mon Sep 17 00:00:00 2001
From: Minijackson <minijackson@riseup.net>
Date: Thu, 1 Sep 2022 14:43:59 +0200
Subject: [PATCH] formats.systemd: init INI-style systemd config file format

---
 pkgs/pkgs-lib/formats.nix | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/pkgs/pkgs-lib/formats.nix b/pkgs/pkgs-lib/formats.nix
index 3cbda3a7ebdd..950547c4f001 100644
--- a/pkgs/pkgs-lib/formats.nix
+++ b/pkgs/pkgs-lib/formats.nix
@@ -142,6 +142,20 @@ rec {
 
   };
 
+  # As defined by systemd.syntax(7)
+  #
+  # null does not set any value, which allows for RFC42 modules to specify
+  # optional config options.
+  systemd = let
+    mkValueString = lib.generators.mkValueStringDefault {};
+    mkKeyValue = k: v:
+      if v == null then "# ${k} is unset"
+      else "${k} = ${mkValueString v}";
+  in ini {
+    listsAsDuplicateKeys = true;
+    inherit mkKeyValue;
+  };
+
   keyValue = {
     # Represents lists as duplicate keys
     listsAsDuplicateKeys ? false,