From b4e162a109eb84911c68d1695a3e524b7650da90 Mon Sep 17 00:00:00 2001
From: Adam Stephens <adam@valkor.net>
Date: Thu, 21 Sep 2023 20:05:25 -0400
Subject: [PATCH] nixos/networking: warn when both networkd and dhcpcd can
 collide

---
 nixos/modules/tasks/network-interfaces.nix | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/nixos/modules/tasks/network-interfaces.nix b/nixos/modules/tasks/network-interfaces.nix
index 0d4033ca9430..5dd3f47a3bc3 100644
--- a/nixos/modules/tasks/network-interfaces.nix
+++ b/nixos/modules/tasks/network-interfaces.nix
@@ -1326,7 +1326,10 @@ in
 
   config = {
 
-    warnings = concatMap (i: i.warnings) interfaces;
+    warnings = (concatMap (i: i.warnings) interfaces) ++ (lib.optional
+      (config.systemd.network.enable && cfg.useDHCP && !cfg.useNetworkd) ''
+        The combination of `systemd.network.enable = true`, `networking.useDHCP = true` and `networking.useNetworkd = false` can cause both networkd and dhcpcd to manage the same interfaces. This can lead to loss of networking. It is recommended you choose only one of networkd (by also enabling `networking.useNetworkd`) or scripting (by disabling `systemd.network.enable`)
+      '');
 
     assertions =
       (forEach interfaces (i: {