networking.dhcpcd: Don't add to system closure when using networkd (#18436)

nixos/modules/services/networking/dhcpcd.nix

@@ -10,7 +10,8 @@ let
 
   interfaces = attrValues config.networking.interfaces;
 
-  enableDHCP = config.networking.useDHCP || any (i: i.useDHCP == true) interfaces;
+  enableDHCP = config.networking.dhcpcd.enable &&
+        (config.networking.useDHCP || any (i: i.useDHCP == true) interfaces);
 
   # Don't start dhcpcd on explicitly configured interfaces or on
   # interfaces that are part of a bridge, bond or sit device.
@@ -85,6 +86,15 @@ in
 
   options = {
 
+    networking.dhcpcd.enable = mkOption {
+      type = types.bool;
+      default = true;
+      description = ''
+        Whether to enable dhcpcd for device configuration. This is mainly to
+        explicitly disable dhcpcd (for example when using networkd).
+      '';
+    };
+
     networking.dhcpcd.persistent = mkOption {
       type = types.bool;
       default = false;

nixos/modules/tasks/network-interfaces-systemd.nix

@@ -43,7 +43,7 @@ in
       message = "networking.bridges.${n}.rstp is not supported by networkd.";
     });
 
-    systemd.services.dhcpcd.enable = mkDefault false;
+    networking.dhcpcd.enable = mkDefault false;
 
     systemd.services.network-local-commands = {
       after = [ "systemd-networkd.service" ];