Load extra layers from machines repo

configuration.nix

 # This is the entry point for my NixOS configuration.
-{ name, path, channel, isIso }:
+{ name, path, channel, isIso, extraLayersDir }:
 { lib, config, pkgs, ... }:
 
 let
@@ -8,8 +8,19 @@ let
   layerPath = layerName: let
     filePath = ./layers + "/${layerName}.nix";
     dirPath = ./layers + "/${layerName}";
+    extraDirFilePath = extraLayersDir + "/${layerName}.nix";
+    extraDirDirPath = extraLayersDir + "/${layerName}";
   in
-    if builtins.pathExists filePath then filePath else dirPath;
+  if builtins.pathExists filePath
+    then filePath
+    else if builtins.pathExists dirPath
+      then dirPath
+      else if builtins.pathExists extraDirFilePath
+        then extraDirFilePath
+        else if builtins.pathExists extraDirDirPath
+          then extraDirDirPath
+          else builtins.throw "Cannot find layer `${layerName}`";
+
   layerImports = map layerPath dotfilesConfig.layers;
 in
 ({

machine-manager.nix

 # entry point for machine configurations:
 # (import <repo-path> { machinesDir=./machines }).<netname>.configurations.<hostname>
 
-{ machinesDir }:
+{ machinesDir, extraLayersDir }:
 
 with builtins;
 let
@@ -33,7 +33,7 @@ let
   withMachines = lambda: listToAttrs (map (m: {name = m; value = lambda { name = m; path = (machinesDir + "/${m}"); }; }) machineNames);
   mkMachineConfig = { name, path, isIso ? false }: (
     import ./configuration.nix {
-      inherit name path isIso;
+      inherit name path isIso extraLayersDir;
       channel = machineChannels.${name};
     }
   );
@@ -82,4 +82,4 @@ in
   nixosIsoDerivations = withMachines mkNixosIsoDerivation;
   machineTemplates = withMachines ({name, path}: import (path + /template.nix));
   channels = machineChannels;
-}
\ No newline at end of file
+}