home: zsh: don't hard-code '$XDG_CONFIG_HOME'

home/zsh/default.nix

@@ -1,6 +1,14 @@
 { config, pkgs, lib, ... }:
 let
   cfg = config.my.home.zsh;
+
+  # Have a nice relative path for XDG_CONFIG_HOME, without leading `/`
+  relativeXdgConfig =
+    let
+      noHome = lib.removePrefix config.home.homeDirectory;
+      noSlash = lib.removePrefix "/";
+    in
+    noSlash (noHome config.xdg.configHome);
 in
 {
   options.my.home.zsh = with lib; {
@@ -16,7 +24,7 @@ in
 
     programs.zsh = {
       enable = true;
-      dotDir = ".config/zsh"; # Don't clutter $HOME
+      dotDir = "${relativeXdgConfig}/zsh"; # Don't clutter $HOME
       enableCompletion = true;
 
       history = {