From f473b21c9fbb6b9af0400442448e44514d44a452 Mon Sep 17 00:00:00 2001
From: Daiderd Jordan <daiderd@gmail.com>
Date: Sun, 26 Aug 2018 14:09:01 +0200
Subject: [PATCH] environment: add darwinConfig option to set darwin-config in
 NIX_PATH

This simplifies using a non default configuration.nix without requiring
a symlink or redefining NIX_PATH.

The nix.nixPath option only defines a default which means defining a value
will drop all of the defaults. This is because correct merge behaviour
isn't very clear for named entries.
---
 modules/environment/default.nix | 13 +++++++++++++
 modules/nix/default.nix         |  2 +-
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/modules/environment/default.nix b/modules/environment/default.nix
index 3ab07564..6d77cd63 100644
--- a/modules/environment/default.nix
+++ b/modules/environment/default.nix
@@ -63,6 +63,19 @@ in {
       description = "List of directories to be symlinked in <filename>/run/current-system/sw</filename>.";
     };
 
+    environment.darwinConfig = mkOption {
+      type = types.either types.path types.str;
+      default = "$HOME/.nixpkgs/darwin-configuration.nix";
+      description = ''
+        The path of the darwin configuration.nix used to configure the system,
+        this updates the default darwin-config entry in NIX_PATH. Since this
+        changes an environment variable it will only apply to new shells.
+
+        NOTE: Changing this requires running <command>darwin-rebuild switch -I darwin-config=/path/to/configuration.nix</command>
+        the first time to make darwin-rebuild aware of the custom location.
+      '';
+    };
+
     environment.loginShell = mkOption {
       type = types.str;
       default = "$SHELL";
diff --git a/modules/nix/default.nix b/modules/nix/default.nix
index 082649dd..79ae41ab 100644
--- a/modules/nix/default.nix
+++ b/modules/nix/default.nix
@@ -314,7 +314,7 @@ in
       type = types.listOf types.str;
       default =
         [ # Include default path <darwin-config>.
-          "darwin-config=$HOME/.nixpkgs/darwin-configuration.nix"
+          "darwin-config=${config.environment.darwinConfig}"
           "/nix/var/nix/profiles/per-user/root/channels"
           "$HOME/.nix-defexpr/channels"
         ];