From 9db6a84f0bcce1602f17eca3fa17f5a016a93aac Mon Sep 17 00:00:00 2001
From: "Nicolas B. Pierron" <nicolas.b.pierron@gmail.com>
Date: Fri, 19 Dec 2014 22:33:24 +0100
Subject: [PATCH] nixos-option: Print the outPath of derivation for option
 values.

---
 nixos/modules/installer/tools/nixos-option.sh | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/nixos/modules/installer/tools/nixos-option.sh b/nixos/modules/installer/tools/nixos-option.sh
index 96d09c3a605..a2b963d7661 100644
--- a/nixos/modules/installer/tools/nixos-option.sh
+++ b/nixos/modules/installer/tools/nixos-option.sh
@@ -76,7 +76,18 @@ evalAttr(){
   local prefix="$1"
   local strict="$2"
   local suffix="$3"
-  echo "(import <nixos> {}).$prefix${option:+.$option}${suffix:+.$suffix}" | evalNix ${strict:+--strict}
+  evalNix ${strict:+--strict} <<EOF
+let
+  reach = attrs: attrs${option:+.$option}${suffix:+.$suffix};
+  nixos = import <nixos> {};
+  nixpkgs = import <nixpkgs> {};
+  cleanOutput = x: with nixpkgs.lib;
+    if isDerivation x then x.outPath
+    else if isFunction x then "<CODE>"
+    else x;
+in
+  cleanOutput (reach nixos.$prefix)
+EOF
 }
 
 evalOpt(){