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 1/3] 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(){

From b2abfe54b3da8eddda3135561c0c841c3023966d Mon Sep 17 00:00:00 2001
From: "Nicolas B. Pierron" <nicolas.b.pierron@gmail.com>
Date: Fri, 19 Dec 2014 23:00:00 +0100
Subject: [PATCH 2/3] nixos-option: Print derivation outPath within attribute
 sets and list, when the strict mode is used.

---
 nixos/modules/installer/tools/nixos-option.sh | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/nixos/modules/installer/tools/nixos-option.sh b/nixos/modules/installer/tools/nixos-option.sh
index a2b963d7661..b5f69f07826 100644
--- a/nixos/modules/installer/tools/nixos-option.sh
+++ b/nixos/modules/installer/tools/nixos-option.sh
@@ -76,14 +76,23 @@ evalAttr(){
   local prefix="$1"
   local strict="$2"
   local suffix="$3"
+
+  # If strict is set, then set it to "true".
+  test -n "$strict" && strict=true
+
   evalNix ${strict:+--strict} <<EOF
 let
   reach = attrs: attrs${option:+.$option}${suffix:+.$suffix};
   nixos = import <nixos> {};
   nixpkgs = import <nixpkgs> {};
+  strict = ${strict:-false};
   cleanOutput = x: with nixpkgs.lib;
     if isDerivation x then x.outPath
     else if isFunction x then "<CODE>"
+    else if strict then
+      if isAttrs x then mapAttrs (n: cleanOutput) x
+      else if isList x then map cleanOutput x
+      else x
     else x;
 in
   cleanOutput (reach nixos.$prefix)

From cd2f7ce9f9f10894c6d2a5995f06fb9d2a7f6795 Mon Sep 17 00:00:00 2001
From: "Nicolas B. Pierron" <nicolas.b.pierron@gmail.com>
Date: Fri, 19 Dec 2014 23:00:52 +0100
Subject: [PATCH 3/3] nixos-option: Improve error messages to avoid reporting
 internal location and traces.

---
 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 b5f69f07826..4478059813d 100644
--- a/nixos/modules/installer/tools/nixos-option.sh
+++ b/nixos/modules/installer/tools/nixos-option.sh
@@ -69,7 +69,18 @@ fi
 #############################
 
 evalNix(){
-  nix-instantiate - --eval-only "$@"
+  result=$(nix-instantiate - --eval-only "$@" 2>&1)
+  if test $? -eq 0; then
+      cat <<EOF
+$result
+EOF
+      return 0;
+  else
+      sed -n '/error/ { s/, at (string):[0-9]*:[0-9]*//; p; }' <<EOF
+$result
+EOF
+      return 1;
+  fi
 }
 
 evalAttr(){