From d05a3cd763cedce9690ec21b2180425e8d70dabf Mon Sep 17 00:00:00 2001
From: Tim Cuthbertson <tim@gfxmonk.net>
Date: Mon, 29 Feb 2016 22:10:26 +1100
Subject: [PATCH] stdenv: don't overwrite $NIX_ENFORCE_PURITY setting

Close #13583.
---
 pkgs/stdenv/darwin/default.nix | 2 +-
 pkgs/stdenv/linux/default.nix  | 2 +-
 pkgs/stdenv/nix/default.nix    | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/pkgs/stdenv/darwin/default.nix b/pkgs/stdenv/darwin/default.nix
index 0af7071e218..fa6bb55009d 100644
--- a/pkgs/stdenv/darwin/default.nix
+++ b/pkgs/stdenv/darwin/default.nix
@@ -25,7 +25,7 @@ in rec {
   allPackages = import ../../top-level/all-packages.nix;
 
   commonPreHook = ''
-    export NIX_ENFORCE_PURITY=1
+    export NIX_ENFORCE_PURITY="''${NIX_ENFORCE_PURITY-1}"
     export NIX_IGNORE_LD_THROUGH_GCC=1
     stripAllFlags=" " # the Darwin "strip" command doesn't know "-s"
     export MACOSX_DEPLOYMENT_TARGET=10.7
diff --git a/pkgs/stdenv/linux/default.nix b/pkgs/stdenv/linux/default.nix
index 3e94391c426..1841c3a0693 100644
--- a/pkgs/stdenv/linux/default.nix
+++ b/pkgs/stdenv/linux/default.nix
@@ -22,7 +22,7 @@ rec {
 
   commonPreHook =
     ''
-      export NIX_ENFORCE_PURITY=1
+      export NIX_ENFORCE_PURITY="''${NIX_ENFORCE_PURITY-1}"
       ${if system == "x86_64-linux" then "NIX_LIB64_IN_SELF_RPATH=1" else ""}
       ${if system == "mips64el-linux" then "NIX_LIB32_IN_SELF_RPATH=1" else ""}
     '';
diff --git a/pkgs/stdenv/nix/default.nix b/pkgs/stdenv/nix/default.nix
index 30ac92837cb..0e3434be017 100644
--- a/pkgs/stdenv/nix/default.nix
+++ b/pkgs/stdenv/nix/default.nix
@@ -5,7 +5,7 @@ import ../generic rec {
 
   preHook =
     ''
-      export NIX_ENFORCE_PURITY=1
+      export NIX_ENFORCE_PURITY="''${NIX_ENFORCE_PURITY-1}"
       export NIX_IGNORE_LD_THROUGH_GCC=1
     '';