From 1bffd83e1a9cdf3271c2b178daa611c6b9c22f58 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Vladim=C3=ADr=20=C4=8Cun=C3=A1t?= <vladimir.cunat@nic.cz>
Date: Thu, 11 Aug 2016 17:09:04 +0200
Subject: [PATCH] nix-build: extend the meaning of $IN_NIX_SHELL

An equivalent was originally filed against the perl version:
https://github.com/NixOS/nix/pull/933
---
 src/nix-build/nix-build.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/nix-build/nix-build.cc b/src/nix-build/nix-build.cc
index 4d80a0c53..ee6d2699a 100755
--- a/src/nix-build/nix-build.cc
+++ b/src/nix-build/nix-build.cc
@@ -332,7 +332,7 @@ int main(int argc, char ** argv)
         }
 
         if (runEnv)
-            setenv("IN_NIX_SHELL", "1", 1);
+            setenv("IN_NIX_SHELL", pure ? "pure" : "impure", 1);
 
         for (auto & expr : exprs) {
             // Instantiate.