From dbb4012fdc7f91bdabb75ffd64160b2cbf934d0a Mon Sep 17 00:00:00 2001
From: Peter Simons <simons@cryp.to>
Date: Sun, 11 Jan 2015 11:37:49 +0100
Subject: [PATCH] haskell-generic-builder: add a helpful message that explains
 why it makes no sense to build an 'env' attribute

---
 pkgs/development/haskell-modules/generic-builder.nix | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/pkgs/development/haskell-modules/generic-builder.nix b/pkgs/development/haskell-modules/generic-builder.nix
index 96aa02155eb..22f82b9d0fc 100644
--- a/pkgs/development/haskell-modules/generic-builder.nix
+++ b/pkgs/development/haskell-modules/generic-builder.nix
@@ -215,6 +215,12 @@ stdenv.mkDerivation ({
       name = "interactive-${optionalString hasActiveLibrary "haskell-"}${pname}-${version}-environment";
       nativeBuildInputs = [ (ghc.withPackages (p: haskellBuildInputs)) systemBuildInputs ];
       shellHook = "eval $(grep export $(type -p ghc))";
+      buildCommand = ''
+        echo >&2 ""
+        echo >&2 "*** Haskell 'env' attributes are intended for interactive nix-shell sessions, not for building! ***"
+        echo >&2 ""
+        exit 1
+      '';
     };
 
   };