From cdaced58aec376965e3e5ee422e098df526e4726 Mon Sep 17 00:00:00 2001
From: aszlig <aszlig@redmoonstudios.org>
Date: Wed, 12 Mar 2014 06:34:42 +0100
Subject: [PATCH] libpng12/cross: Don't add zlib for Darwin builds.

Cross builds for Darwin already include the CoreFoundation and the
libraries from XCode, so zlib already exists on that platform.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>
---
 pkgs/development/libraries/libpng/12.nix | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/pkgs/development/libraries/libpng/12.nix b/pkgs/development/libraries/libpng/12.nix
index 031e2aa1a914..b7fad76acaa3 100644
--- a/pkgs/development/libraries/libpng/12.nix
+++ b/pkgs/development/libraries/libpng/12.nix
@@ -1,6 +1,6 @@
 { stdenv, fetchurl, zlib, xz }:
 
-assert zlib != null;
+assert !(stdenv ? cross) -> zlib != null;
 
 stdenv.mkDerivation rec {
   name = "libpng-1.2.50";
@@ -16,6 +16,11 @@ stdenv.mkDerivation rec {
 
   passthru = { inherit zlib; };
 
+  crossAttrs = stdenv.lib.optionalAttrs (stdenv.cross.libc == "libSystem") {
+    propagatedBuildInputs = [];
+    passthru = {};
+  };
+
   meta = {
     description = "The official reference implementation for the PNG file format";
     homepage = http://www.libpng.org/pub/png/libpng.html;