buildRubyGem: fix missing libobjc in darwin

This was preventing any ruby gem with a c extension to build.

mkmf would fail with a misleading error:

    /nix/store/dmkcai8fnv21qxiasx628nim3mq4r4wg-ruby-2.2.3-p0/lib/ruby/2.2.0/mkmf.rb:456:in `try_do': The compiler failed to generate an executable file. (RuntimeError)
    You have to install development tools first.

2 files changed, 3 insertions, 6 deletions

diff --git a/pkgs/development/interpreters/ruby/build-ruby-gem/default.nix b/pkgs/development/interpreters/ruby/build-ruby-gem/default.nix
index d050faca245..c5b9fba37aa 100644
--- a/pkgs/development/interpreters/ruby/build-ruby-gem/default.nix
+++ b/pkgs/development/interpreters/ruby/build-ruby-gem/default.nix
@@ -18,7 +18,8 @@
 # Normal gem packages can be used outside of bundler; a binstub is created in
 # $out/bin.
 
-{ lib, ruby, rubygems, bundler, fetchurl, fetchgit, makeWrapper, git, buildRubyGem
+{ lib, ruby, rubygems, bundler, fetchurl, fetchgit, makeWrapper, git,
+  buildRubyGem, darwin
 } @ defs:
 
 lib.makeOverridable (
@@ -85,6 +86,7 @@ stdenv.mkDerivation (attrs // {
   buildInputs = [
     ruby rubygems makeWrapper
   ] ++ lib.optionals (type == "git") [ git bundler ]
+    ++ lib.optional stdenv.isDarwin darwin.libobjc
     ++ buildInputs;
 
   name = attrs.name or (namePrefix + gemName);
diff --git a/pkgs/development/interpreters/ruby/gemconfig/default.nix b/pkgs/development/interpreters/ruby/gemconfig/default.nix
index ae8c0ee6e6a..787c3be54e3 100644
--- a/pkgs/development/interpreters/ruby/gemconfig/default.nix
+++ b/pkgs/development/interpreters/ruby/gemconfig/default.nix
@@ -79,7 +79,6 @@ in
       "--with-exslt-lib=${libxslt}/lib"
       "--with-exslt-include=${libxslt}/include"
     ] ++ lib.optional stdenv.isDarwin "--with-iconv-dir=${libiconv}";
-    buildInputs = lib.optional stdenv.isDarwin darwin.libobjc;
   };
 
   patron = attrs: {
@@ -143,10 +142,6 @@ in
     '';
   };
 
-  unf_ext = attrs: {
-    buildInputs = lib.optional stdenv.isDarwin darwin.libobjc;
-  };
-
   xapian-ruby = attrs: {
     # use the system xapian
     dontBuild = false;