anchor.diff:    '';
   
     buildInputs = [
  -    ruby rubyLibs.bundler libiconv libxslt libxml2 pkgconfig libffi
  +    ruby rubyLibs.bundler 
  +  ] ++ (if (libiconvOrNull != null) then [libiconv] else []) ++ [
  +    libxslt libxml2 pkgconfig libffi
       imagemagickBig postgresql
     ];
   
  
positive.code: { stdenv, fetchurl, ruby, rubyLibs, libiconv, libxslt, libxml2, pkgconfig, libffi, imagemagickBig, postgresql }:
  
  let
    gemspec = map (gem: fetchurl { url=gem.url; sha256=gem.hash; }) (import ./Gemfile.nix);
  
negative.code: 
      bundle config build.nokogiri \
        --use-system-libraries \
        --with-iconv-dir=${libiconvOrLibc} \
        --with-xslt-dir=${libxslt} \
        --with-xml2-dir=${libxml2} \
        --with-pkg-config \
  