Error FOR gem install nokogiri AND bundle install FOR Middleman app - ruby-on-rails

Question

I’m starting a Middleman app from scratch. Whenever I attempt to run the server, i.e. middleman server I get an error (below) that tells me “error occurred while installing nokogiri (1.6.6.2), and Bundler cannot continue.”
However, when I attempt to install nokogiri (1.6.6.2), I get another error (below) that says me “ERROR: Error installing nokogiri: ERROR: Failed to build gem native extension.”
I then attempt to bundle install my gemfile but receive another error. Can anyone tell me what I might be overlooking?
Whenever I attempt to run my middleman server command, I get this:
/Library/Ruby/Site/2.0.0/rubygems/dependency.rb:315:in `to_specs': Could not find 'nokogiri' (>= 1.3.3) among 67 total gem(s) (Gem::LoadError)
Checked in 'GEM_PATH=/Users/Wilhelm/.gem/ruby/2.0.0:/Library/Ruby/Gems/2.0.0:/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/gems/2.0.0', execute `gem env` for more information
from /Library/Ruby/Site/2.0.0/rubygems/specification.rb:1311:in `block in activate_dependencies'
from /Library/Ruby/Site/2.0.0/rubygems/specification.rb:1300:in `each'
from /Library/Ruby/Site/2.0.0/rubygems/specification.rb:1300:in `activate_dependencies'
from /Library/Ruby/Site/2.0.0/rubygems/specification.rb:1282:in `activate'
from /Library/Ruby/Site/2.0.0/rubygems/specification.rb:1314:in `block in activate_dependencies'
from /Library/Ruby/Site/2.0.0/rubygems/specification.rb:1300:in `each'
from /Library/Ruby/Site/2.0.0/rubygems/specification.rb:1300:in `activate_dependencies'
from /Library/Ruby/Site/2.0.0/rubygems/specification.rb:1282:in `activate'
from /Library/Ruby/Site/2.0.0/rubygems/core_ext/kernel_gem.rb:67:in `block in gem'
from /Library/Ruby/Site/2.0.0/rubygems/core_ext/kernel_gem.rb:66:in `synchronize'
from /Library/Ruby/Site/2.0.0/rubygems/core_ext/kernel_gem.rb:66:in `gem'
from /usr/bin/middleman:22:in `<main>'
Here are the contents of my Gemfile:
# If you do not have OpenSSL installed, update
# the following line to use "http://" instead
source 'https://rubygems.org'
gem "middleman", "~>3.4.0"
# Live-reloading plugin
gem "middleman-livereload", "~> 3.1.0"
# For faster file watcher updates on Windows:
gem "wdm", "~> 0.1.0", :platforms => [:mswin, :mingw]
# Windows does not come with time zone data
gem "tzinfo-data", platforms: [:mswin, :mingw, :jruby]
and here are the results from my bundle install:
Fetching gem metadata from https://rubygems.org/.............
Fetching version metadata from https://rubygems.org/...
Fetching dependency metadata from https://rubygems.org/..
Resolving dependencies...
Using i18n 0.7.0
Using json 1.8.3
Using minitest 5.8.0
Using thread_safe 0.3.5
Using tzinfo 1.2.2
Using activesupport 4.2.4
Using bundler 1.8.2
Using mime-types 2.6.1
Using mini_portile 0.6.2
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.
/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby -r ./siteconf20150828-20513-wkpoce.rb extconf.rb --use-system-libraries
checking if the C compiler accepts ... yes
checking if the C compiler accepts -Wno-error=unused-command-line-argument-hard-error-in-future... no
Building nokogiri using system libraries.
libxml2 version 2.6.21 or later is required!
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers. Check the mkmf.log file for more details. You may
need configuration options.
Provided configuration options:
--with-opt-dir
--without-opt-dir
--with-opt-include
--without-opt-include=${opt-dir}/include
--with-opt-lib
--without-opt-lib=${opt-dir}/lib
--with-make-prog
--without-make-prog
--srcdir=.
--curdir
--ruby=/System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby
--help
--clean
--use-system-libraries
--with-zlib-dir
--without-zlib-dir
--with-zlib-include
--without-zlib-include=${zlib-dir}/include
--with-zlib-lib
--without-zlib-lib=${zlib-dir}/lib
--with-xml2-dir
--without-xml2-dir
--with-xml2-include
--without-xml2-include=${xml2-dir}/include
--with-xml2-lib
--without-xml2-lib=${xml2-dir}/lib
--with-libxml-2.0-config
--without-libxml-2.0-config
--with-pkg-config
--without-pkg-config
--with-xslt-dir
--without-xslt-dir
--with-xslt-include
--without-xslt-include=${xslt-dir}/include
--with-xslt-lib
--without-xslt-lib=${xslt-dir}/lib
--with-libxslt-config
--without-libxslt-config
--with-exslt-dir
--without-exslt-dir
--with-exslt-include
--without-exslt-include=${exslt-dir}/include
--with-exslt-lib
--without-exslt-lib=${exslt-dir}/lib
--with-libexslt-config
--without-libexslt-config
extconf failed, exit code 1
Gem files will remain installed in /var/folders/zn/zh_8qnr573x4wgbjz6gqz72w0000gn/T/bundler20150828-20513-11hlulx/nokogiri-1.6.6.2/gems/nokogiri-1.6.6.2 for inspection.
Results logged to /var/folders/zn/zh_8qnr573x4wgbjz6gqz72w0000gn/T/bundler20150828-20513-11hlulx/nokogiri-1.6.6.2/extensions/universal-darwin-14/2.0.0/nokogiri-1.6.6.2/gem_make.out
An error occurred while installing nokogiri (1.6.6.2), and Bundler cannot
continue.
Make sure that `gem install nokogiri -v '1.6.6.2'` succeeds before bundling.
and here are the results from my sudo gem install nokogiri -v '1.6.6.2':
Building native extensions. This could take a while...
ERROR: Error installing nokogiri:
ERROR: Failed to build gem native extension.
/Users/Wilhelm/.rbenv/versions/1.9.3-dev/bin/ruby extconf.rb
checking if the C compiler accepts ... yes
checking if the C compiler accepts -Wno-error=unused-command-line-argument-hard-error-in-future... no
Building nokogiri using packaged libraries.
-----
The file "/usr/include/iconv.h" is missing in your build environment,
which means you haven't installed Xcode Command Line Tools properly.
To install Command Line Tools, try running `xcode-select --install` on
terminal and follow the instructions. If it fails, open Xcode.app,
select from the menu "Xcode" - "Open Developer Tool" - "More Developer
Tools" to open the developer site, download the installer for your OS
version and run it.
-----
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers. Check the mkmf.log file for more
details. You may need configuration options.
Provided configuration options:
--with-opt-dir
--without-opt-dir
--with-opt-include
--without-opt-include=${opt-dir}/include
--with-opt-lib
--without-opt-lib=${opt-dir}/lib
--with-make-prog
--without-make-prog
--srcdir=.
--curdir
--ruby=/Users/Wilhelm/.rbenv/versions/1.9.3-dev/bin/ruby
--help
--clean
--use-system-libraries
--enable-static
--disable-static
--with-zlib-dir
--without-zlib-dir
--with-zlib-include
--without-zlib-include=${zlib-dir}/include
--with-zlib-lib
--without-zlib-lib=${zlib-dir}/lib
--enable-cross-build
--disable-cross-build
Gem files will remain installed in /Users/Wilhelm/.rbenv/versions/1.9.3-dev/lib/ruby/gems/1.9.1/gems/nokogiri-1.6.6.2 for inspection.
Results logged to /Users/Wilhelm/.rbenv/versions/1.9.3-dev/lib/ruby/gems/1.9.1/gems/nokogiri-1.6.6.2/ext/nokogiri/gem_make.out

Answer 1

I have encountered this on a couple of system configs. It always ends up being a dev library dependency. If it were me, one at a time, I'd install these and try to bundle install:
libxslt-dev
libxml2-dev
ruby-dev
Depending on your system (I think on centos they are -devel not -dev).

Answer 2

This command:
sudo gem install nokogiri -- --with-xml2-include=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.10.sdk/usr/include/libxml2 --use-system-libraries
found in this github issue, solved my problem. Honestly, I'm not entirely sure why so if anyone could append a comment, elucidating what exactly is going on it would be much appreciated.