Trouble with gem installations - ruby

Question

I am in a coding bootcamp and I have encountered an error in which I am having a hard time fixing. I currently in an exercise where I am learning how to create dynamic routes. Every time I run my server I am getting errors when I go to my routes and it states that:
Could not find nokogiri-1.8.2 in any of the sources
Run `bundle install` to install missing gems.
I tried to bundle install after adding nokogiri to my gemfile but all I get is this error below. I need some help cause I don't know what is going on and I am a total noob in regards to this stuff.
Ignoring unf_ext-0.0.7.5 because its extensions are not built. Try: gem pristine unf_ext --version 0.0.7.5
Ignoring websocket-driver-0.7.0 because its extensions are not built. Try: gem pristine websocket-driver --version 0.7.0
Fetching gem metadata from http://rubygems.org/........
Using rake 12.3.0
Using concurrent-ruby 1.0.5
Using i18n 0.9.5
Using minitest 5.11.3
Using thread_safe 0.3.6
Using tzinfo 1.2.5
Using activesupport 5.1.5
Using activemodel 5.1.5
Using arel 8.0.0
Using activerecord 5.1.5
Using public_suffix 3.0.2
Using addressable 2.5.2
Using bundler 1.16.6
Using mini_mime 1.0.0
Using mini_portile2 2.3.0
Fetching nokogiri 1.8.2
Installing nokogiri 1.8.2 with native extensions
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.
current directory:
/Users/kenkuts/.rvm/gems/ruby-2.5.0/gems/nokogiri-1.8.2/ext/nokogiri
/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/bin/ruby -r
./siteconf20181215-54662-1izm05e.rb extconf.rb --use-system-libraries
Ignoring unf_ext-0.0.7.5 because its extensions are not built. Try: gem pristine
unf_ext --version 0.0.7.5
Ignoring websocket-driver-0.7.0 because its extensions are not built. Try: gem
pristine websocket-driver --version 0.7.0
checking if the C compiler accepts ... *** 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/2.3/usr/bin/$(RUBY_BASE_NAME)
--help
--clean
/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/mkmf.rb:456:in
`try_do': The compiler failed to generate an executable file. (RuntimeError)
You have to install development tools first.
from
/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/mkmf.rb:571:in
`block in try_compile'
from
/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/mkmf.rb:522:in
`with_werror'
from
/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/mkmf.rb:571:in
`try_compile'
from extconf.rb:138:in `nokogiri_try_compile'
from extconf.rb:162:in `block in add_cflags'
from
/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/mkmf.rb:629:in
`with_cflags'
from extconf.rb:161:in `add_cflags'
from extconf.rb:410:in `<main>'
To see why this extension failed to compile, please check the mkmf.log which can
be found here:
/Users/kenkuts/.rvm/gems/ruby-2.5.0/extensions/universal-darwin-18/2.3.0/nokogiri-1.8.2/mkmf.log
extconf failed, exit code 1
Gem files will remain installed in
/Users/kenkuts/.rvm/gems/ruby-2.5.0/gems/nokogiri-1.8.2 for inspection.
Results logged to
/Users/kenkuts/.rvm/gems/ruby-2.5.0/extensions/universal-darwin-18/2.3.0/nokogiri-1.8.2/gem_make.out
An error occurred while installing nokogiri (1.8.2), and Bundler cannot
continue.
Make sure that `gem install nokogiri -v '1.8.2' --source 'http://rubygems.org/'`
succeeds before bundling.
In Gemfile:
capybara was resolved to 2.18.0, which depends on
xpath was resolved to 3.0.0, which depends on
nokogiri

Answer 1

You may need to download Xcode from the App Store, and run the commands
xcode-select --install
sudo xcodebuild -license`
The nokogiri install instructions mention this:
https://www.nokogiri.org/tutorials/installing_nokogiri.html#install_with_included_libraries__recommended_

Answer 2

This isn't an "answer" as much as a set of (hopefully) helpful things too long for a comment.
Sandbox your gems
I always run bundler in the following way now, so that one project's dependencies have no impact on the gems I use system wide or on other projects:
bundle install --binstubs --path=vendor.noindex
That will put all executables in PROJECT_DIR/bin and all gems in PROJECT_DIR/vendor.noindex. The "noindex" bit stops Spotlight from indexing the gems. To run rspec would now be:
bin/rspec
To start from a clean slate I run:
rm -rf .bundle bin Gemfile.lock vendor.noindex
Note: Always be careful using an rm -rf!!!!
Installing and finding dependencies
The last time I installed Nokogiri using the gem install command it looked like this:
gem install nokogiri -- \
--use-system-libraries \
--with-xml2-include=/opt/pkg/include/libxml2 \
--with-xml2-lib=/opt/pkg/lib \
--with-xslt-include=/opt/pkg/include/libxslt \
--with-xslt-lib=/opt/pkg/lib
As other commenters have noticed, this shows that you need XCode installed (always worth checking for updates) and that I've used libraries installed by another package manager (I've used pkgrsc above though you could use Macports or Homebrew and maybe some others).
To find the libs you need to link to try running:
find `/usr` -name libxml2 -type d 2> >(grep -v 'Permission denied' >&2)
Or change the /usr to /opt if you're installing there via pkgsrc/Macports/Fink etc. You may need to put a sudo in front depending on the permissions.
There's also the locate command, e.g.
locate libxml2
Which will bring up lots of stuff.