Я использую Windows и мойGemfile имеет эту строку:

gem 'rugged'

Когда я бегуbundle install это дает мне эту ошибку:

Installing rugged 0.21.0 with native extensions

Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

    C:/Ruby21/bin/ruby.exe extconf.rb --use-system-libraries
    checking for cmake... no 
    ERROR: CMake is required to build Rugged.

*** 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=C:/Ruby21/bin/ruby

extconf failed, exit code 1

Gem files will remain installed in
C:/Ruby21/lib/ruby/gems/2.1.0/gems/rugged-0.21.0 for inspection.
Results logged to C:/Ruby21/lib/ruby/gems/2.1.0/extensions/x86-mingw32/2.1.0/rugged-0.21.0/gem_make.out

An error occurred while installing rugged(0.21.0), and Bundler cannot continue.

Make sure that `gem install rugged -v '0.21.0'` succeeds before
bundling.

Я предполагаю, что это как-то связано сlibgit2 но я не уверен.