build_extensions

# File lib/rubygems/specification.rb, line 1636
  def build_extensions # :nodoc:
    return if default_gem?
    return if extensions.empty?
    return if installed_by_version < Gem::Version.new('2.2.0.preview.2')
    return if File.exist? gem_build_complete_path
    return if !File.writable?(base_dir)
    return if !File.exist?(File.join(base_dir, 'extensions'))

    begin
      # We need to require things in $LOAD_PATH without looking for the
      # extension we are about to build.
      unresolved_deps = Gem::Specification.unresolved_deps.dup
      Gem::Specification.unresolved_deps.clear

      require 'rubygems/config_file'
      require 'rubygems/ext'
      require 'rubygems/user_interaction'

      ui = Gem::SilentUI.new
      Gem::DefaultUserInteraction.use_ui ui do
        builder = Gem::Ext::Builder.new self
        builder.build_extensions
      end
    ensure
      ui.close if ui
      Gem::Specification.unresolved_deps.replace unresolved_deps
    end
  end