bundle_install_fast.rb

require 'bundler'

# First attempt a bundle install without remote resolution.  In the
# happy case, all gems are already installed, and checking this is
# quick.  If it fails, attempt a remote resolution.  This is slow
# (probably largely because of how many dang gem versions we have in
# our local gem server), but it will install anything that is missing.
#
# Bundler uses lots of class-level configuration, and thus isn't
# designed to be called repeatedly with different options, but we're
# giving it a shot.
#
# Developed against bundler 1.2.3.  There's no guarantee this will
# continue to work with future versions.
def bundle_install_fast(gemfile = 'Gemfile', lockfile = nil)
  # lets pretend ENV['GEM_HOME'] etc. have already been configured

  # bundle exec restricts this to what's in the current Gemfile; we
  # need to open it up to other Gemfiles
  gem_spec_all = Gem::Specification.all
  Gem::Specification.all = nil
  default_gemfile = ENV['BUNDLE_GEMFILE']
  ENV['BUNDLE_GEMFILE'] = gemfile
  begin
    lockfile ||= gemfile + '.lock'
    Bundler.settings[:frozen] = true
    unlock = false

    make_definition = proc {
      definition = Bundler::Definition.build(gemfile, lockfile, unlock)
      definition.ensure_equivalent_gemfile_and_lockfile
      definition
    }

    specs = begin
              definition = make_definition.call
              definition.specs
            rescue Bundler::GemNotFound => e
              warn "some gems not already installed (#{e})"
              warn 'resolving remotely...'
              definition = make_definition.call
              definition.resolve_remotely!
              definition.specs
            end

    installer = Bundler::Installer.new(File.dirname(gemfile), definition)
    Bundler::Installer.post_install_messages = {}
    specs.each do |spec|
      installer.send(:install_gem_from_spec, spec)
    end
  ensure
    Gem::Specification.all = gem_spec_all
    ENV['BUNDLE_GEMFILE'] = default_gemfile
  end
end