microgems

link-gems

#!/usr/bin/env ruby

# Take a Gemfile.lock and a GEM_PATH.  Create a new GEM_HOME at
# the given path, with only the selected gems symlinked in.
# Ignores groups.

new_gem_home = ARGV.shift or
  raise "Specify the new GEM_HOME"

current_gem_path = ENV['GEM_PATH'].to_s.split(":").first
if current_gem_path.empty?
  # This probably isn't correct, but the methods on Gem don't give
  # much of a clue
  current_gem_path = Gem.default_dir
end

gems_to_link = parse_gemfile( STDIN )
make_gem_home( gems_to_link,
               current_gem_path,
               new_gem_home )


BEGIN {
  require 'fileutils'

  def parse_gemfile( io )
    io.read.scan(/^    (\w+) \((\S+?)\)/).map{|name,ver|
      {name:name,ver:ver}
    }
  end

  def make_gem_home( gems_to_link,
                     current_gem_path,
                     new_gem_home)
    full_current_path = File.expand_path current_gem_path
    FileUtils.mkdir_p new_gem_home + "/gems"
    gems_to_link.each do |hsh|
      link_basename = "#{hsh[:name]}"
      target_basename = "#{hsh[:name]}-#{hsh[:ver]}"

      link_path = File.join new_gem_home, "gems", link_basename
      target_path = File.join full_current_path, "gems", target_basename

      FileUtils.ln_sf target_path, link_path
    end
  end
}

microgems.rb

# encoding: utf-8

# Smallest possible gem loader that might ever work.  
# Assumes one version of each gem per $GEM_PATH, to go with link-gems.
# Assumes that the only code you want to require is in lib/.
# Only patches $LOAD_PATH, doesn't touch #require.

module Microgems
  def self.setup( gem_path, load_path )
    lib_glob = File.join( gem_path, "gems", "*", "lib" )
    Dir[lib_glob].each do |lib_path|
      load_path << lib_path
    end
  end
end

Microgems.setup( ENV.fetch('GEM_PATH',"").split(":").first,
                 $LOAD_PATH )