Check if your environment can use the latest libv8 without compiling it

libv8_check.rb

require 'rubygems'
require 'rubygems/dependency_installer'

require 'json'
require 'open-uri'

class GemVersions
  def initialize(gem)
    @gem = gem
    @versions = JSON.parse(
      open("http://rubygems.org/api/v1/versions/#{gem}.json").read
    )
  end

  def native(plat=Platform.new)
    @versions.select{|x|
      x["platform"] == plat.platform.to_s
    }.map{|x|
      x["number"]
    }.first
  end

  def latest
    @versions.first["number"]
  end
end

class Platform
  def initialize(platform=nil)
    @platform = platform ?
       Gem::Platform.new(platform) :
       Gem::Platform.new(RUBY_PLATFORM)
  end

  def platform=(platform)
    new_plat = Gem::Platform.new(platform)
    @platform = new_plat
    return platform
  rescue => e
    nil
  end

  def platform
    @platform.to_s
  end
end

if $0 == __FILE__
  gem = "libv8"
  version = GemVersions.new(gem)
  if version.native
    puts "gem '#{gem}', '#{version.native}'"
  else
    puts "gem '#{gem}', '~> #{version.latest}'"
  end
end