gem_prelude.rb

# depends on: array.rb dir.rb env.rb file.rb hash.rb module.rb regexp.rb

# empty gem_prelude.rb
#
# p defined?(Gem)

if defined?(Gem) then

  module Kernel

    def gem(gem_name, *version_requirements)
      Gem.push_gem_version_on_load_path(gem_name, *version_requirements)
    end

  end

  module Gem

    ConfigMap = {
      :sitedir => RbConfig::CONFIG["sitedir"],
      :ruby_version => RbConfig::CONFIG["ruby_version"],
      :libdir => RbConfig::CONFIG["libdir"],
      :sitelibdir => RbConfig::CONFIG["sitelibdir"],
      :arch => RbConfig::CONFIG["arch"],
      :bindir => RbConfig::CONFIG["bindir"],
      :EXEEXT => RbConfig::CONFIG["EXEEXT"],
      :RUBY_SO_NAME => RbConfig::CONFIG["RUBY_SO_NAME"],
      :ruby_install_name => RbConfig::CONFIG["ruby_install_name"]
    }

    class << self

      def default_dir
        if defined? RUBY_FRAMEWORK_VERSION
          return File.join(File.dirname(ConfigMap[:sitedir]), "Gems")
        else
          File.join(ConfigMap[:libdir], 'ruby', 'gems', ConfigMap[:ruby_version])
        end
      end

      def dir
        @gem_home ||= nil
        set_home(ENV['GEM_HOME'] || default_dir) unless @gem_home
        @gem_home
      end

      def path
        @gem_path ||= nil
        unless @gem_path
          paths = [ENV['GEM_PATH']]
          paths << APPLE_GEM_HOME if defined? APPLE_GEM_HOME
          set_paths(paths.compact.join(File::PATH_SEPARATOR))
        end
        @gem_path
      end

      # Set the Gem home directory (as reported by +dir+).
      def set_home(home)
        @gem_home = home
        ensure_gem_subdirectories(@gem_home)
      end

      def set_paths(gpaths)
        if gpaths
          @gem_path = gpaths.split(File::PATH_SEPARATOR)
          @gem_path << Gem.dir
        else
          @gem_path = [Gem.dir]
        end
        @gem_path.uniq!
        @gem_path.each do |gp| ensure_gem_subdirectories(gp) end
      end

      def ensure_gem_subdirectories(path)
      end

    end

    module QuickLoader

      class << self
        def load_full_rubygems_library
          class << Gem
            Gem.methods(false).each do |method_name|
              undef_method method_name
            end
          end

          Kernel.module_eval do
            undef_method :gem if method_defined? :gem
          end

          $".delete File.join(Gem::ConfigMap[:libdir], 'ruby',
                              Gem::ConfigMap[:ruby_version], 'rubygems.rb')

          require 'rubygems'
        end
      end

      GemPaths = {}
      GemVersions = {}

      def push_gem_version_on_load_path(gem_name, *version_requirements)
        if version_requirements.empty?
          unless GemPaths.has_key?(gem_name)
            raise LoadError.new("Could not find RubyGem #{gem_name} (>= 0)\n") 
          end

          # highest version gems already active
          return false
        else
          if version_requirements.length > 1
            QuickLoader.load_full_rubygems_library
            return gem(gem_name, *version_requirements)
          end

          requirement, version = version_requirements[0].split
          requirement.strip!

          if requirement == ">" || requirement == ">="
            if (GemVersions[gem_name] <=> Gem.calculate_integers_for_gem_version(version)) >= 0
              return false 
            end
          elsif requirement == "~>"
            loaded_version = GemVersions[gem_name]
            required_version = Gem.calculate_integers_for_gem_version(version)
            if loaded_version && (loaded_version[0] == required_version[0])
              return false
            end
          end

          QuickLoader.load_full_rubygems_library
          gem(gem_name, *version_requirements)
        end
      end

      def calculate_integers_for_gem_version(gem_version)
        numbers = gem_version.split(".").collect {|n| n.to_i}
        numbers.pop while numbers.last == 0
        numbers << 0 if numbers.empty?
        numbers
      end

      def push_all_highest_version_gems_on_load_path
        Gem.path.each do |path|
          gems_directory = File.join(path, "gems")
          if File.exist?(gems_directory)
            Dir.entries(gems_directory).each do |gem_directory_name|
              next if gem_directory_name == "." || gem_directory_name == ".."
              dash = gem_directory_name.rindex("-")
              next if dash.nil?
              gem_name = gem_directory_name[0...dash]
              current_version = GemVersions[gem_name]
              new_version = calculate_integers_for_gem_version(gem_directory_name[dash+1..-1])
              if current_version
                if (current_version <=> new_version) == -1
                  GemVersions[gem_name] = new_version
                  GemPaths[gem_name] = File.join(gems_directory, gem_directory_name)
                end
              else
                GemVersions[gem_name] = new_version
                GemPaths[gem_name] = File.join(gems_directory, gem_directory_name)
              end
            end
          end
        end

        require_paths = []

        GemPaths.values.each do |path|
          if File.exist?(File.join(path, ".require_paths"))
            require_paths.concat(File.read(File.join(path, ".require_paths")).split.map {|require_path| File.join(path, require_path)})
          else
            require_paths << File.join(path, "bin") if File.exist?(File.join(path, "bin"))
            require_paths << File.join(path, "lib") if File.exist?(File.join(path, "lib"))
          end
        end

        # "tag" the first require_path inserted into the $LOAD_PATH to enable
        # indexing correctly with rubygems proper when it inserts an explicitly
        # gem version
        unless require_paths.empty?
          require_paths.first.instance_variable_set(:@gem_prelude_index, true)
        end
        # gem directories must come after -I and ENV['RUBYLIB']
        $:[$:.index(ConfigMap[:sitelibdir]),0] = require_paths
      end

      def const_missing(constant)
        QuickLoader.load_full_rubygems_library
        if Gem.const_defined?(constant)
          Gem.const_get(constant)
        else
          super
        end
      end

      def method_missing(method, *args, &block)
        QuickLoader.load_full_rubygems_library
        super unless Gem.respond_to?(method)
        Gem.send(method, *args, &block)
      end
    end

    extend QuickLoader

  end

  begin
    Gem.push_all_highest_version_gems_on_load_path
    $" << File.join(Gem::ConfigMap[:libdir], "ruby",
                    Gem::ConfigMap[:ruby_version], "rubygems.rb")
  rescue Exception => e
    puts "Error loading gem paths on load path in gem_prelude"
    puts e
    puts e.backtrace.join("\n")
  end

end