rails--rails/railties/lib/rails_generator/lookup.rb

require File.dirname(__FILE__) + '/spec'

class Object
  class << self
    # Lookup missing generators using const_missing.  This allows any
    # generator to reference another without having to know its location:
    # RubyGems, ~/.rails/generators, and RAILS_ROOT/script/generators all
    # cooperate to get the job done.  The greatest use of const_missing
    # autoloading is to easily subclass existing generators.  Example:
    #   class HorsebackGenerator < PostbackGenerator
    # We don't know whether the postback generator is built in, installed
    # as a gem, or in the user's home directory, and we shouldn't have to.
    unless respond_to?(:pre_generator_const_missing)
      alias_method :pre_generator_const_missing, :const_missing

      def const_missing(class_id)
        if md = /(.+)Generator$/.match(class_id.to_s)
          name = md.captures.first.demodulize.underscore
          Rails::Generator::Base.lookup(name).klass
        else
          pre_generator_const_missing(class_id)
        end
      end
    end
  end
end

# User home directory lookup adapted from RubyGems.
def Dir.user_home
  if ENV['HOME']
    ENV['HOME']
  elsif ENV['USERPROFILE']
    ENV['USERPROFILE']
  elsif ENV['HOMEDRIVE'] and ENV['HOMEPATH']
    "#{ENV['HOMEDRIVE']}:#{ENV['HOMEPATH']}"
  else
    File.expand_path '~'
  end
end


module Rails
  module Generator

    # Generator lookup is managed by a list of sources which return specs
    # describing where to find and how to create generators.  This module
    # provides class methods for manipulating the source list and looking up
    # generator specs, and an #instance wrapper for quickly instantiating
    # generators by name.
    #
    # A spec is not a generator:  it's a description of where to find
    # the generator and how to create it.  A source is anything that
    # yields generators from #each.  PathSource and GemSource are provided.
    module Lookup
      def self.append_features(base)
        super
        base.extend(ClassMethods)
        base.use_component_sources!
      end

      # Convenience method to instantiate another generator.
      def instance(generator_name, args, runtime_options = {})
        self.class.instance(generator_name, args, runtime_options)
      end

      module ClassMethods
        # The list of sources where we look, in order, for generators.
        def sources
          read_inheritable_attribute(:sources) or use_component_sources!
        end

        # Add a source to the end of the list.
        def append_sources(*args)
          sources.concat(args.flatten)
          invalidate_cache!
        end

        # Add a source to the beginning of the list.
        def prepend_sources(*args)
          write_inheritable_array(:sources, args.flatten + sources)
          invalidate_cache!
        end

        # Reset the source list.
        def reset_sources
          write_inheritable_attribute(:sources, [])
          invalidate_cache!
        end

        # Use application generators (app, ?).
        def use_application_sources!
          reset_sources
          sources << PathSource.new(:builtin, "#{File.dirname(__FILE__)}/generators/applications")
        end

        # Use component generators (model, controller, etc).
        # 1.  Rails application.  If RAILS_ROOT is defined we know we're
        #     generating in the context of a Rails application, so search
        #     RAILS_ROOT/script/generators.
        # 2.  User home directory.  Search ~/.rails/generators.
        # 3.  RubyGems.  Search for gems named *_generator.
        # 4.  Builtins.  Model, controller, mailer, scaffold.
        def use_component_sources!
          reset_sources
          sources << PathSource.new(:app, "#{Object.const_get(:RAILS_ROOT)}/script/generators") if Object.const_defined?(:RAILS_ROOT)
          sources << PathSource.new(:user, "#{Dir.user_home}/.rails/generators")
          sources << GemSource.new if Object.const_defined?(:Gem)
          sources << PathSource.new(:builtin, "#{File.dirname(__FILE__)}/generators/components")
        end

        # Lookup knows how to find generators' Specs from a list of Sources.
        # Searches the sources, in order, for the first matching name.
        def lookup(generator_name)
          @found ||= {}
          generator_name = generator_name.to_s.downcase
          @found[generator_name] ||= cache.find { |spec|
            spec.name == generator_name
          } or raise GeneratorError, "Couldn't find '#{generator_name}' generator"
        end

        # Convenience method to lookup and instantiate a generator.
        def instance(generator_name, args = [], runtime_options = {})
          lookup(generator_name).klass.new(args, full_options(runtime_options))
        end

        private
          # Lookup and cache every generator from the source list.
          def cache
            @cache ||= sources.inject([]) { |cache, source| cache + source.map }
          end

          # Clear the cache whenever the source list changes.
          def invalidate_cache!
            @cache = nil
          end
      end
    end

    # Sources enumerate (yield from #each) generator specs which describe
    # where to find and how to create generators.  Enumerable is mixed in so,
    # for example, source.collect will retrieve every generator.
    # Sources may be assigned a label to distinguish them.
    class Source
      include Enumerable

      attr_reader :label
      def initialize(label)
        @label = label
      end

      # The each method must be implemented in subclasses.
      # The base implementation raises an error.
      def each
        raise NotImplementedError
      end

      # Return a convenient sorted list of all generator names.
      def names
        map { |spec| spec.name }.sort
      end
    end


    # PathSource looks for generators in a filesystem directory.
    class PathSource < Source
      attr_reader :path

      def initialize(label, path)
        super label
        @path = path
      end

      # Yield each eligible subdirectory.
      def each
        Dir["#{path}/[a-z]*"].each do |dir|
          if File.directory?(dir)
            yield Spec.new(File.basename(dir), dir, label)
          end
        end
      end
    end


    # GemSource hits the mines to quarry for generators.  The latest versions
    # of gems named *_generator are selected.
    class GemSource < Source
      def initialize
        super :RubyGems
      end

      # Yield latest versions of generator gems.
      def each
        Gem::cache.search(/_generator$/).inject({}) { |latest, gem|
          hem = latest[gem.name]
          latest[gem.name] = gem if hem.nil? or gem.version > hem.version
          latest
        }.values.each { |gem|
          yield Spec.new(gem.name.sub(/_generator$/, ''), gem.full_gem_path, label)
        }
      end
    end

  end
end