Add Gemfile entry when creating a plugin in application's directory

After vendor/plugins were removed from rails, the new method to create
plugins is to create gem plugins. Most of the time if you create a
new plugin in rails application's directory, you want to extract
something from that application and use it immediately, ie. add
such line to Gemfile:

  gem 'foo', :path => './vendor/foo'

This commit makes plugin new generator to add such line automatically.

railties/lib/rails/generators/rails/plugin_new/plugin_new_generator.rb

@@ -133,6 +133,16 @@ task :default => :test
       end
       chmod "script", 0755, :verbose => false
     end
+
+    def gemfile_entry
+      return unless inside_application?
+
+      gemfile_in_app_path = File.join(rails_app_path, "Gemfile")
+      if File.exist? gemfile_in_app_path
+        entry = "gem '#{name}', :path => '#{relative_path}'"
+        append_file gemfile_in_app_path, entry
+      end
+    end
   end
 
   module Generators
@@ -153,6 +163,10 @@ task :default => :test
       class_option :skip_gemspec, :type => :boolean, :default => false,
                                   :desc => "Skip gemspec file"
 
+      class_option :skip_gemfile_entry, :type => :boolean, :default => false,
+                                        :desc => "If creating plugin in application's directory " +
+                                                 "skip adding entry to Gemfile"
+
       def initialize(*args)
         raise Error, "Options should be given after the plugin name. For details run: rails plugin --help" if args[0].blank?
 
@@ -208,6 +222,10 @@ task :default => :test
         create_dummy_app
       end
 
+      def update_gemfile
+        build(:gemfile_entry) unless options[:skip_gemfile_entry]
+      end
+
       def finish_template
         build(:leftovers)
       end
@@ -313,6 +331,19 @@ end
       def mute(&block)
         shell.mute(&block)
       end
+
+      def rails_app_path
+        APP_PATH.sub("/config/application", "") if defined?(APP_PATH)
+      end
+
+      def inside_application?
+        rails_app_path && app_path =~ /^#{rails_app_path}/
+      end
+
+      def relative_path
+        return unless inside_application?
+        app_path.sub(/^#{rails_app_path}\//, '')
+      end
     end
   end
 end

railties/test/generators/plugin_new_generator_test.rb

@@ -241,7 +241,7 @@ class PluginNewGeneratorTest < Rails::Generators::TestCase
     assert_file "spec/dummy/config/application.rb"
     assert_no_file "test"
   end
-  
+
   def test_ensure_that_gitignore_can_be_generated_from_a_template_for_dummy_path
     FileUtils.cd(Rails.root)
     run_generator([destination_root, "--dummy_path", "spec/dummy" "--skip-test-unit"])
@@ -263,6 +263,37 @@ class PluginNewGeneratorTest < Rails::Generators::TestCase
     assert_no_file "bukkits.gemspec"
   end
 
+  def test_creating_plugin_in_app_directory_adds_gemfile_entry
+    # simulate application existance
+    gemfile_path = "#{Rails.root}/Gemfile"
+    Object.const_set('APP_PATH', Rails.root)
+    FileUtils.touch gemfile_path
+
+    run_generator [destination_root]
+
+    assert_file gemfile_path, /gem 'bukkits', :path => '.\/tmp\/bukkits'/
+  ensure
+    Object.send(:remove_const, 'APP_PATH')
+    FileUtils.rm gemfile_path
+  end
+
+  def test_skipping_gemfile_entry
+    # simulate application existance
+    gemfile_path = "#{Rails.root}/Gemfile"
+    Object.const_set('APP_PATH', Rails.root)
+    FileUtils.touch gemfile_path
+
+    run_generator [destination_root, "--skip-gemfile-entry"]
+
+    assert_file gemfile_path do |contents|
+      assert_no_match(/gem 'bukkits', :path => '.\/tmp\/bukkits'/, contents)
+    end
+  ensure
+    Object.send(:remove_const, 'APP_PATH')
+    FileUtils.rm gemfile_path
+  end
+
+
 protected
 
   def action(*args, &block)