Prefer loading Rack and Bundler from RubyGems instead of 'vendor_ruby'

Closes GH-1478. Closes GH-1480.

CHANGELOG

@@ -5,6 +5,7 @@ Release 5.0.7
  * Request-specific environment variables are no longer cached. This fixes a number of issues, such as Shibboleth not working properly and conflicts between HTTPS and non-HTTPS virtual hosts. Closes GH-1472.
  * Re-introduced signal catchers during shutdown, to allow clean shutdown in Foreman. Closes GH-1454.
  * `passenger-status --show=xml` no longer outputs the non-XML header by default. This fixes a regression as reported in a comment in GH-1136.
+ * Passenger now prefers to load Rack and Bundler from RubyGems instead of from `vendor_ruby`. This solves some issues with Rack and Bundler on Debian systems. Closes GH-1480 and GH-1478.
  * [Standalone] It is now possible to configure the Ruby, Node.js and Python executable to use in Passenger Standalone through the command line options --ruby, --nodejs and --python. Closes GH-1442.
  * [Nginx] Introduces the `passenger_read_timeout` option for rare cases when server needs more than the default 10 minute timeout. Contributed by pkmiec. Closes [GH-PR-34](https://github.com/phusion/passenger/pull/34).
  * [Nginx] The Nginx module now looks for index.html if the path ends in / so that it works intuitively, without needing to use try_files.

helper-scripts/rack-loader.rb

@@ -1,7 +1,7 @@
 #!/usr/bin/env ruby
 # encoding: binary
 #  Phusion Passenger - https://www.phusionpassenger.com/
-#  Copyright (c) 2013-2014 Phusion
+#  Copyright (c) 2013-2015 Phusion
 #
 #  "Phusion Passenger" is a trademark of Hongli Lai & Ninh Bui.
 #
@@ -94,12 +94,8 @@ def self.load_app
       LoaderSharedHelpers.before_loading_app_code_step1('config.ru', options)
       LoaderSharedHelpers.run_load_path_setup_code(options)
       LoaderSharedHelpers.before_loading_app_code_step2(options)
+      LoaderSharedHelpers.activate_gem 'rack'
 
-      begin
-        require 'rubygems'
-      rescue LoadError
-      end
-      require 'rack'
       rackup_file = options["startup_file"] || "config.ru"
       rackup_code = ::File.open(rackup_file, 'rb') do |f|
         f.read

helper-scripts/rack-preloader.rb

@@ -98,12 +98,8 @@ def self.preload_app
       LoaderSharedHelpers.before_loading_app_code_step1('config.ru', options)
       LoaderSharedHelpers.run_load_path_setup_code(options)
       LoaderSharedHelpers.before_loading_app_code_step2(options)
+      LoaderSharedHelpers.activate_gem 'rack'
 
-      begin
-        require 'rubygems'
-      rescue LoadError
-      end
-      require 'rack'
       rackup_file = options["startup_file"] || "config.ru"
       rackup_code = ::File.open(rackup_file, 'rb') do |f|
         f.read

lib/phusion_passenger/loader_shared_helpers.rb

@@ -1,6 +1,6 @@
 # encoding: binary
 #  Phusion Passenger - https://www.phusionpassenger.com/
-#  Copyright (c) 2011-2013 Phusion
+#  Copyright (c) 2011-2015 Phusion
 #
 #  "Phusion Passenger" is a trademark of Hongli Lai & Ninh Bui.
 #
@@ -274,8 +274,7 @@ def run_load_path_setup_code(options)
         # there's always the load_path_setup_file option and
         # setup_load_paths.rb.
         running_bundler(options) do
-          require 'rubygems'
-          require 'bundler/setup'
+          activate_gem 'bundler', 'bundler/setup'
         end
       end
 
@@ -376,6 +375,27 @@ def after_handling_requests
       PhusionPassenger.call_event(:stopping_worker_process)
     end
 
+    # Activate a gem and require it. This method exists in order to load
+    # a library from RubyGems instead of from vendor_ruby. For example,
+    # on Debian systems, Rack may be installed from APT, but that is usually
+    # a very old version which we don't want. This method ensures that the
+    # RubyGems-installed version is loaded, not the the version in vendor_ruby.
+    # See the following threads for discussion:
+    # https://github.com/phusion/passenger/issues/1478
+    # https://github.com/phusion/passenger/issues/1480
+    def activate_gem(gem_name, library_name = nil)
+      if !defined?(::Gem)
+        begin
+          require 'rubygems'
+        rescue LoadError
+        end
+      end
+      if Kernel.respond_to?(:gem, true)
+        gem(gem_name)
+      end
+      require(library_name || gem_name)
+    end
+
   private
     def running_bundler(options)
       yield