Fix handling SCRIPT_NAME from within mounted engine's

When you mount your application at a path, for example /myapp, server
should set SCRIPT_NAME to /myapp. With such information, rails
application knows that it's mounted at /myapp path and it should generate
routes relative to that path.

Before this patch, rails handled SCRIPT_NAME correctly only for regular
apps, but it failed to do it for mounted engines. The solution was to
hardcode default_url_options[:script_name], which is not the best answer
- it will work only when application is mounted at a fixed path.

This patch fixes the situation by respecting original value of
SCRIPT_NAME when generating application's routes from engine and the
other way round - when you generate engine's routes from application.

This is done by using one of 2 pieces of information in env - current
SCRIPT_NAME or SCRIPT_NAME for a corresponding router. This is because
we have 2 cases to handle:

- generating engine's route from application: in this situation
  SCRIPT_NAME is basically SCRIPT_NAME set by the server and it
  indicates the place where application is mounted, so we can just pass
  it as :original_script_name in url_options. :original_script_name is
  used because if we use :script_name, router will ignore generating
  prefix for engine

- generating application's route from engine: in this situation we
  already lost information about the SCRIPT_NAME that server used. For
  example if application is mounted at /myapp and engine is mounted at
  /blog, at this point SCRIPT_NAME is equal /myapp/blog. Because of that
  we need to keep reference to /myapp SCRIPT_NAME by binding it to the
  current router. Later on we can extract it and use when generating url

Please note that starting from now you *should not* use
default_url_options[:script_name] explicitly if your server already
passes correct SCRIPT_NAME to rack env.

(closes #6933)

7 files changed, 78 insertions, 41 deletions

diff --git a/actionpack/lib/action_controller/metal/url_for.rb b/actionpack/lib/action_controller/metal/url_for.rb
index dd5ceb3478..0cdd17bc2e 100644
--- a/actionpack/lib/action_controller/metal/url_for.rb
+++ b/actionpack/lib/action_controller/metal/url_for.rb
@@ -30,9 +30,15 @@ module ActionController
         :_recall => request.symbolized_path_parameters
       ).freeze
 
-      if _routes.equal?(env["action_dispatch.routes"])
+      if (same_origin = _routes.equal?(env["action_dispatch.routes"])) ||
+         (script_name = env["ROUTES_#{_routes.object_id}_SCRIPT_NAME"]) ||
+         (original_script_name = env['SCRIPT_NAME'])
         @_url_options.dup.tap do |options|
-          options[:script_name] = request.script_name.dup
+          if original_script_name
+            options[:original_script_name] = original_script_name
+          else
+            options[:script_name] = same_origin ? request.script_name.dup : script_name
+          end
           options.freeze
         end
       else
diff --git a/actionpack/lib/action_dispatch/routing/route_set.rb b/actionpack/lib/action_dispatch/routing/route_set.rb
index cc53e298cc..d3f66f042c 100644
--- a/actionpack/lib/action_dispatch/routing/route_set.rb
+++ b/actionpack/lib/action_dispatch/routing/route_set.rb
@@ -163,9 +163,9 @@ module ActionDispatch
         private
 
           def define_named_route_methods(name, route)
-            define_url_helper route, :"#{name}_path", 
+            define_url_helper route, :"#{name}_path",
               route.defaults.merge(:use_route => name, :only_path => true)
-            define_url_helper route, :"#{name}_url", 
+            define_url_helper route, :"#{name}_url",
               route.defaults.merge(:use_route => name, :only_path => false)
           end
 
@@ -465,7 +465,7 @@ module ActionDispatch
         def use_recall_for(key)
           if @recall[key] && (!@options.key?(key) || @options[key] == @recall[key])
             if !named_route_exists? || segment_keys.include?(key)
-              @options[key] = @recall.delete(key) 
+              @options[key] = @recall.delete(key)
             end
           end
         end
@@ -574,7 +574,8 @@ module ActionDispatch
       end
 
       RESERVED_OPTIONS = [:host, :protocol, :port, :subdomain, :domain, :tld_length,
-                          :trailing_slash, :anchor, :params, :only_path, :script_name]
+                          :trailing_slash, :anchor, :params, :only_path, :script_name,
+                          :original_script_name]
 
       def mounted?
         false
@@ -594,7 +595,13 @@ module ActionDispatch
 
         user, password = extract_authentication(options)
         recall  = options.delete(:_recall)
-        script_name    = options.delete(:script_name).presence || _generate_prefix(options)
+
+        original_script_name = options.delete(:original_script_name).presence
+        script_name = options.delete(:script_name).presence || _generate_prefix(options)
+
+        if script_name && original_script_name
+          script_name = original_script_name + script_name
+        end
 
         path_options = options.except(*RESERVED_OPTIONS)
         path_options = yield(path_options) if block_given?
diff --git a/actionpack/test/dispatch/prefix_generation_test.rb b/actionpack/test/dispatch/prefix_generation_test.rb
index ab2f7612ce..6d75c5ec7a 100644
--- a/actionpack/test/dispatch/prefix_generation_test.rb
+++ b/actionpack/test/dispatch/prefix_generation_test.rb
@@ -166,18 +166,6 @@ module TestGenerationPrefix
       assert_equal "/generate", last_response.body
     end
 
-    test "[ENGINE] generating application's url includes default_url_options[:script_name]" do
-      RailsApplication.routes.default_url_options = {:script_name => "/something"}
-      get "/pure-awesomeness/blog/url_to_application"
-      assert_equal "/something/generate", last_response.body
-    end
-
-    test "[ENGINE] generating application's url should give higher priority to default_url_options[:script_name]" do
-      RailsApplication.routes.default_url_options = {:script_name => "/something"}
-      get "/pure-awesomeness/blog/url_to_application", {}, 'SCRIPT_NAME' => '/foo'
-      assert_equal "/something/generate", last_response.body
-    end
-
     test "[ENGINE] generating engine's url with polymorphic path" do
       get "/pure-awesomeness/blog/polymorphic_path_for_engine"
       assert_equal "/pure-awesomeness/blog/posts/1", last_response.body
@@ -200,12 +188,6 @@ module TestGenerationPrefix
       assert_equal "/something/awesome/blog/posts/1", last_response.body
     end
 
-    test "[APP] generating engine's route should give higher priority to default_url_options[:script_name]" do
-      RailsApplication.routes.default_url_options = {:script_name => "/something"}
-      get "/generate", {}, 'SCRIPT_NAME' => "/foo"
-      assert_equal "/something/awesome/blog/posts/1", last_response.body
-    end
-
     test "[APP] generating engine's url with polymorphic path" do
       get "/polymorphic_path_for_engine"
       assert_equal "/awesome/blog/posts/1", last_response.body
diff --git a/railties/CHANGELOG.md b/railties/CHANGELOG.md
index 18c130e828..851f41249a 100644
--- a/railties/CHANGELOG.md
+++ b/railties/CHANGELOG.md
@@ -1,5 +1,10 @@
 ## Rails 4.0.0 (unreleased) ##
 
+*   Correctly handle SCRIPT_NAME when generating routes to engine in application
+    that's mounted at a sub-uri. With this behavior, you *should not* use
+    default_url_options[:script_name] to set proper application's mount point by
+    yourself. *Piotr Sarnacki*
+
 *   The migration generator will now produce AddXXXToYYY/RemoveXXXFromYYY migrations with references statements, for instance
 
         rails g migration AddReferencesToProducts user:references supplier:references{polymorphic}
diff --git a/railties/lib/rails/engine.rb b/railties/lib/rails/engine.rb
index f469c334a7..40f35ae5a6 100644
--- a/railties/lib/rails/engine.rb
+++ b/railties/lib/rails/engine.rb
@@ -494,7 +494,11 @@ module Rails
 
     # Define the Rack API for this engine.
     def call(env)
-      app.call(env.merge!(env_config))
+      env.merge!(env_config)
+      if env['SCRIPT_NAME']
+        env.merge! "ROUTES_#{routes.object_id}_SCRIPT_NAME" => env['SCRIPT_NAME'].dup
+      end
+      app.call(env)
     end
 
     # Defines additional Rack env configuration that is added on each call.
diff --git a/railties/test/railties/engine_test.rb b/railties/test/railties/engine_test.rb
index 63814f7a04..e52b3efdab 100644
--- a/railties/test/railties/engine_test.rb
+++ b/railties/test/railties/engine_test.rb
@@ -1193,6 +1193,54 @@ YAML
                    last_response.body.split("\n").map(&:strip)
     end
 
+    test "paths are properly generated when application is mounted at sub-path" do
+      @plugin.write "lib/bukkits.rb", <<-RUBY
+        module Bukkits
+          class Engine < ::Rails::Engine
+            isolate_namespace Bukkits
+          end
+        end
+      RUBY
+
+      app_file "app/controllers/bar_controller.rb", <<-RUBY
+        class BarController < ApplicationController
+          def index
+            render :text => bukkits.bukkit_path
+          end
+        end
+      RUBY
+
+      app_file "config/routes.rb", <<-RUBY
+        AppTemplate::Application.routes.draw do
+          get '/bar' => 'bar#index', :as => 'bar'
+          mount Bukkits::Engine => "/bukkits", :as => "bukkits"
+        end
+      RUBY
+
+      @plugin.write "config/routes.rb", <<-RUBY
+        Bukkits::Engine.routes.draw do
+          get '/bukkit' => 'bukkit#index'
+        end
+      RUBY
+
+
+      @plugin.write "app/controllers/bukkits/bukkit_controller.rb", <<-RUBY
+        class Bukkits::BukkitController < ActionController::Base
+          def index
+            render :text => main_app.bar_path
+          end
+        end
+      RUBY
+
+      boot_rails
+
+      get("/bukkits/bukkit", {}, {'SCRIPT_NAME' => '/foo'})
+      assert_equal '/foo/bar', last_response.body
+
+      get("/bar", {}, {'SCRIPT_NAME' => '/foo'})
+      assert_equal '/foo/bukkits/bukkit', last_response.body
+    end
+
   private
     def app
       Rails.application
diff --git a/railties/test/railties/mounted_engine_test.rb b/railties/test/railties/mounted_engine_test.rb
index 4c0fdee556..bd13c3aba3 100644
--- a/railties/test/railties/mounted_engine_test.rb
+++ b/railties/test/railties/mounted_engine_test.rb
@@ -163,24 +163,14 @@ module ApplicationTests
       end
     end
 
-    def reset_script_name!
-      Rails.application.routes.default_url_options = {}
-    end
-
-    def script_name(script_name)
-      Rails.application.routes.default_url_options = {:script_name => script_name}
-    end
-
     test "routes generation in engine and application" do
       # test generating engine's route from engine
       get "/john/blog/posts"
       assert_equal "/john/blog/posts/1", last_response.body
 
       # test generating engine's route from engine with default_url_options
-      script_name "/foo"
       get "/john/blog/posts", {}, 'SCRIPT_NAME' => "/foo"
       assert_equal "/foo/john/blog/posts/1", last_response.body
-      reset_script_name!
 
       # test generating engine's route from application
       get "/engine_route"
@@ -193,14 +183,11 @@ module ApplicationTests
       assert_equal "/john/blog/posts", last_response.body
 
       # test generating engine's route from application with default_url_options
-      script_name "/foo"
       get "/engine_route", {}, 'SCRIPT_NAME' => "/foo"
       assert_equal "/foo/anonymous/blog/posts", last_response.body
 
-      script_name "/foo"
       get "/url_for_engine_route", {}, 'SCRIPT_NAME' => "/foo"
       assert_equal "/foo/john/blog/posts", last_response.body
-      reset_script_name!
 
       # test generating application's route from engine
       get "/someone/blog/generate_application_route"
@@ -210,10 +197,8 @@ module ApplicationTests
       assert_equal "/", last_response.body
 
       # test generating application's route from engine with default_url_options
-      script_name "/foo"
       get "/someone/blog/generate_application_route", {}, 'SCRIPT_NAME' => '/foo'
       assert_equal "/foo/", last_response.body
-      reset_script_name!
 
       # test polymorphic routes
       get "/polymorphic_route"