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)

1 files changed, 5 insertions, 1 deletions

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.