2 files changed, 21 insertions, 10 deletions
diff --git a/actionpack/lib/action_dispatch/routing/mapper.rb b/actionpack/lib/action_dispatch/routing/mapper.rb
index bfba8d143d..4bf2dc6e23 100644
--- a/actionpack/lib/action_dispatch/routing/mapper.rb
+++ b/actionpack/lib/action_dispatch/routing/mapper.rb
@@ -3,6 +3,7 @@ require 'active_support/core_ext/hash/reverse_merge'
 require 'active_support/core_ext/hash/slice'
 require 'active_support/core_ext/enumerable'
 require 'active_support/core_ext/array/extract_options'
+require 'active_support/core_ext/module/remove_method'
 require 'active_support/inflector'
 require 'action_dispatch/routing/redirection'
 
@@ -546,11 +547,11 @@ module ActionDispatch
             _routes = @set
             app.routes.define_mounted_helper(name)
             app.routes.singleton_class.class_eval do
-              define_method :mounted? do
+              redefine_method :mounted? do
                 true
               end
 
-              define_method :_generate_prefix do |options|
+              redefine_method :_generate_prefix do |options|
                 prefix_options = options.slice(*_route.segment_keys)
                 # we must actually delete prefix segment keys to avoid passing them to next url_for
                 _route.segment_keys.each { |k| options.delete(k) }
diff --git a/actionpack/lib/action_dispatch/routing/redirection.rb b/actionpack/lib/action_dispatch/routing/redirection.rb
index cbf4c5aa8b..b08e62543b 100644
--- a/actionpack/lib/action_dispatch/routing/redirection.rb
+++ b/actionpack/lib/action_dispatch/routing/redirection.rb
@@ -26,14 +26,19 @@ module ActionDispatch
         end
 
         uri = URI.parse(path(req.symbolized_path_parameters, req))
+        
+        unless uri.host
+          if relative_path?(uri.path)
+            uri.path = "#{req.script_name}/#{uri.path}"
+          elsif uri.path.empty?
+            uri.path = req.script_name.empty? ? "/" : req.script_name
+          end
+        end
+          
         uri.scheme ||= req.scheme
         uri.host   ||= req.host
         uri.port   ||= req.port unless req.standard_port?
 
-        if relative_path?(uri.path)
-          uri.path = "#{req.script_name}/#{uri.path}"
-        end
-
         body = %(<html><body>You are being <a href="#{ERB::Util.h(uri.to_s)}">redirected</a>.</body></html>)
 
         headers = {
@@ -112,11 +117,16 @@ module ActionDispatch
           url_options[:path] = (url_options[:path] % escape_path(params))
         end
 
-        if relative_path?(url_options[:path])
-          url_options[:path] = "/#{url_options[:path]}"
-          url_options[:script_name] = request.script_name
+        unless options[:host] || options[:domain]
+          if relative_path?(url_options[:path])
+            url_options[:path] = "/#{url_options[:path]}"
+            url_options[:script_name] = request.script_name
+          elsif url_options[:path].empty?
+            url_options[:path] = request.script_name.empty? ? "/" : ""
+            url_options[:script_name] = request.script_name
+          end
         end
-
+        
         ActionDispatch::Http::URL.url_for url_options
       end