Ensure we override Rack::Request's POST method too

actionpack/lib/action_controller/request.rb

@@ -387,6 +387,7 @@ def raw_post
     def parameters
       @parameters ||= request_parameters.merge(query_parameters).update(path_parameters).with_indifferent_access
     end
+    alias_method :params, :parameters
 
     def path_parameters=(parameters) #:nodoc:
       @env["rack.routing_args"] = parameters
@@ -418,9 +419,11 @@ def GET
     end
     alias_method :query_parameters, :GET
 
-    def request_parameters
+    # Override Rack's POST method to support nested query strings
+    def POST
       @parser.request_parameters
     end
+    alias_method :request_parameters, :POST
 
     def body_stream #:nodoc:
       @env['rack.input']

actionpack/test/controller/query_string_parsing_test.rb

-class QueryStringParsingTest <ActionController::IntegrationTest
+require 'abstract_unit'
+
+class QueryStringParsingTest < ActionController::IntegrationTest
   class TestController < ActionController::Base
     class << self
       attr_accessor :last_query_parameters