fix the variable name

activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb

@@ -4,28 +4,28 @@ class JoinTableResolver
       KnownTable = Struct.new :join_table
 
       class KnownClass
-        def initialize(rhs_class, lhs_class_name)
-          @rhs_class      = rhs_class
-          @lhs_class_name = lhs_class_name
+        def initialize(lhs_class, rhs_class_name)
+          @lhs_class      = lhs_class
+          @rhs_class_name = rhs_class_name
           @join_table     = nil
         end
 
         def join_table
-          @join_table ||= [@rhs_class.table_name, klass.table_name].sort.join("\0").gsub(/^(.*_)(.+)\0\1(.+)/, '\1\2_\3').gsub("\0", "_")
+          @join_table ||= [@lhs_class.table_name, klass.table_name].sort.join("\0").gsub(/^(.*_)(.+)\0\1(.+)/, '\1\2_\3').gsub("\0", "_")
         end
 
         private
-        def klass; @lhs_class_name.constantize; end
+        def klass; @rhs_class_name.constantize; end
       end
 
-      def self.build(rhs_class, name, options)
+      def self.build(lhs_class, name, options)
         if options[:join_table]
           KnownTable.new options[:join_table]
         else
           class_name = options.fetch(:class_name) {
             name.to_s.camelize.singularize
           }
-          KnownClass.new rhs_class, class_name
+          KnownClass.new lhs_class, class_name
         end
       end
     end