I N C E P T I O N: flatten_deeper works around a bug in Ruby 1.8.2.

activerecord/lib/active_record/associations/association_collection.rb

@@ -125,7 +125,7 @@ def <<(*records)
         load_target if @owner.new_record?
 
         transaction do
-          flatten_deeper(records).each do |record|
+          records.flatten.each do |record|
             raise_on_type_mismatch(record)
             add_record_to_target_with_callbacks(record) do |r|
               result &&= insert_record(record) unless @owner.new_record?
@@ -501,7 +501,7 @@ def build_record(attrs, &block)
         end
 
         def remove_records(*records)
-          records = flatten_deeper(records)
+          records = records.flatten
           records.each { |record| raise_on_type_mismatch(record) }
 
           transaction do

activerecord/lib/active_record/associations/has_association.rb

@@ -37,18 +37,6 @@ def construct_conditions
           conditions << Arel.sql(sql_conditions) if sql_conditions
           aliased_table.create_and(conditions)
         end
-
-        if RUBY_VERSION < '1.9.2'
-          # Array#flatten has problems with recursive arrays before Ruby 1.9.2.
-          # Going one level deeper solves the majority of the problems.
-          def flatten_deeper(array)
-            array.collect { |element| (element.respond_to?(:flatten) && !element.is_a?(Hash)) ? element.flatten : element }.flatten
-          end
-        else
-          def flatten_deeper(array)
-            array.flatten
-          end
-        end
     end
   end
 end

activerecord/lib/active_record/associations/has_many_through_association.rb

@@ -10,7 +10,7 @@ class HasManyThroughAssociation < HasManyAssociation #:nodoc:
 
       def destroy(*records)
         transaction do
-          delete_records(flatten_deeper(records))
+          delete_records(records.flatten)
           super
         end
       end