Revert "save on parent should not cascade to child unless child changed [#3353 state:open]"

Please check Lighthouse for more information.

This reverts commit 4a0d7c1a.

activerecord/lib/active_record/autosave_association.rb

@@ -372,9 +372,7 @@ def save_belongs_to_association(reflection)
         if autosave && association.marked_for_destruction?
           association.destroy
         elsif autosave != false
-          if association.new_record? || ( autosave && association.changed? )
-            saved = association.save(:validate => !autosave) 
-          end
+          saved = association.save(:validate => !autosave) if association.new_record? || autosave
 
           if association.updated?
             association_id = association.send(reflection.options[:primary_key] || :id)

activerecord/test/cases/autosave_association_test.rb

@@ -632,8 +632,6 @@ def test_a_parent_marked_for_destruction_should_not_be_destroyed_twice
   end
 
   def test_should_rollback_destructions_if_an_exception_occurred_while_saving_a_parent
-    #association save method only trigged when association is changed 
-    @ship.pirate.catchphrase = "new catch phrase"
     # Stub the save method of the @ship.pirate instance to destroy and then raise an exception
     class << @ship.pirate
       def save(*args)
@@ -882,22 +880,6 @@ def setup
     @pirate = @ship.create_pirate(:catchphrase => "Don' botharrr talkin' like one, savvy?")
   end
 
-  def test_should_not_call_belongs_to_after_save_callbacks_if_no_changes
-    @ship.attributes = { :name => "Titanic", :pirate_attributes => {:id => @pirate.id} }
-    #here there are no changes to pirate so if save on ship causes save on pirate
-    #this callback will fail pirate save.(pirate save shouldn't happen)
-    @ship.pirate.cancel_save_from_callback = true
-    @ship.save
-    assert_equal 'Titanic', @ship.reload.name
-  end
-
-  def test_should_call_belongs_to_save_if_belongs_to_has_changes
-    @ship.attributes = { :name => "Titanic", :pirate_attributes => { :catchphrase => 'Jack', :id => @pirate.id} }
-    @ship.save
-    assert_equal 'Titanic', @ship.reload.name
-    assert_equal 'Jack', @pirate.reload.catchphrase
-  end
-
   def test_should_still_work_without_an_associated_model
     @pirate.destroy
     @ship.reload.name = "The Vile Insanity"