Don't expose these new APIs yet (added in 877ea78 / #16189)

WARNING: don't use them! They might change or go away between future beta/RC/
patch releases!

Also added a CHANGELOG entry for this.

activemodel/lib/active_model/dirty.rb

@@ -114,7 +114,7 @@ module ActiveModel
     include ActiveModel::AttributeMethods
 
     included do
-      attribute_method_suffix '_changed?', '_change', '_will_change!', '_was', '_was='
+      attribute_method_suffix '_changed?', '_change', '_will_change!', '_was'
       attribute_method_affix prefix: 'reset_', suffix: '!'
       attribute_method_affix prefix: 'restore_', suffix: '!'
     end
@@ -180,26 +180,13 @@ module ActiveModel
       attribute_changed?(attr) ? changed_attributes[attr] : __send__(attr)
     end
 
-    # Handle <tt>*_was=</tt> for +method_missing+
-    def attribute_was=(attr, old_value)
-      attributes_changed_by_setter[attr] = old_value
-    end
-    alias_method :set_attribute_was, :attribute_was=
-
     # Restore all previous data of the provided attributes.
     def restore_attributes(attributes = changed)
       attributes.each { |attr| restore_attribute! attr }
     end
 
-    # Remove changes information for the provided attributes.
-    def clear_attribute_changes(attributes)
-      attributes_changed_by_setter.except!(*attributes)
-    end
-
     private
 
-      alias_method :attributes_changed_by_setter, :changed_attributes # :nodoc:
-
       # Removes current changes and makes them accessible through +previous_changes+.
       def changes_applied # :doc:
         @previously_changed = changes
@@ -249,5 +236,19 @@ module ActiveModel
           clear_attribute_changes([attr])
         end
       end
+
+      # This is necessary because `changed_attributes` might be overridden in
+      # other implemntations (e.g. in `ActiveRecord`)
+      alias_method :attributes_changed_by_setter, :changed_attributes # :nodoc:
+
+      # Force an attribute to have a particular "before" value
+      def set_attribute_was(attr, old_value)
+        attributes_changed_by_setter[attr] = old_value
+      end
+
+      # Remove changes information for the provided attributes.
+      def clear_attribute_changes(attributes)
+        attributes_changed_by_setter.except!(*attributes)
+      end
   end
 end

activerecord/CHANGELOG.md

@@ -1,3 +1,8 @@
+*   `*_was` and `changes` now work correctly for in-place attribute changes as
+    well.
+
+    *Sean Griffin*
+
 *   Fix regression on after_commit that didnt fire when having nested transactions.
 
     Fixes #16425

activerecord/lib/active_record/associations/has_many_association.rb

@@ -103,7 +103,7 @@ module ActiveRecord
           if has_cached_counter?(reflection)
             counter = cached_counter_attribute_name(reflection)
             owner[counter] += difference
-            owner.clear_attribute_changes([counter]) # eww
+            owner.send(:clear_attribute_changes, counter) # eww
           end
         end