Make restore_attributes public

Also make it accept a list of attributes to be changed. This will make
possible to restore only a subset of the changed attributes.

Closes #16203

activemodel/lib/active_model/dirty.rb

@@ -180,6 +180,11 @@ module ActiveModel
       attribute_changed?(attr) ? changed_attributes[attr] : __send__(attr)
     end
 
+    # Restore all previous data of the provided attributes.
+    def restore_attributes(attributes = changed)
+      attributes.each { |attr| restore_attribute! attr }
+    end
+
     private
 
       # Removes current changes and makes them accessible through +previous_changes+.
@@ -199,11 +204,6 @@ module ActiveModel
         clear_changes_information
       end
 
-      # Restore all previous data.
-      def restore_attributes # :doc:
-        changed_attributes.each_key { |attr| restore_attribute! attr }
-      end
-
       # Handle <tt>*_change</tt> for +method_missing+.
       def attribute_change(attr)
         [changed_attributes[attr], __send__(attr)] if attribute_changed?(attr)

activemodel/test/cases/dirty_test.rb

@@ -49,10 +49,6 @@ class DirtyTest < ActiveModel::TestCase
     def deprecated_reload
       reset_changes
     end
-
-    def rollback
-      restore_attributes
-    end
   end
 
   setup do
@@ -209,10 +205,24 @@ class DirtyTest < ActiveModel::TestCase
     @model.name = 'Bob'
     @model.color = 'White'
 
-    @model.rollback
+    @model.restore_attributes
 
     assert_not @model.changed?
     assert_equal 'Dmitry', @model.name
     assert_equal 'Red', @model.color
   end
+
+  test "restore_attributes can restore only some attributes" do
+    @model.name = 'Dmitry'
+    @model.color = 'Red'
+    @model.save
+    @model.name = 'Bob'
+    @model.color = 'White'
+
+    @model.restore_attributes(['name'])
+
+    assert @model.changed?
+    assert_equal 'Dmitry', @model.name
+    assert_equal 'White', @model.color
+  end
 end