2 files changed, 18 insertions, 3 deletions
diff --git a/activerecord/lib/active_record/attribute_methods/dirty.rb b/activerecord/lib/active_record/attribute_methods/dirty.rb
index b0e1391cb9..31c1e687dc 100644
--- a/activerecord/lib/active_record/attribute_methods/dirty.rb
+++ b/activerecord/lib/active_record/attribute_methods/dirty.rb
@@ -275,7 +275,17 @@ module ActiveRecord
 
         def attribute_will_change!(attr_name)
           super
-          mutations_from_database.force_change(attr_name)
+          if self.class.has_attribute?(attr_name)
+            mutations_from_database.force_change(attr_name)
+          else
+            ActiveSupport::Deprecation.warn(<<-EOW.squish)
+              #{attr_name} is not an attribute known to Active Record.
+              This behavior is deprecated and will be removed in the next
+              version of Rails. If you'd like #{attr_name} to be managed
+              by Active Record, add `attribute :#{attr_name} to your class.
+            EOW
+            mutations_from_database.deprecated_force_change(attr_name)
+          end
         end
 
         def _update_record(*)
diff --git a/activerecord/lib/active_record/attribute_mutation_tracker.rb b/activerecord/lib/active_record/attribute_mutation_tracker.rb
index 3417090830..4de993e169 100644
--- a/activerecord/lib/active_record/attribute_mutation_tracker.rb
+++ b/activerecord/lib/active_record/attribute_mutation_tracker.rb
@@ -5,6 +5,7 @@ module ActiveRecord
     def initialize(attributes)
       @attributes = attributes
       @forced_changes = Set.new
+      @deprecated_forced_changes = Set.new
     end
 
     def changed_values
@@ -31,7 +32,7 @@ module ActiveRecord
     end
 
     def any_changes?
-      attr_names.any? { |attr| changed?(attr) }
+      attr_names.any? { |attr| changed?(attr) } || deprecated_forced_changes.any?
     end
 
     def changed?(attr_name, from: OPTION_NOT_GIVEN, to: OPTION_NOT_GIVEN)
@@ -60,11 +61,15 @@ module ActiveRecord
       forced_changes << attr_name.to_s
     end
 
+    def deprecated_force_change(attr_name)
+      deprecated_forced_changes << attr_name.to_s
+    end
+
     # TODO Change this to private once we've dropped Ruby 2.2 support.
     # Workaround for Ruby 2.2 "private attribute?" warning.
     protected
 
-      attr_reader :attributes, :forced_changes
+      attr_reader :attributes, :forced_changes, :deprecated_forced_changes
 
     private