Deprecate calling `attr_will_change!` with non-attributes

This was never really intended to work (at least not without calling
`define_attribute_methods`, which is less common with Active Record). As
we move forward the intention is to require the use of `attribute` over
`attr_accessor` for more complex model behavior both on Active Record
and Active Model, so this behavior is deprecated.

Fixes #27956.
Close #27963.

[Alex Serban & Sean Griffin]

1 files changed, 11 insertions, 1 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(*)