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, 8 insertions, 0 deletions

diff --git a/activerecord/test/cases/dirty_test.rb b/activerecord/test/cases/dirty_test.rb
index 0e58e65a07..c0d6ddcea7 100644
--- a/activerecord/test/cases/dirty_test.rb
+++ b/activerecord/test/cases/dirty_test.rb
@@ -301,6 +301,14 @@ class DirtyTest < ActiveRecord::TestCase
     assert_equal ["arr", "arr matey!"], pirate.catchphrase_change
   end
 
+  def test_virtual_attribute_will_change
+    assert_deprecated do
+      parrot = Parrot.create!(name: "Ruby")
+      parrot.send(:attribute_will_change!, :cancel_save_from_callback)
+      assert parrot.has_changes_to_save?
+    end
+  end
+
   def test_association_assignment_changes_foreign_key
     pirate = Pirate.create!(catchphrase: "jarl")
     pirate.parrot = Parrot.create!(name: "Lorre")