Ignores a default subclass when `becomes(Parent)`

Fixes issue described in #30399: A default value on the
inheritance column prevented `child.becomes(Parent)` to return
an instance of `Parent` as expected, instead it returns an instance
of the default subclass.

The change was introduced by #17169 and it was meant to affect
initialization, alone. Where `Parent.new` is expected to return
an instance of the default subclass.

1 files changed, 2 insertions, 1 deletions

diff --git a/activerecord/lib/active_record/persistence.rb b/activerecord/lib/active_record/persistence.rb
index cdd54cc502..a45d011d75 100644
--- a/activerecord/lib/active_record/persistence.rb
+++ b/activerecord/lib/active_record/persistence.rb
@@ -359,7 +359,8 @@ module ActiveRecord
     # Any change to the attributes on either instance will affect both instances.
     # If you want to change the sti column as well, use #becomes! instead.
     def becomes(klass)
-      became = klass.new
+      became = klass.allocate
+      became.send(:initialize)
       became.instance_variable_set("@attributes", @attributes)
       became.instance_variable_set("@mutations_from_database", @mutations_from_database) if defined?(@mutations_from_database)
       became.instance_variable_set("@new_record", new_record?)