Provide a better error message for unsupported classes in `serialize`

We only support classes which provide a no-args constructor to use as a
default value. We can provide a more helpful error message if we catch
this when `serialize` is called, rather than letting it error when you
try to assign the attribute.

Fixes #18224

1 files changed, 6 insertions, 0 deletions

diff --git a/activerecord/test/cases/serialized_attribute_test.rb b/activerecord/test/cases/serialized_attribute_test.rb
index c8441201ca..c261a5b1c0 100644
--- a/activerecord/test/cases/serialized_attribute_test.rb
+++ b/activerecord/test/cases/serialized_attribute_test.rb
@@ -264,4 +264,10 @@ class SerializedAttributeTest < ActiveRecord::TestCase
 
     assert_not topic.content_changed?
   end
+
+  def test_classes_without_no_arg_constructors_are_not_supported
+    assert_raises(ArgumentError) do
+      Topic.serialize(:content, Regexp)
+    end
+  end
 end