Memoize user provided defaults before type casting

When a proc is given as a default value, the form builder ends up
displaying `Proc#to_s` when the default is used. That's because we
didn't handle the proc until type casting. This issue technically can
occur any time that a proc is the value before type casting, but in
reality the only place that will occur is when a proc default is
provided through the attributes API, so the best place to handle this
edge case is there.

I've opted to memoize instead of just moving the `Proc#call` up, as this
made me realize that it could potentially interact very poorly with
dirty checking.

The code here is a little redundant, but I don't want to rely on how
`value_before_type_cast` is implemented in the super class, even if it's
just an `attr_reader`.

Fixes #24249

Close #24306

1 files changed, 11 insertions, 0 deletions

diff --git a/activerecord/test/cases/attributes_test.rb b/activerecord/test/cases/attributes_test.rb
index 2991ca8b76..2bebbfa205 100644
--- a/activerecord/test/cases/attributes_test.rb
+++ b/activerecord/test/cases/attributes_test.rb
@@ -135,6 +135,17 @@ module ActiveRecord
       assert_equal 2, klass.new.counter
     end
 
+    test "procs are memoized before type casting" do
+      klass = Class.new(OverloadedType) do
+        @@counter = 0
+        attribute :counter, :integer, default: -> { @@counter += 1 }
+      end
+
+      model = klass.new
+      assert_equal 1, model.counter_before_type_cast
+      assert_equal 1, model.counter_before_type_cast
+    end
+
     test "user provided defaults are persisted even if unchanged" do
       model = OverloadedType.create!