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, 10 insertions, 5 deletions

diff --git a/activerecord/lib/active_record/attribute/user_provided_default.rb b/activerecord/lib/active_record/attribute/user_provided_default.rb
index 6dbd92ce28..4580813364 100644
--- a/activerecord/lib/active_record/attribute/user_provided_default.rb
+++ b/activerecord/lib/active_record/attribute/user_provided_default.rb
@@ -4,20 +4,25 @@ module ActiveRecord
   class Attribute # :nodoc:
     class UserProvidedDefault < FromUser # :nodoc:
       def initialize(name, value, type, database_default)
+        @user_provided_value = value
         super(name, value, type, database_default)
       end
 
-      def type_cast(value)
-        if value.is_a?(Proc)
-          super(value.call)
+      def value_before_type_cast
+        if user_provided_value.is_a?(Proc)
+          @memoized_value_before_type_cast ||= user_provided_value.call
         else
-          super
+          @user_provided_value
         end
       end
 
       def with_type(type)
-        self.class.new(name, value_before_type_cast, type, original_attribute)
+        self.class.new(name, user_provided_value, type, original_attribute)
       end
+
+      protected
+
+      attr_reader :user_provided_value
     end
   end
 end