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

3 files changed, 28 insertions, 5 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 3cfebdc2d0..53b669dc72 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,10 @@
+*   The form builder now properly displays values when passing a proc form
+    default to the attributes API.
+
+    Fixes #24249.
+
+    *Sean Griffin*
+
 *   MySQL: strict mode respects other SQL modes rather than overwriting them.
     Setting `strict: true` adds `STRICT_ALL_TABLES` to `sql_mode`. Setting
     `strict: false` removes `STRICT_TRANS_TABLES`, `STRICT_ALL_TABLES`, and
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
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!