Allow attributes with a proc default to be marshalled

We don't implement much custom marshalling logic for these objects, but
the proc default case needs to be handled separately. Unfortunately
there's no way to just say "do what you would have done but with this
value for one ivar", so we have to manually implement `marshal_load` as
well.

The test case is a little bit funky, but I'd really like an equality
test in there, and there's no easy way to add one now that this is out
of AR (since the `attributes` method isn't here)

Fixes #31216

3 files changed, 38 insertions, 0 deletions

diff --git a/activemodel/CHANGELOG.md b/activemodel/CHANGELOG.md
index b67a803b9d..86353674d9 100644
--- a/activemodel/CHANGELOG.md
+++ b/activemodel/CHANGELOG.md
@@ -1,7 +1,14 @@
+*   Models using the attributes API with a proc default can now be marshalled.
+
+    Fixes #31216.
+
+    *Sean Griffin*
+
 *   Fix to working before/after validation callbacks on multiple contexts.
 
     *Yoshiyuki Hirano*
 
+
 ## Rails 5.2.0.beta2 (November 28, 2017) ##
 
 *   No changes.
diff --git a/activemodel/lib/active_model/attribute/user_provided_default.rb b/activemodel/lib/active_model/attribute/user_provided_default.rb
index f274b687d4..a5dc6188d2 100644
--- a/activemodel/lib/active_model/attribute/user_provided_default.rb
+++ b/activemodel/lib/active_model/attribute/user_provided_default.rb
@@ -22,6 +22,28 @@ module ActiveModel
         self.class.new(name, user_provided_value, type, original_attribute)
       end
 
+      def marshal_dump
+        result = [
+          name,
+          value_before_type_cast,
+          type,
+          original_attribute,
+        ]
+        result << value if defined?(@value)
+        result
+      end
+
+      def marshal_load(values)
+        name, user_provided_value, type, original_attribute, value = values
+        @name = name
+        @user_provided_value = user_provided_value
+        @type = type
+        @original_attribute = original_attribute
+        if values.length == 5
+          @value = value
+        end
+      end
+
       protected
 
         attr_reader :user_provided_value
diff --git a/activemodel/test/cases/attributes_test.rb b/activemodel/test/cases/attributes_test.rb
index e43bf15335..7c1d813ce0 100644
--- a/activemodel/test/cases/attributes_test.rb
+++ b/activemodel/test/cases/attributes_test.rb
@@ -64,5 +64,14 @@ module ActiveModel
 
       assert_equal "4.4", data.integer_field
     end
+
+    test "attributes with proc defaults can be marshalled" do
+      data = ModelForAttributesTest.new
+      attributes = data.instance_variable_get(:@attributes)
+      round_tripped = Marshal.load(Marshal.dump(data))
+      new_attributes = round_tripped.instance_variable_get(:@attributes)
+
+      assert_equal attributes, new_attributes
+    end
   end
 end