Ensure that instances of `ActiveModel::Errors` can be marshalled

We now use default procs inside of the errors object, which gets
included by default when marshaling anything that includes
`ActiveModel::Validations`. This means that Active Record objects cannot
be marshalled. We strip and apply the default proc ourselves. This will
ensure the objects are YAML serializable as well, since YAML falls back
to marshal implementations now. This is less important, however, as the
errors aren't included when dumping Active Record objects.

This commit does not include a changelog entry, as 5.0 is still in RC
status at the time of writing, and 5.0.0 will not release with the bug
this fixes.

Fixes #25165

1 files changed, 9 insertions, 0 deletions

diff --git a/activemodel/test/cases/errors_test.rb b/activemodel/test/cases/errors_test.rb
index fbf208836f..c90ee7021c 100644
--- a/activemodel/test/cases/errors_test.rb
+++ b/activemodel/test/cases/errors_test.rb
@@ -427,4 +427,13 @@ class ErrorsTest < ActiveModel::TestCase
     assert_equal [:name], person.errors.messages.keys
     assert_equal [:name], person.errors.details.keys
   end
+
+  test "errors are marshalable" do
+    errors = ActiveModel::Errors.new(Person.new)
+    errors.add(:name, :invalid)
+    serialized = Marshal.load(Marshal.dump(errors))
+
+    assert_equal errors.messages, serialized.messages
+    assert_equal errors.details, serialized.details
+  end
 end