Enumerized ActiveModel::Attributes readers return a raw String on Rails 8.1 (value predicates raise NoMethodError) #482

Summary

For a plain ActiveModel object (include ActiveModel::Attributes + extend Enumerize, not ActiveRecord), enumerized attribute readers return the raw assigned value instead of an Enumerize::Value on Rails 8.1. Value-level predicate methods then raise NoMethodError.

Environment

Reproduction

Self-contained, using only activemodel + enumerize:

require "active_model"
require "enumerize"

class Filter
  include ActiveModel::Model
  include ActiveModel::Attributes
  extend Enumerize
  enumerize :mode, in: %i[default full_text], default: :default
end

f = Filter.new(mode: "full_text")
f.mode.class      # Rails <= 8.0: Enumerize::Value ; Rails 8.1: String
f.mode.full_text? # Rails 8.1: NoMethodError: undefined method `full_text?' for an instance of String

Root cause

Enumerize::ActiveModelAttributesSupport::Type (a subclass of ActiveModel::Type::Value) overrides deserialize but not cast. ActiveRecord reads go through deserialize (DB value → wrapped), so ActiveRecord is unaffected. Plain ActiveModel::Attributes assignment resolves reads through cast, which returns the raw value.

It historically "worked" only because enumerize's own reader module (from define_methods!) re-wraps via find_value(super) and used to sit above the ActiveModel-generated attribute-methods module in the ancestor chain. Rails 8.1 reordered attribute-method module inclusion so the generated reader now outranks enumerize's module — exposing that cast never wrapped.

The manifestation depends on declaration order:

• Declaring a plain attribute :x before enumerize keeps enumerize's module on top, so the bug is hidden (this is why the existing ActiveModelUser test fixture, which declares attribute :name, :string first, still passes on Rails 8.1).
• Declaring enumerize first (or only enumerized attributes, as above) exposes it.

Confirmed via MRO: the reader's owner is the ActiveModel-generated module, sitting above Enumerize::Module in .ancestors.

Fix

Define Type#cast to wrap values (returning invalid single values unchanged so inclusion validation still rejects them), keeping deserialize intact. This makes correctness independent of ancestor-chain ordering. I have verified it green on Rails 8.1.3 / 8.0.5 / 7.2.3.1.

This looks like the same problem that #476 already targets. I've reproduced and validated that approach. Also added model-level (predicate) regression tests + a CHANGELOG entry in persona-id#3.

Related

• Inconsistent Behavior of Predicate Methods with Different Enum (for Non-column-backed) Attribute Types rails/rails#53985 — the closest public (Rails-side) symptom report.