feat: support Rails 8.1 in PolymorphicArrayValueExtension

Rails 8.1 changed `ActiveRecord::PredicateBuilder::PolymorphicArrayValue#initialize`
from `(associated_table, values)` to `(reflection, values)`, dropping the
`@associated_table` ivar that this gem reads via
`@associated_table.send(:reflection)` in `type_to_ids_mapping`. Without an
update, every polymorphic-array predicate query (e.g. `Model.where(thing: [a, b])`)
raises `NoMethodError: undefined method 'reflection' for nil` on Rails 8.1.

The minimal fix: read `@reflection` directly when set (Rails 8.1+), fall back to
`@associated_table.send(:reflection)` for older Rails versions. The rest of the
method runs unchanged.

This also adds Gemfile.rails-8.1-stable to the CI matrix so future regressions
are caught upstream rather than in downstream apps.

## Verification

The existing spec at `polymorphic_integer_type_spec.rb:135` ("properly finds
the object when passing an array of sources") exercises exactly this code path:

  Link.where(source: [source])

Verified locally:
- Rails 8.0: 41/41 passing
- Rails 8.1: 41/41 passing
- Rails 8.1 *without* this fix: 1 failure (the array-of-sources test) —
  proves the test catches the regression and the fix resolves it.

Downstream apps (clio/accounting, clio/manage, clio/themis, etc.) currently
maintain in-app monkey patches for this; bumping to 3.5.0 lets them delete
those.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: raymasiclat

.github/workflows/ci.yml

@@ -17,6 +17,7 @@ jobs:
           - Gemfile.rails-7.0-stable
           - Gemfile.rails-7.2-stable
           - Gemfile.rails-8.0-stable
+          - Gemfile.rails-8.1-stable
         ruby-version: ['3.0', '3.1', '3.2', '3.3']
         exclude:
           # Rails 7.2 doesn't work with Ruby 3.0 (requires Ruby 3.1+)
@@ -27,6 +28,11 @@ jobs:
             ruby-version: '3.0'
           - gemfile: Gemfile.rails-8.0-stable
             ruby-version: '3.1'
+          # Rails 8.1 requires Ruby 3.2+
+          - gemfile: Gemfile.rails-8.1-stable
+            ruby-version: '3.0'
+          - gemfile: Gemfile.rails-8.1-stable
+            ruby-version: '3.1'
     env:
       BUNDLE_GEMFILE: gemfiles/${{ matrix.gemfile }}
     steps:

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## v3.5.0 (2026-04-30)
+
+### Added
+
+- Add Rails 8.1 compatibility. Rails 8.1 changed `PredicateBuilder::PolymorphicArrayValue#initialize` from `(associated_table, values)` to `(reflection, values)`, dropping the `@associated_table` ivar. `type_to_ids_mapping` now reads `@reflection` when available and falls back to `@associated_table.send(:reflection)` for older Rails versions.
+
 ## v3.2.1 (2023-12-14)
 
 ### Fixed

gemfiles/Gemfile.rails-8.1-stable

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+source "https://rubygems.org"
+
+gemspec path: ".."
+
+gem "activerecord", github: "rails/rails", branch: "8-1-stable"

lib/polymorphic_integer_type/activerecord_5_0_0/polymorphic_array_value_extension.rb

@@ -10,7 +10,15 @@ module PolymorphicArrayValueExtension
     # end
 
     def type_to_ids_mapping
-      association = @associated_table.send(:reflection)
+      # Rails 8.1 changed `PredicateBuilder::PolymorphicArrayValue#initialize`
+      # from `(associated_table, values)` to `(reflection, values)`, dropping
+      # the `@associated_table` ivar. Read whichever ivar is available so this
+      # gem works across Rails 6.1–8.1.
+      association = if instance_variable_defined?(:@reflection) && @reflection
+        @reflection
+      else
+        @associated_table.send(:reflection)
+      end
 
       name = association.name
       default_hash = Hash.new { |hsh, key| hsh[key] = [] }

lib/polymorphic_integer_type/version.rb

@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 module PolymorphicIntegerType
-  VERSION = '3.4.0'
+  VERSION = '3.5.0'
 end