Resolve model attribute types on schema load

When running tests in parallel, a new database is created for each test
worker (via `ActiveRecord::TestDatabases.create_and_load_schema`).  Each
of these databases use different OID numbers for custom defined types
such as enums.  If model schemas are loaded before forking -- as done in
`railties/lib/rails/testing/maintain_test_schema.rb` when `eager_load`
is true -- Rails will hold on to the OID numbers from the original
database.  Thus each test worker does not recognize the OID numbers when
resolving model attribute types.

This commit sidesteps the problem by resolving model attribute types on
schema load.  This does not address the conflicting OID numbers, but
each test worker will inherit properly resolved attribute types.

Fixes rails#52607.

Author: jonathanhefner

activerecord/lib/active_record/model_schema.rb

@@ -595,6 +595,8 @@ def load_schema!
           columns_hash = columns_hash.except(*ignored_columns) unless ignored_columns.empty?
           @columns_hash = columns_hash.freeze
 
+          _default_attributes # Precompute to cache DB-dependent attribute types
+
           super
         end
 

railties/test/application/test_test.rb

@@ -342,6 +342,46 @@ class User < ApplicationRecord
       assert_unsuccessful_run "models/user_test.rb", "Unknown enum attribute 'type' for User"
     end
 
+    test "database-dependent attribute types are resolved when parallel tests are run in eager load context" do
+      use_postgresql
+      rails "db:drop", "db:create"
+
+      output = rails("generate", "model", "user")
+      version = output.match(/(\d+)_create_users\.rb/)[1]
+
+      app_file "db/schema.rb", <<~RUBY
+        ActiveRecord::Schema.define(version: #{version}) do
+          create_enum "user_favorite_color", ["red", "green", "blue"]
+
+          create_table :users do |t|
+            t.enum :favorite_color, enum_type: :user_favorite_color
+          end
+        end
+      RUBY
+
+      app_file "config/initializers/enable_eager_load.rb", <<~RUBY
+        Rails.application.config.eager_load = true
+      RUBY
+
+      app_file "test/models/user_test.rb", <<~RUBY
+        require "test_helper"
+        class UserTest < ActiveSupport::TestCase
+          ENV.delete("PARALLEL_WORKERS")
+          parallelize threshold: 1, workers: 2
+
+          2.times do |i|
+            test "favorite_color uses database type (worker \#{i})" do
+              assert_instance_of ActiveRecord::ConnectionAdapters::PostgreSQL::OID::Enum, User.type_for_attribute("favorite_color")
+            end
+          end
+        end
+      RUBY
+
+      assert_successful_test_run "models/user_test.rb"
+    ensure
+      rails "db:drop" rescue nil
+    end
+
     private
       def assert_unsuccessful_run(name, message)
         result = run_test_file(name)