Use __id__ to dedup records for transactional callbacks

While not a particularly good idea, it's possible to use `object_id` as
an attribute name, typically by defining a polymorphic association named
`object`. Since 718a32ca74, transactional
callbacks deduplicate records by their `object_id`, but this causes
incorrect behaviour when the record has an attribute with that name.

Using `__id__` instead makes a naming collision much less likely.

activerecord/lib/active_record/connection_adapters/abstract/transaction.rb

@@ -101,7 +101,7 @@ module ActiveRecord
 
       def rollback_records
         return unless records
-        ite = records.uniq(&:object_id)
+        ite = records.uniq(&:__id__)
         already_run_callbacks = {}
         while record = ite.shift
           trigger_callbacks = record.trigger_transactional_callbacks?
@@ -121,7 +121,7 @@ module ActiveRecord
 
       def commit_records
         return unless records
-        ite = records.uniq(&:object_id)
+        ite = records.uniq(&:__id__)
         already_run_callbacks = {}
         while record = ite.shift
           if @run_commit_callbacks

activerecord/test/cases/transaction_callbacks_test.rb

@@ -501,6 +501,43 @@ class TransactionCallbacksTest < ActiveRecord::TestCase
     assert flag
   end
 
+  def test_saving_two_records_that_override_object_id_should_run_after_commit_callbacks_for_both
+    klass = Class.new(TopicWithCallbacks) do
+      define_method(:object_id) { 42 }
+    end
+
+    records = [klass.new, klass.new]
+
+    klass.transaction do
+      records.each do |record|
+        record.after_commit_block { |r| r.history << :after_commit }
+        record.save!
+      end
+    end
+
+    assert_equal [:after_commit], records.first.history
+    assert_equal [:after_commit], records.second.history
+  end
+
+  def test_saving_two_records_that_override_object_id_should_run_after_rollback_callbacks_for_both
+    klass = Class.new(TopicWithCallbacks) do
+      define_method(:object_id) { 42 }
+    end
+
+    records = [klass.new, klass.new]
+
+    klass.transaction do
+      records.each do |record|
+        record.after_rollback_block { |r| r.history << :after_rollback }
+        record.save!
+      end
+      raise ActiveRecord::Rollback
+    end
+
+    assert_equal [:after_rollback], records.first.history
+    assert_equal [:after_rollback], records.second.history
+  end
+
   private
     def add_transaction_execution_blocks(record)
       record.after_commit_block(:create) { |r| r.history << :commit_on_create }