Restore the frozen state on rollback. Fixes #6417.

This is a 3-2-stable backport for #6420 which was merged into master.

Currently, when saving a frozen record, an exception would be thrown
which causes a rollback. However, there is a bug in active record that
"defrost" the record as a side effect:

    >> t = Topic.new
    => #<Topic id: nil, ...>
    >> t.freeze
    => #<Topic id: nil, ...>
    >> t.save
    RuntimeError: can't modify a frozen Hash
    >> t.frozen?
    => false
    >> t.save
    => true

This patch fixes the bug by explictly restoring the frozen state on the
attributes Hash after every rollback.

1 files changed, 10 insertions, 0 deletions

diff --git a/activerecord/test/cases/transactions_test.rb b/activerecord/test/cases/transactions_test.rb
index 203dd054f1..a9ccd00fac 100644
--- a/activerecord/test/cases/transactions_test.rb
+++ b/activerecord/test/cases/transactions_test.rb
@@ -362,6 +362,16 @@ class TransactionTest < ActiveRecord::TestCase
     end
   end
 
+  def test_rollback_when_saving_a_frozen_record
+    topic = Topic.new(:title => 'test')
+    topic.freeze
+    e = assert_raise(RuntimeError) { topic.save }
+    assert_equal "can't modify frozen Hash", e.message
+    assert !topic.persisted?, 'not persisted'
+    assert_nil topic.id
+    assert topic.frozen?, 'not frozen'
+  end
+
   def test_restore_active_record_state_for_all_records_in_a_transaction
     topic_1 = Topic.new(:title => 'test_1')
     topic_2 = Topic.new(:title => 'test_2')