Fix potenital stack level too deep with autosave or validation

When associations checked for autosave have a cycle, and
none of them is dirty, then changed_for_autosave? will be an
infinite loop. We now remember if we're in the check and
will short circuit the recursion.

1 files changed, 10 insertions, 0 deletions

diff --git a/activerecord/test/cases/autosave_association_test.rb b/activerecord/test/cases/autosave_association_test.rb
index 04d5a2869c..52765881d0 100644
--- a/activerecord/test/cases/autosave_association_test.rb
+++ b/activerecord/test/cases/autosave_association_test.rb
@@ -1030,6 +1030,16 @@ class TestAutosaveAssociationOnAHasOneAssociation < ActiveRecord::TestCase
     assert_equal 'The Vile Insanity', @pirate.reload.ship.name
   end
 
+  def test_changed_for_autosave_should_handle_cycles
+    @ship.pirate = @pirate
+    assert_queries(0) { @ship.save! }
+
+    @parrot = @pirate.parrots.create(name: "some_name")
+    @parrot.name="changed_name"
+    assert_queries(1) { @ship.save! }
+    assert_queries(0) { @ship.save! }
+  end
+
   def test_should_automatically_save_bang_the_associated_model
     @pirate.ship.name = 'The Vile Insanity'
     @pirate.save!