Ensure cyclic associations w/ autosave don't cause duplicate errors

This code is so fucked. Things that cause this bug not to replicate:

- Defining the validation before the association (we end up calling
  `uniq!` on the errors in the autosave validation)
- Adding `accepts_nested_attributes_for` (I have no clue why. The only
  thing it does that should affect this is adds `autosave: true` to the
  inverse reflection, and doing that manually doesn't fix this).

This solution is a hack, and I'm almost certain there's a better way to
go about it, but this shouldn't cause a huge hit on validation times,
and is the simplest way to get it done.

Fixes #20874.

1 files changed, 8 insertions, 0 deletions

diff --git a/activerecord/test/cases/autosave_association_test.rb b/activerecord/test/cases/autosave_association_test.rb
index 676b29ed7c..6b69b96e21 100644
--- a/activerecord/test/cases/autosave_association_test.rb
+++ b/activerecord/test/cases/autosave_association_test.rb
@@ -67,6 +67,14 @@ class TestAutosaveAssociationsInGeneral < ActiveRecord::TestCase
     assert_no_difference_when_adding_callbacks_twice_for Pirate, :parrots
   end
 
+  def test_cyclic_autosaves_do_not_add_multiple_validations
+    ship = ShipWithoutNestedAttributes.new
+    ship.prisoners.build
+
+    assert_not ship.valid?
+    assert_equal 1, ship.errors[:name].length
+  end
+
   private
 
   def assert_no_difference_when_adding_callbacks_twice_for(model, association_name)