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, 7 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/autosave_association.rb b/activerecord/lib/active_record/autosave_association.rb
index 0792d19c3e..5f38bd51f6 100644
--- a/activerecord/lib/active_record/autosave_association.rb
+++ b/activerecord/lib/active_record/autosave_association.rb
@@ -222,6 +222,7 @@ module ActiveRecord
               true
             end
             validate validation_method
+            after_validation :_ensure_no_duplicate_errors
           end
         end
     end
@@ -456,5 +457,11 @@ module ActiveRecord
           end
         end
       end
+
+      def _ensure_no_duplicate_errors
+        errors.messages.each_key do |attribute|
+          errors[attribute].uniq!
+        end
+      end
   end
 end