AC::Parameters no longer being a Hash has broken nested attributes

[twalpole]

Since AC::Parameters is no longer derived from Hash, and each nested "hash" inside Parameters is also an instance of AC::Parameters, https://github.com/rails/rails/blob/master/activerecord/lib/active_record/nested_attributes.rb#L446 raises an error since it only allows Hash or Array, https://github.com/rails/rails/blob/master/activerecord/lib/active_record/nested_attributes.rb#L446 calls #map which isnt supported on AC::Parameters, and https://github.com/rails/rails/blob/master/activerecord/lib/active_record/nested_attributes.rb#L471 calls #with_indifferent_access which isn't supported on AC::Parameters.

I'm willing to submit a fix if wanted, just wondered whether the preferred solution would be to have AC::Parameters call #to_h on accessed elements so they return filtered hashes rather than AC::Parameters instances, or update the nested_attributes code to support AC::Parameters

[jonatack]

Yes. Experiencing this issue as well.

[jonatack]

Needs test coverage in addition to a fix. The current test suite is passing.

[robin850]

/cc @sikachu

[sgrif]

I've pushed a fix for this problem, and added an isolated test case for it. However I'm going to leave this issue open. This should have never passed CI and I consider our lack of integration test coverage a bug. We need to make sure that we have the tests required to prevent this from happening in the future.

[jonatack]

Thank you, Sean, for looking into this! However, with has_many associations the issue still remains.

Hash or Array expected, got ActionController::Parameters 

[twalpole]

@sgrif Your fix only fixed this issue for singular associations - PR #20932 continues that for collection associations

[jonatack]

@twalpole Good call. Tried out your PR #20932 and it appears to fix the remaining issue.

[sgrif]

I've opened a separate issue for the testing problem.

[sgrif]

I forgot the link (#20945)