Support nested attribute names for validation error messages

Hello,

I'm trying to override a nested attribute's name that gets show in the validation message, but it doesn't seem possible for nested params

I want to override registration[total_capacity] attribute name:

my params:

params :sessions_params do
  optional :registration_allowed, type: Boolean, desc: 'registration allowed for session?'
  optional :registration, type: Hash, desc: 'session registration settings' do
    requires :total_capacity, type: Integer, desc: 'session registration total capacity', message: :name_required
    requires :waiting_list_enabled, type: Boolean, desc: 'is session registration waiting list enabled?'
  end
end

en.yml

en:
  grape:
    errors:
      format: ! '%{attributes} %{message}'
      messages:
        name_required: 'must be present'
      attributes:
        registration:
          total_capacity: 'Total capacity'

expected error message if total capacity is not sent:

"Total capacity must be present"

actual error message:

"registration[total_capacity] must be present"

is this not possible or is there a problem with my code?

using grape 0.16.2, ruby 2.3.3, rails 4.2

thanks

Reproduce the nested params definition and locale configuration shown in the issue, then trace how the validation error formats the attribute name and looks up nested translations. Done means a missing registration[total_capacity] value produces “Total capacity must be present” while preserving the existing message behavior for other attributes.