read_only attributes not being added to metadata when not using default serializer

[marktran]

I'm seeing an issue where read_only attributes aren't in the read_only metadata if e.g. I have an EventsController that uses a serializer named BasicEventSerializer (or anything that's not the default EventSerializer).

Looks like it's because RenderJsonMeta::MetadataReadOnly only looks for the default serializer:

daylight/rails/extensions/render_json_meta.rb

Line 68 in 010ed7b

serializer = model.try(:active_model_serializer)

class EventsController < APIController
  handles :show

  def show
    render(
      json: self.record = model.find(params[primary_key]),
      serializer: BasicEventSerializer
    )
  end
end

class BasicEventSerializer < ActiveModel::Serializer
  embed :ids

  attributes :id
  read_only :created_at
end

{
  "event": {
    "id": 24522,
    "created_at": "2014-11-24T16:02:08.383Z"
  },
  "meta": {
    "event": {
      "read_only": [],
      "nested_resources": []
    }
  }
}

[marktran]

Looks like it might be better to grab the serializer being use from the options hash with the serializer key:

daylight/rails/extensions/render_json_meta.rb

Line 7 in 010ed7b

def _render_option_json(resource, options)