Serializing an empty array should maintain the root key

[NullVoxPopuli]

Relates to: #1153

[bf4]

serializer.name.remove('Serializer') 🤷

[bf4]

Let's hold off on merging this till we clarify which arguments, serializer vs. each_serializer we should be passing to manually specify the serializer for a non-compliant resource (i.e. would fail the Lint).

See my comment in the OP's issue: #1153 (comment)

[NullVoxPopuli]

@bf4 for an empty object (Array, or Hash) - would it matter which serializer vs each_serializer we're using? there isn't really anything to serialize aside from the root key.

it would either be

{
  root: {}
}

or

{
  roots: []
}

[bf4]

So, AMS doesn't handle primitives, and when they find their way it, they are passed through as is. ( Specifically, when you're not rendering an object with a defined serializer.)

How options are parsed

1. serializable_resource = ActiveModel::SerializableResource.new(resource, options)
2. if serializable_resource.serializer?
   • Where serializer? is use_adapter? && !!(serializer)
     • Where use_adapter?: 'True when no explicit adapter given, or explicit appear is truthy (non-nil); False when explicit adapter is falsy (nil or false)'
     • Where serializer:
       1. from explicit :serializer option, else
       2. implicitly from resource ActiveModel::Serializer.serializer_for(resource)
   • The :serializer option is removed from the serializer_opts hash
   • If the :each_serializer option is present, it is removed from the serializer_opts hash and set as the :serializer option
3. The serializer and adapter are created as
   1. serializer_instance = serializer.new(resource, serializer_opts)
   2. adapter_instance = ActiveModel::Serializer::Adapter.create(serializer_instance, adapter_opts)
4. If the serializer_instance was a ArraySerializer and the :serializer serializer_opts is present, then that serializer is passed into each resource:

   active_model_serializers/lib/active_model/serializer/array_serializer.rb

   Lines 14 to 16 in a54d237

   	serializer_class = options.fetch(:serializer) do
   	ActiveModel::Serializer.serializer_for(resource)
   	end

The upshot of which is that

• for a collection, the collection serializer is the :serializer option and :each_serializer is used as the serializer for each resource in the collection
• for a single resource, the :serializer option is the resource serializer

Aside, the the collection serializer (ArraySerializer) cannot identify a serializer for a resource in its collection, it raises NoSerializerError which is rescued in build_association which sets the association value directly: reflection_options[:virtual_value] = association_value.try(:as_json) || association_value

[NullVoxPopuli]

that is a fantastic explanation!

thanks -- I'll close this PR.