JSONAPI::Rails.is_collection? confused by 'size' attribute

[dmolesUC]

Expected Behavior

• Single model instance with size attribute is recognized as not a collection

Actual Behavior

• Single model instance with size attribute mistakenly believed to be a collection
  due to this heuristic in JSONAPI::Rails.is_collection?
• Serialization fails with NoMethodError when attempting to call any? here in JSONAPI::Rails.add_renderer!

Steps to Reproduce the Problem

1. Create a model with an attribute size of type string.
2. Try to serialize it, e.g. with render jsonapi: @the_instance in a controller method.

Possible solutions

Consider using resource.is_a?(Enumerable) instead of respond_to?(:any?). This seems to be what jsonapi-serializer does now after first realizing size was a problem and trying each instead, then deciding that was more trouble than it was worth.

Specifications

• Version: 1.7.0
• Ruby version: 3.0.3
• jsonapi-serializer version: 2.2.0

[stas]

Hey,
thanks for the issue @dmolesUC

You're right, this needs to be updated, as we already did in jsonapi-serializer/jsonapi-serializer#75
(probably as easy as to just call the jsonapi-serializer implementation 🤔 )

Happy to merge it if you have time to prepare a PR.

[dmolesUC]

@stas Will do. I had a look at calling the json-serializer implementation, but since it's inside a class_methods block it was nontrivial, so I'm just going to do it the easy way for now.