fix: more flexible polymorphic types lookup

lib/jsonapi/relationship.rb

@@ -90,14 +90,37 @@ def self.polymorphic_types(name)
       @poly_hash ||= {}.tap do |hash|
         ObjectSpace.each_object do |klass|
           next unless Module === klass
-          if ActiveRecord::Base > klass
+          is_active_record_inspectable = ActiveRecord::Base > klass
+          is_active_record_inspectable &&= klass.respond_to?(:reflect_on_all_associations, true)
+          is_active_record_inspectable &&= format_polymorphic_klass_type(klass).present?
+          if is_active_record_inspectable
             klass.reflect_on_all_associations(:has_many).select { |r| r.options[:as] }.each do |reflection|
-              (hash[reflection.options[:as]] ||= []) << klass.name.underscore
+              (hash[reflection.options[:as]] ||= []) << format_polymorphic_klass_type(klass).underscore
             end
           end
         end
       end
-      @poly_hash[name.to_sym]
+      @poly_hash.fetch(name.to_sym) do
+        klass = name.classify.safe_constantize
+        if klass.nil?
+          warn "[POLYMORPHIC TYPE NOT FOUND] No polymorphic types found for #{name}"
+        else
+          polymorphic_type = format_polymorphic_klass_type(klass)
+          warn "[POLYMORPHIC TYPE] Found polymorphic types through reflection for #{name}: #{polymorphic_type}"
+          @poly_hash[name.to_sym] = [polymorphic_type]
+        end
+      end
+    end
+
+    def format_polymorphic_klass_type(klass)
+      klass.name ||
+        begin
+          klass.model_name.name
+        rescue ArgumentError => ex
+          # klass.base_class may be nil
+          warn "[POLYMORPHIC TYPE] #{__callee__} #{klass} #{ex.inspect}"
+          nil
+        end
     end
 
     def resource_types
@@ -203,7 +226,7 @@ def polymorphic_type
       def setup_implicit_relationships_for_polymorphic_types(exclude_linkage_data: true)
         types = self.class.polymorphic_types(_relation_name)
         unless types.present?
-          warn "No polymorphic types found for #{parent_resource.name} #{_relation_name}"
+          warn "[POLYMORPHIC TYPE] No polymorphic types found for #{parent_resource.name} #{_relation_name}"
           return
         end