class BiDiGenerate::Schema

def union_ref?(name)

scalar sibling. A record arm would raise on one, so it is not carried.
True when a ref (following aliases) is a union — the only arm whose from_json tolerates a 
def union_ref?(name)
  type = @types[name]
  return false unless type
  return union_ref?(type['type']['ref']) if type['kind'] == 'alias' && type['type'].key?('ref')
  type['kind'] == 'union'
end