class GraphQL::StaticValidation::FragmentTypesExist

def validate(context)
  FRAGMENTS_ON_TYPES.each do |node_class|
    context.visitor[node_class] << -> (node, parent) { validate_type_exists(node, context) }
  end
end

def validate_type_exists(node, context)
  return unless node.type
  type = context.schema.types.fetch(node.type, nil)
  if type.nil?
    context.errors << message("No such type #{node.type}, so it can't be a fragment condition", node, context: context)
    GraphQL::Language::Visitor::SKIP
  end
end