module Opal::Cache

def runtime_key
  @runtime_key ||= begin
    files = Opal.dependent_files
    digest [
      files.sort.map { |f| "#{f}:#{File.size(f)}:#{File.mtime(f).to_f}" },
      RUBY_VERSION,
      RUBY_PATCHLEVEL
    ].join('/')
  end
end