code: func OpenInstanceFile(ctx context.Context, path string, opts OpenInstanceOpts) (pkg.Instance, error) {
  	file, err := os.Open(path)
  	if err != nil {
  		return nil, err
  	}
  	inst, err := OpenInstance(ctx, fileSource{file}, opts)
  	if err != nil {
  		file.Close()
  		return nil, err
  	}
  	return inst, nil
  }
docs: // OpenInstanceFile opens a package instance by reading it from a file on disk.
  //
  // The caller is responsible for closing the instance when done with it. This
  // will close the underlying file too.