cmp/options.go
func normalizeOption(src Option) Option {
	switch opts := flattenOptions(nil, Options{src}); len(opts) {
	case 0:
		return nil
	case 1:
		return opts[0]
	default:
		return opts
	}
}
func normalizeOption(src Option) Option {
	switch opts := flattenOptions(nil, Options{src}); len(opts) {
	case 0:
		return nil
	case 1:
		return opts[0]
	default:
		return opts
	}
}
// normalizeOption normalizes the input options such that all Options groups
// are flattened and groups with a single element are reduced to that element.
// Only coreOptions and Options containing coreOptions are allowed.