datastore/metadata.go
func Namespaces(ctx context.Context) ([]string, error) {
	// TODO(djd): Support range queries.
	q := NewQuery(namespaceKind).KeysOnly()
	keys, err := q.GetAll(ctx, nil)
	if err != nil {
		return nil, err
	}
	// The empty namespace key uses a numeric ID (==1), but luckily
	// the string ID defaults to "" for numeric IDs anyway.
	return keyNames(keys), nil
}
func Namespaces(ctx context.Context) ([]string, error) {
	// TODO(djd): Support range queries.
	q := NewQuery(namespaceKind).KeysOnly()
	keys, err := q.GetAll(ctx, nil)
	if err != nil {
		return nil, err
	}
	// The empty namespace key uses a numeric ID (==1), but luckily
	// the string ID defaults to "" for numeric IDs anyway.
	return keyNames(keys), nil
}
// Namespaces returns all the datastore namespaces.