You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: user.go
    path of file: ./repos/sealer/vendor/github.com/containers/buildah/pkg/chrootuser
    
    the code of the file until where you have to start completion: package chrootuser

import (
	"errors"
	"fmt"
	"os/user"
	"strconv"
	"strings"
)

v
    
func GetAdditionalGroupsForUser(rootdir string, userid uint64) ([]uint32, error) {
	gids, err := lookupAdditionalGroupsForUIDInContainer(rootdir, userid)
	if err != nil {
		return nil, fmt.Errorf("error looking up supplemental groups for uid %d: %w", userid, err)
	}
	return gids, nil
}