prow/repoowners/repoowners.go
func (a RepoAliases) ExpandAliases(logins sets.String) sets.String {
	if a == nil {
		return logins
	}
	// Make logins a copy of the original set to avoid modifying the original.
	logins = logins.Union(nil)
	for _, login := range logins.List() {
		if expanded := a.ExpandAlias(login); len(expanded) > 0 {
			logins.Delete(login)
			logins = logins.Union(expanded)
		}
	}
	return logins
}
func (a RepoAliases) ExpandAliases(logins sets.String) sets.String {
	if a == nil {
		return logins
	}
	// Make logins a copy of the original set to avoid modifying the original.
	logins = logins.Union(nil)
	for _, login := range logins.List() {
		if expanded := a.ExpandAlias(login); len(expanded) > 0 {
			logins.Delete(login)
			logins = logins.Union(expanded)
		}
	}
	return logins
}
// ExpandAliases returns members of multiple aliases, duplicates are pruned