presto-parser/src/main/java/io/prestosql/sql/parser/AstBuilder.java/AstBuilder/visitShowRoles
class AstBuilder:    @Override
    public Node visitShowRoles(SqlBaseParser.ShowRolesContext context)
    {
        return new ShowRoles(
                getLocation(context),
                getIdentifierIfPresent(context.identifier()),
                context.CURRENT() != null);
    }