presto-parser/src/main/java/io/prestosql/sql/SqlFormatter.java/SqlFormatter/visitShowRoles
class SqlFormatter:        @Override
        protected Void visitShowRoles(ShowRoles node, Integer context)
        {
            builder.append("SHOW ");
            if (node.isCurrent()) {
                builder.append("CURRENT ");
            }
            builder.append("ROLES");

            if (node.getCatalog().isPresent()) {
                builder.append(" FROM ")
                        .append(node.getCatalog().get());
            }

            return null;
        }