presto-main/src/main/java/io/prestosql/sql/planner/planprinter/PlanPrinter.java/Visitor/visitIndexSource
class Visitor:        @Override
        public Void visitIndexSource(IndexSourceNode node, Void context)
        {
            NodeRepresentation nodeOutput = addNode(node,
                    "IndexSource",
                    format("[%s, lookup = %s]", node.getIndexHandle(), node.getLookupSymbols()));

            for (Map.Entry<Symbol, ColumnHandle> entry : node.getAssignments().entrySet()) {
                if (node.getOutputSymbols().contains(entry.getKey())) {
                    nodeOutput.appendDetailsLine("%s := %s", entry.getKey(), entry.getValue());
                }
            }
            return null;
        }