presto-main/src/main/java/io/prestosql/sql/planner/optimizations/IndexJoinOptimizer.java/IndexSourceRewriter/visitIndexSource
class IndexSourceRewriter:        @Override
        public PlanNode visitIndexSource(IndexSourceNode node, RewriteContext<Context> context)
        {
            throw new IllegalStateException("Should not be trying to generate an Index on something that has already been determined to use an Index");
        }