presto-main/src/main/java/io/prestosql/sql/planner/LocalExecutionPlanner.java/LocalExecutionPlanContext/createSubContext
class LocalExecutionPlanContext:        public LocalExecutionPlanContext createSubContext()
        {
            checkState(!indexSourceContext.isPresent(), "index build plan can not have sub-contexts");
            return new LocalExecutionPlanContext(taskContext, types, driverFactories, indexSourceContext, dynamicFiltersCollector, nextPipelineId);
        }