Hello, I am trying to write a rule that matches (among other things) the root of a RelNode tree.
Unfortunately, it seems that HepRuleCall.parents is only initialized and populated if the rule extends CommonRelSubExpr, which doesn’t really apply in my case. (see: https://github.com/apache/calcite/blob/master/core/src/main/java/org/apache/calcite/plan/hep/HepPlanner.java#L526) Is there a way to identify a node as being a root node during RelRule.match? Or more generally, is there a way to collect the parents of an arbitrary RelNode? Thanks.
