we use PlannerGlobal
{
   Oid            basenodeSessionVarid;
   Bitmapset *checkSelectPermVarids;
}
to solve the self-assigned corner case SELECT privilege.
(let v1.a =v1.a; in this case, we need have SELECT priv for v1.a
but let v1.a = 1, we don't need SELECT priv for v1.a).

i found out these two field value(information) most case is the same
as PlannerGlobal.sessionVariables;
I came up with another solution, introduce a bool (Query.is_Variable_assigned),
and get rid of PlannerGlobal.basenodeSessionVarid,
PlannerGlobal.checkSelectPermVarids.
not sure it make sense to you, refer
v1-0002-refactoring-LET-statement-self-assign-privileg.no-cfbot

It is true, so bitmapset checkSelectPermVarids contains almost all the same data like sessionVariables.

But checkSelectPermVarids allows fast checking if a variable is used already, and sessionVariables list ensures necessary order.

My implementation needs more memory (one bitmapset), but I think it is very simple and less error prone (doesn't depend on iteration order).

In this case and this moment I prefer my bitmapset based solution. It can be optimized maybe later - I thought about a dedicated item in sessionVariables for the basenode parameter.

This should be a clear winner for value passed types, but for varlena types (for long varlena types), it can force passing content of some session variable twice.

Regards

Pavel