proposal: parentid and naturalid for plpgsql nodes

Hi

I propose two enhancing of PLpgSQL_stmt structure

1. parentid

This is the id (stmtid) of the near outer statement. Why do I need it?
Inside the plpgsql_check profiler I need to handle exceptions. Exceptions
are not supported by the plpgsql debug API, so I need to hold a stack of
executed statements. When any statements start, I need to check this stack
and sometimes (after a handled exception) I need to reduce this stack until
I find a statement that has the same parenid as the parentid of the current
statement.

Currently I hold an array with parentid outside, but it is not practical
and increases the complexity of plpgsql_check.

2. naturalid

stmtid is assigned by the plpgsql parser. It is unique, but has a little
bit of a messy order, and when something like a statement id is displayed
in some reports, then it is confusing for users. I propose extra id (that
is unique too), but with order based on searching statements tree

example

BEGIN --> stmtid = 3
PERFORM --> stmtid = 1
PERFORM --> stmtid = 2

BEGIN --> naturalid = 1
PERFORM --> naturalid = 2
PERFORM --> naturalid = 3

Maybe the ordering of stmtid can be changed, and then naturalid can be
useless.

Proposed change can reduce complexity of plpgsql_check, but I believe it
can help with other exceptions that use pl debug api.

Comments, notes?

Regards

Pavel