Re: Errors when update a view with conditional-INSTEAD rules

Tracing it through, this seems to be a result of
cab5dc5daf2f6f5da0ce79deb399633b4bb443b5 which added support for
updatable views with a mix of updatable and non-updatable columns.
That included a change to rewriteTargetListIU() to prevent it from
adding dummy targetlist entries for unassigned-to attributes for
auto-updatable views, in case they are no longer simple references to
the underlying relation. Instead, that is left to expand_targetlist(),
as for a normal table. However, in this case (an UPDATE on a view with
a conditional rule), the target relation of the original query isn't
rewritten (we leave it to the executor to report the error), and so
expand_targetlist() ends up adding a new targetlist entry that
references the target relation, which is still the original view. But
when the planner bulds the simple_rel_array, it only adds entries for
relations referenced in the query's jointree, which only includes the
base table by this point, not the view. Thus the new targetlist entry
added by expand_targetlist() refers to a NULL slot in the
simple_rel_array, and it blows up.

Given that this is a query that's going to fail anyway, I'm inclined
to think that the right thing to do is to throw the error sooner, in
rewriteQuery(), rather than attempting to plan a query that cannot be
executed.