Re: BUG #16671: "generated always as" is ignored when updating table through view

I wrote:
> PG Bug reporting form <noreply(at)postgresql(dot)org> writes:
>> [ updating via a view fails to recalculate GENERATED columns ]

> Yeah, that's surely a bug. In fact, it's a regression, because
> the test case works as-expected in v12. Not sure where we broke it.

git bisect blames

c6679e4fca21d253ced84c51ac1a31c1b2aec72f is the first bad commit
commit c6679e4fca21d253ced84c51ac1a31c1b2aec72f
Author: Peter Eisentraut <peter(at)eisentraut(dot)org>
Date: Mon Feb 17 15:19:58 2020 +0100

Optimize update of tables with generated columns

When updating a table row with generated columns, only recompute those
generated columns whose base columns have changed in this update and
keep the rest unchanged. This can result in a significant performance
benefit. The required information was already kept in
RangeTblEntry.extraUpdatedCols; we just have to make use of it.

Reviewed-by: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
Discussion: https://www.postgresql.org/message-id/flat/b05e781a-fa16-6b52-6738-761181204567(at)2ndquadrant(dot)com

regards, tom lane