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It's unsafe to do this at parse time because addition of generated columns to a table would not invalidate stored rules containing UPDATEs on the table ... but there might now be dependent generated columns that were not there when the rule was made. This also fixes an oversight that rewriteTargetView failed to update extraUpdatedCols when transforming an UPDATE on an updatable view. (Since the new calculation is downstream of that, rewriteTargetView doesn't actually need to do anything; but before, there was a demonstrable bug there.) In v13 and HEAD, this leads to easily-visible bugs because (since commit c6679e4fc) we won't recalculate generated columns that aren't listed in extraUpdatedCols. In v12 this bitmap is mostly just used for trigger-firing decisions, so you'd only notice a problem if a trigger cared whether a generated column had been updated. I'd complained about this back in May, but then forgot about it until bug #16671 from Michael Paul Killian revived the issue. Back-patch to v12 where this field was introduced. If existing stored rules contain any extraUpdatedCols values, they'll be ignored because the rewriter will overwrite them, so the bug will be fixed even for existing rules. (But note that if someone were to update to 13.1 or 12.5, store some rules with UPDATEs on tables having generated columns, and then downgrade to a prior minor version, they might observe issues similar to what this patch fixes. That seems unlikely enough to not be worth going to a lot of effort to fix.) Discussion: https://postgr.es/m/10206.1588964727@sss.pgh.pa.us Discussion: https://postgr.es/m/16671-2fa55851859fb166@postgresql.org
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