I wrote:
> I propose changing things so that
> (B) We enforce that leafType agrees with the opclass opckeytype,
> ensuring the index tupdesc can be used for leaf tuples.
After looking at PostGIS I realized that a hard restriction of this
sort won't fly, because it'd make upgrades impossible for them.
They have some lossy SPGiST opclasses, in which leafType is returned
as different from the original input datatype. Since up to now
we've disallowed the STORAGE clause for user-defined SPGiST
opclasses, they are unable to declare these opclasses honestly in
existing releases, but it didn't matter. If we enforce that STORAGE
matches leafType then their existing opclass definitions won't work
in v14, but they can't fix them before upgrading either.
So I backed off the complaint about that to be just an amvalidate
warning, and pushed it.
This means the INCLUDE patch will still have to account for the
possibility that the index tupdesc is an inaccurate representation
of the actual leaf tuple contents, but we can treat that case less
efficiently without feeling bad about it. So we should be able to
do something similar for the leaf tupdesc as for the index-only-scan
output tupdesc, that is use the relcache's tupdesc if it's got the
right first column type, otherwise copy-and-modify that tupdesc.
regards, tom lane