Re: [PATCH] btree_gist: add cross-type integer operator support for GiST

Hey Maxime!

Thank you for reviewing my changes so far and for proposing the changes in your
patch! And thank you for the kind words!

1)

I think we still need to check `InvalidOid` because execIndexing.c:~800
initializes scan keys ('ScanKeyEntryInitialize') with `InvalidOid` as the
subtype. Running the 'not_equal', 'partitions' and 'without_overlaps' tests
confirms that 'InvalidOid' must be handled. I can add the check again in the
switch. (attaching patch)

2) and 3)

I completely agree, your patch makes it much cleaner.
I applied your patch (with the 'InvalidOid' fix) on top of mine and ran all the
tests and benchmarks that I prepared previously. These are the results before
the entire patchset and after:

duration=15s/run, reps=10, 1 client, interleaved, lower is better
------------------------------------------------------------------------
before consistent min/med/mean = 51.246   51.361   51.378 ms
after consistent min/med/mean    = 51.849   51.958   51.967 ms
------------------------------------------------------------------------
before distance min/med/mean = 76.441    76.561   76.567 ms
after distance min/med/mean    = 76.568   76.678   76.681 ms
------------------------------------------------------------------------

I added one more commit that adds a small description of this fix in the docs.

The current patchset has been rebased on top of ef01ca6dbca54e9bf3abea01c357b346847ebcf3

Best regards!