I wonder if the logic for setting BTScanInsertData.anynullkeys inside _bt_mkscankey() is the place to put your test for rel->rd_index->indnullsnotdistinct -- not inside _bt_doinsert(). That would probably necessitate renaming anynullkeys, but that's okay. This feels more natural to me because a NULL key column in a NULLS NOT DISTINCT unique constraint is very similar to a NULL non-key column in an INCLUDE index, as far as our requirements go -- and so both cases should probably be dealt with at the same point.
