Should we add xid_current() or a int8->xid cast?

Hi,

we have txid_current(), which returns an int8. But there's no convenient
way to convert that to type 'xid'. Which is fairly inconvenient, given
that we expose xids in various places.

My current need for this was just a regression test to make sure that
system columns (xmin/xmax in particular) don't get broken again for ON
CONFLICT. But I've needed this before in other scenarios - e.g. age(xid)
can be useful to figure out how old a transaction is, but age() doesn't
work with txid_current()'s return value.

Seems easiest to just add xid_current(), or add a cast from int8 to xid
(probably explicit?) that handles the wraparound logic correctly?

Greetings,

Andres Freund