Re: Use an enum for RELKIND_*?

Out of curiosity I built with -Wswitch-enum to see if it would be
possible to just enable it. It looks like the main culprits are the
node types and if those were switched to #defines it might be feasible
to do so though it would still be a lot of hassle to add case labels
all over the place.

But I had a second look to see if the output pointed out any actual
bugs. I found one though it's pretty minor:

lockfuncs.c:234:3: warning: enumeration value
‘LOCKTAG_SPECULATIVE_TOKEN’ not handled in switch [-Wswitch-enum]
switch ((LockTagType) instance->locktag.locktag_type)
^~~~~~

It just causes speculative locks to be printed wrong in the
pg_lock_status view. And speculative locks are only held transiently
so unless you're do a bulk load using ON CONFLICT (and also cared
about pg_lock_status, perhaps in some monitoring tool) you wouldn't
even notice this:

postgres***=# select * from pg_lock_status() where locktype =
'speculative token';
┌───────────────────┬──────────┬──────────┬──────┬───────┬────────────┬───────────────┬─────────┬───────┬──────────┬────────────────────┬───────┬───────────────┬─────────┬──────────┐
│ locktype │ database │ relation │ page │ tuple │ virtualxid
│ transactionid │ classid │ objid │ objsubid │ virtualtransaction │
pid │ mode │ granted │ fastpath │
├───────────────────┼──────────┼──────────┼──────┼───────┼────────────┼───────────────┼─────────┼───────┼──────────┼────────────────────┼───────┼───────────────┼─────────┼──────────┤
│ speculative token │ 634 │ │ │ │
│ │ 1 │ 0 │ 0 │ 4/32 │
18652 │ ExclusiveLock │ t │ f │
└───────────────────┴──────────┴──────────┴──────┴───────┴────────────┴───────────────┴─────────┴───────┴──────────┴────────────────────┴───────┴───────────────┴─────────┴──────────┘

The speculative lock is actually on a transaction ID and "speculative
lock token" so the "database", "objid", and "objsubid" are bogus here.