Re: BUG #14515: tsquery with only a negative term doesn't match empty tsvector

I wrote:
> pgsql(at)tomd(dot)cc writes:
>> Basically while `select 'somethingelse'::tsvector @@ '!foo'::tsquery`
>> returns true, `select ''::tsvector @@ '!foo'::tsquery` returns false, which
>> was surprising to me.

> Not sure about this. A plausible reading of '!foo' is "there is a lexeme
> that is not foo". But even if that was Oleg & Teodor's intention,
> I would not want to swear that the tsquery stuff is totally consistent
> about it ...

After further poking at it, I found that a GIN index search will return
empty tsvectors, matching your expectation! So indeed we are being
inconsistent, which means that there is certainly a bug here no matter
which interpretation you favor.

Also, while a GIST index search doesn't return empty entries, it turns
out that that's only because it always applies recheck, so that the
fast-path exit in ts_match_vq() is what's rejecting the empty value
in that case too.

Otherwise, it seems pretty clear to me that the interpretation (most of?)
the code is using is that "!foo" means "foo does not appear in the value".

A look around at other callers of TS_execute indicate that none of the
rest of them are trying to "optimize" empty value, only empty query.

In short, I now agree both that this is a bug, and that you've correctly
identified the cause. Will patch.

regards, tom lane