Why no jsonb_exists_path()?

Dmitry, Alexander:

I'm noticing a feature gap for JSONB operators; we have no way to do this:

jsonb_col ? ARRAY['key1','key2','key3']

... that is, there is no way for us to check for key existence in an
indexable fashion.  Given that @> already can check the whole path
including the value, is there some challenge to stopping just short of
the value I'm not seeing?  Or is this just a "didn't get to it yet" issue?

I'm trying to estimate the difficulty of creating this operator in an
extension (obviously we're not doing it for 9.5), and maybe for 9.6.

-- 
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com