Re: jsonb_set for nested new item?

Please note that only the first case is not supported in jsonb_set(),
which was a very important addition to PostgreSQL 9.5.
If this case would be added, a simple call with the same path
'{boo,baz}' and '"newvalue"' would always be sufficient.

Goal: first path level (boo) does not exist, create subelement, but if
there is a second path level (baz) requested, create a subdict instead
of just the given value (newvalue).

-- Creating a new 2nd-level dict with a missing 1st-level key/dict just
in the path does not work
SELECT jsonb_set('{"foo": "bar"}'::jsonb, '{boo,baz}', '"newvalue"');

jsonb_set
----------------
{"foo": "bar"}

-- Only with the complete subdict as value the new 1st-level key 'boo'
is added(so the caller has to know if the key is missing)
SELECT jsonb_set('{"foo": "bar"}'::jsonb, '{boo}', '{"baz": "newvalue"}');

jsonb_set
--------------------------------------------
{"boo": {"baz": "newvalue"}, "foo": "bar"}

-- All other cases work fine (when the 1st-level key 'boo' already exists)
SELECT jsonb_set('{"foo": "bar", "boo": {"otherkey":
"othervalue"}}'::jsonb, '{boo,baz}', '"newvalue"');

jsonb_set
----------------------------------------------------------------------
{"boo": {"baz": "newvalue", "otherkey": "othervalue"}, "foo": "bar"}

SELECT jsonb_set('{"foo": "bar", "boo": {"baz": "oldvalue", "otherkey":
"othervalue"}}'::jsonb, '{boo,baz}', '"newvalue"');

jsonb_set
----------------------------------------------------------------------
{"boo": {"baz": "newvalue", "otherkey": "othervalue"}, "foo": "bar"}