jsonb_to_tsvector should be immutable

Wanted to pull this out of my general report, because nobody seems to
have seen it:

P3: apparently jsonb_to_tsvector with lang parameter isn't immutable?
This means that it can't be used for indexing:

libdata=# create index bookdata_fts on bookdata using gin ((
to_tsvector('english',bookdata)));
ERROR: functions in index expression must be marked IMMUTABLE

... and indeed it's not:

select proname, prosrc, proargtypes, provolatile from pg_proc where
proname = 'to_tsvector';
proname | prosrc | proargtypes | provolatile
-------------+------------------------+-------------+-------------
to_tsvector | jsonb_to_tsvector | 3802 | s
to_tsvector | to_tsvector_byid | 3734 25 | i
to_tsvector | to_tsvector | 25 | s
to_tsvector | json_to_tsvector | 114 | s
to_tsvector | jsonb_to_tsvector_byid | 3734 3802 | s
to_tsvector | json_to_tsvector_byid | 3734 114 | s

Both of the _byid functions should be marked immutable, no? Otherwise
how can users use the new functions for indexing?

--
Josh Berkus
Containers & Databases Oh My!