Re: PATCH: Implement value_to_json for single-datum conversion

OK, opr_sanity was failing because I added the value_to_json(text) alias
to ensure that:

value_to_json('some_literal')

worked, following the same approach as quote_literal(anyelement) and
quote_literal(text). That should be reasonable, right? The comments on
the affected check in opr_sanity say that it's not necessarily wrong so
long as the called function is prepared to handle the different
arguments its self - which it is, since it's already accepting anyelement.

The test comment reads:

Note that the expected output of this part of the test will
need to be modified whenever new pairs of types are made
binary-equivalent,
or when new polymorphic built-in functions are added

so that seems reasonable.

postgres=# \df quote_literal
List of functions
Schema | Name | Result data type | Argument data types |
Type
------------+---------------+------------------+---------------------+--------
pg_catalog | quote_literal | text | anyelement | normal
pg_catalog | quote_literal | text | text | normal
(2 rows)

postgres=# \df value_to_json
List of functions
Schema | Name | Result data type | Argument data types |
Type
------------+---------------+------------------+---------------------+--------
pg_catalog | value_to_json | json | anyelement | normal
pg_catalog | value_to_json | json | text | normal
(2 rows)

Revised patch that tweaks the expected result of opr_sanity attached.

--
Craig Ringer