BUG #14364: json_populate_record doesn't accept JSON arrays

The following bug has been logged on the website:

Bug reference: 14364
Logged by: Jörg Sonnenberger
Email address: joerg(at)bec(dot)de
PostgreSQL version: 9.4.9
Operating system: Linux
Description:

json_populate_record expects arrays in fields using the PG array literal
syntax, it doesn't support JSON arrays. This is highly annoying as the JSON
output functions like row_to_json will create JSON arrays, so round-trip
fidelity is lost.

Small example:

CREATE TEMPORARY TABLE test (a int, b int[]);
SELECT json_populate_record(NULL::test, '{"a": 5, "b": [1,2]}');

gives:

ERROR: malformed array literal: "[1,2]"
DETAIL: Missing "]" after array dimensions.

But

SELECT json_populate_record(NULL::test, '{"a": 5, "b": "{1,2}"}');

is accepted. Accepting JSON arrays directly would be backwards-compatible.