BUG #14458: PQfmod returns -1 for aggregate functions

The following bug has been logged on the website:

Bug reference: 14458
Logged by: Garfield Lewis
Email address: garfield(dot)lewis(at)lzlabs(dot)com
PostgreSQL version: 9.5.2
Operating system: Linux
Description:

I am trying to get the type modification information from a describe of a
select statement where the column is the result of an aggregate function
(i.e. rtrim, max, min, etc.). I've posted a question on StackOverflow
regarding this but have had no responses to this point so I am asking here
now. The StackOverflow posting can be found here:

http://stackoverflow.com/questions/41021883/postgres-describe-of-aggregate-function-returning-type-modification-value-of-1

BTW, I have verified the this does fail with or without my own custom
type.

Regards,
Garfield