ORDER/GROUP BY expression not found in targetlist

Hi,

trying to reproduce a performance problem I just found:

=# CREATE TABLE twocol(col01 int, col02 int);
=# SELECT DISTINCT col01, col02, col01 FROM twocol ;
ERROR:  XX000: ORDER/GROUP BY expression not found in targetlist
LOCATION:  get_sortgroupref_tle, tlist.c:341

which appears to be a 9.6 regression, presumable fallout from the path
restructuring.

Greetings,

Andres Freund