planner failure with ProjectSet + aggregation + parallel query

While trying to track down a bug today, I found a different bug.

As of 6946280cded903b6f5269fcce105f8ab1d455d33:

rhaas=# create table foo (a int);
CREATE TABLE
rhaas=# set min_parallel_table_scan_size = 0;
SET
rhaas=# set parallel_setup_cost = 0;
SET
rhaas=# set parallel_tuple_cost = 0;
SET
rhaas=# select generate_series(1, a) from foo group by a;
ERROR: ORDER/GROUP BY expression not found in targetlist

Without the SET commands, or without the GROUP BY, or without the SRF,
it successfully constructs a plan.

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company