pgsql: Avoid reference to nonexistent array element in ExecInitAgg().

Avoid reference to nonexistent array element in ExecInitAgg().

When considering an empty grouping set, we fetched
phasedata->eqfunctions[-1]. Because the eqfunctions array is
palloc'd, that would always be an aset pointer in released versions,
and thus the code accidentally failed to malfunction (since it would
do nothing unless it found a null pointer). Nonetheless this seems
like trouble waiting to happen, so add a check for length == 0.

It's depressing that our valgrind testing did not catch this.
Maybe we should reconsider the choice to not mark that word NOACCESS?

Richard Guo

Discussion: https://postgr.es/m/CAMbWs4-vZuuPOZsKOYnSAaPYGKhmacxhki+vpOKk0O7rymccXQ@mail.gmail.com

Branch
------
REL_13_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/19adcaf00f7d8480f231bcfbb6b7a4401a531ce5

Modified Files
--------------
src/backend/executor/nodeAgg.c | 5 +++++
1 file changed, 5 insertions(+)