Relcache leak when row triggers on partitions are fired by COPY

Hi hackers,

While testing the patch I'm writing for the transition table open
item, I noticed that we can leak Relation objects like this:

postgres=# create table parent (a text, b int) partition by list (a);
CREATE TABLE
postgres=# create table child partition of parent for values in ('AAA');
CREATE TABLE
postgres=# create or replace function my_trigger_func() returns
trigger language plpgsql as $$ begin raise notice 'hello'; return
null; end; $$;
CREATE FUNCTION
postgres=# create trigger child_trigger after insert or update or
delete on child for each row execute procedure my_trigger_func();
CREATE TRIGGER
postgres=# copy parent (a, b) from stdin;
Enter data to be copied followed by a newline.
End with a backslash and a period on a line by itself.
>> AAA 42
>> \.
NOTICE: hello
WARNING: relcache reference leak: relation "child" not closed
COPY 1

The leaked object is created by ExecGetTriggerResultRel, called by
afterTriggerInvokeEvents. That function relies on someone, usually
ExecEndPlan or EvalPlanQualEnd, to clean up es_trig_target_relations.
Shouldn't copy.c do the same thing (see attached)? Or perhaps there
should there be an ExecCleanupTriggerState(estate) used by all places?

--
Thomas Munro
http://www.enterprisedb.com