EXPLAIN(VERBOSE) to CTE with SEARCH BREADTH FIRST fails

Hi,

While working on [1], we found that EXPLAIN(VERBOSE) to CTE with SEARCH
BREADTH FIRST ends up ERROR.

This can be reproduced at the current HEAD(4c3478859b7359912d7):

=# create table graph0( f int, t int, label text);
CREATE TABLE

=# insert into graph0 values (1, 2, 'arc 1 -> 2'),(1, 3, 'arc 1 ->
3'),(2, 3, 'arc 2 -> 3'),(1, 4, 'arc 1 -> 4'),(4, 5, 'arc 4 -> 5');
INSERT 0 5

=# explain(verbose) with recursive search_graph(f, t, label) as (
select * from graph0 g
union all
select g.*
from graph0 g, search_graph sg
where g.f = sg.t
) search breadth first by f, t set seq
select * from search_graph order by seq;
ERROR: failed to find plan for CTE sg

Is this a bug?

[1]
https://www.postgresql.org/message-id/flat/cf8501bcd95ba4d727cbba886ba9eea8(at)oss(dot)nttdata(dot)com

Regards,

--
Atsushi Torikoshi
NTT DATA CORPORATION