BUG #15100: sequence behavior on failed insert to a partitioned table

The following bug has been logged on the website:

Bug reference:      15100
Logged by:          Istvan Kassai
Email address:      kassai1972@gmail.com
PostgreSQL version: 10.3
Operating system:   linux
Description:

Hi!
I started to deal with the new declarative table partitioning in 10.
I found that a failed insert (due to the field I've tried to insert is out
of partition range) also increments the sequence of the base table, even if
the insert is rejected.

A simple sample:

  Column  |          Type          | Collation | Nullable |
Default                 | Storage  | Stats target | Description 

----------+------------------------+-----------+----------+-----------------------------------------+----------+--------------+-------------
 sor_azon | integer                |           | not null |
nextval('teszt_sor_azon_seq'::regclass) | plain    |              | 
 szoveg   | character varying(100) |           |          |
                       | extended |              | 
Partition key: RANGE (szoveg)
Partitions: teszt_a FOR VALUES FROM ('a%') TO ('b%'),
            teszt_b FOR VALUES FROM ('b%') TO ('c%')

I've inserted two rows to test if it is working well:

o=# insert into teszt (szoveg) values('aladár');
INSERT 0 1
o=# insert into teszt (szoveg) values('béla');
INSERT 0 1

then I inserted an out-of-range value:
o=# insert into teszt (szoveg) values('cicu');
ERROR:  no partition of relation "teszt" found for row
DETAIL:  Partition key of the failing row contains (szoveg) = (cicu).

It is working as expected.

After it I queried the content for the table:
o=# select * from teszt;
 sor_azon | szoveg 
----------+--------
        1 | aladár
        2 | béla
(2 rows)

Seems all is good. BUT!
After it I created a new partition:

o=# CREATE TABLE teszt_c PARTITION OF teszt


                                        FOR VALUES FROM ('c%') TO ('z%');
CREATE TABLE


Then I tried to insert the last recently rejected value again:

o=# insert into teszt (szoveg) values('cicu');
INSERT 0 1


And a query again:

o=# select * from teszt;
 sor_azon | szoveg 
----------+--------
        1 | aladár
        2 | béla
        4 | cicu
(3 rows)

As you can see the sor_azon isn't continous. The #3 is missing.
As I think the sequence hasn't rolled back after a failed insert.

I'm not sure is it a bug, but it is better you know about it.

bye
Istvan