BUG #16616: Segmentation fault when use explain

The following bug has been logged on the website:

Bug reference:      16616
Logged by:          Dan Liu
Email address:      139250065@qq.com
PostgreSQL version: 12.4
Operating system:   18.04.5 LTS (Bionic Beaver)
Description:

I created a extension by C language, and deltatype is a new data type 

CREATE TYPE     deltatype;
CREATE FUNCTION deltatype_in(cstring)       RETURNS deltatype IMMUTABLE
STRICT LANGUAGE C AS '$libdir/bz', 'deltatype_in';
CREATE FUNCTION deltatype_out(deltatype)    RETURNS cstring   IMMUTABLE
STRICT LANGUAGE C AS '$libdir/bz', 'deltatype_out';
CREATE FUNCTION deltatype_receive(internal) RETURNS deltatype IMMUTABLE
STRICT LANGUAGE C AS '$libdir/bz', 'deltatype_receive';
CREATE FUNCTION deltatype_send(deltatype)   RETURNS bytea     IMMUTABLE
STRICT LANGUAGE C AS '$libdir/bz', 'deltatype_send';

CREATE TYPE deltatype 
(
    INPUT   = deltatype_in, 
    OUTPUT  = deltatype_out, 
    RECEIVE = deltatype_receive,
    SEND    = deltatype_send,
    INTERNALLENGTH = 1, 
    ALIGNMENT = char,
    PASSEDBYVALUE
);   

It works well execpt when I use  explain in psql

> explain select 'new'::deltatype <> 'old'::deltatype;
                QUERY PLAN
------------------------------------------
 Result  (cost=0.00..0.01 rows=1 width=1)
(1 row)

> explain select * from contract_index64s where delta_type <> 0 limit 1;
                                   QUERY PLAN
--------------------------------------------------------------------------------
 Limit  (cost=0.00..0.03 rows=1 width=57)
   ->  Seq Scan on contract_index64s  (cost=0.00..4424.69 rows=147405
width=57)
         Filter: (delta_type <> 0)
(3 rows)

> explain select * from contract_index64s where delta_type <> 'new'::text
limit 1;
                                  QUERY PLAN
-------------------------------------------------------------------------------
 Limit  (cost=0.00..0.10 rows=1 width=57)
   ->  Seq Scan on contract_index64s  (cost=0.00..4424.69 rows=44537
width=57)
         Filter: (delta_type <> 'new'::text)
(3 rows)

> select * from contract_index64s where delta_type <> 'new'::deltatype limit
1;
 block_num | seq_no | delta_type |    code    |   scope    |    tab     |
primary_key |   payer    | secondary_key
-----------+--------+------------+------------+------------+------------+-------------+------------+---------------
 13698527  | 0      | removed    | snatchgame | snatchgame | snatchgame | 0
         | snatchgame | 1
(1 row)

Time: 3.863 ms


> explain select * from contract_index64s where delta_type <>
'new'::deltatype limit 1;
server closed the connection unexpectedly
        This probably means the server terminated abnormally
        before or while processing the request.
The connection to the server was lost. Attempting reset: Failed.
Time: 118.896 ms
10:21:53 (@:)!>?

in log file: /var/log/postgresql/postgresql-12-main.log
2020-09-15 10:21:53.143 CST::@:[858]: LOG:  server process (PID 2902) was
terminated by signal 11: Segmentation fault
2020-09-15 10:21:53.143 CST::@:[858]: DETAIL:  Failed process was running:
explain select * from contract_index64s where delta_type <> 'new'::deltatype
limit 1;
2020-09-15 10:21:53.143 CST::@:[858]: LOG:  terminating any other active
server processes
2020-09-15 10:21:53.143 CST:[local]:baozi@baozi_db:[3256]: FATAL:  the
database system is in recovery mode
2020-09-15 10:21:53.144 CST::@:[925]: WARNING:  terminating connection
because of crash of another server process
2020-09-15 10:21:53.144 CST::@:[925]: DETAIL:  The postmaster has commanded
this server process to roll back the current transaction and exit, because
another server process exited abnormally and possibly corrupted shared
memory.
2020-09-15 10:21:53.144 CST::@:[925]: HINT:  In a moment you should be able
to reconnect to the database and repeat your command.
2020-09-15 10:21:53.145 CST::@:[858]: LOG:  all server processes terminated;
reinitializing
2020-09-15 10:21:53.180 CST::@:[3259]: LOG:  database system was
interrupted; last known up at 2020-09-15 10:05:38 CST
2020-09-15 10:21:53.180 CST::@:[3259]: LOG:  database system was not
properly shut down; automatic recovery in progress
2020-09-15 10:21:53.182 CST::@:[3259]: LOG:  redo starts at 4F/15D550
2020-09-15 10:21:53.182 CST::@:[3259]: LOG:  invalid record length at
4F/15D638: wanted 24, got 0
2020-09-15 10:21:53.182 CST::@:[3259]: LOG:  redo done at 4F/15D600
2020-09-15 10:21:53.191 CST::@:[858]: LOG:  database system is ready to
accept connections