Remove assertion for replication origins in PREPARE TRANSACTION

When using replication origins, pg_replication_origin_xact_setup() is an
optional choice to be able to set a LSN and a timestamp to mark the
origin, which would be additionally added to WAL for transaction commits
or aborts (including 2PC transactions).  An assertion in the code path
of PREPARE TRANSACTION assumed that this data should always be set, so
it would trigger when using replication origins without setting up an
origin LSN.  Some tests are added to cover more this kind of scenario.

Oversight in commit 1eb6d652.

Per discussion with Amit Kapila and Masahiko Sawada.

Discussion: https://postgr.es/m/YbbBfNSvMm5nIINV@paquier.xyz
Backpatch-through: 11

contrib/test_decoding/expected/replorigin.out

@@ -181,3 +181,79 @@ SELECT pg_replication_origin_drop('regress_test_decoding: regression_slot');
  
 (1 row)
 
+-- Set of transactions with no origin LSNs and commit timestamps set for
+-- this session.
+SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot_no_lsn', 'test_decoding');
+ ?column? 
+----------
+ init
+(1 row)
+
+SELECT pg_replication_origin_create('regress_test_decoding: regression_slot_no_lsn');
+ pg_replication_origin_create 
+------------------------------
+                            1
+(1 row)
+
+-- mark session as replaying
+SELECT pg_replication_origin_session_setup('regress_test_decoding: regression_slot_no_lsn');
+ pg_replication_origin_session_setup 
+-------------------------------------
+ 
+(1 row)
+
+-- Simple transactions
+BEGIN;
+INSERT INTO origin_tbl(data) VALUES ('no_lsn, commit');
+COMMIT;
+BEGIN;
+INSERT INTO origin_tbl(data) VALUES ('no_lsn, rollback');
+ROLLBACK;
+-- 2PC transactions
+BEGIN;
+INSERT INTO origin_tbl(data) VALUES ('no_lsn, commit prepared');
+PREPARE TRANSACTION 'replorigin_prepared';
+COMMIT PREPARED 'replorigin_prepared';
+BEGIN;
+INSERT INTO origin_tbl(data) VALUES ('no_lsn, rollback prepared');
+PREPARE TRANSACTION 'replorigin_prepared';
+ROLLBACK PREPARED 'replorigin_prepared';
+SELECT local_id, external_id,
+       remote_lsn <> '0/0' AS valid_remote_lsn,
+       local_lsn <> '0/0' AS valid_local_lsn
+       FROM pg_replication_origin_status;
+ local_id |                  external_id                  | valid_remote_lsn | valid_local_lsn 
+----------+-----------------------------------------------+------------------+-----------------
+        1 | regress_test_decoding: regression_slot_no_lsn | f                | t
+(1 row)
+
+SELECT data FROM pg_logical_slot_get_changes('regression_slot_no_lsn', NULL, NULL, 'skip-empty-xacts', '1', 'include-xids', '0');
+                                        data                                         
+-------------------------------------------------------------------------------------
+ BEGIN
+ table public.origin_tbl: INSERT: id[integer]:4 data[text]:'no_lsn, commit'
+ COMMIT
+ BEGIN
+ table public.origin_tbl: INSERT: id[integer]:6 data[text]:'no_lsn, commit prepared'
+ COMMIT
+(6 rows)
+
+-- Clean up
+SELECT pg_replication_origin_session_reset();
+ pg_replication_origin_session_reset 
+-------------------------------------
+ 
+(1 row)
+
+SELECT pg_drop_replication_slot('regression_slot_no_lsn');
+ pg_drop_replication_slot 
+--------------------------
+ 
+(1 row)
+
+SELECT pg_replication_origin_drop('regress_test_decoding: regression_slot_no_lsn');
+ pg_replication_origin_drop 
+----------------------------
+ 
+(1 row)
+

contrib/test_decoding/sql/replorigin.sql

@@ -87,3 +87,35 @@ SELECT data FROM pg_logical_slot_get_changes('regression_slot', NULL, NULL, 'inc
 
 SELECT pg_drop_replication_slot('regression_slot');
 SELECT pg_replication_origin_drop('regress_test_decoding: regression_slot');
+
+-- Set of transactions with no origin LSNs and commit timestamps set for
+-- this session.
+SELECT 'init' FROM pg_create_logical_replication_slot('regression_slot_no_lsn', 'test_decoding');
+SELECT pg_replication_origin_create('regress_test_decoding: regression_slot_no_lsn');
+-- mark session as replaying
+SELECT pg_replication_origin_session_setup('regress_test_decoding: regression_slot_no_lsn');
+-- Simple transactions
+BEGIN;
+INSERT INTO origin_tbl(data) VALUES ('no_lsn, commit');
+COMMIT;
+BEGIN;
+INSERT INTO origin_tbl(data) VALUES ('no_lsn, rollback');
+ROLLBACK;
+-- 2PC transactions
+BEGIN;
+INSERT INTO origin_tbl(data) VALUES ('no_lsn, commit prepared');
+PREPARE TRANSACTION 'replorigin_prepared';
+COMMIT PREPARED 'replorigin_prepared';
+BEGIN;
+INSERT INTO origin_tbl(data) VALUES ('no_lsn, rollback prepared');
+PREPARE TRANSACTION 'replorigin_prepared';
+ROLLBACK PREPARED 'replorigin_prepared';
+SELECT local_id, external_id,
+       remote_lsn <> '0/0' AS valid_remote_lsn,
+       local_lsn <> '0/0' AS valid_local_lsn
+       FROM pg_replication_origin_status;
+SELECT data FROM pg_logical_slot_get_changes('regression_slot_no_lsn', NULL, NULL, 'skip-empty-xacts', '1', 'include-xids', '0');
+-- Clean up
+SELECT pg_replication_origin_session_reset();
+SELECT pg_drop_replication_slot('regression_slot_no_lsn');
+SELECT pg_replication_origin_drop('regress_test_decoding: regression_slot_no_lsn');

src/backend/access/transam/twophase.c

@@ -1129,7 +1129,6 @@ EndPrepare(GlobalTransaction gxact)
 
 	if (replorigin)
 	{
-		Assert(replorigin_session_origin_lsn != InvalidXLogRecPtr);
 		hdr->origin_lsn = replorigin_session_origin_lsn;
 		hdr->origin_timestamp = replorigin_session_origin_timestamp;
 	}