Assert failure in base_yyparse

Hello.

Got an assert failure when fuzzing the raw_parser function.
The query to reproduce:
SELECT xmltable.* FROM xmltest2, LATERAL xmltable('/d/r' PASSING x
COLUMNS a int PATH '' || lower(_path) is_not_null|| 'c');

If I understand correctly, is_not_null is considered as a valid keyword
in xmltable, but it gets the type T_A_Expr.

Postgres output:
$ ./postgres -D data
2025-03-28 12:19:19.945 +06 [53058] LOG:  starting PostgreSQL 18devel on
x86_64-pc-linux-gnu, compiled by x86_64-alt-linux-gcc (GCC) 10.3.1
20210703 (ALT Sisyphus 10.3.1-alt2), 64-bit
2025-03-28 12:19:19.946 +06 [53058] LOG:  listening on IPv4 address
"127.0.0.1", port 5432
2025-03-28 12:19:20.032 +06 [53058] LOG:  listening on Unix socket
"/tmp/.s.PGSQL.5432"
2025-03-28 12:19:20.281 +06 [53064] LOG:  database system was shut down
at 2025-03-28 12:18:37 +06
2025-03-28 12:19:20.342 +06 [53058] LOG:  database system is ready to
accept connections
TRAP: failed Assert("ptr == NULL || nodeTag(ptr) == type"), File:
"../../../src/include/nodes/nodes.h", Line: 177, PID: 53069
postgres: user postgres 127.0.0.1(56762)
idle(ExceptionalCondition+0x141)[0x5561768c0fb6]
postgres: user postgres 127.0.0.1(56762) idle(+0x585784)[0x556175e03784]
postgres: user postgres 127.0.0.1(56762)
idle(base_yyparse+0x30578)[0x556175e33f83]
postgres: user postgres 127.0.0.1(56762)
idle(raw_parser+0xf5)[0x556175ec0f47]
postgres: user postgres 127.0.0.1(56762)
idle(pg_parse_query+0x63)[0x556176550a67]
postgres: user postgres 127.0.0.1(56762) idle(+0xcd3bcf)[0x556176551bcf]
postgres: user postgres 127.0.0.1(56762)
idle(PostgresMain+0x14ef)[0x55617655ca54]
postgres: user postgres 127.0.0.1(56762) idle(+0xccc207)[0x55617654a207]
postgres: user postgres 127.0.0.1(56762)
idle(postmaster_child_launch+0x2ae)[0x5561763ad6e8]
postgres: user postgres 127.0.0.1(56762) idle(+0xb3bc75)[0x5561763b9c75]
postgres: user postgres 127.0.0.1(56762) idle(+0xb3686b)[0x5561763b486b]
postgres: user postgres 127.0.0.1(56762)
idle(PostmasterMain+0x288f)[0x5561763b3bdb]
postgres: user postgres 127.0.0.1(56762) idle(main+0x5dc)[0x55617616dfbd]
/lib64/libc.so.6(__libc_start_main+0xcd)[0x7f36ef05fefd]
postgres: user postgres 127.0.0.1(56762) idle(_start+0x2a)[0x556175b4a39a]
2025-03-28 12:19:24.020 +06 [53058] LOG:  client backend (PID 53069) was
terminated by signal 6: Aborted
2025-03-28 12:19:24.020 +06 [53058] DETAIL:  Failed process was running:
SELECT xmltable.* FROM xmltest2, LATERAL xmltable('/d/r' PASSING x
COLUMNS a int PATH '' || lower(_path) is_not_null|| 'c');
2025-03-28 12:19:24.020 +06 [53058] LOG:  terminating any other active
server processes
2025-03-28 12:19:24.021 +06 [53058] LOG:  all server processes
terminated; reinitializing
2025-03-28 12:19:24.220 +06 [53080] LOG:  database system was
interrupted; last known up at 2025-03-28 12:19:20 +06
2025-03-28 12:19:28.268 +06 [53080] LOG:  database system was not
properly shut down; automatic recovery in progress
2025-03-28 12:19:28.296 +06 [53080] LOG:  invalid record length at
0/17864A0: expected at least 24, got 0
2025-03-28 12:19:28.296 +06 [53080] LOG:  redo is not required
2025-03-28 12:19:28.414 +06 [53081] LOG:  checkpoint starting:
end-of-recovery immediate wait
2025-03-28 12:19:28.561 +06 [53081] LOG:  checkpoint complete: wrote 0
buffers (0.0%), wrote 3 SLRU buffers; 0 WAL file(s) added, 0 removed, 0
recycled; write=0.014 s, sync=0.004 s, total=0.183 s; sync files=2,
longest=0.002 s, average=0.002 s; distance=0 kB, estimate=0 kB;
lsn=0/17864A0, redo lsn=0/17864A0
2025-03-28 12:19:28.618 +06 [53058] LOG:  database system is ready to
accept connections
^C2025-03-28 12:19:30.116 +06 [53058] LOG:  received fast shutdown request
2025-03-28 12:19:30.259 +06 [53058] LOG:  aborting any active transactions
2025-03-28 12:19:30.313 +06 [53081] LOG:  shutting down
2025-03-28 12:19:30.464 +06 [53081] LOG:  checkpoint starting: shutdown
immediate
2025-03-28 12:19:30.515 +06 [53081] LOG:  checkpoint complete: wrote 0
buffers (0.0%), wrote 0 SLRU buffers; 0 WAL file(s) added, 0 removed, 0
recycled; write=0.001 s, sync=0.001 s, total=0.202 s; sync files=0,
longest=0.000 s, average=0.000 s; distance=0 kB, estimate=0 kB;
lsn=0/1786518, redo lsn=0/1786518
2025-03-28 12:19:30.665 +06 [53058] LOG:  database system is shut down

Prepared a patch to fix it, but there may be a better solution.