[sqlsmith] Failed assertion in adjust_appendrel_attrs_mutator

Hi,

testing master as of 7c981590c2, sqlsmith just triggered the following
assertion:

TRAP: FailedAssertion("!(!((((const Node*)(node))->type) == T_SubLink))", File: "prepunion.c", Line: 2231)

I can reproduce it on a vanilla regression database with the following
query:

--8<---------------cut here---------------start------------->8---
explain delete from public.road
where
EXISTS (
select
ref_1.tablename
from
public.renamecolumnchild as ref_0
right join pg_catalog.pg_policies as ref_1
on (true)
where EXISTS (
select
public.road.name as c1,
ref_1.with_check as c3,
ref_2.b as c6
from
public.itest4 as ref_2));
--8<---------------cut here---------------end--------------->8---

Backtrace below.

regards,
Andreas

Core was generated by `postgres: smith regression [local] DELETE '.
Program terminated with signal SIGABRT, Aborted.
#0 0x00007f70c2dacfcf in raise () from /lib/x86_64-linux-gnu/libc.so.6
#1 0x00007f70c2dae3fa in abort () from /lib/x86_64-linux-gnu/libc.so.6
#2 0x0000564d8ce587b3 in ExceptionalCondition (conditionName=conditionName(at)entry=0x564d8cfe87b0 "!(!((((const Node*)(node))->type) == T_SubLink))", errorType=errorType(at)entry=0x564d8cea483d "FailedAssertion", fileName=fileName(at)entry=0x564d8cfea866 "prepunion.c", lineNumber=lineNumber(at)entry=2231) at assert.c:54
#3 0x0000564d8ccaf7dc in adjust_appendrel_attrs_mutator (node=0x564d91e0d2a0, context=0x7fff0a33caa0) at prepunion.c:2231
#4 0x0000564d8cc4d8ef in expression_tree_mutator (node=0x564d91e0ccd8, mutator=0x564d8ccaf1d0 <adjust_appendrel_attrs_mutator>, context=0x7fff0a33caa0) at nodeFuncs.c:2554
#5 0x0000564d8cc4d88f in expression_tree_mutator (node=0x564d91e0df90, mutator=mutator(at)entry=0x564d8ccaf1d0 <adjust_appendrel_attrs_mutator>, context=context(at)entry=0x7fff0a33caa0) at nodeFuncs.c:3008
#6 0x0000564d8ccaf29f in adjust_appendrel_attrs_mutator (node=0x564d91e0df90, context=0x7fff0a33caa0) at prepunion.c:2151
#7 0x0000564d8cc4dafb in expression_tree_mutator (node=<optimized out>, mutator=0x564d8ccaf1d0 <adjust_appendrel_attrs_mutator>, context=0x7fff0a33caa0) at nodeFuncs.c:2903
#8 0x0000564d8cc4e589 in range_table_mutator (rtable=<optimized out>, mutator=mutator(at)entry=0x564d8ccaf1d0 <adjust_appendrel_attrs_mutator>, context=context(at)entry=0x7fff0a33caa0, flags=flags(at)entry=3) at nodeFuncs.c:3146
#9 0x0000564d8cc4e78e in query_tree_mutator (query=0x564d91e30c20, query(at)entry=0x564d90fbe090, mutator=mutator(at)entry=0x564d8ccaf1d0 <adjust_appendrel_attrs_mutator>, context=context(at)entry=0x7fff0a33caa0, flags=flags(at)entry=3) at nodeFuncs.c:3096
#10 0x0000564d8ccb1499 in adjust_appendrel_attrs (root=root(at)entry=0x564d910bab58, node=node(at)entry=0x564d90fbe090, nappinfos=nappinfos(at)entry=1, appinfos=appinfos(at)entry=0x7fff0a33cba8) at prepunion.c:1964
#11 0x0000564d8cca3406 in inheritance_planner (root=<optimized out>) at planner.c:1200
#12 subquery_planner (glob=glob(at)entry=0x564d910baac0, parse=parse(at)entry=0x564d90fbe090, parent_root=parent_root(at)entry=0x0, hasRecursion=hasRecursion(at)entry=0 '\000', tuple_fraction=tuple_fraction(at)entry=0) at planner.c:857
#13 0x0000564d8cca3dbf in standard_planner (parse=0x564d90fbe090, cursorOptions=256, boundParams=0x0) at planner.c:352
#14 0x0000564d8cd4ef5d in pg_plan_query (querytree=0x564d90fbe090, cursorOptions=256, boundParams=0x0) at postgres.c:807
#15 0x0000564d8cd4f03e in pg_plan_queries (querytrees=<optimized out>, cursorOptions=cursorOptions(at)entry=256, boundParams=boundParams(at)entry=0x0) at postgres.c:873
#16 0x0000564d8cd4f519 in exec_simple_query (query_string=0x564d8ed5c330 "[...]") at postgres.c:1048
#17 0x0000564d8cd51151 in PostgresMain (argc=<optimized out>, argv=argv(at)entry=0x564d8ed66c50, dbname=<optimized out>, username=<optimized out>) at postgres.c:4139
#18 0x0000564d8ca56032 in BackendRun (port=0x564d8ed6d460) at postmaster.c:4364
#19 BackendStartup (port=0x564d8ed6d460) at postmaster.c:4036
#20 ServerLoop () at postmaster.c:1755
#21 0x0000564d8ccd628c in PostmasterMain (argc=3, argv=0x564d8ed3c5a0) at postmaster.c:1363
#22 0x0000564d8ca5761d in main (argc=3, argv=0x564d8ed3c5a0) at main.c:228