BUG #16577: Segfault on altering a table located in a dropped tablespace

The following bug has been logged on the website:

Bug reference:      16577
Logged by:          Alexander Lakhin
Email address:      exclusion@gmail.com
PostgreSQL version: 13beta2
Operating system:   Ubuntu 20.04
Description:

When executing the following query (a modified excerpt from the tablespace
regression test):
CREATE TABLESPACE regress_tblspace LOCATION '@testtablespace@';
CREATE TABLE test_default_tab_p(id bigint, val bigint)
    PARTITION BY LIST (id) TABLESPACE regress_tblspace;
CREATE INDEX test_index2 on test_default_tab_p (val) TABLESPACE
regress_tblspace;
DROP TABLESPACE regress_tblspace;
\d+ test_default_tab_p;
ALTER TABLE test_default_tab_p ALTER val TYPE bigint;

I get a segfault with the stacktrace:
Core was generated by `postgres: law regression [local] ALTER TABLE
                        '.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  quote_identifier (ident=0x0) at ruleutils.c:10754
10754           safe = ((ident[0] >= 'a' && ident[0] <= 'z') || ident[0] ==
'_');
(gdb) bt
#0  quote_identifier (ident=0x0) at ruleutils.c:10754
#1  0x000055cd6c3798d3 in pg_get_indexdef_worker
(indexrelid=indexrelid@entry=16389, colno=colno@entry=0, 
    excludeOps=excludeOps@entry=0x0, attrsOnly=attrsOnly@entry=false,
keysOnly=keysOnly@entry=false, 
    showTblSpc=showTblSpc@entry=true, inherits=true, prettyFlags=0,
missing_ok=false) at ruleutils.c:1460
#2  0x000055cd6c379ab1 in pg_get_indexdef_string
(indexrelid=indexrelid@entry=16389) at ruleutils.c:1161
#3  0x000055cd6c0ca0c1 in RememberIndexForRebuilding (indoid=16389,
tab=tab@entry=0x55cd6c89df20) at tablecmds.c:11718
#4  0x000055cd6c0cd764 in ATExecAlterColumnType
(tab=tab@entry=0x55cd6c89df20, rel=rel@entry=0x7f0e3cef3570, 
    cmd=<optimized out>, lockmode=lockmode@entry=8) at tablecmds.c:11280
#5  0x000055cd6c0dece5 in ATExecCmd (wqueue=wqueue@entry=0x7ffe0dcc7a30,
tab=tab@entry=0x55cd6c89df20, 
    rel=rel@entry=0x7f0e3cef3570, cmd=<optimized out>,
lockmode=lockmode@entry=8, cur_pass=cur_pass@entry=1, 
    context=0x7ffe0dcc7b40) at tablecmds.c:4523
#6  0x000055cd6c0df155 in ATRewriteCatalogs
(wqueue=wqueue@entry=0x7ffe0dcc7a30, lockmode=lockmode@entry=8, 
    context=context@entry=0x7ffe0dcc7b40) at
../../../src/include/nodes/nodes.h:594
#7  0x000055cd6c0df3a0 in ATController
(parsetree=parsetree@entry=0x55cd6c712040, rel=rel@entry=0x7f0e3cef3570, 
    cmds=0x55cd6c712008, recurse=true, lockmode=lockmode@entry=8,
context=context@entry=0x7ffe0dcc7b40)
    at tablecmds.c:3971
#8  0x000055cd6c0df42a in AlterTable (stmt=stmt@entry=0x55cd6c712040,
lockmode=lockmode@entry=8, 
    context=context@entry=0x7ffe0dcc7b40) at tablecmds.c:3627
#9  0x000055cd6c2af6f8 in ProcessUtilitySlow
(pstate=pstate@entry=0x55cd6c89ddb0, pstmt=pstmt@entry=0x55cd6c7120e8, 
    queryString=queryString@entry=0x55cd6c711350 "ALTER TABLE
test_default_tab_p ALTER val TYPE bigint;", 
    context=context@entry=PROCESS_UTILITY_TOPLEVEL, params=params@entry=0x0,
queryEnv=queryEnv@entry=0x0, 
    dest=0x55cd6c712388, qc=0x7ffe0dcc8060) at utility.c:1269
#10 0x000055cd6c2af1f2 in standard_ProcessUtility (pstmt=0x55cd6c7120e8, 
    queryString=0x55cd6c711350 "ALTER TABLE test_default_tab_p ALTER val
TYPE bigint;", 
    context=PROCESS_UTILITY_TOPLEVEL, params=0x0, queryEnv=0x0,
dest=0x55cd6c712388, qc=0x7ffe0dcc8060)
    at utility.c:1069
#11 0x000055cd6c2af2d1 in ProcessUtility (pstmt=pstmt@entry=0x55cd6c7120e8,
queryString=<optimized out>, 
    context=context@entry=PROCESS_UTILITY_TOPLEVEL, params=<optimized out>,
queryEnv=<optimized out>, 
    dest=dest@entry=0x55cd6c712388, qc=0x7ffe0dcc8060) at utility.c:524
#12 0x000055cd6c2ab73c in PortalRunUtility
(portal=portal@entry=0x55cd6c7747f0, pstmt=pstmt@entry=0x55cd6c7120e8, 
    isTopLevel=isTopLevel@entry=true,
setHoldSnapshot=setHoldSnapshot@entry=false, dest=dest@entry=0x55cd6c712388,

    qc=qc@entry=0x7ffe0dcc8060) at pquery.c:1157
#13 0x000055cd6c2ac270 in PortalRunMulti
(portal=portal@entry=0x55cd6c7747f0, isTopLevel=isTopLevel@entry=true, 
    setHoldSnapshot=setHoldSnapshot@entry=false,
dest=dest@entry=0x55cd6c712388, altdest=altdest@entry=0x55cd6c712388, 
    qc=qc@entry=0x7ffe0dcc8060) at pquery.c:1303
#14 0x000055cd6c2acf52 in PortalRun (portal=portal@entry=0x55cd6c7747f0,
count=count@entry=9223372036854775807, 
    isTopLevel=isTopLevel@entry=true, run_once=run_once@entry=true,
dest=dest@entry=0x55cd6c712388, 
    altdest=altdest@entry=0x55cd6c712388, qc=0x7ffe0dcc8060) at
pquery.c:779
#15 0x000055cd6c2a93bc in exec_simple_query (
    query_string=query_string@entry=0x55cd6c711350 "ALTER TABLE
test_default_tab_p ALTER val TYPE bigint;")
    at postgres.c:1239
#16 0x000055cd6c2ab2d8 in PostgresMain (argc=<optimized out>,
argv=argv@entry=0x55cd6c73ca88, dbname=<optimized out>, 
    username=<optimized out>) at postgres.c:4315
#17 0x000055cd6c216e67 in BackendRun (port=port@entry=0x55cd6c735380) at
postmaster.c:4523
#18 0x000055cd6c219fdd in BackendStartup (port=port@entry=0x55cd6c735380) at
postmaster.c:4215
#19 0x000055cd6c21a224 in ServerLoop () at postmaster.c:1727
#20 0x000055cd6c21b74d in PostmasterMain (argc=8, argv=<optimized out>) at
postmaster.c:1400
#21 0x000055cd6c164bed in main (argc=8, argv=0x55cd6c70b9e0) at main.c:210

Best regards,
Alexander