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Avoid double transformation of json_array()'s subquery.

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transformJsonArrayQueryConstructor() applied transformStmt() to
the same subquery tree twice.  While this causes no issue in many
cases, there are some where it causes a coredump, thanks to the
parser's habit of scribbling on its input.

Fix by making a copy before the first transformation (compare
0f43083d1).  This is quite brute-force, but then so is the
whole business of transforming the input twice.  Per discussion
in the bug thread, this implementation of json_array() parsing
should be replaced completely.  But that will take some work
and will surely not be back-patchable, so for the moment let's
take the easy way out.

Oversight in 7081ac46a.  Back-patch to v16 where that came in.

Bug: #18877
Reported-by: Yu Liang <luy70@psu.edu>
Author: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/18877-c3c3ad75845833bb@postgresql.org
Backpatch-through: 16
This commit is contained in:
Tom Lane
2025-04-05 12:13:35 -04:00
parent 5db3bf7391
commit e33f2335a9
3 changed files with 9 additions and 1 deletions
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2
src/backend/parser/parse_expr.c
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@ -3772,7 +3772,7 @@ transformJsonArrayQueryConstructor(ParseState *pstate,
/* Transform query only for counting target list entries. */
qpstate = make_parsestate(pstate);
query = transformStmt(qpstate, ctor->query);
query = transformStmt(qpstate, copyObject(ctor->query));
if (count_nonjunk_tlist_entries(query->targetList) != 1)
ereport(ERROR,