From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sat, 5 Apr 2025 16:13:35 +0000 (-0400)
Subject: Avoid double transformation of json_array()'s subquery.
X-Git-Tag: REL_18_BETA1~248
X-Git-Url: http://git.postgresql.org/gitweb/?a=commitdiff_plain;h=e33f2335a9d9754ccf3bf7181085cfa581ee03c3;p=postgresql.git

Avoid double transformation of json_array()'s subquery.

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
---

diff --git a/src/backend/parser/parse_expr.c b/src/backend/parser/parse_expr.c
index 9caf1e481a2..bc602f00ae3 100644
--- a/src/backend/parser/parse_expr.c
+++ b/src/backend/parser/parse_expr.c
@@ -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,
diff --git a/src/test/regress/expected/sqljson.out b/src/test/regress/expected/sqljson.out
index eb320f003f5..bed43aadd8c 100644
--- a/src/test/regress/expected/sqljson.out
+++ b/src/test/regress/expected/sqljson.out
@@ -751,6 +751,12 @@ SELECT JSON_ARRAY(SELECT i FROM (VALUES (3), (1), (NULL), (2)) foo(i) ORDER BY i
  [1, 2, 3]
 (1 row)
 
+SELECT JSON_ARRAY(WITH x AS (SELECT 1) VALUES (TRUE));
+ json_array 
+------------
+ [true]
+(1 row)
+
 -- Should fail
 SELECT JSON_ARRAY(SELECT FROM (VALUES (1)) foo(i));
 ERROR:  subquery must return only one column
diff --git a/src/test/regress/sql/sqljson.sql b/src/test/regress/sql/sqljson.sql
index 3fd6ac260b8..343d344d270 100644
--- a/src/test/regress/sql/sqljson.sql
+++ b/src/test/regress/sql/sqljson.sql
@@ -199,6 +199,8 @@ SELECT JSON_ARRAY(SELECT i FROM (VALUES (NULL::int[]), ('{1,2}'), (NULL), (NULL)
 --SELECT JSON_ARRAY(SELECT i FROM (VALUES (NULL::int[]), ('{1,2}'), (NULL), (NULL), ('{3,4}'), (NULL)) foo(i) NULL ON NULL);
 --SELECT JSON_ARRAY(SELECT i FROM (VALUES (NULL::int[]), ('{1,2}'), (NULL), (NULL), ('{3,4}'), (NULL)) foo(i) NULL ON NULL RETURNING jsonb);
 SELECT JSON_ARRAY(SELECT i FROM (VALUES (3), (1), (NULL), (2)) foo(i) ORDER BY i);
+SELECT JSON_ARRAY(WITH x AS (SELECT 1) VALUES (TRUE));
+
 -- Should fail
 SELECT JSON_ARRAY(SELECT FROM (VALUES (1)) foo(i));
 SELECT JSON_ARRAY(SELECT i, i FROM (VALUES (1)) foo(i));