Avoid double transformation of json_array()'s subquery.

tglsfdc · tglsfdc · commit ca54f9b706f6 · 2025-04-05T12:13:35.000-04:00
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 0f43083). 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 7081ac4. 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
@@ -3626,7 +3626,7 @@ 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
@@ -445,6 +445,12 @@ 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
@@ -124,6 +124,8 @@ 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));
