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 <[email protected]>
Author: Tom Lane <[email protected]>
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 9caf1e481a2081117732c5add0b5ae9d17e6e7c6..bc602f00ae3dd19593718cb547e7e151fba9315d 100644 (file)
--- 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 eb320f003f57689be00442076f3415efdf262b58..bed43aadd8c58f1d687b667e7c49ac816b2a34a5 100644 (file)
--- 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 3fd6ac260b8ed2079fa0d5881bb0b1c3bd517966..343d344d2707f40bbb4f9acd17b0ec5e0772b545 100644 (file)
--- 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));