From e37d621a1220db68cf9af4a9fed8757793592b59 Mon Sep 17 00:00:00 2001
From: Serguey Zefirov <serguey.zefirov@mariadb.com>
Date: Tue, 25 Feb 2025 08:09:49 +0000
Subject: [PATCH] fix(MCOL-5842): Fix JSON_OBJECT's handling of empty strings

JSON_OBJECT() (and probably some other JSON functions) now properly
handle empty strings in their arguments - JSON_OBJECT used to return
NULL, now it returns empty string.
---
 .../MCOL-5842-group-concat-json-object.result        | 12 ++++++++++++
 .../bugfixes/MCOL-5842-group-concat-json-object.test | 12 ++++++++++++
 utils/funcexp/jsonhelpers.cpp                        |  2 +-
 3 files changed, 25 insertions(+), 1 deletion(-)
 create mode 100644 mysql-test/columnstore/bugfixes/MCOL-5842-group-concat-json-object.result
 create mode 100644 mysql-test/columnstore/bugfixes/MCOL-5842-group-concat-json-object.test

diff --git a/mysql-test/columnstore/bugfixes/MCOL-5842-group-concat-json-object.result b/mysql-test/columnstore/bugfixes/MCOL-5842-group-concat-json-object.result
new file mode 100644
index 000000000..8d8f9b3aa
--- /dev/null
+++ b/mysql-test/columnstore/bugfixes/MCOL-5842-group-concat-json-object.result
@@ -0,0 +1,12 @@
+DROP DATABASE IF EXISTS MCOL5842;
+CREATE DATABASE MCOL5842;
+USE MCOL5842;
+CREATE TABLE tcs(t TEXT) ENGINE=Columnstore;
+INSERT INTO tcs(t) VALUES ('');
+SELECT JSON_OBJECT('t', t, 'a', 'b') FROM tcs;
+JSON_OBJECT('t', t, 'a', 'b')
+{"t": "", "a": "b"}
+SELECT GROUP_CONCAT(JSON_OBJECT('t', t, 'a', 'b')) FROM tcs;
+GROUP_CONCAT(JSON_OBJECT('t', t, 'a', 'b'))
+{"t": "", "a": "b"}
+DROP DATABASE MCOL5842;
diff --git a/mysql-test/columnstore/bugfixes/MCOL-5842-group-concat-json-object.test b/mysql-test/columnstore/bugfixes/MCOL-5842-group-concat-json-object.test
new file mode 100644
index 000000000..6e203ac27
--- /dev/null
+++ b/mysql-test/columnstore/bugfixes/MCOL-5842-group-concat-json-object.test
@@ -0,0 +1,12 @@
+--disable_warnings
+DROP DATABASE IF EXISTS MCOL5842;
+--enable_warnings
+CREATE DATABASE MCOL5842;
+USE MCOL5842;
+
+CREATE TABLE tcs(t TEXT) ENGINE=Columnstore;
+INSERT INTO tcs(t) VALUES ('');
+SELECT JSON_OBJECT('t', t, 'a', 'b') FROM tcs;
+SELECT GROUP_CONCAT(JSON_OBJECT('t', t, 'a', 'b')) FROM tcs;
+
+DROP DATABASE MCOL5842;
diff --git a/utils/funcexp/jsonhelpers.cpp b/utils/funcexp/jsonhelpers.cpp
index 042a3f33a..a1a0ca4a6 100644
--- a/utils/funcexp/jsonhelpers.cpp
+++ b/utils/funcexp/jsonhelpers.cpp
@@ -32,7 +32,7 @@ bool appendEscapedJS(string& ret, const CHARSET_INFO* retCS, const utils::NullSt
   int strLen = jsLen * 12 * jsCS->mbmaxlen / jsCS->mbminlen;
   char* buf = (char*)alloca(strLen);
   if ((strLen = json_escape(retCS, (const uchar*)rawJS, (const uchar*)rawJS + jsLen, jsCS, (uchar*)buf,
-                            (uchar*)buf + strLen)) > 0)
+                            (uchar*)buf + strLen)) >= 0)
   {
     buf[strLen] = '\0';
     ret.append(buf, strLen);