From 0cd731864e6e4d88b75bfea4f02454871aedb89e Mon Sep 17 00:00:00 2001
From: Alexey Botchkov <holyfoot@askmonty.org>
Date: Tue, 12 Sep 2017 15:21:53 +0400
Subject: [PATCH] MDEV-13104 Json functions.

        An extra ',' added to the JSON_MERGE result making it invalid.
---
 mysql-test/r/func_json.result |  3 +++
 mysql-test/t/func_json.test   |  5 +++++
 sql/item_jsonfunc.cc          | 17 ++++++++++++++---
 3 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/mysql-test/r/func_json.result b/mysql-test/r/func_json.result
index 80de41ccb07..fc4eb16a067 100644
--- a/mysql-test/r/func_json.result
+++ b/mysql-test/r/func_json.result
@@ -683,3 +683,6 @@ JSON_OBJECT("foo", "bar`bar")
 SELECT JSON_SET('{}', '$.age', 87);
 JSON_SET('{}', '$.age', 87)
 {"age": 87}
+SELECT JSON_MERGE('[]', '{"c":"d"}');
+JSON_MERGE('[]', '{"c":"d"}')
+[{"c": "d"}]
diff --git a/mysql-test/t/func_json.test b/mysql-test/t/func_json.test
index 6d640f42003..8fc1f321928 100644
--- a/mysql-test/t/func_json.test
+++ b/mysql-test/t/func_json.test
@@ -333,3 +333,8 @@ SELECT JSON_OBJECT("foo", "bar`bar");
 #
 SELECT JSON_SET('{}', '$.age', 87);
 
+#
+# MDEV-13104 Json functions.
+#
+SELECT JSON_MERGE('[]', '{"c":"d"}');
+
diff --git a/sql/item_jsonfunc.cc b/sql/item_jsonfunc.cc
index e5544c6265d..52b3f570844 100644
--- a/sql/item_jsonfunc.cc
+++ b/sql/item_jsonfunc.cc
@@ -1971,14 +1971,25 @@ continue_j2:
   else
   {
     const uchar *end1, *beg1, *end2, *beg2;
+    int empty_array= 0;
 
     beg1= je1->value_begin;
 
     /* Merge as a single array. */
     if (je1->value_type == JSON_VALUE_ARRAY)
     {
-      if (json_skip_level(je1))
+      int cur_level= je1->stack_p;
+      empty_array= 1;
+      while (json_scan_next(je1) == 0)
+      {
+        if (je1->stack_p < cur_level)
+          break;
+        empty_array= 0;
+      }
+
+      if (je1->s.error)
         return 1;
+
       end1= je1->s.c_str - je1->sav_c_len;
     }
     else
@@ -1995,8 +2006,8 @@ continue_j2:
         end1= je1->value_end;
     }
 
-    if (str->append((const char*) beg1, end1 - beg1),
-        str->append(", ", 2))
+    if (str->append((const char*) beg1, end1 - beg1) ||
+        (!empty_array && str->append(", ", 2)))
       return 3;
 
     if (json_value_scalar(je2))