MDEV-13703 Illegal mix of collations for operation 'json_object' on

using JSON_UNQUOTE as an argument.

        The coercibility and repertoire should be set properly for the
        JSON_UNQUOTE.

mysql-test/r/func_json.result

@@ -405,6 +405,13 @@ abc
 select json_unquote('abc');
 json_unquote('abc')
 abc
+create table t1 (c VARCHAR(8)) DEFAULT CHARSET=latin1;
+insert into t1 values ('abc'),('def');
+select json_object('foo', json_unquote(json_object('bar', c)),'qux', c) as fld from t1;
+fld
+{"foo": "{\"bar\": \"abc\"}", "qux": "abc"}
+{"foo": "{\"bar\": \"def\"}", "qux": "def"}
+drop table t1;
 select json_object("a", json_object("b", "abcd"));
 json_object("a", json_object("b", "abcd"))
 {"a": {"b": "abcd"}}

mysql-test/t/func_json.test

@@ -164,6 +164,14 @@ drop table t1;
 
 select json_unquote('"abc"');
 select json_unquote('abc');
+#
+# MDEV-13703 Illegal mix of collations for operation 'json_object' on using JSON_UNQUOTE as an argument.
+#
+create table t1 (c VARCHAR(8)) DEFAULT CHARSET=latin1;
+insert into t1 values ('abc'),('def');
+ 
+select json_object('foo', json_unquote(json_object('bar', c)),'qux', c) as fld from t1;
+drop table t1;
 
 select json_object("a", json_object("b", "abcd"));
 select json_object("a", '{"b": "abcd"}');

sql/item_jsonfunc.cc

@@ -581,7 +581,8 @@ String *Item_func_json_quote::val_str(String *str)
 
 void Item_func_json_unquote::fix_length_and_dec()
 {
-  collation.set(&my_charset_utf8_general_ci);
+  collation.set(&my_charset_utf8_general_ci,
+                DERIVATION_COERCIBLE, MY_REPERTOIRE_ASCII);
   max_length= args[0]->max_length;
   maybe_null= 1;
 }
@@ -1458,7 +1459,8 @@ void Item_func_json_array::fix_length_and_dec()
 
   if (arg_count == 0)
   {
-    collation.set(&my_charset_utf8_general_ci);
+    collation.set(&my_charset_utf8_general_ci,
+                  DERIVATION_COERCIBLE, MY_REPERTOIRE_ASCII);
     tmp_val.set_charset(&my_charset_utf8_general_ci);
     max_length= 2;
     return;