MDEV-37864: mysql-test/mtr --cursor main.func_json fails

Analysis:
Maximum length of the field of the temorary table that cursor protocol uses
is not enough, which it actually gets when we prepare the
json_array_intersect() function and set the max length of the result.
So even though the entire result is sent, only partial is actually copied
because the field length is not enough.

Fix:
Have enough max_length.

Author: mariadb-RuchaDeodhar

mysql-test/main/func_json.result

@@ -5297,4 +5297,14 @@ result
 SELECT ( WITH x AS ( WITH x ( x ) AS ( SELECT ( 1.000000 ) ) SELECT x FROM x ) SELECT * FROM x WHERE ( SELECT AVG ( x ) OVER ( ORDER BY JSON_ARRAY_INTERSECT ( '[["1", "7"], ["2", "6"], ["3", "8"]]' , '[["2","6"],["3","8"],["4","5"],["1","7"]]' ) ) FROM x ) );
 ( WITH x AS ( WITH x ( x ) AS ( SELECT ( 1.000000 ) ) SELECT x FROM x ) SELECT * FROM x WHERE ( SELECT AVG ( x ) OVER ( ORDER BY JSON_ARRAY_INTERSECT ( '[["1", "7"], ["2", "6"], ["3", "8"]]' , '[["2","6"],["3","8"],["4","5"],["1","7"]]' ) ) FROM x ) )
 1.000000
+#
+# MDEV-37864: mysql-test/mtr --cursor main.func_json fails
+#
+select json_array_intersect('[["1", "7"], ["2", "6"], ["4", "5"], ["3", "8"]]', '[["2","6"],["3","8"],["4","5"],["1","7"]]') from mysql.user;
+json_array_intersect('[["1", "7"], ["2", "6"], ["4", "5"], ["3", "8"]]', '[["2","6"],["3","8"],["4","5"],["1","7"]]')
+[["2", "6"], ["3", "8"], ["4", "5"], ["1", "7"]]
+[["2", "6"], ["3", "8"], ["4", "5"], ["1", "7"]]
+[["2", "6"], ["3", "8"], ["4", "5"], ["1", "7"]]
+[["2", "6"], ["3", "8"], ["4", "5"], ["1", "7"]]
+[["2", "6"], ["3", "8"], ["4", "5"], ["1", "7"]]
 # End of 11.4 Test

mysql-test/main/func_json.test

@@ -4196,4 +4196,10 @@ SELECT json_array_intersect(@a,@b);
 select json_array_intersect('[["1", "7"], ["2", "6"], ["4", "5"], ["3", "8"]]', '[["2","6"],["3","8"],["4","5"],["1","7"]]') as result from mysql.user;
 SELECT ( WITH x AS ( WITH x ( x ) AS ( SELECT ( 1.000000 ) ) SELECT x FROM x ) SELECT * FROM x WHERE ( SELECT AVG ( x ) OVER ( ORDER BY JSON_ARRAY_INTERSECT ( '[["1", "7"], ["2", "6"], ["3", "8"]]' , '[["2","6"],["3","8"],["4","5"],["1","7"]]' ) ) FROM x ) );
 
+--echo #
+--echo # MDEV-37864: mysql-test/mtr --cursor main.func_json fails
+--echo #
+
+select json_array_intersect('[["1", "7"], ["2", "6"], ["4", "5"], ["3", "8"]]', '[["2","6"],["3","8"],["4","5"],["1","7"]]') from mysql.user;
+
 --echo # End of 11.4 Test

sql/item_jsonfunc.cc

@@ -5501,8 +5501,8 @@ bool Item_func_json_array_intersect::prepare_json_and_create_hash(json_engine_t
       null_value= 1;
     }
 
-    max_length= (args[0]->max_length < args[1]->max_length) ?
-                 args[0]->max_length : args[1]->max_length;
+    max_length= 2*(args[0]->max_length < args[1]->max_length ?
+                 args[0]->max_length : args[1]->max_length);
 
     return false;
 }