[MDEV-6572] "USE dbname" with a bad sequence erroneously connects to a wrong database - Jira

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I create a database with some question marks in the name:

DROP DATABASE IF EXISTS `test????`;

CREATE DATABASE `test????`;

Now I run a "USE" query with a bad byte sequence:

SET NAMES utf8;

USE `test��`;

SELECT DATABASE(), HEX(DATABASE());

(notice. '��' is a four-byte UTF-8 character, which is considered as a wrong
byte sequence by MariaDB's 3-byte "utf8").

It erroneously connects to the database 'test????':

ariaDB [(none)]> SET NAMES utf8;

Query OK, 0 rows affected (0.00 sec)

MariaDB [(none)]> USE `test��`;

Database changed

MariaDB [test��]> SELECT DATABASE(), HEX(DATABASE());

+------------+------------------+

| DATABASE() | HEX(DATABASE())  |

+------------+------------------+

| test????   | 746573743F3F3F3F |

+------------+------------------+

1 row in set (0.00 sec)

The correct behaviour would be report either "unknown database",
or "bad database name" or "Invalid utf8 character string: 'test\xF0\x9F\x98\x81'".

The latter would be consistent with what's reported on attempt to
create a database with such a broken name:

MariaDB [test]> CREATE DATABASE `test��`;

ERROR 1300 (HY000): Invalid utf8 character string: 'test\xF0\x9F\x98\x81'

A similar problem also happens with table names.
I create a table with question marks in its name:

SET NAMES utf8;

DROP TABLE IF EXISTS `test????`;

CREATE TABLE `test????` (a INT);

INSERT INTO `test????` values (10);

Now I change the connection character set to utf8mb4 and run a SELECT query:

SET NAMES utf8mb4;

SELECT * FROM `test��������`;

It returns rows from the table `test????`:

+------+

| a    |

+------+

|   10 |

+------+

1 row in set (0.01 sec)

The expected behaviour would be to return some error.

is blocked by

MDEV-6566 Different INSERT behaviour on bad bytes with and without character set conversion

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