MySQL adapter silently truncates strings with 4 byte UTF-8 chars

MySQL does not support 4 byte characters in UTF-8 strings. If you try to insert/update a row with a string containing a 4 byte character, the statement succeeds, but the string is truncated at the position of the character. Only the warnings indicate that something went wrong:

mysql> set names 'utf8';                                                        Query OK, 0 rows affected (0.00 sec)
mysql> update test set `test` = 'AAAAAAAAAAAAA𝑖BBBBBBBBB';
Query OK, 0 rows affected, 1 warnings (0.00 sec)
Rows matched: 3  Changed: 0  Warnings: 0

mysql> show warnings;
+---------+------+----------------------------------------------------------------------------+
| Level   | Code | Message                                                                    |
+---------+------+----------------------------------------------------------------------------+
| Warning | 1366 | Incorrect string value: '\xF0\x9D\x91\x96AA...' for column 'test' at row 1 | 
+---------+------+----------------------------------------------------------------------------+
3 rows in set (0.02 sec)

-> column test now contains "AAAAAAAAAAAAA".

Since Activerecord does not evaluate the warnings, the problem can not be detected by the application.

AR should probably promote this warning to an error.