…tional index)

https://jira.percona.com/browse/PS-7745

**Problem:**

A Stored Procedure execution fails after some executions when a functional index is present in the SP definition. The error behaves differently depending on the versions I tested:

8.0.23 (PS, Community): It only fails when using a temporary table. After the third execution, all the subsequent executions fail.

8.0.25 (Community): It also fails on normal tables.

How to Repeat

```
DROP PROCEDURE IF EXISTS `sproc`;
DELIMITER $$
CREATE PROCEDURE `sproc`()
BEGIN
DROP TEMPORARY TABLE IF EXISTS `T1`;
CREATE TEMPORARY TABLE `T1`(
`C1` INT,
KEY ( ( `C1` > 0 ) )
);

SELECT 1 FROM ( SELECT 1 `C2` ) `T2`;
END$$
DELIMITER ;
Now if you invoke that procedure 3 times in a row:

mysql> CALL `sproc`(); CALL `sproc`(); CALL `sproc`();
+---+
| 1 |
+---+
| 1 |
+---+
1 row in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)

+---+
| 1 |
+---+
| 1 |
+---+
1 row in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)

ERROR 3107 (HY000): Generated column can refer only to generated columns defined prior to it.
On 8.0.25 (Community) The error is

ERROR 3754 (HY000): Functional index 'functional_index' cannot refer to an auto-increment column.
```

**Cause:**

The issue happens when checks are performed again during a query
in the function `pre_validate_value_generator_expr()`
and column index of the functional index is not available.

**Solution:**

This solution disables some checks if a column index is not available
in the function `pre_validate_value_generator_expr()` during the second
and later queries.
It is safe because these checks are done in the function
`validate_value_generator_expr()` during the first query.
The column index is available there.

… a functional index)