Fix inconsistency in PDO transaction state

[nikic]

This addresses an issue introduced by #4996 and reported in https://bugs.php.net/bug.php?id=80260.

Now that PDO::inTransaction() reports the real transaction state of the connection, there may be a mismatch with PDOs internal transaction state (in_tcx). This is compounded by the fact that MySQL performs implicit commits for DDL queries.

This PR fixes the issue by making beginTransaction/commit/rollBack work on the real transaction state provided by the driver as well (or falling back to in_tcx if the driver does not support it).

This does mean that writing something like

$pdo->beginTransaction();
$pdo->exec('CREATE DATABASE ...');
$pdo->rollBack(); // <- illegal

will now result in an error, because the CREATE DATABASE already committed the transaction. I believe this behavior is both correct and desired -- otherwise, there is no indication that the code did not behave correctly and the rollBack() was effectively ignored. However, this is still a BC break, so I wanted to double check this point.

If we don't do this change, I think we need to revert #4996 and not add full inTransaction() support for MySQL.

[mvorisek]

👍 from me

but what about other DB vendors? I think, the original PR:
https://github.com/php/php-src/pull/4996/files#diff-02177c92c94307ce53e201a823f1731aac9421e10896b335668ccb04b4107b1cR556
fixed only MySQL and at least Sqlite is unfixed:

php-src/ext/pdo_sqlite/sqlite_driver.c

Line 732 in e735de6

NULL, /* in_transaction */

[nikic]

@mvorisek This change has no effect on database drivers that don't implement custom in_transaction reporting.

[othercorey]

The original PR suggested the motivation was to allow mixing manual and PDO transaction commands. Should the test it added be adjusted to include scenarios like manually executing BEGIN then calling PDO::rollback()?

[nikic]

@othercorey Indeed, I've added some test coverage for that as well.