Bug: Transactions already disposed

[PhMemmel]

Debug-Info:  Transactions already disposed
Error code: dmltransactionexception

Stack trace: 
line 103 of /lib/dml/moodle_transaction.php: dml_transaction_exception thrown
line 1969 of /mod/ratingallocate/locallib.php: call to moodle_transaction->rollback()
line 382 of /mod/ratingallocate/locallib.php: call to ratingallocate->save_ratings_to_db()
line 1262 of /mod/ratingallocate/locallib.php: call to ratingallocate->process_action_give_rating()
line 59 of /mod/ratingallocate/view.php: call to ratingallocate->handle_view()

To reproduce:

• Create new ratingallocate instance
• Configure times so voting is possible
• Set Completion conditions to "Students must manually mark the activity as done"
• As student go to the ratingallocate instance and try to vote, you will see the exception

Reason is the line $completion->update_state($this->coursemodule, COMPLETION_UNKNOWN, $userid); which throws an exception here: https://github.com/moodle/moodle/blob/30692df8495bd16fc579f4c448bb322ece29cf84/lib/completionlib.php#L649

I'm not too deep into the completion code so I cannot really see what exactly is the issue with the completion here unless investing a lot of time I currently unfortunately do not have.

But besides that I feel like the transaction handling should also be improved: Exceptions being caused after the transaction has been commited must not trigger the rollback.

Tested with latest master on latest vanilla main. Issue at least exists also since de61f8d.

[dlmsr]

Thanks for the report. We will have a look :)