In discussing another topic with @LasseAztec, we’ve uncovered another issue of fee abstraction:
Be mindful that if part of a transaction is reverting, say the public part of a call, it will revert the entire transaction. Similarly to Ethereum, it might be possible for the block builder to create a block such that your valid transaction reverts because of altered state, e.g., trade incurring too much slippage or the like. (source)
This means that the fact that the user has submitted a valid proof for their private execution, which includes the fee payment, is no guarantee that the fee will be paid, because a depending public function execution that comes later could revert the whole thing, leaving the sequencer without their fee.
I can think of two ways around this:
- Enqueued public function calls do not revert their associated private executions (this breaks @LasseAztec’s proposal for access control).
- We reintroduce a “signature validation and fee payment phase” for each tx, which is not allowed to make public calls, and is not reverted if a public call downstream fails.