TimelockController 'salt' is unrecoverable yet required for execution

When scheduling a transaction using the TimelockController, one is required to provide a salt to distinguish otherwise identical transactions. The salt parameter is not emitted in the CallScheduled event which makes it impossible to recover. Yet salt is required for executing the scheduled transaction transaction, even though it isn’t necessary and more gas efficient if id is used instead.

💻 Environment

Openzeppelin v4.5.0 / hardhat

📝 Details

salt is missing from the CallScheduled event: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/458697be32f41946e1ab66e946c7cf373c79577d/contracts/governance/TimelockController.sol#L35

salt is required for the execute & executeBatch calls: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/458697be32f41946e1ab66e946c7cf373c79577d/contracts/governance/TimelockController.sol#L267

Instead of salt the execute methods should be consuming the hashed operation (id) directly, since that id is readily available via event data. This would also save on gas since there is no need to re-run the hashing operation.

Happy to submit a PR

[frangio]

So we need to emit the salt in an event, but we can’t change the existing event because it changes the event selector, which is a little concerning because any monitoring infrastructure in place will not see the new event.

We can emit the salt in a new event ProposalSalt(uint256 indexed proposalId, bytes32 salt).

[Amxx]

@ashwinYardi Cancel doesn’t have other params. It just cancels the proposal that has a given ID.

We could have required the cancel call to send all the details, hash them, and cancel that, but it would have been more expensive, and not safer.

In short

• execute: we are actually executing, so we need the execution details and we have to validate them;
• cancel: we are just internally canceling, we don’t need the execution details.