vm.cool cheatcode

[Philogy]

Component

Forge

Have you ensured that all of these are up to date?

• Foundry
• Foundryup

What version of Foundry are you on?

forge 0.2.0 (2865fa5 2022-04-14T21:44:28.244220110+00:00)

What command(s) is the bug in?

forge test

Operating System

Linux

Describe the bug

With the introduction of the Berlin hardfork EIP2929 was implemented and went live on the Ethereum blockchain. This EIP introduced cost changes to storage and account accessing opcodes, including (but not limited to): SLOAD, SSTORE, CALL, BALANCE etc. Specifically these opcodes received an additional cost the first time they are used to access storage slots and/or accounts within a transaction. These costs are however not always properly accounted for in foundry solidity tests. Specifically addresses and storage slots seem to remain warm between calls within the context of a single test, falsely reducing the cost of calls and certain contract executions. This not only leads to inaccurate traces but gas usage dependent tests may also incorrectly fail / pass.

This bug may or may not be a feature. It is likely more useful / straightforward if accounts and storage slots do not remain warm between calls within a single test by default. Cheat codes may be added to purposefully keep accounts and storage slots warm or potentially even pre-warm to simulate transactions with access lists (EIP2930).

EDIT(onbjerg): I am requesting a vm.cool(address) cheatcode to cool off warm accounts

[onbjerg]

If you call the same contract multiple times within a single test, then the storage slot remains warm. This is intended, and largely a very very very hard fix, so I don't think the cost of changing this behavior is worth it. In some cases, it might even be the preferred behavior, further complicating the change, since we would probably need a way to switch between one or the other

However, the first time you call a contract within a test, that gas usage should be correct. It might be slightly off, see #960

[Philogy]

Ah ok, must of overlooked it in the documentation. I guess I should create a feature request for cool off accounts and storage slots cheat code

[onbjerg]

I changed the issue to request a vm.cool(address) cheatcode - does this make sense to you?

[Philogy]

Yes, thank you!

[clauBv23]

Hi there,

If this cheatcode already on life?

I see this seems completed and #5830 is merged however I'm not able to use vm.cool and it is not in the documentation.

[norswap]

@clauBv23 I came with the same question, looks like it was rollback and there is a new PR here, but it's pretty dead: #5852 (no activity since december)

An alternative is to use the --isolate option in forge test to make whatever changes you need to the slots in a first call, then do the code you care about in another call where the slots will be cool again. Doesn't cover all the use cases for vm.cool but it's probably going to work for us (yet to be tested though).