getting values of emitted events

[stillmatic]

I'm looking at updating https://github.com/optionality/clone-factory and testing it with forge.

One of the functions does the following, and emits an event with the clone address (vs returning it)

    function createThing(string memory _name, uint256 _value) public {
        address clone = createClone(libraryAddress);
        Thing(clone).init(_name, _value);
        emit ThingCreated(clone, libraryAddress);
    }

the tests then pick up this address by doing

 _factory.createThing(name, value)
          .then(tx => {
            return Thing.at(tx.logs[0].args.newThingAddress);
          })

Is there a similar way to get the logged / emitted events and their arguments in forge?

[onbjerg]

That's not currently possible but it would definitely make sense to explore a cheatcode like that. Ergonomics wise it probably wouldn't be very good since you would need to do some manual abi.decode calls etc.

[fubhy]

I just ran into a case like that too. This is also slightly related to what's been discussed in #512 as extracting parameters from loosely matched events could also be a reasonable solution for that one.

[mds1]

I agree this we should have log functionality like this, though like @onbjerg mentioned UX will be probably be pretty gross unless we implement solidity pre-processing first

One note is that in this specific use case you can precaclulate the expected address, then assert there's code at the address after the createThing call. If you use create2 you can do this now, if you use create you'd need #554 to be implemented first

[gakonst]

In this use case, I'd manually calculate the create2/create address via their corresponding algos using from/nonce/salt/bytecode hash.

More generally, similar to how we record accessed storage slots, should we add a captureLogs and getLogs cheatcode perhaps? Not sure what the ideal UX here would be, cc @brockelmore, and nice abi decoding automatically seems hard

[bentobox19]

Is this in the roadmap somewhere? I was porting some Ethernaut, and while you can modify the contract Ethernaut.sol to return you the values instead of emitting an event, would be great to have a cheat code capturing that info for you.

I have 3 days of experience with forge 😅, @gakonst is talking above of some gotchas on implementing this, however I see that the logs are outputted at the traces.:

Anyways, I'm happy to brush up my rust skills and implement this cheat code if it is in the roadmap. Where should I go? Who should I talk to?

[onbjerg]

You can use expectEmit for now, but yeah, we plan to add this at some point

[bentobox19]

Started work on implementing vm.captureLogs

https://github.com/bentobox19/foundry/commits/feature/capture-logs

I'd like to set a draft PR in this repository

[bentobox19]

Alright, just started a draft PR. Hope I can squeeze the hours to get it done 😅

#2161