Add a vm.mockCallRevert cheatcode

[fubhy]

Component

Forge

Describe the feature you would like

I might be missing something but it seems like it's currently only possible to mock return values, but not reverts. For now, in my case I can simply create a Mock contract that does that for me but I'd imagine it could be handy to allow this via a cheatcode for convenience.

vm.mockCallRevert("revert reason / error")

Additional context

No response

[onbjerg]

Makes sense

[mds1]

IMO if this is added we can also close foundry-rs/forge-std#46, as cheatcodes would then cover the majority of mocking use cases

[tynes]

Could you mock a revert by returning abi.encodeWithSignature("Error(string)", abi.encode("my error message")) or if its a custom revert just abi encoding the custom error?

[mds1]

I don't think so, because the call's success output would still be true instead of false

[tynes]

I suppose you could make vm.mockCall aware of the data passed in and check to see if the 4byte selector matches Error(string) or any of the custom errors and have it return false, but that adds complexity to the implementation of mock call. I'd be happy as long as whatever solution could work with custom errors. Also wondering if something like this could be used to test exceptional errors like evm out of gas in a subcall

[onbjerg]

Also wondering if something like this could be used to test exceptional errors like evm out of gas in a subcall

No, that would make the EVM unwind entirely. No way to stop that.

[tynes]

Also wondering if something like this could be used to test exceptional errors like evm out of gas in a subcall

No, that would make the EVM unwind entirely. No way to stop that.

I mean something like:

vm.ExpectRevert(RevertReasons.OUT_OF_GAS);
(bool success, ) = target.call{ gas: 1 }(...);

Where you pass a defined amount of gas to a subcall and it reverts there but there is still gas left in the higher level call to continue. This is probably a more fringe usecase so not super important

[onbjerg]

This would still cause the EVM to unwind 😄

[adhusson]

This would be very useful.

[sendra]

How is the state of this? It would be very useful

[reubenr0d]

I have a working mvp here: #4343

Shall I take things forward?

[mds1]

That would be awesome, thanks @reubenr0d. I'll assign this to you. I think we need two functions, one that requires value, and one that doesn't:

function mockCallRevert(address, bytes calldata, bytes calldata) external;
function mockCallRevert(address, uint256, bytes calldata, bytes calldata) external;

[reubenr0d]

Thanks @mds1, I've made an attempt here: #4343
I'm still learning the ropes with rust and would appreciate a little help with this. The tests that mockCallRevert on an already mockCalled call and vice versa fail right now.