feat: getStateDiff / getStateDiffJson decode storage for non local contracts

[sakulstra]

Component

Forge

Describe the feature you would like

We're using foundry to analyze transactions via getStateDiff[Json].

For this case it would be very useful to have state decoding also for touched contracts that are not part of the current codebase. Not exactly sure about how it works on tracing, but i guess it would be a matter of downloading the contracts from the explorer when running the tests.

Additional context

getStateDiff[Json] already is a huge improvement to local transaction analysis, but it falls short when using foundry for testing upgrades against forks / interacting with pre-deployed existing contracts.
Therefore it would be great to have the ability (even if with a flag) to have state decoding on external contracts as well.

[mathecodemoon]

Can i try it ?

[pjdurden]

Hi @sakulstra — I'd like to work on this (saw @simon0820s asked but there's no PR yet).

Approach: extend getStateDiff / getStateDiffJson so storage slots for touched contracts that aren't part of the local project are still decoded, by fetching the ABI for those addresses from the configured explorer (reusing the existing explorer/etherscan client) and caching per-address for the run. When no ABI or explorer key is available it would fall back to the current raw-slot output so fork/upgrade tests still work offline, and the network fetch would be gated behind the existing explorer config.

Does that direction work for you?