feat(cheatcodes): decode and show mismatched params on expectEmit

[yash-atreya]

Motivation

Supersedes #8686
Closes #592
Closes #8506

Solution

• Improves the revert message for expectEmits when there is a mismatch in params.
• log != expected log has been replaced with the named event variant: ComplexEvent != expected SimpleEvent if decoding is successful
• In the improved error message the parameter index is specified along with the expected and got (actual) data. For example, consider the following test:

// in src/
contract EventEmitter {
    event SimpleEvent(uint256 indexed a, uint256 indexed b, uint256 c);
    function emitSimple(uint256 a, uint256 b, uint256 c) public {
        emit SimpleEvent(a, b, c);
    }
}

// in test/
contract EmitterTest is Test {
    event SimpleEvent(uint256 indexed a, uint256 indexed b, uint256 c);

    function testParamMismatch() public {
        EventEmitter eventEmitter = new EventEmitter();
        vm.expectEmit(true, true, true, true);
        emit SimpleEvent(100, 200, 300);
        eventEmitter.emitSimple(100, 999, 300); // param (b) mismatch
    }
}

This test will fail with:

[FAIL: SimpleEvent param mismatch at b: expected=200, got=999] testParamMismatch()

• We're checking both the indexed params of an event i.e log.topics and also the non-indexed params which are part of the log.data.
• Param index starts from 0.
• If there is an emitter mismatch: the log emitter mismatch: expected=0x..., got=0x... error is thrown
• To decode the events and their params, the SignaturesIdentifier has now been added to the Cheatcodes struct -Decoding only works over local selectors cache.
• Note: Decoding does not work for anonymous events.

PR Checklist

• Added Tests
• Added Documentation
• Breaking changes

[grandizzy]

that's awesome, is there any way we could decode and show mismatched values?

[yash-atreya]

that's awesome, is there any way we could decode and show mismatched values?

I think we should be able to do it with SignatureIdentifier in offline mode ?

[zerosnacks]

Much better! 👍

[grandizzy]

thank you, left some initial nits / questions

[grandizzy]

isn't this logic already covered in get_indexed_event fn so we could just do here

  let event = foundry_common::block_on(identifier.identify_event(t0))?;
  let indexed_event = get_indexed_event(event, log);

  // Try to decode the event
  if let Ok(decoded) = indexed_event.decode_log(log) {
...

?

[yash-atreya]

This is because get_indexed_event is using a heuristic which gives preference to an address while categorizing whether a param is indexed or not.

It incorrectly guesses the number of indexed parameters for:

event MixedEventNumbering(
        uint256 indexed param0,
        address indexed param1,
        uint256 param2,
        uint256 param3,
        address param4 // Marks this as `indexed` leading to decoding failure.
    );

This is due to this if condition:

if num_inputs == indexed_params
                || (num_address_params == indexed_params && param.ty == "address") // 2nd condition is true for above event 
            {
                param.indexed = true;
            }

So, TL;DR don't use get_indexed_event if we already know the indexed params

[grandizzy]

lgtm, thank you, left one more optional nit