bug(`cheatcodes`): expectEmit behaves weirdly

[MathisGD]

Component

Forge

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

• Foundry
• Foundryup

What version of Foundry are you on?

1.1.0-stable

What version of Foundryup are you on?

0.3.3

What command(s) is the bug in?

forge t

Operating System

None

Describe the bug

in a call following a expectEmit, if a reverts happens before the event emission the test will fail with log != expected log. It seems way more natural to fail with EvmError: Revert for two reasons: nobody should be testing even emission on failing paths (events are not emitted if the call reverted), and reverts are "more important" than wrong log. Also the inconsistent behaviour if the event is emitted before the revert is weird (the event will not be emitted if the call reverts).

minimal example:

    event Foo();

    function revertingBefore() external {
        revert();
        emit Foo();
    }

    function revertingAfter() external {
        emit Foo();
        revert();
    }

    // this test fails with `log != expected log`
    function testBefore() public {
        vm.expectEmit();
        emit Foo();
        this.revertingBefore(); // reverting call
    }

    // this test fails with `EvmError: Revert`
    function testAfter() public {
        vm.expectEmit();
        emit Foo();
        this.revertingAfter(); // reverting call
    }

https://github.com/MathisGD/forge-expect-emit-bug/

[zerosnacks]

Hey @MathisGD, thanks for the report - I agree, it would be expected that this reverts with EvmError: Revert

Related section:

foundry/crates/cheatcodes/src/inspector.rs

Lines 1645 to 1665 in 292d248

	// Not all emits were matched.
	if self.expected_emits.iter().any(|(expected, _)| !expected.found) {
	outcome.result.result = InstructionResult::Revert;
	outcome.result.output = "log != expected log".abi_encode().into();
	return outcome;
	}
	if !expected_counts.is_empty() {
	let msg = if outcome.result.is_ok() {
	let (expected, count) = expected_counts.first().unwrap();
	format!("log emitted {count} times, expected {}", expected.count)
	} else {
	"expected an emit, but the call reverted instead. \
	ensure you're testing the happy path when using `expectEmit`"
	.to_string()
	};
	outcome.result.result = InstructionResult::Revert;
	outcome.result.output = Error::encode(msg);
	return outcome;
	}