Code coverage showing [derive(Debug)] as missed region

[Wameuh]

I tried this code:

#[derive(PartialEq, Debug)]
pub enum EnumCov{
    First,
    Second,
    Third,
    Fourth
}



#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_cov() {
        let one = EnumCov::First;
        let two = EnumCov::Second;
        let three = EnumCov::Third;
        let four = EnumCov::Fourth;

        assert_eq!(one, EnumCov::First);
        assert_eq!(two, EnumCov::Second);
        assert_eq!(three, EnumCov::Third);
        assert_eq!(four, EnumCov::Fourth);
    }
}

Running these commands to get the code coverage report

cargo llvm-cov --html

Same issue with RUSTFLAGS="-C instrument-coverage" cargo test --tests merge/report/show

I expected to see this happen: coverage 100%

Instead, this happened: Debug is shown as missed region

It's quite the same as #83601

Meta

rustc --version --verbose:

rustc 1.65.0 (897e37553 2022-11-02)

binary: rustc

commit-hash: 897e37553bba8b42751c67658967889d11ecd120

commit-date: 2022-11-02

host: x86_64-unknown-linux-gnu

release: 1.65.0

LLVM version: 15.0.0

Backtrace not applicable.

Thanks!

[taiki-e]

@rustbot label +A-code-coverage

[ruuda]

The coverage report is correct, in the sense that <EnumCov as Debug>::fmt which is generated by #[derive(Debug)] is not executed by your test.

Being technically correct is not so helpful in the case of Debug though. Most of the time you don‘t expect it to be covered. The impl has to be there for assert_eq! to be able to print the counterexample, but when the test pass, the Debug impl is intentionally not covered. It would be nice to have a way to exclude it from coverage.

The same applies to expressions inside panic!, unreachable!, etc. — they are not covered, but they are not intended to ever be.

[Sycrosity]

Has anyone found a "good" solution to preventing coverage from marking #[derive(Debug)] and panic! macros as uncovered? Seeing as its not an actual issue with coverage, it would still be nice to be able to mark these instances as covered.

[VladasZ]

I have exactly the same problem. Is there a way to silence this? Or do I need to add dbg!() call for each struct?

[ruuda]

A possible workaround when using grcov is to use --excl-line to exclude e.g. #\[derive\(.