Ignore benchmarks when using stable/beta

Question

I have a file with some benchmarks and tests and would like to test against stable, beta and nightly. However, either I don\'t use the benchmark or stable/beta complain. Is ther

Answer 1

In my projects, I place benchmarks in a separate module, just like I do for tests. I then create a Cargo feature that enables them. In this excerpt, I used the feature name unstable, but you can use anything you'd like:

Cargo.toml

# ...

[features]
unstable = []

# ...

src/lib.rs

#![cfg_attr(feature = "unstable", feature(test))]

#[cfg(test)]
mod tests {
    #[test]
    fn a_test() {
        assert_eq!(1, 1);
    }
}

#[cfg(all(feature = "unstable", test))]
mod bench {
    extern crate test;
    use self::test::Bencher;

    #[bench]
    fn a_bench(b: &mut Bencher) {
        let z = b.iter(|| {
            test::black_box(|| {
                1 + 1
            })
        });
    }
}

The line #[cfg(all(feature = "unstable", test))] says to only compile the following item if the feature is set and we are compiling in test mode anyway. Likewise, #![cfg_attr(feature = "unstable", feature(test))] only enables the test feature flag when the unstable feature is enabled.

Here's an example in the wild.