Gracefully handle ErrorKind::BrokenPipe (public-api ... | head -n 1)

[Enselic]

So that we don't get an error when doing something like this:

% RUSTDOCFLAGS='-Z unstable-options --output-format json' cargo +nightly doc  --manifest-path tests/crates/comprehensive_api/Cargo.toml --lib --no-deps
% ./target/debug/public-api tests/crates/comprehensive_api/target/doc/comprehensive_api.json | head -n 1
pub async fn comprehensive_api::functions::async_fn() -> impl Future<Output = ()>
Error: Os { code: 32, kind: BrokenPipe, message: "Broken pipe" }

[Enselic]

Hmm maybe we should implement the fix with the #[pipefail] functionality of https://github.com/myrrlyn/calm_io. The test can still be re-used.

Cons:

• Requires a new dependency, and I try to keep number of dependencies minimal for public-api

Pros:

• Only one line required to fix the problem (it seems)

For cargo-public-api I'd say it is fine to use the extra dependency. I'll think about it some more (and try it out) for public-api.

[Enselic]

I found a way that I consider lightweight enough to not warrant an additional dependency. I will think about this for one more day and then merge.

(rust-lang/rust#96647 was just approved so we will need to make a release any day now to keep working with latest nightly)