Generate coverage with Rust nightly

[garious]

Fixes #177

Thanks @marco-c!

[mvines]

Need to update https://github.com/solana-labs/solana/blob/master/ci/coverage.sh#L13 as well

[garious]

Hey @mvines, I can't seem to reproduce the nightly build within docker on macos. It gets stuck compiling pnet_transport when installing cargo-cov.

In CI, this build fails because gcov fails, which is called by the codecov bash script. To fix, we probably need a gcov version that matches Rust's coverage instrumentation. The cargo-cov repo suggests installing libclang-common-6.0-dev on Ubuntu. I assume that'll install llvm.gcov. We'd need to tell the codecov script to use that gcov_exe instead of gcov. Ideally, Rust would deploy llvm.gcov. There's an open ticket to add some LLVM tools, but that list doesn't currently include llvm.gcov: rust-lang/rust#49584 @marco-c, any related info we should be aware of?

[marco-c]

The problem is that the codecov tool is trying to use gcov, but gcov is the gcc tool which parses a different version of the gcno/gcda format.
It should use llvm-cov.
A possible solution is to generate the codecov output yourself (e.g. using grcov) and upload it yourself. Perhaps we should add this to cargo-cov.

[marco-c]

Or you could try this "hack": codecov/codecov-bash#55 (comment) (with latest llvm-cov, not llvm-cov-3.8).

[codecov]

Codecov Report

Merging #378 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #378   +/-   ##
=======================================
  Coverage   91.34%   91.34%           
=======================================
  Files          36       36           
  Lines        3583     3583           
=======================================
  Hits         3273     3273           
  Misses        310      310

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[marco-c]

(to use grcov with Rust-generated files you need to pass the --llvm option)

[garious]

Thanks @marco-c, I confirmed that adding the --llvm option gets grcov to run out-of-the-box on macOS.