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COVERAGE.md

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Generating Rust Code Coverage for Coveralls

Install cargo-cov, and make sure llvm-cov is on your path:

cargo install cargo-cov
which llvm-cov

Run cargo-cov with nightly rust in the crate needing coverage:

cd /path/to/crate-root
rustup run nightly cargo cov test [-p package-name] [--bin binary-name] # for testing specific packages / binaries

Cargo-cov will instrument the crate's code with rustc's -Zprofiling flag, enabling coverage analysis. There must be NO panics in the crate being analyzed, or its tests. This may change in the future.

After a successful run of the crate's tests, cargo-cov outputs .gcda / .gcno files to crate-root/target/cov/build/{gcda,gcno}.

If you only want a nice chart of the coverage statistics, run rustup run nightly cargo cov report [--open], to generate a nice HTML readout.

Getting .gcov files from gcda / gcno sources for coveralls

This part is a little trickier. There is a tool by @marco-c called grcov which ingests gcda / gcno files, and outputs coveralls (and other) formatted files. At the time of writing, the tool runs into issues with gcda / gcno files generated using both llvm and gcc code.

It is still possible to get .gcov files using llvm-cov gcov, which falls back to a format compatible with GCC 4.2 (gcov format breaking changes after 4.2).

Cargo-cov's output files come with a leading hash to make merging work across multiple runs. So, the first thing to do is remove these leading hashes, and place all the gcda / gcno files in a single directory.

Another sticking point, llvm-cov gcov assumes that the gcda / gcno files share the same name as the instrumented source file (hangover from C/C++). That convention is fine, since llvm-cov allows one to specify gcda / gcno files manually.

As an example:

cd path/to/crate-root
mkdir gcov
cd gcov
llvm-cov gcov -b -gcda=../target/cov/build/gcda/analyzed-source-file.gcda -gcno=../target/cov/build/gcno/analyzed-source-file.gcno ../path/to/analyzed-source-file.rs

This will generate a number of .gcov files in the current working directory, complete with line and branching statistics (w/ the -b flag)!

There appear to be a couple tools avalailable for uploading .gcov to coveralls using their JSON API.