Cross-language code coverage

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Has anyone built code coverage infrastructure for a crate that also includes C++ code?

I'm using the new (as of 1.60) Rust-based code coverage instrumentation, which I'm generally liking very well. What I'd like to do is to also observe coverage for the C++ code that acts as an FFI for an underlying C++ library.

My attempt at that was here: Generate code coverage for ffi.cpp by scouten-adobe · Pull Request #64 · adobe/xmp-toolkit-rs · GitHub, but did not achieve the desired results. (No coverage info was generated for the ffi.cpp file.)

Any suggestions? Is this even possible?

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It looks to me like you're using gcov instrumentation on the C++ side (notice that CI fails to link because of missing gcov related symbols). While it's probably possible to mix gcov instrumentation on the C++ side with source based code coverage on the Rust side, I suspect the easiest thing to do would be to also use source based code coverage via Clang on the C++ side.

That will require changing your C++ compiler to Clang, if it isn't already, and then passing -fprofile-instr-generate -fcoverage-mapping when compiling.

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