Rust code-coverage in Emacs

December 10, 2025

After Shapr found cov (updated from cov.el) I once again attempted to make coverage appear in Emacs.

This time with success!

For a Rust project I’m currently working on, this means:

• run cargo install cargo-llvm-cov
• run your tests with the above, asking for “LCOV” ouput: cargo llvm-cov --lcov > src/coverage.info
• note the re-direct: you need to put a “.info” file beside your “*.rs” files.
• now, open e.g. ./src/lib.rs and do M-x cov-mode
• this should find the coverage and use the “fringe” to colourize lines