Warnalyzer

Remove unused code from multi-crate Rust projects.

The dead_code lint family of rustc is limited to one crate only and thus can't tell whether some public API is used inside a multi-crate project or not.

This tool, warnalyzer, provides unused code detection functionality for such multi-crate projects.

Usage (scip backend)

This backend supports stable, but it requires rust-analyzer to be available. Obtain it through rustup component add rust-analyzer.

• To run warnalyzer, invoke it via warnalyzer <path-to-project-dir>. It will generate the needed .scip file in the target directory.
• Alternatively, you can generate an scip file manually, via rust-analyzer scip for example, and pass it that file instead of the path.

Limitations

• The logic to find the target directory into which to put the .scip files is a bit rudimentary. Ideally we would somehow involve cargo in finding out where the target directory is.

save-analysis backend

Note

The save-analysis backend depends on the nightly feature save-analysis which was removed in February 2023. In order to use warnalyzer, use a nightly Rust version before February 16, 2023. (Issue)

Usage (save-analysis backend)

• Navigate to the project you want to analyze and run RUSTFLAGS="-Z save-analysis" cargo +nightly check.
• This command puts save analysis data into a path like target/debug/deps/save-analysis/cratename-longhash.json.
• Then, from the warnalyzer repo, do cargo run <path-to-json>
• It will list any items that it thinks weren't used.
• Make sure that you chose the json of the leaf crate. Using any other json file won't give you the full list of unused code.

Known bugs

It's still early on. There are a couple of bugs of the tool.

false-positives

These are the false positives known to me:

• Any usage by macros is not seen by the tool (save-analysis has bad macro support)
• #[allow(dead_code)] has no effect
• Entry points (main function, etc) are detected as unused

Other bugs

• Enum variants are not recognized (worked around in the code but it would be cool to have the rustc bug fixed)
• Uses in enum struct variants are not recognized as such (upstream bug)
• For loops: The expr part of for pat in expr {} is not seen as "use" of whatever the expression contains.
• No recursion like the dead_code lint of rustc, so if something only gets used by unused code, it doesn't get reported while it should.
• Multi-leaf crate trees are not supported (yet). Some projects may have multiple binaries they produce. Almost every project has tests. Some functions may only be used by some of those roots.

Trophy case

• servo: PR 1, PR 2, PR 3, PR 4
• rustc: PR 1, PR 2

License

This crate is distributed under the terms of both the MIT license and the Apache License (Version 2.0), at your option.

See LICENSE for details.

License of your contributions

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.