## 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

* 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.

### Requirements

Nightly rust is required, as [save-analysis is unstable](https://github.com/rust-lang/rust/issues/43606).
Despite the name, warnalyzer [does not use rust-analyzer](https://github.com/rust-analyzer/rust-analyzer) (yet).

### 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](https://github.com/rust-lang/rust/issues/49178#issuecomment-375454487))
* `#[allow(dead_code)]` has no effect
* Entry points (main function, etc) [are detected as unused](https://github.com/est31/warnalyzer/issues/6)

### Other bugs

* Enum variants are not recognized (worked around in the code but [it would be cool to have the rustc bug fixed](https://github.com/rust-lang/rust/issues/61302))
* Uses in enum struct variants are not recognized as such ([upstream bug](https://github.com/rust-lang/rust/issues/61385))
* 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](https://github.com/servo/servo/pull/23477), [PR 2](https://github.com/servo/servo/pull/23498), [PR 3](https://github.com/servo/servo/pull/23499), [PR 4](https://github.com/servo/servo/pull/23532)
* rustc: [PR 1](https://github.com/rust-lang/rust/pull/77739), [PR 2](https://github.com/rust-lang/rust/pull/83185)

### License
[license]: #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](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.