---
title: "cargo careful: run your Rust code with extra careful debug checking"
categories: rust
+reddit: /rust/comments/xogayv/cargo_careful_run_your_rust_code_with_extra/
---
Did you know that the standard library is full of useful checks that users never get to see?
-There are plenty of debug assertions in the standard library that will do things like check that `char::from_u32_unchecked` is called on a valid `char`, that `CStr::from_bytes_with_nul_unchecked` does not have internal nul bytes, or that pointer functions such as `read`, `copy`, or `copy_nonoverlapping` are called on suitably aligned non-null (and non-overlapping) pointers.
+There are plenty of debug assertions in the standard library that will do things like check that `char::from_u32_unchecked` is called on a valid `char`, that `CStr::from_bytes_with_nul_unchecked` does not have internal nul bytes, or that pointer functions such as `copy` or `copy_nonoverlapping` are called on suitably aligned non-null (and non-overlapping) pointers.
However, the regular standard library that is distributed by rustup is compiled without debug assertions, so there is no easy way for users to benefit from all this extra checking.
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[`cargo careful`](https://github.com/RalfJung/cargo-careful) is here to close this gap:
when invoked the first time, it builds a standard library with debug assertions from source, and then runs your program or test suite with that standard library.
-Installing `cargo careful` is as easy as `cargo install cargo-careful`, and then you can do `cargo careful run`/`cargo careful test` to execute your binary crates and test suites with an extra amount of debug checking.
+Installing `cargo careful` is as easy as `cargo install cargo-careful`, and then you can do `cargo +nightly careful run`/`cargo +nightly careful test` to execute your binary crates and test suites with an extra amount of debug checking.
This will naturally be slower than a regular debug or release build, but it is *much* faster than executing your program in [Miri](https://github.com/rust-lang/miri) and still helps find some Undefined Behavior.
Unlike Miri, it is fully FFI-compatible (though the code behind the FFI barrier is completely unchecked).
Meanwhile, if you have some `unsafe` code that for one reason or another you cannot test with Miri, give [`cargo careful`] a try and let me know how it is doing. :)
[`cargo careful`]: https://github.com/RalfJung/cargo-careful
+
+*By the way, I am soon [starting as a professor at ETH Zürich]({% post_url 2022-08-16-eth %}), so if you are interested in working with me on programming language theory as a master student, PhD student, or post-doc, then please [reach out](https://research.ralfj.de/contact.html)!*
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