cargo-careful

cargo careful is a tool to run your Rust code extra carefully -- opting into a bunch of nightly-only extra checks that help detect Undefined Behavior, and using a standard library with debug assertions.

To use cargo careful, first install it:

cargo install cargo-careful

and then run the following in your project:

cargo +nightly careful test

Running cargo careful requires a recent nightly toolchain. You can also cargo +nightly careful run to execute a binary crate. All cargo test and cargo run flags are supported.

The first time you run cargo careful, it needs to run some setup steps, which requires the rustc-src rustup component -- the tool will offer to install it for you if needed.

What does it do?

The most important thing cargo careful does is that it builds the standard library with debug assertions. The standard library already contains quite a few sanity checks that are enabled as debug assertions, but the usual rustup distrubtion compiles them all away to avoid run-time checks. Furthermore, cargo careful sets some nightly-only flags that tell rustc to insert extra run-time checks to guard some unsafe operations against UB.

Here are some of the checks this enables:

• get_unchecked in slices performs bounds checks
• copy, copy_nonoverlapping, and write_bytes check that pointers are aligned and non-null and (if applicable) non-overlapping
• {NonNull,NonZero*,...}::new_unchecked check that the value is valid
• plenty of internal consistency checks in the collection types
• mem::zeroed and the deprecated mem::uninitialized panic if the type does not allow that kind of initialization

Note that some of these checks cause an abrupt abort (on Unix, this is a SIGILL) instead of panicking to reduce their performance impact.

That said, there is a lot of Undefined Behavior that is not detected by cargo careful; check out Miri if you want to be fully covered. The advantage of cargo careful over Miri is that it works on all code, supprts using arbitrary system and C FFI functions, and is much faster.