Rust 1.88 adds support for naked functions

Rust 1.88 has been released, featuring support for writing naked functions, as well as backing for Boolean literals.

The update of the popular fast and safe programming language was announced June 26 by the Rust Release Team. Current Rust users can get Rust 1.88 by running rustup update stable.

Rust 1.88 adds language support for writing naked functions with no compiler-generated epilogue and prologue. This allows full control over the generated assembly for a particular function. The Rust team said this was a more ergonomic alternative to defining functions in a global_asm! block. A naked function is marked with the #[unsafe(naked)]attribute; its body consists of a single naked_asm! call. The team showed an example where a handwritten assembly block defines the entire function body. For naked functions, the compiler does not add any special handling for return values or arguments, unlike non-naked functions. Naked functions are used in low-level settings such as Rust’s compiler-builtins, operating systems, and embedded applications.

With Rust 1.88, the cfg predicate language now backs Boolean literals, true and false, acting as a configuration that is always enabled or disabled. This works in Rust conditional compilation with cfgand cfg_attr attributes, in the built-in cfg! macro, and in Cargo [target] tables in both configuration and manifests, the Rust team said. Previously, empty predicate lists could be used for unconditional configuration, like cfg(all()) for enabled and cfg(any()) for disabled, but cfg(true) and cfg(false) offer a more direct way to say what is meant, the team said.

Also with Rust 1.88, let statements now can be chained (&&) inside if and while conditions, and even intermingle with Boolean expressions. Thusly, there is less distinction between if and if let and between while and while let. The patterns inside the let sub-expressions can be refutable or irrefutable, and bindings are usable in later parts of the chain as well as the body, according to the Rust team.

Finally, the Cargo package manager now automatically runs garbage collection on the cache in its home directory. In explaining this change, the Rust team said that when building, Cargo downloads and caches crates needed as dependencies. Historically, these downloaded files were never cleaned up, leading to an unbounded amount of disk usage in Cargo’s home directory. With Rust 1.88, Cargo introduces a garbage collection mechanism to automatically clean up old files.

Rust 1.88 follows last month’s Rust 1.87 release, which brought accommodations for anonymous pipes and architecture intrinsics.