The Rust team is happy to announce a new version of Rust, 1.84.0. Rust is a programming language empowering everyone to build reliable and efficient software. If you have a previous version of Rust installed via rustup, you can get 1.84.0 with: rustup $ rustup update stable $ rustup update stable If you don't have it already, you can get rustup from the appropriate page on our website, and check out the detailed release notes for 1.84.0. get rustup detailed release notes for 1.84.0 If you'd like to help us out by testing future releases, you might consider updating locally to use the beta channel (rustup default beta) or the nightly channel (rustup default nightly). Please report any bugs you might come across! rustup default beta rustup default nightly report What's in 1.84.0 stable Cargo considers Rust versions for dependency version selection 1.84.0 stabilizes the minimum supported Rust version (MSRV) aware resolver, which prefers dependency versions compatible with the project's declared MSRV. With MSRV-aware version selection, the toil is reduced for maintainers to support older toolchains by not needing to manually select older versions for each dependency. MSRV You can opt-in to the MSRV-aware resolver via .cargo/config.toml: .cargo/config.toml [resolver]
incompatible-rust-versions = "fallback" [resolver]
incompatible-rust-versions = "fallback" Then when adding a dependency: $ cargo add clap
    Updating crates.io index
warning: ignoring clap@4.5.23 (which requires rustc 1.74) to maintain demo's rust-version of 1.60
      Adding clap v4.0.32 to dependencies
    Updating crates.io index
     Locking 33 packages to latest Rust 1.60 compatible versions
      Adding clap v4.0.32 (available: v4.5.23, requires Rust 1.74) $ cargo add clap
    Updating crates.io index
warning: ignoring clap@4.5.23 (which requires rustc 1.74) to maintain demo's rust-version of 1.60
      Adding clap v4.0.32 to dependencies
    Updating crates.io index
     Locking 33 packages to latest Rust 1.60 compatible versions
      Adding clap v4.0.32 (available: v4.5.23, requires Rust 1.74) When verifying the latest dependencies in CI, you can override this: verifying the latest dependencies in CI $ CARGO_RESOLVER_INCOMPATIBLE_RUST_VERSIONS=allow cargo update
    Updating crates.io index
     Locking 12 packages to latest compatible versions
    Updating clap v4.0.32 -> v4.5.23 $ CARGO_RESOLVER_INCOMPATIBLE_RUST_VERSIONS=allow cargo update
    Updating crates.io index
     Locking 12 packages to latest compatible versions
    Updating clap v4.0.32 -> v4.5.23 You can also opt-in by setting package.resolver = "3" in the Cargo.toml manifest file though that will require raising your MSRV to 1.84. The new resolver will be enabled by default for projects using the 2024 edition (which will stabilize in 1.85). package.resolver = "3" This gives library authors more flexibility when deciding their policy on adopting new Rust toolchain features. Previously, a library adopting features from a new Rust toolchain would force downstream users of that library who have an older Rust version to either upgrade their toolchain or manually select an old version of the library compatible with their toolchain (and avoid running cargo update). Now, those users will be able to automatically use older library versions compatible with their older toolchain. cargo update See the documentation for more considerations when deciding on an MSRV policy. documentation Migration to the new trait solver begins The Rust compiler is in the process of moving to a new implementation for the trait solver. The next-generation trait solver is a reimplementation of a core component of Rust's type system. It is not only responsible for checking whether trait-bounds - e.g. Vec<T>: Clone - hold, but is also used by many other parts of the type system, such as normalization - figuring out the underlying type of <Vec<T> as IntoIterator>::Item - and equating types (checking whether T and U are the same). Vec<T>: Clone <Vec<T> as IntoIterator>::Item T U In 1.84, the new solver is used for checking coherence of trait impls. At a high level, coherence is responsible for ensuring that there is at most one implementation of a trait for a given type while considering not yet written or visible code from other crates. This stabilization fixes a few mostly theoretical correctness issues of the old implementation, resulting in potential "conflicting implementations of trait ..." errors that were not previously reported. We expect the affected patterns to be very rare based on evaluation of available code through Crater. The stabilization also improves our ability to prove that impls do not overlap, allowing more code to be written in some cases. Crater not For more details, see a previous blog post and the stabilization report. previous blog post stabilization report Strict provenance APIs In Rust, pointers are not simply an "integer" or "address". For instance, a "use after free" is undefined behavior even if you "get lucky" and the freed memory gets reallocated before your read/write. As another example, writing through a pointer derived from an &i32 reference is undefined behavior, even if writing to the same address via a different pointer is legal. The underlying pattern here is that the way a pointer is computed matters, not just the address that results from this computation. For this reason, we say that pointers have provenance: to fully characterize pointer-related undefined behavior in Rust, we have to know not only the address the pointer points to, but also track which other pointer(s) it is "derived from". pointers are not simply an "integer" or "address" &i32 the way a pointer is computed matters provenance Most of the time, programmers do not need to worry much about provenance, and it is very clear how a pointer got derived. However, when casting pointers to integers and back, the provenance of the resulting pointer is underspecified. With this release, Rust is adding a set of APIs that can in many cases replace the use of integer-pointer-casts, and therefore avoid the ambiguities inherent to such casts. In particular, the pattern of using the lowest bits of an aligned pointer to store extra information can now be implemented without ever casting a pointer to an integer or back. This makes the code easier to reason about, easier to analyze for the compiler, and also benefits tools like Miri and architectures like CHERI that aim to detect and diagnose pointer misuse. Miri CHERI For more details, see the standard library documentation on provenance. documentation on provenance Stabilized APIs Ipv6Addr::is_unique_local
Ipv6Addr::is_unicast_link_local
core::ptr::with_exposed_provenance
core::ptr::with_exposed_provenance_mut
<ptr>::addr
<ptr>::expose_provenance
<ptr>::with_addr
<ptr>::map_addr
<int>::isqrt
<int>::checked_isqrt
<uint>::isqrt
NonZero::isqrt
core::ptr::without_provenance
core::ptr::without_provenance_mut
core::ptr::dangling
core::ptr::dangling_mut
Pin::as_deref_mut Ipv6Addr::is_unique_local Ipv6Addr::is_unique_local Ipv6Addr::is_unicast_link_local Ipv6Addr::is_unicast_link_local core::ptr::with_exposed_provenance core::ptr::with_exposed_provenance core::ptr::with_exposed_provenance_mut core::ptr::with_exposed_provenance_mut <ptr>::addr <ptr>::addr <ptr>::expose_provenance <ptr>::expose_provenance <ptr>::with_addr <ptr>::with_addr <ptr>::map_addr <ptr>::map_addr <int>::isqrt <int>::isqrt <int>::checked_isqrt <int>::checked_isqrt <uint>::isqrt <uint>::isqrt NonZero::isqrt NonZero::isqrt core::ptr::without_provenance core::ptr::without_provenance core::ptr::without_provenance_mut core::ptr::without_provenance_mut core::ptr::dangling core::ptr::dangling core::ptr::dangling_mut core::ptr::dangling_mut Pin::as_deref_mut Pin::as_deref_mut These APIs are now stable in const contexts AtomicBool::from_ptr
AtomicPtr::from_ptr
AtomicU8::from_ptr
AtomicU16::from_ptr
AtomicU32::from_ptr
AtomicU64::from_ptr
AtomicUsize::from_ptr
AtomicI8::from_ptr
AtomicI16::from_ptr
AtomicI32::from_ptr
AtomicI64::from_ptr
AtomicIsize::from_ptr
<ptr>::is_null
<ptr>::as_ref
<ptr>::as_mut
Pin::new
Pin::new_unchecked
Pin::get_ref
Pin::into_ref
Pin::get_mut
Pin::get_unchecked_mut
Pin::static_ref
Pin::static_mut AtomicBool::from_ptr AtomicBool::from_ptr AtomicPtr::from_ptr AtomicPtr::from_ptr AtomicU8::from_ptr AtomicU8::from_ptr AtomicU16::from_ptr AtomicU16::from_ptr AtomicU32::from_ptr AtomicU32::from_ptr AtomicU64::from_ptr AtomicU64::from_ptr AtomicUsize::from_ptr AtomicUsize::from_ptr AtomicI8::from_ptr AtomicI8::from_ptr AtomicI16::from_ptr AtomicI16::from_ptr AtomicI32::from_ptr AtomicI32::from_ptr AtomicI64::from_ptr AtomicI64::from_ptr AtomicIsize::from_ptr AtomicIsize::from_ptr <ptr>::is_null <ptr>::is_null <ptr>::as_ref <ptr>::as_ref <ptr>::as_mut <ptr>::as_mut Pin::new Pin::new Pin::new_unchecked Pin::new_unchecked Pin::get_ref Pin::get_ref Pin::into_ref Pin::into_ref Pin::get_mut Pin::get_mut Pin::get_unchecked_mut Pin::get_unchecked_mut Pin::static_ref Pin::static_ref Pin::static_mut Pin::static_mut Other changes Check out everything that changed in Rust, Cargo, and Clippy. Rust Cargo Clippy Contributors to 1.84.0 Many people came together to create Rust 1.84.0. We couldn't have done it without all of you. Thanks! Thanks! The Rust Release Team Also published here here Photo by Pablo Gentile on Unsplash Pablo Gentile Unsplash

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