Announcing Rust 1.85.0 and Rust 2024

Author: cuviper

posts/2025-02-20-Rust-1.85.0.md

@@ -0,0 +1,202 @@
+---
+layout: post
+title: "Announcing Rust 1.85.0 and Rust 2024"
+author: The Rust Release Team
+release: true
+---
+
+The Rust team is happy to announce a new version of Rust, 1.85.0. This stabilizes the 2024 edition as well.
+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 1.85.0 with:
+
+```console
+$ rustup update stable
+```
+
+If you don't have it already, you can [get `rustup`](https://www.rust-lang.org/install.html) from the appropriate page on our website, and check out the [detailed release notes for 1.85.0](https://doc.rust-lang.org/stable/releases.html#version-1850-2025-02-20).
+
+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](https://github.com/rust-lang/rust/issues/new/choose) any bugs you might come across!
+
+## What's in 1.85.0 stable
+
+### Rust 2024
+
+We are excited to announce that the Rust 2024 Edition is now stable!
+Editions are a mechanism for opt-in changes that may otherwise pose a backwards compatibility risk. See [the edition guide](https://doc.rust-lang.org/edition-guide/editions/index.html) for details on how this is achieved, and detailed instructions on how to migrate.
+
+This is the largest edition we have released. The [edition guide](https://doc.rust-lang.org/edition-guide/rust-2024/index.html) contains detailed information about each change, but as a summary, here are all the changes:
+
+- Language
+  - [RPIT lifetime capture rules](https://doc.rust-lang.org/edition-guide/rust-2024/rpit-lifetime-capture.html) — Changes the default impl trait `use<..>` capturing.
+  - [`if let` temporary scope](https://doc.rust-lang.org/edition-guide/rust-2024/temporary-if-let-scope.html) — Changes the scope of temporaries for `if let` expressions.
+  - [Tail expression temporary scope](https://doc.rust-lang.org/edition-guide/rust-2024/temporary-tail-expr-scope.html) — Changes the scope of temporaries for the tail expression in a block.
+  - [Match ergonomics reservations](https://doc.rust-lang.org/edition-guide/rust-2024/match-ergonomics.html) — New restrictions on pattern binding modes.
+  - [Unsafe `extern` blocks](https://doc.rust-lang.org/edition-guide/rust-2024/unsafe-extern.html) — `extern` blocks now require the `unsafe` keyword.
+  - [Unsafe attributes](https://doc.rust-lang.org/edition-guide/rust-2024/unsafe-attributes.html) — The `export_name`, `link_section`, and `no_mangle` attributes must now be marked as `unsafe`.
+  - [`unsafe_op_in_unsafe_fn` warning](https://doc.rust-lang.org/edition-guide/rust-2024/unsafe-op-in-unsafe-fn.html) — The [`unsafe_op_in_unsafe_fn`](https://doc.rust-lang.org/rustc/lints/listing/allowed-by-default.html#unsafe-op-in-unsafe-fn) lint now warns by default, requiring explicit `unsafe {}` blocks in `unsafe` functions.
+  - [Disallow references to `static mut`](https://doc.rust-lang.org/edition-guide/rust-2024/static-mut-references.html) — References to `static mut` items now generate a deny-by-default error.
+  - [Never type fallback change](https://doc.rust-lang.org/edition-guide/rust-2024/never-type-fallback.html) — Changes to how the never type `!` coerces, and changes the [`never_type_fallback_flowing_into_unsafe`](https://doc.rust-lang.org/rustc/lints/listing/warn-by-default.html#never-type-fallback-flowing-into-unsafe) lint level to "deny".
+  - [Macro fragment specifiers](https://doc.rust-lang.org/edition-guide/rust-2024/macro-fragment-specifiers.html) — The `expr` macro fragment specifier in `macro_rules!` macros now also matches `const` and `_` expressions.
+  - [Missing macro fragment specifiers](https://doc.rust-lang.org/edition-guide/rust-2024/missing-macro-fragment-specifiers.html) — The [`missing_fragment_specifier`](https://doc.rust-lang.org/rustc/lints/listing/deny-by-default.html#missing-fragment-specifier) lint is now a hard error, rejecting macro meta variables without a fragment specifier kind.
+  - [`gen` keyword](https://doc.rust-lang.org/edition-guide/rust-2024/gen-keyword.html) — Reserves the `gen` keyword in anticipation of adding generator blocks in the future.
+  - [Reserved syntax](https://doc.rust-lang.org/edition-guide/rust-2024/reserved-syntax.html) — Reserves `#"foo"#` style strings and `##` tokens in anticipation of changing how guarded string literals may change in the future.
+- Standard library
+  - [Changes to the prelude](https://doc.rust-lang.org/edition-guide/rust-2024/prelude.html) — Adds `Future` and `IntoFuture` to the prelude.
+  - [Add `IntoIterator` for `Box<[T]>`](https://doc.rust-lang.org/edition-guide/rust-2024/intoiterator-box-slice.html) — Changes how iterators work with boxed slices.
+  - [Newly unsafe functions](https://doc.rust-lang.org/edition-guide/rust-2024/newly-unsafe-functions.html) — `std::env::set_var`, `std::env::remove_var`, and `std::os::unix::process::CommandExt::before_exec` are now unsafe functions.
+- Cargo
+  - [Cargo: Rust-version aware resolver](https://doc.rust-lang.org/edition-guide/rust-2024/cargo-resolver.html) — Changes the default dependency resolver behavior to consider the `rust-version` field.
+  - [Cargo: Table and key name consistency](https://doc.rust-lang.org/edition-guide/rust-2024/cargo-table-key-names.html) — Removes some outdated `Cargo.toml` keys.
+  - [Cargo: Reject unused inherited default-features](https://doc.rust-lang.org/edition-guide/rust-2024/cargo-inherited-default-features.html) — Changes how `default-features = false` works with inherited workspace dependencies.
+- Rustdoc
+  - [Rustdoc combined tests](https://doc.rust-lang.org/edition-guide/rust-2024/rustdoc-doctests.html) — Doctests are now combined into a single executable, significantly improving performance.
+  - [Rustdoc nested `include!` change](https://doc.rust-lang.org/edition-guide/rust-2024/rustdoc-nested-includes.html) — Changes to the relative path behavior of nested `include!` files.
+- Rustfmt
+  - [Rustfmt: Style edition](https://doc.rust-lang.org/edition-guide/rust-2024/rustfmt-style-edition.html) — Introduces the concept of "style editions", which allow you to independently control the formatting edition from the Rust edition.
+  - [Rustfmt: Formatting fixes](https://doc.rust-lang.org/edition-guide/rust-2024/rustfmt-formatting-fixes.html) — A large number of fixes to formatting various situations.
+  - [Rustfmt: Combine all delimited exprs as last argument](https://doc.rust-lang.org/edition-guide/rust-2024/rustfmt-overflow-delimited-expr.html) — Changes to multi-line expressions as the last argument.
+  - [Rustfmt: Raw identifier sorting](https://doc.rust-lang.org/edition-guide/rust-2024/rustfmt-raw-identifier-sorting.html) — Changes to how `r#foo` identifiers are sorted.
+  - [Rustfmt: Version sorting](https://doc.rust-lang.org/edition-guide/rust-2024/rustfmt-version-sorting.html) — Changes to how identifiers that contain integers are sorted.
+
+#### Migrating to 2024
+
+The guide includes migration instructions for all new features, and in general
+[transitioning an existing project to a new edition](https://doc.rust-lang.org/edition-guide/editions/transitioning-an-existing-project-to-a-new-edition.html).
+In many cases `cargo fix` can automate the necessary changes. You may even find that no changes in your code are needed at all for 2024!
+
+*Many* people came together to create this edition. We'd like to thank them all for their hard work!
+
+### `async` closures
+
+**🚧 TODO 🚧**
+
+- [Stabilize async closures](https://github.com/rust-lang/rust/pull/132706)
+  See [RFC 3668](https://rust-lang.github.io/rfcs/3668-async-closures.html) for more details.
+
+### Hiding trait implementations from diagnostics
+
+- [Stabilize `#[diagnostic::do_not_recommend]`](https://github.com/rust-lang/rust/pull/132056)
+
+The new `#[diagnostic::do_not_recommend]` attribute is a hint to the compiler to not show the annotated trait implementation as part of a diagnostic message. For library authors, this is a way to keep the compiler from making suggestions that may be unhelpful or misleading. For example:
+
+```rust
+pub trait Foo {}
+pub trait Bar {}
+
+impl<T: Foo> Bar for T {}
+
+struct MyType;
+
+fn main() {
+    let _object: &dyn Bar = &MyType;
+}
+```
+
+```text
+error[E0277]: the trait bound `MyType: Bar` is not satisfied
+ --> src/main.rs:9:29
+  |
+9 |     let _object: &dyn Bar = &MyType;
+  |                             ^^^^ the trait `Foo` is not implemented for `MyType`
+  |
+note: required for `MyType` to implement `Bar`
+ --> src/main.rs:4:14
+  |
+4 | impl<T: Foo> Bar for T {}
+  |         ---  ^^^     ^
+  |         |
+  |         unsatisfied trait bound introduced here
+  = note: required for the cast from `&MyType` to `&dyn Bar`
+```
+
+For some APIs, it might make good sense for you to implement `Foo`, and get `Bar` indirectly by that blanket implementation. For others, it might be expected that most users should implement `Bar` directly, so that `Foo` suggestion is a red herring. In that case, adding the diagnostic hint will change the error message like so:
+
+```rust
+#[diagnostic::do_not_recommend]
+impl<T: Foo> Bar for T {}
+```
+
+```text
+error[E0277]: the trait bound `MyType: Bar` is not satisfied
+  --> src/main.rs:10:29
+   |
+10 |     let _object: &dyn Bar = &MyType;
+   |                             ^^^^ the trait `Bar` is not implemented for `MyType`
+   |
+   = note: required for the cast from `&MyType` to `&dyn Bar`
+```
+
+See [RFC 2397](https://rust-lang.github.io/rfcs/2397-do-not-recommend.html) for the original motivation, and the current [reference](https://doc.rust-lang.org/reference/attributes/diagnostics.html#the-diagnosticdo_not_recommend-attribute) for more details.
+
+### `FromIterator` and `Extend` for tuples
+
+Earlier versions of Rust implemented convenience traits for iterators of `(T, U)` tuple pairs to behave like `Iterator::unzip`, with `Extend` in 1.56 and `FromIterator` in 1.79. These have now been *extended* to more tuple lengths, from singleton `(T,)` through to 12 items long, `(T1, T2, .., T11, T12)`. For example, you can now use `collect()` to fanout into multiple collections at once:
+
+```rust
+use std::collections::{LinkedList, VecDeque};
+fn main() {
+    let (squares, cubes, tesseracts): (Vec<_>, VecDeque<_>, LinkedList<_>) =
+        (0i32..10).map(|i| (i * i, i.pow(3), i.pow(4))).collect();
+    println!("{squares:?}");
+    println!("{cubes:?}");
+    println!("{tesseracts:?}");
+}
+```
+
+```text
+[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
+[0, 1, 8, 27, 64, 125, 216, 343, 512, 729]
+[0, 1, 16, 81, 256, 625, 1296, 2401, 4096, 6561]
+```
+
+### Updates to `home_dir()`
+
+`std::env::home_dir()` has been deprecated for years, because it can give surprising results in some Windows configurations if the `HOME` environment variable is set (which is not the normal configuration on Windows). We had previously avoided changing its behavior, out of concern for compatibility with code depending on this non-standard configuration. Given how long this function has been deprecated, we're now updating its behavior as a bug fix, and a subsequent release will remove the deprecation for this function.
+
+### Stabilized APIs
+
+- [`BuildHasherDefault::new`](https://doc.rust-lang.org/stable/std/hash/struct.BuildHasherDefault.html#method.new)
+- [`ptr::fn_addr_eq`](https://doc.rust-lang.org/std/ptr/fn.fn_addr_eq.html)
+- [`io::ErrorKind::QuotaExceeded`](https://doc.rust-lang.org/stable/std/io/enum.ErrorKind.html#variant.QuotaExceeded)
+- [`io::ErrorKind::CrossesDevices`](https://doc.rust-lang.org/stable/std/io/enum.ErrorKind.html#variant.CrossesDevices)
+- [`{float}::midpoint`](https://doc.rust-lang.org/core/primitive.f32.html#method.midpoint)
+- [Unsigned `{integer}::midpoint`](https://doc.rust-lang.org/std/primitive.u64.html#method.midpoint)
+- [`NonZeroU*::midpoint`](https://doc.rust-lang.org/std/num/type.NonZeroU32.html#method.midpoint)
+- [impl `std::iter::Extend` for tuples with arity 1 through 12](https://doc.rust-lang.org/stable/std/iter/trait.Extend.html#impl-Extend%3C(A,)%3E-for-(EA,))
+- [`FromIterator<(A, ...)>` for tuples with arity 1 through 12](https://doc.rust-lang.org/stable/std/iter/trait.FromIterator.html#impl-FromIterator%3C(EA,)%3E-for-(A,))
+- [`std::task::Waker::noop`](https://doc.rust-lang.org/stable/std/task/struct.Waker.html#method.noop)
+
+These APIs are now stable in const contexts
+
+- [`mem::size_of_val`](https://doc.rust-lang.org/stable/std/mem/fn.size_of_val.html)
+- [`mem::align_of_val`](https://doc.rust-lang.org/stable/std/mem/fn.align_of_val.html)
+- [`Layout::for_value`](https://doc.rust-lang.org/stable/std/alloc/struct.Layout.html#method.for_value)
+- [`Layout::align_to`](https://doc.rust-lang.org/stable/std/alloc/struct.Layout.html#method.align_to)
+- [`Layout::pad_to_align`](https://doc.rust-lang.org/stable/std/alloc/struct.Layout.html#method.pad_to_align)
+- [`Layout::extend`](https://doc.rust-lang.org/stable/std/alloc/struct.Layout.html#method.extend)
+- [`Layout::array`](https://doc.rust-lang.org/stable/std/alloc/struct.Layout.html#method.array)
+- [`std::mem::swap`](https://doc.rust-lang.org/stable/std/mem/fn.swap.html)
+- [`std::ptr::swap`](https://doc.rust-lang.org/stable/std/ptr/fn.swap.html)
+- [`NonNull::new`](https://doc.rust-lang.org/stable/std/ptr/struct.NonNull.html#method.new)
+- [`HashMap::with_hasher`](https://doc.rust-lang.org/stable/std/collections/struct.HashMap.html#method.with_hasher)
+- [`HashSet::with_hasher`](https://doc.rust-lang.org/stable/std/collections/struct.HashSet.html#method.with_hasher)
+- [`BuildHasherDefault::new`](https://doc.rust-lang.org/stable/std/hash/struct.BuildHasherDefault.html#method.new)
+- [`<float>::recip`](https://doc.rust-lang.org/stable/std/primitive.f32.html#method.recip)
+- [`<float>::to_degrees`](https://doc.rust-lang.org/stable/std/primitive.f32.html#method.to_degrees)
+- [`<float>::to_radians`](https://doc.rust-lang.org/stable/std/primitive.f32.html#method.to_radians)
+- [`<float>::max`](https://doc.rust-lang.org/stable/std/primitive.f32.html#method.max)
+- [`<float>::min`](https://doc.rust-lang.org/stable/std/primitive.f32.html#method.min)
+- [`<float>::clamp`](https://doc.rust-lang.org/stable/std/primitive.f32.html#method.clamp)
+- [`<float>::abs`](https://doc.rust-lang.org/stable/std/primitive.f32.html#method.abs)
+- [`<float>::signum`](https://doc.rust-lang.org/stable/std/primitive.f32.html#method.signum)
+- [`<float>::copysign`](https://doc.rust-lang.org/stable/std/primitive.f32.html#method.copysign)
+- [`MaybeUninit::write`](https://doc.rust-lang.org/stable/std/mem/union.MaybeUninit.html#method.write)
+
+### Other changes
+
+Check out everything that changed in [Rust](https://github.com/rust-lang/rust/releases/tag/1.85.0), [Cargo](https://doc.rust-lang.org/nightly/cargo/CHANGELOG.html#cargo-185-2025-02-20), and [Clippy](https://github.com/rust-lang/rust-clippy/blob/master/CHANGELOG.md#rust-185).
+
+## Contributors to 1.85.0
+
+Many people came together to create Rust 1.85.0. We couldn't have done it without all of you. [Thanks!](https://thanks.rust-lang.org/rust/1.85.0/)