Draft release notes for 1.64

posts/2022-09-22-Rust-1.64.0.md

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+---
+layout: post
+title: "Announcing Rust 1.64.0"
+author: Josh Triplett
+team: The Release Team <https://www.rust-lang.org/governance/teams/release>
+release: true
+---
+
+The Rust team is happy to announce a new version of Rust, 1.64.0. 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 1.64.0
+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
+1.64.0](https://github.com/rust-lang/rust/blob/stable/RELEASES.md#version-1640-2022-09-22)
+on GitHub.
+
+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 1.64.0 stable
+
+### C-compatible ffi types in core and alloc
+
+When calling or being called by C ABIs, Rust code can use types like `c_uint`
+or `c_ulong` to match the corresponding types from C on any target, without
+requiring target-specific code or conditionals.
+
+Previously, these types were only available in `std`, so code written for
+embedded targets and other scenarios that could only use `core` or `alloc`
+could not use these types.
+
+Rust 1.64 now provides all of the `c_*` types in
+[`core::ffi`](https://doc.rust-lang.org/core/ffi/index.html), as well as
+[`core::ffi::CStr`](https://doc.rust-lang.org/core/ffi/struct.CStr.html) for
+working with C strings. Rust 1.64 also provides
+[`alloc::ffi::CString`](https://doc.rust-lang.org/alloc/ffi/struct.CString.html)
+for working with owned C strings using only the `alloc` crate, rather than the
+full `std` library.
+
+### New internal layout for network structures
+
+The standard library network data structures
+[`Ipv4Addr`](https://doc.rust-lang.org/std/net/struct.Ipv4Addr.html),
+[`Ipv6Addr`](https://doc.rust-lang.org/std/net/struct.Ipv6Addr.html),
+[`SocketAddrV4`](https://doc.rust-lang.org/std/net/struct.SocketAddrV4.html),
+and
+[`SocketAddrV6`](https://doc.rust-lang.org/std/net/struct.SocketAddrV6.html)
+now use a more compact, memory-efficient layout, rather than using the memory
+layout of the underlying OS data structure.
+
+Normally, such a change would be an entirely internal detail of the standard
+library, with the only user-visible effect being less memory usage. However,
+some crates relied on the internal implementation details of the standard
+library, by using
+[`std::mem::transmute`](https://doc.rust-lang.org/std/mem/fn.transmute.html) or
+similar to access the internal representation and pass it directly to OS
+functions.
+
+Such internal implementation details of the standard library are *never*
+considered a stable interface. Nonetheless, because multiple crates relied on
+this, we first worked with the authors of all of the still-maintained crates
+doing so to arrange for the release of new versions, and to yank the old ones,
+before making this change.
+
+See <https://github.com/rust-lang/rust/pull/78802> for more details.
+
+### Warning about unused tuple-struct fields
+
+If you define a struct containing fields that are never used, rustc will warn
+about the unused fields. Now, in Rust 1.64, you can enable the
+`unused_tuple_struct_fields` lint to get the same warnings about unused fields
+in a tuple struct. In future versions, we plan to make this lint warn by
+default.
+
+Fields of type unit (`()`) do not produce a warning, to make it easier to
+migrate existing code without having to change tuple indices.
+
+### Enhancing `.await` with `IntoFuture`
+
+Rust 1.64 stabilizes the
+[`IntoFuture`](https://doc.rust-lang.org/std/future/trait.IntoFuture.html)
+trait. `IntoFuture` is a trait similar to
+[`IntoIterator`](https://doc.rust-lang.org/std/iter/trait.IntoIterator.html),
+but rather than supporting `for ... in ...` loops, `IntoFuture` changes how
+`.await` works. With `IntoFuture`, the `.await` keyword can await mor ethan
+just futures; it can await _anything which can be converted into a `Future` via
+`IntoFuture`_ - which can help make your APIs more user-friendly!
+
+Take for example a builder which constructs requests to some storage provider
+over the network:
+
+```rust
+pub struct Error { ... }
+pub struct StorageResponse { ... }:
+pub struct StorageRequest(bool);
+
+impl StorageRequest {
+    /// Create a new instance of `StorageRequest`.
+    pub fn new() -> Self { ... }
+    /// Decide whether debug mode should be enabled.
+    pub fn set_debug(self, b: bool) -> Self { ... }
+    /// Send the request and receive a response.
+    pub async fn send(self) -> Result<StorageResponse, Error> { ... }
+}
+```
+
+Typical usage would likely look something like this:
+
+```rust
+let response = StorageRequest::new()  // 1. create a new instance
+    .set_debug(true)                  // 2. set some option
+    .send()                           // 3. construct the future
+    .await?;                          // 4. run the future + propagate errors
+```
+
+This is not bad, but we can do better here. Using `IntoFuture` we can combine
+_"construct the future"_ (line 3) and _"run the future"_ (line 4) into a single
+step:
+```rust
+let response = StorageRequest::new()  // 1. create a new instance
+    .set_debug(true)                  // 2. set some option
+    .await?;                          // 3. construct + run the future + propagate errors
+```
+
+We can do this by implementing `IntoFuture` for `StorageRequest`. `IntoFuture`
+requires us to have a named future we can return, which we can do by creating a
+"boxed future" and defining a type alias for it:
+
+```rust
+// First we must import some new types into the scope.
+use std::pin::Pin;
+use std::future::{Future, IntoFuture};
+
+pub struct Error { ... }
+pub struct StorageResponse { ... }
+pub struct StorageRequest(bool);
+
+impl StorageRequest {
+    /// Create a new instance of `StorageRequest`.
+    pub fn new() -> Self { ... }
+    /// Decide whether debug mode should be enabled.
+    pub fn set_debug(self, b: bool) -> Self { ... }
+    /// Send the request and receive a response.
+    pub async fn send(self) -> Result<StorageResponse, Error> { ... }
+}
+
+// The new implementations:
+// 1. create a new named future type
+// 2. implement `IntoFuture` for `StorageRequest`
+pub type StorageRequestFuture = Pin<Box<dyn Future<Output = Result<StorageResponse, Error> + Send + 'static>>
+impl IntoFuture for StorageRequest {
+    type IntoFuture = StorageRequestFuture;
+    type Output = <StorageRequestFuture as Future>::Output;
+    fn into_future(self) -> Self::IntoFuture {
+        Box::pin(self.send())
+    }
+}
+```
+This takes a bit more code to implement, but provides a simpler API for users.
+
+In the future, the Rust Async WG hopes to simplify the creating new named
+futures by supporting [`impl Trait` in `type` aliases (Type Alias Impl Trait or
+TAIT)](https://rust-lang.github.io/impl-trait-initiative/explainer/tait.html).
+This should make implementing `IntoFuture` easier by simplifying the type
+alias' signature, and make it more performant by removing the `Box` from the
+type alias.
+
+### Stabilizing `ready!` and `poll_fn`
+
+When working with the low-level details of futures, you'll currently often
+encounter the [`Poll`](https://doc.rust-lang.org/std/task/enum.Poll.html) type.
+We've stabilized a few helpers for working with this type:
+
+- [`ready!`](https://doc.rust-lang.org/std/task/macro.ready.html) takes a
+  `Poll` and returns from the containing function for `Poll::Pending`, or
+  returns the contained value in a `Poll::Ready`. This can be useful when
+  implementing futures manually using `Poll`.
+- [`poll_fn`](https://doc.rust-lang.org/std/future/fn.poll_fn.html) turns a
+  function returning `Poll` into a future.
+
+In the future, we hope to provide simpler APIs that require less use of
+low-level details like `Poll` and `Pin`, but in the meantime, these helpers
+make it easier to write such code.
+
+### Minimum required kernel and glibc versions increased
+
+As [previously
+announced](https://blog.rust-lang.org/2022/08/01/Increasing-glibc-kernel-requirements.html),
+`linux` targets now require at least Linux kernel 3.2 (except for targets which
+already required a newer kernel), and `linux-gnu` targets now require glibc
+2.17 (except for targets which already required a newer glibc).
+
+### Profile-guided optimization (PGO) for Windows targets
+
+Windows builds of the Rust compiler now use profile-guided optimization,
+providing performance improvements of 10-20% for compiling Rust code on
+Windows.
+
+### `rust-analyzer` now available via `rustup`, no longer in preview
+
+Users of `rust-analyzer` can now obtain it via `rustup` on the stable and beta
+channels, not just on nightly.
+
+### Cargo workspace inheritance
+
+When working with collections of related libraries or binary crates in one
+Cargo workspace, you can now avoid duplication of common field values between
+crates, such as common version numbers, repository URLs, or `rust-version`.
+This also helps keep these values in sync between crates when updating them.
+For more details, see
+[`workspace.package`](https://doc.rust-lang.org/cargo/reference/workspaces.html#the-workspacepackage-table),
+[`workspace.dependencies`](https://doc.rust-lang.org/cargo/reference/workspaces.html#the-workspacedependencies-table),
+and ["inheriting a dependency from a
+workspace"](https://doc.rust-lang.org/cargo/reference/specifying-dependencies.html#inheriting-a-dependency-from-a-workspace).
+
+### Cargo multi-target builds
+
+When building for multiple targets, you can now pass multiple `--target`
+options to `cargo build`, to build all of those targets at once. You can also
+set [`build.target`](https://doc.rust-lang.org/cargo/reference/config.html#buildtarget) to an array of multiple targets in `.cargo/config.toml` to
+build for multiple targets by default.
+
+### Stabilized APIs
+
+The following methods and trait implementations are now stabilized:
+
+- ...
+
+These APIs are now usable in const contexts:
+
+- ...
+
+### Other changes
+
+There are other changes in the Rust 1.64.0 release. Check out what changed in
+[Rust](https://github.com/rust-lang/rust/blob/stable/RELEASES.md#version-1640-2022-09-22),
+[Cargo](https://github.com/rust-lang/cargo/blob/master/CHANGELOG.md#cargo-164-2022-09-22),
+and [Clippy](https://github.com/rust-lang/rust-clippy/blob/master/CHANGELOG.md#rust-164).
+
+### Contributors to 1.64.0
+
+Many people came together to create Rust 1.64.0.
+We couldn't have done it without all of you.
+[Thanks!](https://thanks.rust-lang.org/rust/1.64.0/)