Announcing Rust 1.68.0

posts/2023-03-09-Rust-1.68.0.md

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+---
+layout: post
+title: "Announcing Rust 1.68.0"
+author: The Rust Release Team
+release: true
+---
+
+The Rust team is happy to announce a new version of Rust, 1.68.0. 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 1.68.0
+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
+1.68.0](https://github.com/rust-lang/rust/blob/master/RELEASES.md#version-1680-2023-03-09)
+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 1.68.0 stable
+
+### Cargo's sparse protocol
+
+Cargo's "sparse" registry protocol has been stabilized for reading the index of
+crates, along with infrastructure at `https://index.crates.io/` for those
+published in the primary crates.io registry. The prior git protocol (which is
+still the default) clones a repository that indexes _all_ crates available in
+the registry, but this has started to hit scaling limitations, with noticeable
+delays while updating that repository. The new protocol should provide a
+significant performance improvement when accessing crates.io, as it will only
+download information about the subset of crates that you actually use.
+
+To use the sparse protocol with crates.io, set the environment variable
+`CARGO_REGISTRIES_CRATES_IO_PROTOCOL=sparse`, or edit your
+[`.cargo/config.toml` file](https://doc.rust-lang.org/cargo/reference/config.html)
+to add:
+
+```toml
+[registries.crates-io]
+protocol = "sparse"
+```
+
+The sparse protocol is currently planned to become the default for crates.io in
+the 1.70.0 release in a few months. For more information, please see the prior
+[announcement](https://blog.rust-lang.org/inside-rust/2023/01/30/cargo-sparse-protocol.html)
+on the Inside Rust Blog, as well as
+[RFC 2789](https://rust-lang.github.io/rfcs/2789-sparse-index.html)
+and the current
+[documentation](https://doc.rust-lang.org/stable/cargo/reference/registry-index.html#sparse-protocol)
+in the Cargo Book.
+
+### Local `Pin` construction
+
+The new [`pin!`](https://doc.rust-lang.org/stable/std/pin/macro.pin.html) macro
+constructs a `Pin<&mut T>` from a `T` expression, anonymously captured in local
+state. This is often called stack-pinning, but that "stack" could also be the
+captured state of an `async fn` or block. This macro is similar to some crates,
+like [`tokio::pin!`](https://docs.rs/tokio/1/tokio/macro.pin.html), but the
+standard library can take advantage of `Pin` internals and [temporary lifetime
+extension](https://doc.rust-lang.org/stable/reference/destructors.html#temporary-lifetime-extension)
+for a more expression-like macro.
+
+```rust
+/// Runs a future to completion.
+fn block_on<F: Future>(future: F) -> F::Output {
+    let waker_that_unparks_thread = todo!();
+    let mut cx = Context::from_waker(&waker_that_unparks_thread);
+    // Pin the future so it can be polled.
+    let mut pinned_future = pin!(future);
+    loop {
+        match pinned_future.as_mut().poll(&mut cx) {
+            Poll::Pending => thread::park(),
+            Poll::Ready(result) => return result,
+        }
+    }
+}
+```
+
+In this example, the original `future` will be moved into a temporary local,
+referenced by the new `pinned_future` with type `Pin<&mut F>`, and that pin is
+subject to the normal borrow checker to make sure it can't outlive that local.
+
+### Default `alloc` error handler
+
+When allocation fails in Rust, APIs like `Box::new` and `Vec::push` have no way
+to indicate that failure, so some divergent execution path needs to be taken.
+When using the `std` crate, the program will print to `stderr` and abort. But
+with `#![no_std]` and the `alloc` crate, it was required to provide a
+`#[alloc_error_handler]` function, similar to `#[panic_handler]`, but that
+attribute is still unstable.
+
+Now in Rust 1.68.0, a default handler is provided which turns that `alloc` error
+into a `panic!`, which may be processed in a `#[panic_handler]` like any other.
+
+### Stabilized APIs
+
+- [`{core,std}::pin::pin!`](https://doc.rust-lang.org/stable/std/pin/macro.pin.html)
+- [`impl From<bool> for {f32,f64}`](https://doc.rust-lang.org/stable/std/primitive.f32.html#impl-From%3Cbool%3E-for-f32)
+- [`std::path::MAIN_SEPARATOR_STR`](https://doc.rust-lang.org/stable/std/path/constant.MAIN_SEPARATOR_STR.html)
+- [`impl DerefMut for PathBuf`](https://doc.rust-lang.org/stable/std/path/struct.PathBuf.html#impl-DerefMut-for-PathBuf)
+
+These APIs are now stable in const contexts:
+
+- [`VecDeque::new`](https://doc.rust-lang.org/stable/std/collections/struct.VecDeque.html#method.new)
+
+### Other changes
+
+* As [previously announced](https://blog.rust-lang.org/2023/01/09/android-ndk-update-r25.html),
+  Android platform support in Rust is now targeting NDK r25, which corresponds to
+  a minimum supported API level of 19 (KitKat).
+
+Check out everything that changed in
+[Rust](https://github.com/rust-lang/rust/blob/stable/RELEASES.md#version-1680-2023-03-09),
+[Cargo](https://github.com/rust-lang/cargo/blob/master/CHANGELOG.md#cargo-168-2023-03-09),
+and [Clippy](https://github.com/rust-lang/rust-clippy/blob/master/CHANGELOG.md#rust-168).
+
+### Contributors to 1.68.0
+
+Many people came together to create Rust 1.68.0.
+We couldn't have done it without all of you.
+[Thanks!](https://thanks.rust-lang.org/rust/1.68.0/)