Draft of 1.24 announcement

_posts/2018-02-15-Rust-1.24.md

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+---
+layout: post
+title: "Announcing Rust 1.24"
+author: The Rust Core Team
+---
+
+The Rust team is happy to announce a new version of Rust, 1.24.0. Rust is a
+systems programming language focused on safety, speed, and concurrency.
+
+If you have a previous version of Rust installed via rustup, getting Rust
+1.24.0 is as easy as:
+
+```bash
+$ rustup update stable
+```
+
+If you don't have it already, you can [get `rustup`][install] from the
+appropriate page on our website, and check out the [detailed release notes for
+1.24.0][notes] on GitHub.
+
+[install]: https://www.rust-lang.org/install.html
+[notes]: https://github.com/rust-lang/rust/blob/master/RELEASES.md#version-1240-2018-02-15
+
+## What's in 1.24.0 stable
+
+This release contains two very exciting new features: `rustfmt` and incremental compilation!
+
+#### `rustfmt`
+
+For years now, we've wanted a tool that automatically can reformat your Rust code to some sort
+of "standard style." With this release, we're happy to announce that a *preview* of `rustfmt`
+can be used with 1.24 stable. Before we get into the details, here's how to install `rustfmt`:
+
+```bash
+$ rustup component add rustfmt-preview
+```
+
+Notably, you should *not* install `rustfmt` through `cargo install`. Why not? Well, `rustfmt`
+relies on using the compiler as a library to do its job. As such, the exact right version of
+`rustfmt` for the exact compiler version you're using is critical, otherwise, it will not work.
+`rustup` knows what compiler version you're using, and so is able to pair it with the correct
+`rustfmt` version. Once you've added this component to a given toolchain, `rustup` will
+automatically update it as well. Run the command once, and then on every future
+`rustup update stable`, `rustfmt-preview` will be updated as well.
+
+> This strategy is expected to be used for other developer tools that integrate tightly with
+> the compiler, like the RLS and Clippy, in the future.
+
+Finally, please take note of that `-preview` in the name: `rustfmt` is still not quite
+at 1.0 yet. Some tweaks to the default styles are still occuring, though they're relatively
+minor. Once `rustfmt` hits 1.0, we'll be releasing a `rustfmt` component and
+deprecating `rustfmt-preview`. Since this is the first major component we're distributing
+this way, we wanted to clearly signal that it is still developing.
+
+For more, please check out [`rustfmt` on GitHub](https://github.com/rust-lang-nursery/rustfmt).
+
+#### Incremental compilation
+
+Back in September, we blogged about [Incremental Compilation](https://blog.rust-lang.org/2016/09/08/incremental.html).
+While that post goes into the details, the idea is basically this: when you're working on
+a project, you often compile it, then change something small, then compile again. Historically,
+the compiler has compiled your *entire* project, no matter how little you've changed the code.
+The idea with incremental compilation is that you only need to compile the code you've actually
+changed, which means that that second build is faster.
+
+As of Rust 1.24, this is now [turned on by default](https://github.com/rust-lang/cargo/pull/4817).
+This means that your builds should get faster!
+
+This is still not the end story for compiler performance generally, nor incremental compilation
+specifically. We have a lot more work planned in the future. For example, another change
+related to performance hit stable this release:
+[`codegen-units` is now set to 16 by default](https://github.com/rust-lang/rust/pull/46910).
+More to come!
+
+#### Other good stuff
+
+There's one other change we'd like to talk about here: undefined behavior. Rust generally
+strives to minimize undefined behavior, having none of it in safe code, and as little as
+possible in unsafe code. One area where you could invoke UB is when a `panic!` goes
+across an FFI boundary. In other words, this:
+
+```rust
+extern "C" fn panic_in_ffi() {
+    panic!("Test");
+}
+```
+
+This cannot work, as the exact mechanism of how panics work would have to be reconciled
+with how the `"C"` ABI works, in this example, or any other ABI in other examples.
+
+In Rust 1.24, [this code will now abort](https://github.com/rust-lang/rust/pull/46833)
+instead of producing undefined behavior.
+
+See the [detailed release notes][notes] for more.
+
+### Library stabilizations
+
+If you're a fan of `str::find`, used to find a given `char` inside of a `&str`, you'll be
+happy to see this pull request: [it's now 10x faster](https://github.com/rust-lang/rust/pull/46735)!
+This is thanks to `memchr`. `[u8]::contains` [uses it too](https://github.com/rust-lang/rust/pull/46713),
+though it doesn't get such an extreme speedup.
+
+Additionally, a few new APIs were stabilized this release:
+
+* [`RefCell::replace`](https://doc.rust-lang.org/std/cell/struct.RefCell.html#method.replace)
+* [`RefCell::swap`](https://doc.rust-lang.org/std/cell/struct.RefCell.html#method.swap)
+* [`std::sync::atomic::spin_loop_hint`](https://doc.rust-lang.org/std/sync/atomic/fn.spin_loop_hint.html)
+
+Finally, these functions may now be used inside a constant expression, for example, to initialize a `static`:
+
+* `Cell`, `RefCell`, and `UnsafeCell`'s `new` functions
+* The `new` functions of the various `Atomic` integer types
+* `{integer}::min_value` and `max_value`
+* `mem`'s `size_of` and `align_of`
+* `ptr::null` and `null_mut`
+
+See the [detailed release notes][notes] for more.
+
+### Cargo features
+
+The big feature of this release was turning on incremental compilation by default, as mentioned above.
+
+See the [detailed release notes][notes] for more.
+
+## Contributors to 1.24.0
+
+Many people came together to create Rust 1.24. We couldn't have done it
+without all of you. [Thanks!](https://thanks.rust-lang.org/rust/1.24.0)