1.25 announcement

_posts/2018-03-29-Rust-1.25.md

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+---
+layout: post
+title: "Announcing Rust 1.25"
+author: The Rust Core Team
+---
+
+The Rust team is happy to announce a new version of Rust, 1.25.0. 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
+1.25.0 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
+1.25.0][notes] on GitHub.
+
+[install]: https://www.rust-lang.org/install.html
+[notes]: https://github.com/rust-lang/rust/blob/master/RELEASES.md#version-1250-2018-03-29
+
+## What's in 1.25.0 stable
+
+The last few releases have been relatively minor, but Rust 1.25 contains a
+bunch of stuff! The first one is straightforward: we've [upgraded to LLVM 6]
+from LLVM 4. This has a number of effects, a major one
+being a step closer to AVR support.
+
+A new way to write `use` statements has landed: [nested import groups]. If you've
+ever written a set of imports like this:
+
+```rust
+use std::fs::File;
+use std::io::Read;
+use std::path::{Path, PathBuf};
+```
+
+You can now write this:
+
+```rust
+// on one line
+use std::{fs::File, io::Read, path::{Path, PathBuf}};
+
+// with some more breathing room
+use std::{
+    fs::File,
+    io::Read,
+    path::{
+        Path,
+        PathBuf
+    }
+};
+```
+
+This can reduce some repetition, and make things a bit more clear.
+
+There are two big documentation changes in this release: first, [Rust By
+Example is now included on doc.rust-lang.org]! We'll be redirecting the old
+domain there shortly. We hope this will bring more attention to a great
+resource, and you'll get a local copy with your local documentation.
+
+Second, back in Rust 1.23, we talked about the change from Hoedown to
+pulldown-cmark. In Rust 1.25, pulldown-cmark is now the default rendering. We
+have finally removed the last bit of C from rustdoc, and now properly follow
+the CommonMark spec.
+
+Finally, in [RFC 1358], `#[repr(align(x))]` was accepted. In Rust
+1.25, [it is now stable]! This attribute lets you set the [alignment]
+of your `struct`s:
+
+```rust
+struct Number(i32);
+
+assert_eq!(std::mem::align_of::<Number>(), 4);
+assert_eq!(std::mem::size_of::<Number>(), 4);
+
+#[repr(align(16))]
+struct Align16(i32);
+
+assert_eq!(std::mem::align_of::<Align16>(), 16);
+assert_eq!(std::mem::size_of::<Align16>(), 16);
+```
+
+If you're working with low-level stuff, control of these kinds of things
+can be very important!
+
+[upgraded to LLVM 6]: https://github.com/rust-lang/rust/pull/47828
+[nested import groups]: https://github.com/rust-lang/rust/pull/47948
+[Rust By Example is now included on doc.rust-lang.org]: https://doc.rust-lang.org/rust-by-example/
+[RFC 1358]: https://github.com/rust-lang/rfcs/blob/master/text/1358-repr-align.md
+[it is now stable]: https://github.com/rust-lang/rust/pull/47006
+[alignment]: https://en.wikipedia.org/wiki/Data_structure_alignment
+
+See the [detailed release notes][notes] for more.
+
+### Library stabilizations
+
+The biggest story in libraries this release is [`std::ptr::NonNull<T>`]. This type
+is similar to `*mut T`, but is non-null and covariant. This blog post isn't the right
+place to explain variance, but in a nutshell, `NonNull<T>`, well, guarantees that it
+won't be null, which means that `Option<NonNull<T>>` is the same size as `Option<T>`.
+If you're building a data structure with unsafe code, `NonNull<T>` is often the right
+type for you!
+
+[`std::ptr::NonNull<T>`]: https://doc.rust-lang.org/std/ptr/struct.NonNull.html
+
+`libcore` has [gained a `time` module](https://doc.rust-lang.org/core/time/),
+containing the `Duration` type previously only available in `libstd`.
+
+Additionally, the `from_secs`, and `from_milis` functions associated with
+`Duration` were made `const fn`s, allowing them to be used to create a
+`Duration` as a constant expression.
+
+See the [detailed release notes][notes] for more.
+
+### Cargo features
+
+Cargo's CLI has one really important change this release: `cargo new` will
+[now default](https://github.com/rust-lang/cargo/pull/5029) to generating a
+binary, rather than a library. We try to keep Cargo's CLI quite stable, but
+this change is important, and is unlikely to cause breakage.
+
+For some background, `cargo new` accepts two flags: `--lib`, for creating libraries,
+and `--bin`, for creating binaries, or executables. If you don't pass one of these
+flags, in previous versions of Cargo, it would default to `--lib`. We made this
+decision because each binary (often) depends on many libraries, and so the library
+case is more common. However, this is incorrect; each library is *depended upon* by
+many binaries. Furthermore, when getting stated, what you often want is a program
+you can run and play around with. It's not just new Rustaceans though; even very
+long-time community members have said that they find this default surprising.
+As such, we're changing it.
+
+Similarly, `cargo new` previously would be a bit opinionated around the names
+of packages it would create. Specifically, if your package began with `rust-`
+or ended with `-rs`, Cargo would rename it. The intention was that well,
+it's a Rust package, this information is redundant. However, people feel
+quite strongly about naming, and when they bump into this, they're surprised
+and often upset. As such, [we're not going to do that any
+more](https://github.com/rust-lang/cargo/pull/5013).
+
+Many users love `cargo doc`, a way to generate local documentation for their
+Cargo projects. [It's getting a huge speed
+bump](https://github.com/rust-lang/cargo/pull/4976) in this release, as now,
+it uses `cargo check`, rather than a full `cargo build`, so some scenarios
+will get faster.
+
+Additionally, checkouts of git dependencies [should be a lot
+faster](https://github.com/rust-lang/cargo/pull/4919), thanks to the use of
+hard links when possible.
+
+See the [detailed release notes][notes] for more.
+
+## Contributors to 1.25.0
+
+Many people came together to create Rust 1.25. We couldn't have done it
+without all of you. [Thanks!](https://thanks.rust-lang.org/rust/1.25.0)