initial draft of 1.18.0 announcement

Author: steveklabnik

_posts/2017-06-08-Rust-1.18.md

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+---
+layout: post
+title: "Announcing Rust 1.18"
+author: The Rust Core Team
+---
+
+The Rust team is happy to announce the latest version of Rust, 1.18.0. Rust is a
+systems programming language focused on safety, speed, and concurrency.
+
+If you have a previous version of Rust installed, getting Rust 1.18 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
+1.18.0][notes] on GitHub.
+
+[install]: https://www.rust-lang.org/install.html
+[notes]: https://github.com/rust-lang/rust/blob/rust-1.17-relnotes/RELEASES.md#version-1180-2017-06-08
+
+### What's in 1.18.0 stable
+
+Rust 1.18.0 is similar to many of our releases: no big bombshells, just a number
+of improvements, cleanups, and new features.
+
+One of the largest changes is a long time coming: core team members Carol
+Nichols and Steve Klabnik have been writing a new edition of "The Rust
+Programming Language", the official book about Rust. It's being [written openly
+on GitHub](https://github.com/rust-lang/book), and has over a hundred
+contributors in total. This release [includes the first draft of the second
+edition in our online documentation](https://doc.rust-lang.org/stable/book/).
+19 out of 20 chapters have a draft; the draft of chapter 20 will land in the
+Rust 1.19. When the book is done, a print version will be made available through
+[No Starch Press](https://www.nostarch.com/Rust), if you'd like a paper copy.
+While first drafts of the chapters are available, we're still working with the
+editors at No Starch to improve the text, so there's more to do, but we wanted
+to start getting a wider audience now. The new edition is a complete re-write
+from the ground up, using the last two years of knowledge we've gained from
+teaching people Rust. You'll find brand-new explanations for a lot of Rust's
+core concepts, new projects to build, and all kinds of other good stuff. Please
+check it out and let us know what you think!
+
+As for the language itself, an old feature has learned some new tricks: the
+`pub` keyword has been expanded a bit. Experienced Rustaceans will know that
+items are private by default in Rust, and you can use the `pub` keyword to make
+them public. In Rust 1.18.0, `pub` has [gained a new
+form](https://github.com/rust-lang/rust/pull/40556):
+
+```rust
+pub(crate) bar;
+```
+
+The bit inside of `()` is a 'restriction', which refines the notion of how this
+is made public. Using the `crate` keyword like the example above means that
+`bar` would be public to the entire crate, but not outside of it. This makes it
+easier to declare APIs that are "public to your crate", but not exposed to your
+users. This was *possible* with the current module system, but often very awkward.
+
+You can also specify a path, like this:
+
+```rust
+pub(a::b::c) foo;
+```
+
+This means "usable within the hierarchy of `a::b::c`, but not elsewhere." This
+feature was defined in [RFC
+1422](https://github.com/rust-lang/rfcs/blob/master/text/1422-pub-restricted.md)
+
+For our Windows users, Rust 1.18.0 has [a new attribute,
+`#![windows_subsystem]`](https://github.com/rust-lang/rust/pull/40870). It
+works like this:
+
+```rust
+#![windows_subsystem(console)]
+#![windows_subsystem(windows)]
+```
+
+These control the [`/SUBSYSTEM` flag](https://msdn.microsoft.com/en-us/library/fcc1zstk.aspx)
+in the linker. For now, only `console` and `windows` are supported.
+
+When is this useful? In the simplest terms, if you're developing a graphical
+application, and do not specify `windows`, a console window would flash up upon
+your application's start. With this flag, it won't.
+
+Finally, Rust's tuples, enum variant fields, and structs (without `#[repr]`) have
+always had an undefined layout. [We've turned on automatic re-ordering](https://github.com/rust-lang/rust/pull/40377), which can result in smaller sizes
+through reducing padding. Consider a struct like this:
+
+```rust
+struct Suboptimal(u8, u16, u8);
+```
+
+In previous versions of Rust on the x86_64 platform, this struct would have the
+size of six bytes. But looking at the source, you'd expect it to have four. The
+extra two bytes come from padding; given that we have a `u16` here, it should be
+aligned to two bytes. But in this case, it's at offset one. To move it to offset
+two, another byte of padding is placed after the first `u8`. To give the whole struct
+a proper alignment, another byte is added after the second `u8` as well, giving us
+`1 + 1 (padding) + 2 + 1 + 1 (padding) = 6 bytes`.
+
+But what if our struct looked like this?
+
+```rust
+struct Optimal(u8, u8, u16);
+```
+
+This struct is properly aligned; the `u16` lies on a two byte boundary, and so does
+the entire struct. No padding is needed. This gives us `1 + 1 + 2 = 4 bytes`.
+
+When designing Rust, stuff like this is why we left the details here undefined.
+It allows for exactly this kind of thing: the compiler can optimize `Suboptimal`
+into `Optimal` automatically. And if you check the sizes of `Suboptimal` and
+`Optimal` on Rust 1.18.0, you'll see that they both have a size of four bytes.
+
+We've been planning this for a while; previous versions of Rust included this
+optimization on the nightly channel, but some people wrote unsafe code that
+assumed the exact details of the representation. We rolled it back while we fixed
+all instances of this that we know about, but if you find some code breaks due to
+this, you should fix it! In the meantime, there's also a flag you can use to control
+this. Imagine we have `Suboptimal` in a file named `foo.rs`, along with a `main`
+function that prints out its size:
+
+```rust
+> rustc foo.rs
+> ./foo
+4
+> rustc foo.rs -Z fuel=foo=0
+optimization-fuel-exhausted: Reorder fields of "Suboptimal"
+> ./foo
+6
+```
+
+This flag is based on an idea called "[Optimization
+fuel](https://www.microsoft.com/en-us/research/wp-content/uploads/2016/07/dfopt-popl10.pdf)":
+
+> It works by giving the optimizer a finite supply of optimization fuel. Each
+> time a rewrite function proposes to replace a node, one unit of fuel is
+> consumed. When the optimizer runs out of fuel, further rewrites are
+> suppressed.
+
+Currently, this is the only optimization that uses the "fuel" concept. By
+setting the fuel to zero, `rustc` will not perform the optimization. This can
+keep your code compiling if you run into a problem, but the longer-term fix is
+to use a `#[repr]` attribute to guarantee a particular layout if you rely on it.
+
+We've been planning on moving `rustdoc` to use a CommonMark compliant markdown
+parser for a long time now. However, just switching over can introduce
+regressions where the CommonMark spec differs from our existing parser, Hoedown.
+As part of the transition plan, [a new flag has been added to
+`rustdoc`](https://github.com/rust-lang/rust/pull/40338), `--enable-commonmark`.
+This will use the new parser instead of the old one. Please give it a try! There's
+no scenario we know of where tweaking your markdown gets identical results on both
+parsers.
+
+Finally, compiling `rustc` itself is now [15%-20% faster](https://github.com/rust-lang/rust/pull/41469). Each commit message in this PR
+goes over the details, but the short of it is that there were some inefficient
+things, and now they've been cleaned up.
+
+See the [detailed release notes][notes] for more.
+
+#### Library stabilizations
+
+Seven new APIs were stabilized this release:
+
+- [`Child::try_wait`] is a non-blocking form of `Child::wait`.
+- [`HashMap::retain`] and  [`HashSet::retain`] bring the `retain` API `Vec<T>` has to these two hash data structures.
+- [`PeekMut::pop`] lets you pop stuff off of a `BinaryHeap<T>`
+- [`TcpStream::peek`], [`UdpSocket::peek`], [`UdpSocket::peek_from`] let you peek at a stream or socket.
+
+[`Child::try_wait`]: https://doc.rust-lang.org/std/process/struct.Child.html#method.try_wait
+[`HashMap::retain`]: https://doc.rust-lang.org/std/collections/struct.HashMap.html#method.retain
+[`HashSet::retain`]: https://doc.rust-lang.org/std/collections/struct.HashSet.html#method.retain
+[`PeekMut::pop`]: https://doc.rust-lang.org/std/collections/binary_heap/struct.PeekMut.html#method.pop
+[`TcpStream::peek`]: https://doc.rust-lang.org/std/net/struct.TcpStream.html#method.peek
+[`UdpSocket::peek_from`]: https://doc.rust-lang.org/std/net/struct.UdpSocket.html#method.peek_from
+[`UdpSocket::peek`]: https://doc.rust-lang.org/std/net/struct.UdpSocket.html#method.peek
+
+See the [detailed release notes][notes] for more.
+
+#### Cargo features
+
+Cargo has [added support](https://github.com/rust-lang/cargo/pull/3842) for the Pijul VCS,
+which is written in Rust. `cargo new my-awesome-project --vcs=pijul` will get you going!
+
+To suppliment the `--all` flag, Cargo now has [several new
+flags](https://github.com/rust-lang/cargo/pull/3901) such as `--bins`,
+`--examples`, `--tests`, and `--benches`, which will let you build all programs of
+that type.
+
+Finally, Cargo now supports [Haiku](https://github.com/rust-lang/cargo/pull/3952) and
+[Android](https://github.com/rust-lang/cargo/pull/3885)!
+
+See the [detailed release notes][notes] for more.
+
+### Contributors to 1.18.0
+
+Many people came together to create Rust 1.18. We couldn't have done it without
+all of you. [Thanks!](https://thanks.rust-lang.org/rust/1.18.0)