Rust 1.12 release announcement

_posts/2016-09-29-Rust-1.12.md

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+---
+layout: post
+title: "Announcing Rust 1.12.0"
+author: The Rust Core Team
+---
+
+The Rust team is happy to announce the latest version of Rust, 1.12.0. Rust is
+a systems programming language with the slogan "fast, reliable, productive:
+pick three."
+
+As always, you can [install Rust 1.12.0][install] from the appropriate page on our
+website, and check out the [detailed release notes for 1.12.0][notes] on GitHub.
+1361 patches were landed in this release.
+
+[install]: https://www.rust-lang.org/install.html
+[notes]: https://github.com/rust-lang/rust/blob/master/RELEASES.md#version-1120-2016-09-29
+
+### What's in 1.12.0 stable
+
+The release of 1.12 might be one of the most significant Rust releases since
+1.0. We have a lot to cover, but if you don't have time for that, here's a
+summary:
+
+The largest user-facing change in 1.12 stable is the new error message format
+emitted by `rustc`. We've [previously talked] about this format and this is the
+first stable release where they are broadly available. These error messages are
+a result of the effort of many hours of [volunteer effort] to design, test, and
+update every one of `rustc`s errors to the new format. We're excited to see
+what you think of them:
+
+![A new borrow-check error](/images/2016-09-Rust-1.12/borrowck-error.png)
+
+The largest internal change in this release is moving to a new compiler backend
+based on the new Rust [MIR]. While this feature does not result in anything
+user-visible, it paves the way for a number of future compiler optimizations,
+and for some codebases it already results in improvements to compile times and
+reductions in code size.
+
+[previously talked]: https://blog.rust-lang.org/2016/08/10/Shape-of-errors-to-come.html
+[volunteer effort]: https://github.com/rust-lang/rust/issues/35233
+[MIR]: https://blog.rust-lang.org/2016/04/19/MIR.html
+
+#### Overhauled error messages
+
+With 1.12 we're introducing a new error format which helps to surface a lot of
+the internal knowledge about why an error is occurring to you, the developer. It
+does this by focusing on your code and the points of interest in your code that
+are relevant to the error.
+
+For example, in 1.11 if a implementation of a trait didn't match the trait
+declaration, you would see an error like the one below:
+
+![An old mismatched trait
+error](/images/2016-09-Rust-1.12/old-mismatched-trait-error.png)
+
+In the new error format we represent the error by instead showing the points in
+the code that matter the most. Here is the relevant line in the trait
+declaration, and the relevant line in the implementation, using labels to
+describe why they don't match:
+
+![A new mismatched trait
+error](/images/2016-09-Rust-1.12/mismatched-trait-error.png)
+
+Initially, this error design was built to aid in understanding borrow-checking
+errors, but we found, as with the error above, the format can be broadly
+applied to a wide variety of errors. If you would like to learn more about the
+design, check out the [previous blog post on the subject][err].
+
+[err]: https://blog.rust-lang.org/2016/08/10/Shape-of-errors-to-come.html
+
+Finally, you can also get these errors as JSON with a flag. Remember that error
+we showed above, at the start of the post? Here's an example of attempting to
+compile that code while passing the `--error-format=json` flag:
+
+```bash
+$ rustc borrowck-assign-comp.rs --error-format=json
+{"message":"cannot assign to `p.x` because it is borrowed","level":"error","spans":[{"file_name":"borrowck-assign-comp.rs","byte_start":562,"byte_end":563,"line_start":15,"line_end":15,"column_start":14,"column_end":15,"is_primary":false,"text":[{"text":"    let q = &p;","highlight_start":14,"highlight_end":15}],"label":"borrow of `p.x` occurs here","suggested_replacement":null,"expansion":null}],"label":"assignment to borrowed `p.x` occurs here","suggested_replacement":null,"expansion":null}],"children":[],"rendered":null}
+{"message":"aborting due to previous error","code":null,"level":"error","spans":[],"children":[],"rendered":null}
+```
+
+We've actually elided a bit of this for brevity's sake, but you get the idea.
+This output is primarily for tooling; we are continuing to invest in supporting
+IDEs and other useful development tools. This output is a small part of that
+effort.
+
+#### MIR code generation
+
+The new Rust "mid-level IR", usually called "MIR", gives the compiler a simpler
+way to think about Rust code than its previous way of operating entirely on the
+Rust abstract syntax tree. It makes analysis and optimizations possible that
+have historically been difficult to implement correctly. The first of many
+upcoming changes to the compiler enabled by MIR is a rewrite of the pass that
+generates LLVM IR, what `rustc` calls "translation", and after many months of
+effort the MIR-based backend has proved itself ready for prime-time.
+
+MIR exposes perfect information about the program's control flow, so the
+compiler knows exactly whether types are moved or not. This means that it knows
+statically whether or not the value's destructor needs to be run. In cases
+where a value may or may not be moved at the end of a scope, the compiler now
+simply uses a single bitflag on the stack, which is in turn easier for
+optimization passes in LLVM to reason about. The end result is less work for
+the compiler and less bloat at runtime. In addition, because MIR is a simpler
+'language' than the full AST, it's also easier to implement compiler passes on,
+and easier to verify that they are correct.
+
+The improvements in compile times of some workloads due to this change alone
+are significant:
+
+|               | 1.11   | 1.12  | compile time |
+|---------------|--------|-------|--------------|
+| inflate-0.1.0 | 10.17s | 4.32s | 2.35x faster |
+| hyper-0.5.0   | 24.03s | 5.23s | 4.58x faster |
+| helloworld    | 0.17s  | 0.14s | 1.20x faster |
+| regex 0.1.30  | 9.63s  | 2.39s | 4.03x faster |
+
+It is worth remembering that not all workloads may see this large of an
+improvement: it depends on a large number of factors.
+
+The compiler's [memory usage](https://en.wikipedia.org/wiki/Resident_set_size)
+while compiling these crates was also improved:
+
+|               | 1.11  | 1.12  | % of original size |
+|---------------|-------|-------|--------------------|
+| inflate-0.1.0 | 175MB | 135MB | 77.1%              |
+| hyper.0.5.0   | 321MB | 302MB | 94.1%              |
+| helloworld    | 127MB | 90MB  | 70.9%              |
+| regex.0.1.30  | 230MB | 194MB | 84.3%              |
+
+#### Other improvements
+
+* Many minor improvements to the documentation.
+* [`rustc` supports three new MUSL targets on ARM: `arm-unknown-linux-musleabi`,
+  `arm-unknown-linux-musleabihf`, and `armv7-unknown-linux-musleabihf`]
+  (https://github.com/rust-lang/rust/pull/35060).
+  These targets produce statically-linked binaries. There are no binary release
+  builds yet though.
+* In error descriptions,
+  [references](https://github.com/rust-lang/rust/pull/35611) and [unknown numeric
+  types](https://github.com/rust-lang/rust/pull/35080) have more human errors.
+* [The compiler can now be built against LLVM 3.9]
+  (https://github.com/rust-lang/rust/pull/35594)
+* [Test binaries now support a `--test-threads` argument to specify the number
+  of threads used to run tests, and which acts the same as the
+  `RUST_TEST_THREADS` environment variable]
+  (https://github.com/rust-lang/rust/pull/35414)  
+* [The test runner now emits a warning when tests run over 60 seconds]
+  (https://github.com/rust-lang/rust/pull/35405)
+* [Rust releases now come with source packages that can be installed by rustup
+  via `rustup component add rust-src`]
+  (https://github.com/rust-lang/rust/pull/34366).
+  The resulting source code can be used by tools and IDES, located in the
+  sysroot under `lib/rustlib/src`.
+
+See the [detailed release notes][notes] for more.
+
+#### Library stabilizations
+
+This release sees a number of small quality of life improvements for various
+types in the standard library:
+
+* [`Cell::as_ptr`](https://doc.rust-lang.org/std/cell/struct.Cell.html#method.as_ptr)
+  and
+  [`RefCell::as_ptr`](https://doc.rust-lang.org/std/cell/struct.RefCell.html#method.as_ptr)
+* `IpAddr`, `Ivp4Addr`, and `Ipv6Addr` have a few new methods.
+* [`LinkedList`](https://doc.rust-lang.org/std/collections/linked_list/struct.LinkedList.html#method.contains)
+  and
+  [`VecDeque`](https://doc.rust-lang.org/std/collections/vec_deque/struct.VecDeque.html#method.contains)
+  have a new `contains` method.
+* [`iter::Product`](https://doc.rust-lang.org/std/iter/trait.Product.html) and
+  [`iter::Sum`](https://doc.rust-lang.org/std/iter/trait.Sum.html)
+* [`Option` implements `From` for its contained type]
+  (https://github.com/rust-lang/rust/pull/34828)
+* [`Cell`, `RefCell` and `UnsafeCell` implement `From` for their contained type]
+  (https://github.com/rust-lang/rust/pull/35392)
+* [`Cow<str>` implements `FromIterator` for `char`, `&str` and `String`]
+  (https://github.com/rust-lang/rust/pull/35064)
+* [Sockets on Linux are correctly closed in subprocesses via `SOCK_CLOEXEC`]
+  (https://github.com/rust-lang/rust/pull/34946)
+* [`String` implements `AddAssign`]
+  (https://github.com/rust-lang/rust/pull/34890)
+* [Unicode definitions have been updated to 9.0]
+  (https://github.com/rust-lang/rust/pull/34599)
+
+See the [detailed release notes][notes] for more.
+
+#### Cargo features
+
+Cargo has some modest improvments:
+
+* [Support local mirrors of
+  registries](https://github.com/rust-lang/cargo/pull/2857)
+* [Speed up noop registry updates](https://github.com/rust-lang/cargo/pull/2974)
+* [Add a `--lib` flag to `cargo new`]
+  (https://github.com/rust-lang/cargo/pull/2921)
+* [Indicate the compilation profile after compiling]
+  (https://github.com/rust-lang/cargo/pull/2909)
+* [Add `--dry-run` to `cargo publish`]
+  (https://github.com/rust-lang/cargo/pull/2849)
+
+See the [detailed release notes][notes] for more.
+
+### Contributors to 1.12.0
+
+We had 176 individuals contribute to 1.12.0. Thank you so much!
+
+* Aaron Gallagher
+* abhi
+* Adam Medziński
+* Ahmed Charles
+* Alan Somers
+* Alexander Altman
+* Alexander Merritt
+* Alex Burka
+* Alex Crichton
+* Amanieu d'Antras
+* Andrea Pretto
+* Andre Bogus
+* Andrew
+* Andrew Cann
+* Andrew Paseltiner
+* Andrii Dmytrenko
+* Antti Keränen
+* Aravind Gollakota
+* Ariel Ben-Yehuda
+* Bastien Dejean
+* Ben Boeckel
+* Ben Stern
+* bors
+* Brendan Cully
+* Brett Cannon
+* Brian Anderson
+* Bruno Tavares
+* Cameron Hart
+* Camille Roussel
+* Cengiz Can
+* CensoredUsername
+* cgswords
+* Chiu-Hsiang Hsu
+* Chris Stankus
+* Christian Poveda
+* Christophe Vu-Brugier
+* Clement Miao
+* Corey Farwell
+* CrLF0710
+* crypto-universe
+* Daniel Campbell
+* David
+* decauwsemaecker.glen@gmail.com
+* Diggory Blake
+* Dominik Boehi
+* Doug Goldstein
+* Dridi Boukelmoune
+* Eduard Burtescu
+* Eduard-Mihai Burtescu
+* Evgeny Safronov
+* Federico Ravasio
+* Felix Rath
+* Felix S. Klock II
+* Fran Guijarro
+* Georg Brandl
+* ggomez
+* gnzlbg
+* Guillaume Gomez
+* hank-der-hafenarbeiter
+* Hariharan R
+* Isaac Andrade
+* Ivan Nejgebauer
+* Ivan Ukhov
+* Jack O'Connor
+* Jake Goulding
+* Jakub Hlusička
+* James Miller
+* Jan-Erik Rediger
+* Jared Manning
+* Jared Wyles
+* Jeffrey Seyfried
+* Jethro Beekman
+* Jonas Schievink
+* Jonathan A. Kollasch
+* Jonathan Creekmore
+* Jonathan Giddy
+* Jonathan Turner
+* Jorge Aparicio
+* José manuel Barroso Galindo
+* Josh Stone
+* Jupp Müller
+* Kaivo Anastetiks
+* kc1212
+* Keith Yeung
+* Knight
+* Krzysztof Garczynski
+* Loïc Damien
+* Luke Hinds
+* Luqman Aden
+* m4b
+* Manish Goregaokar
+* Marco A L Barbosa
+* Mark Buer
+* Mark-Simulacrum
+* Martin Pool
+* Masood Malekghassemi
+* Matthew Piziak
+* Matthias Rabault
+* Matt Horn
+* mcarton
+* M Farkas-Dyck
+* Michael Gattozzi
+* Michael Neumann
+* Michael Rosenberg
+* Michael Woerister
+* Mike Hommey
+* Mikhail Modin
+* mitchmindtree
+* mLuby
+* Moritz Ulrich
+* Murarth
+* Nick Cameron
+* Nick Massey
+* Nikhil Shagrithaya
+* Niko Matsakis
+* Novotnik, Petr
+* Oliver Forral
+* Oliver Middleton
+* Oliver Schneider
+* Omer Sheikh
+* Panashe M. Fundira
+* Patrick McCann
+* Paul Woolcock
+* Peter C. Norton
+* Phlogistic Fugu
+* Pietro Albini
+* Rahiel Kasim
+* Rahul Sharma
+* Robert Williamson
+* Roy Brunton
+* Ryan Scheel
+* Ryan Scott
+* saml
+* Sam Payson
+* Samuel Cormier-Iijima
+* Scott A Carr
+* Sean McArthur
+* Sebastian Thiel
+* Seo Sanghyeon
+* Shantanu Raj
+* ShyamSundarB
+* silenuss
+* Simonas Kazlauskas
+* srdja
+* Srinivas Reddy Thatiparthy
+* Stefan Schindler
+* Stephen Lazaro
+* Steve Klabnik
+* Steven Fackler
+* Steven Walter
+* Sylvestre Ledru
+* Tamir Duberstein
+* Terry Sun
+* TheZoq2
+* Thomas Garcia
+* Tim Neumann
+* Timon Van Overveldt
+* Tobias Bucher
+* Tomasz Miąsko
+* trixnz
+* Tshepang Lekhonkhobe
+* ubsan
+* Ulrik Sverdrup
+* Vadim Chugunov
+* Vadim Petrochenkov
+* Vincent Prouillet
+* Vladimir Vukicevic
+* Wang Xuerui
+* Wesley Wiser
+* William Lee
+* Ximin Luo
+* Yojan Shrestha
+* Yossi Konstantinovsky
+* Zack M. Davis
+* Zhen Zhang
+* 吴冉波