The Rust team is happy to announce the latest version of Rust, 1.12. Rust is
a systems programming language with the slogan “fast, reliable, productive:
pick three.”
As always, you can install Rust 1.12 from the appropriate page on our
website, and check out the detailed release notes for 1.12 on GitHub.
1361 patches were landed in this release.
What’s in 1.12 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 rustcs errors to the new format. We’re excited to see
what you think of them:
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 today, 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.
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 putting your code front and center, highlighting the parts
relevant to the error with annotations describing what went wrong.
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:
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:
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.
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:
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.
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.
These targets produce statically-linked binaries. There are no binary release
builds yet though.
In error descriptions,
references and unknown numeric
types have more human-friendly errors.
The compiler can now be built against LLVM 3.9
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
The test runner now emits a warning when tests run over 60
seconds
Rust releases now come with source packages that can be installed by rustup
via rustup component add
rust-src.
The resulting source code can be used by tools and IDES, located in the
sysroot under lib/rustlib/src.
See the detailed release 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
and
RefCell::as_ptr
IpAddr, Ivp4Addr, and Ipv6Addr have a few new methods.
LinkedList
and
VecDeque
have a new contains method.
iter::Product and
iter::Sum
Option implements From for its contained
type
Cell, RefCell and UnsafeCell implement From for their contained
type
Cow
implements FromIterator for char, &str and
String
Sockets on Linux are correctly closed in subprocesses via
SOCK_CLOEXEC
String implements
AddAssign
Unicode definitions have been updated to
9.0
See the detailed release notes for more.
Cargo features
The biggest feature added to Cargo this cycle is
“workspaces.” Defined in RFC
1525,
workspaces allow a group of Rust packages to share the same Cargo.lock file.
If you have a project that’s split up into multiple packages, this makes it
much easier to keep shared dependencies on a single version. To enable this
feature, most multi-package projects need to add a single key, [workspace],
to their top-level Cargo.toml, but more complex setups may require more
configuration.
Another significant feature is the ability to override the
source of a crate. Using this
with tools like cargo-vendor and cargo-local-registry allow vendoring
dependencies locally in a robust fashion. Eventually this support will be the
foundation of supporting mirrors of crates.io as well.
There are some other improvements as well:
Speed up noop registry
updates
Add a --lib flag to cargo
new
Indicate the compilation profile after
compiling
Add --dry-run to cargo
publish
See the detailed release notes for more.
Contributors to 1.12
We had 176 individuals contribute to 1.12. 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