Announcement for Rust 1.12.1

_posts/2016-10-20-Rust-1.12.1.md

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+---
+layout: post
+title: "Announcing Rust 1.12.1"
+author: The Rust Core Team
+---
+
+The Rust team is happy to announce the latest version of Rust, 1.12.1. Rust is a
+systems programming language with a focus on reliability, performance, and
+concurrency.
+
+As always, you can [install Rust 1.12.1][install] from the appropriate page on our
+website, or install via [rustup] with `rustup update stable`.
+
+[install]: https://www.rust-lang.org/install.html
+
+### What's in 1.12.1 stable
+
+Wait... one-point-twelve-point... one?
+
+In [the release announcement for 1.12][one-twelve] a few weeks ago, we said:
+
+[one-twelve]: https://blog.rust-lang.org/2016/09/29/Rust-1.12.html
+
+> The release of 1.12 might be one of the most significant Rust releases since
+> 1.0.
+
+It was true. One of the biggest changes was turning on a large compiler
+refactoring, [MIR], which re-architects the internals of the compiler. The
+overall process went like this:
+
+[MIR]: https://blog.rust-lang.org/2016/04/19/MIR.html
+
+* Initial MIR support landed in nightlies back in Rust 1.6.
+* While work was being done, a flag, `--enable-orbit`, was added so that
+  people working on the compiler could try it out.
+* Back [in October], we would always attempt to build MIR, even though it
+  was not being used.
+* A flag was added, `-Z orbit`, to allow users on nightly to try and use MIR
+  rather than the traditional compilation step ('trans').
+* After substantial testing over months and months, for Rust 1.12, [we enabled
+  MIR by default].
+* In Rust 1.13, [MIR will be the only option].
+
+[in October]: https://github.com/rust-lang/rust/pull/28748
+[we enabled MIR by default]: https://github.com/rust-lang/rust/pull/34096
+[MIR will be the only option]: https://github.com/rust-lang/rust/pull/35764
+
+A change of this magnitude is huge, and important. So it's also important to do
+it right, and do it carefully. This is why this process took so long; we
+regularly tested the compiler against every crate on crates.io, we asked people
+to try out `-Z orbit` on their private code, and after six weeks of beta, no
+significant problems appeared. So we made the decision to keep it on by default
+in 1.12.
+
+But large changes still have an element of risk, even though we tried to reduce
+that risk as much as possible. And so, after release, 1.12 saw a fair number of
+regressions that we hadn't detected in our testing. Not all of them are
+directly MIR related, but when you change the compiler internals so much, it's
+bound to ripple outward through everything.
+
+### Why make a point release?
+
+Now, given that we have a six-week release cycle, and we're halfway towards
+Rust 1.13, you may wonder why we're choosing to cut a patch version of Rust
+1.12 rather than telling users to just wait for the next release. We have
+previously said something like "point releases should only happen in extreme
+situations, such as a security vulnerability in the standard library."
+
+The Rust team cares deeply about the stability of Rust, and about our users'
+experience with it. We could have told you all to wait, but we want you to know
+how seriously we take this stuff. We think it's worth it to demonstrate our
+commitment to you by putting in the work of making a point release in this
+situation.
+
+Furthermore, given that this is not security related, it's a good time to
+practice actually cutting a point release. We've never done it before, and the
+release process is [semi-automated] but still not completely so. Having a point
+release in the world will also [shake out any bugs][bugs] in dealing with point
+releases in other tooling as well, like [rustup]. Making sure that this all goes
+smoothly and getting some practice going through the motions will be useful if
+we ever need to cut some sort of *emergency* point release due to a security
+advisory or anything else.
+
+[semi-automated]: https://forge.rust-lang.org/release-process.html
+[rustup]: https://www.rustup.rs/
+[bugs]: https://github.com/rust-lang/rust/pull/37173#issuecomment-253938822
+
+This is the first Rust point release since [Rust 0.3.1], all the way back in in
+2012, and marks 72 weeks since Rust 1.0, when we established our six week
+release cadence along with a commitment to aggressive stability
+guarantees. While we're disappointed that 1.12 had these regressions, we're
+really proud of Rust's stability and will to continue expanding our efforts to
+ensure that it's a platform you can rely on. We want Rust to be the most
+reliable programming platform in the world.
+
+[Rust 0.3.1]: https://mail.mozilla.org/pipermail/rust-dev/2012-July/002152.html
+
+### A note about testing on beta
+
+One thing that you, as a user of Rust, can do to help us fix these issues
+sooner: test your code against the beta channel! Every beta release is a
+release candidate for the next stable release, so for the cost of an extra
+build in CI, you can help us know if there's going to be some sort of problem
+before it hits a stable release! It's really easy. For example, on
+[Travis](https://travis-ci.org/), you can use this as your `.travis.yml`:
+
+```yaml
+language: rust
+rust:
+  - stable
+  - beta
+```
+
+And you'll test against both. Furthermore, if you'd like to make it so that any
+beta failure doesn't fail your own build, do this:
+
+```yaml
+matrix:
+  allow_failures:
+    - rust: beta
+```
+
+The beta build may go red, but your build will stay green.
+
+Most other CI systems, such as [AppVeyor](https://www.appveyor.com/), should
+support [something
+similar](https://www.appveyor.com/docs/build-configuration/#allow-failing-jobs).
+Check the documentation for your specific continuous integration product for
+full details.
+
+### Full details
+
+There were nine issues fixed in 1.12.1, and all of those fixes have been
+backported to 1.13 beta as well. 
+
+* [ICE: 'rustc' panicked at 'assertion failed: concrete_substs.is_normalized_for_trans()' #36381][36381]
+* [Confusion with double negation and booleans][36856]
+* [rustc 1.12.0 fails with SIGSEGV in release mode (syn crate 0.8.0)][36875]
+* [Rustc 1.12.0 Windows build of `ethcore` crate fails with LLVM error][36924]
+* [1.12.0: High memory usage when linking in release mode with debug info][36926]
+* [Corrupted memory after updated to 1.12][36936]
+* ["Let NullaryConstructor = something;" causes internal compiler error: "tried to overwrite interned AdtDef"][37026]
+* [Fix ICE: inject bitcast if types mismatch for invokes/calls/stores][37112]
+* [debuginfo: Handle spread_arg case in MIR-trans in a more stable way.][37153]
+
+[36381]: https://github.com/rust-lang/rust/issues/36381
+[36856]: https://github.com/rust-lang/rust/issues/36856
+[36875]: https://github.com/rust-lang/rust/issues/36875
+[36924]: https://github.com/rust-lang/rust/issues/36924
+[36926]: https://github.com/rust-lang/rust/issues/36926
+[36936]: https://github.com/rust-lang/rust/issues/36936
+[37026]: https://github.com/rust-lang/rust/issues/37026
+[37112]: https://github.com/rust-lang/rust/issues/37112
+[37153]: https://github.com/rust-lang/rust/issues/37153
+
+In addition, there were four more regressions that we decided not to include
+in 1.12.1 for various reasons, but we'll be working on fixing those as soon
+as possible as well.
+
+* [ICE, possibly related to associated types of associated types?][36325]
+* [Compilation of a crate using a large static map fails on latest i686-pc-windows-gnu Beta][36799]
+* [Regression: "no method found" error when calling same method twice, with HRTB impl][37154]
+* [ICE: fictitious type sizing_type_of][37109]
+
+[36325]: https://github.com/rust-lang/rust/issues/36325
+[36799]: https://github.com/rust-lang/rust/issues/36799
+[37154]: https://github.com/rust-lang/rust/issues/37154
+[37109]: https://github.com/rust-lang/rust/issues/37109
+
+You can see the full diff from 1.12.0 to 1.12.1
+[here](https://github.com/rust-lang/rust/pull/37173).