1.27.2 announcement

_posts/2018-07-20-Rust-1.27.2.md

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+---
+layout: post
+title: "Announcing Rust 1.27.2"
+author: The Rust Core Team
+---
+
+The Rust team is happy to announce a new version of Rust, 1.27.2. 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
+1.27.2 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
+1.27.2][notes] on GitHub.
+
+[install]: https://www.rust-lang.org/install.html
+[notes]: https://github.com/rust-lang/rust/blob/stable/RELEASES.md#version-1272-2018-07-20
+
+## What's in 1.27.2 stable
+
+This patch release fixes a bug in the borrow checker verification of `match` expressions. This bug
+was introduced in 1.27.1 with a different bugfix for [match ergonomics].
+
+```rust
+fn transmute_lifetime<'a, 'b, T>(t: &'a (T,)) -> &'b T {
+    match (&t, ()) {
+        ((t,), ()) => t,
+    }
+}
+
+fn main() {
+    let x = {
+        let y = Box::new((42,));
+        transmute_lifetime(&y)
+    };
+
+    println!("{}", x);
+}
+```
+
+1.27.2 will reject the above code.
+
+## Concern over numerous patches to the match ergonomics feature
+
+Users have expressed concern with the frequency of patch releases to fix bugs in the match
+ergonomics verification by the current borrow checker on a variety of Rust's forums. There are two
+primary reasons for the increased rate of patch releases: significantly higher bandwidth and the
+age of the currently used borrow checker.
+
+With the formation of the Release team, Rust's ability to generate patch releases has
+greatly increased. This means that the investment from the compiler and core teams required to make
+a patch release is greatly reduced, which also makes such a patch release more likely to happen.
+
+The current borrow checker has been around for years now, and is beginning to show its age.  The
+work on a better, more precise borrow checker is underway, and it has detected all of these bugs.
+This work is planned to be stabilized in the next few releases, so expect to hear more about it
+soon.
+
+Together, the lack of good maintenance on the current borrow checker and an increased capacity for
+releases make it feasible for us to ship patch releases on a more rapid and frequent basis.
+
+[match ergonomics]: https://blog.rust-lang.org/2018/05/10/Rust-1.26.html#nicer-match-bindings