1.27.1 announcement

_posts/2018-07-10-Rust-1.27.1.md

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+---
+layout: post
+title: "Announcing Rust 1.27.1"
+author: The Rust Core Team
+---
+
+The Rust team is happy to announce a new version of Rust, 1.27.1. 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
+1.27.1 is as easy as:
+
+```
+$ 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
+1.27.1][notes] on GitHub.
+
+[install]: https://www.rust-lang.org/install.html
+[notes]: https://github.com/rust-lang/rust/blob/stable/RELEASES.md#version-1271-2018-07-10
+
+## What's in 1.27.1 stable
+
+This patch release fixes a bug in the borrow checker verification of `match` expressions.
+This bug was introduced in 1.26.0 with the stabilization of [match ergonomics]. We are
+uncertain that this specific problem actually indicated unsoundness in the borrow checker,
+but suspected that it might be a possibility, so decided to issue at point release. The
+code sample below caused a panic inside the compiler prior to this patch.
+
+```rust
+fn main() {
+    let a = vec!["".to_string()];
+    a.iter().enumerate()
+            .take_while(|(_, &t)| false)
+            .collect::<Vec<_>>();
+}
+```
+
+1.27.1 will reject the above code with this error message:
+
+```
+error[E0507]: cannot move out of borrowed content
+    --> src/main.rs:4:30
+    |
+  4 |             .take_while(|(_, &t)| false)
+    |                              ^-
+    |                              ||
+    |                              |hint: to prevent move, use `ref t` or `ref mut t`
+    |                              cannot move out of borrowed content
+
+error: aborting due to previous error
+```
+
+Alongside the match ergonomics fix, a [security vulnerability] was also found in rustdoc,
+the standard documentation generator for Rust projects. That vulnerability is addressed by
+the second patch contained in this release, by removing the default search path for
+rustdoc plugins. This functionality will be entirely removed in Rust 1.28.0. This plugin
+infrastructure predates Rust 1.0 and has never been usable on stable, and has been
+unusable on nightly for many months. Expect to hear more about the removal in the next
+release: the current patch removes the default search path (instead, users must specify it
+explicitly), while the next release will remove the functionality entirely.
+
+[security vulnerability]: https://blog.rust-lang.org/2018/07/06/security-advisory-for-rustdoc.html
+[match ergonomics]: https://blog.rust-lang.org/2018/05/10/Rust-1.26.html#nicer-match-bindings