Release notes for Rust 1.49.0

Author: steveklabnik

posts/2020-12-31-Rust-1.49.0.md

@@ -0,0 +1,169 @@
+---
+layout: post
+title: "Announcing Rust 1.40.0"
+author: The Rust Release Team
+release: true
+---
+
+The Rust team is happy to announce a new version of Rust, 1.49.0. Rust is a
+programming language that is empowering everyone to build reliable and
+efficient software.
+
+If you have a previous version of Rust installed via rustup, getting Rust
+1.49.0 is as easy as:
+
+```console
+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
+1.49.0][notes] on GitHub.
+
+[install]: https://www.rust-lang.org/install.html
+[notes]: https://github.com/rust-lang/rust/blob/master/RELEASES.md#version-1490-2020-12-31
+
+## What's in 1.49.0 stable
+
+For this release, we have some new targets and an improvement to the test
+framework. See the [detailed release notes][notes] to learn about other
+changes not covered by this post.
+
+### aarch64 targets
+
+We have two big changes to three targets:
+
+* [`aarch64-unknown-linux-gnu` is now Tier 1](https://github.com/rust-lang/rust/pull/78228)
+* [`aarch64-apple-darwin` is now Tier 2](https://github.com/rust-lang/rust/pull/75991)
+* [`aarch64-pc-windows-msvc` is now Tier 2](https://github.com/rust-lang/rust/pull/75914)
+
+If you're not familiar with our "tiers" of support, you can read about that
+on our [platform support
+page](https://doc.rust-lang.org/stable/rustc/platform-support.html). In
+brief, Tier 1 is "guaranteed to work," Tier 2 is "guaranteed to build," and
+Tier 3 is "code exists but is not tested." If you're a 64-bit ARM user, these
+changes mean that Rust programs will work better on your platforms!
+
+### Test framework captures output in threads
+
+Rust's built-in testing framework doesn't have a ton of features, but that
+doesn't mean it can't be improved! Consider a test that looks like this:
+
+```rust
+#[test]
+fn thready_pass() {
+    println!("fee");
+    std::thread::spawn(|| {
+        println!("fie");
+        println!("foe");
+    })
+    .join()
+    .unwrap();
+    println!("fum");
+}
+```
+
+Here's what running this test looks like before Rust 1.49.0:
+
+```text
+❯ cargo test
+   Compiling threadtest v0.1.0 (C:\threadtest)
+    Finished test [unoptimized + debuginfo] target(s) in 0.38s
+     Running target\debug\deps\threadtest-02f42ffd9836cae5.exe
+
+running 1 test
+fie
+foe
+test thready_pass ... ok
+
+test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
+
+   Doc-tests threadtest
+
+running 0 tests
+
+test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
+```
+
+You can see that the output from the thread is printed, which intermixes
+from the output of the test framework itself. Wouldn't it be nice
+if every `println!` worked like that one that prints "`fum`?" Well, [that's
+the behavior in Rust 1.49.0](https://github.com/rust-lang/rust/pull/78227):
+
+```text
+❯ cargo +nightly test
+   Compiling threadtest v0.1.0 (C:\threadtest)
+    Finished test [unoptimized + debuginfo] target(s) in 0.52s
+     Running target\debug\deps\threadtest-40aabfaa345584be.exe
+
+running 1 test
+test thready_pass ... ok
+
+test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
+
+   Doc-tests threadtest
+
+running 0 tests
+
+test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s
+```
+
+But don't worry; if the test were to fail, you'll still see all of the
+output. By adding a `panic!` to the end of the test, we can see what failure
+looks like:
+
+```text
+❯ cargo +nightly test
+   Compiling threadtest v0.1.0 (C:\threadtest)
+    Finished test [unoptimized + debuginfo] target(s) in 0.52s
+     Running target\debug\deps\threadtest-40aabfaa345584be.exe
+
+running 1 test
+test thready_pass ... FAILED
+
+failures:
+
+---- thready_pass stdout ----
+fee
+fie
+foe
+fum
+thread 'thready_pass' panicked at 'explicit panic', src\lib.rs:11:5
+```
+
+Specifically, the test runner makes sure to capture the output, and saves it
+in case the test fails.
+
+### Library changes
+
+In Rust 1.49.0, there are three new stable functions:
+
+- [`slice::select_nth_unstable`]
+- [`slice::select_nth_unstable_by`]
+- [`slice::select_nth_unstable_by_key`]
+
+And two functions were made `const`:
+
+- [`Poll::is_ready`]
+- [`Poll::is_pending`]
+
+See the [detailed release notes][notes] to learn about other changes.
+
+[`slice::select_nth_unstable`]: https://doc.rust-lang.org/nightly/std/primitive.slice.html#method.select_nth_unstable
+[`slice::select_nth_unstable_by`]: https://doc.rust-lang.org/nightly/std/primitive.slice.html#method.select_nth_unstable_by
+[`slice::select_nth_unstable_by_key`]: https://doc.rust-lang.org/nightly/std/primitive.slice.html#method.select_nth_unstable_by_key
+[`Poll::is_ready`]: https://doc.rust-lang.org/stable/std/task/enum.Poll.html#method.is_ready
+[`Poll::is_pending`]: https://doc.rust-lang.org/stable/std/task/enum.Poll.html#method.is_pending
+
+### Other changes
+
+[relnotes-cargo]: https://github.com/rust-lang/cargo/blob/master/CHANGELOG.md#cargo-149-2020-12-31
+[relnotes-clippy]: https://github.com/rust-lang/rust-clippy/blob/master/CHANGELOG.md#rust-149
+
+There are other changes in the Rust 1.49.0 release: check out what changed in
+[Rust][notes], [Cargo][relnotes-cargo], and [Clippy][relnotes-clippy].
+
+## Contributors to 1.49.0
+
+Many people came together to create Rust 1.49.0. We couldn't have done it
+without all of you. [Thanks!](https://thanks.rust-lang.org/rust/1.49.0/)