Blog for Rust 1.49.0

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

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+---
+layout: post
+title: "Announcing Rust 1.49.0"
+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.
+
+### 64-bit ARM Linux reaches Tier 1
+
+The Rust compiler supports [a wide variety of targets][platform-support], but
+the Rust Team can't provide the same level of support for all of them. To
+clearly mark how supported each target is, we use a tiering system:
+
+* Tier 3 targets are technically supported by the compiler, but we don't check
+  whether their code build or passes the tests, and we don't provide any
+  prebuilt binaries as part of our releases.
+* Tier 2 targets are guaranteed to build and we provide prebuilt binaries, but
+  we don't execute the test suite on those platforms: the produced binaries
+  might not work or might have bugs.
+* Tier 1 targets provide the highest support guarantee, and we run the full
+  suite on those platforms for every change merged in the compiler. Prebuilt
+  binaries are also available.
+
+Rust 1.49.0 promotes the `aarch64-unknown-linux-gnu` target to Tier 1 support,
+bringing our highest guarantees to users of 64-bit ARM systems running Linux!
+We expect this change to benefit workloads spanning from embedded to desktops
+and servers.
+
+This is an important milestone for the project, since it's the first time a
+non-x86 target has reached Tier 1 support: we hope this will pave the way for
+more targets to reach our highest tier in the future.
+
+Note that Android is not affected by this change as it uses a different Tier 2
+target.
+
+[platform-support]: https://doc.rust-lang.org/stable/rustc/platform-support.html
+
+### 64-bit ARM macOS and Windows reach Tier 2
+
+Rust 1.49.0 also features two targets reaching Tier 2 support:
+
+* The `aarch64-apple-darwin` target brings support for Rust on Apple M1 systems.
+* The `aarch64-pc-windows-msvc` target brings support for Rust on 64-bit ARM
+  devices running Windows on ARM.
+
+Developers can expect both of those targets to have prebuilt binaries
+installable with `rustup` from now on! The Rust Team is not running the test
+suite on those platforms though, so there might be bugs or instabilities.
+
+### 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/)