Blog post for 1.43.0 (#566)

* Release notes for 1.43.0

* Update posts/2020-04-23-Rust-1.43.0.md

Co-Authored-By: Jonas Schievink <[email protected]>

* Update posts/2020-04-23-Rust-1.43.0.md

Co-Authored-By: Kyle J Strand <[email protected]>

* Update posts/2020-04-23-Rust-1.43.0.md

Co-Authored-By: Kyle J Strand <[email protected]>

* Address some more review comments

Co-authored-by: Jonas Schievink <[email protected]>
Co-authored-by: Kyle J Strand <[email protected]>

Author: 3 people

posts/2020-04-23-Rust-1.43.0.md

@@ -0,0 +1,128 @@
+---
+layout: post
+title: "Announcing Rust 1.43.0"
+author: The Rust Release Team
+release: true
+---
+
+The Rust team is happy to announce a new version of Rust, 1.43.0. 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
+1.43.0 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
+1.43.0][notes] on GitHub.
+
+[install]: https://www.rust-lang.org/install.html
+[notes]: https://github.com/rust-lang/rust/blob/master/RELEASES.md#version-1430-2020-04-23
+
+## What's in 1.43.0 stable
+
+This release is fairly minor. There are no new major features. We have some
+new stabilized APIs, some compiler performance improvements, and a small
+macro-related feature. See the [detailed release notes][notes] to learn about
+other changes not covered by this post.
+
+### `item` fragments
+
+In macros, you can use `item` fragments to interpolate items into the body of traits,
+impls, and extern blocks. For example:
+
+```rust
+macro_rules! mac_trait {
+    ($i:item) => {
+        trait T { $i }
+    }
+}
+mac_trait! {
+    fn foo() {}
+}
+```
+
+This will generate:
+
+```rust
+trait T {
+    fn foo() {}
+}
+```
+
+### Type inference around primitives
+
+The type inference around primitives, references, and binary operations was
+improved. A code sample makes this easier to understand: this code fails to
+compile on Rust 1.42, but compiles in Rust 1.43.
+
+```rust
+let n: f32 = 0.0 + &0.0;
+```
+
+In Rust 1.42, you would get an error that would say "hey, I don't know how to add
+an `f64` and an `&f64` with a result of `f32`." The algorithm now correctly decides
+that both `0.0` and `&0.0` should be `f32`s instead.
+
+### New Cargo environment variable for tests
+
+In a move to help integration testing, [Cargo will set some new environment
+variables](https://github.com/rust-lang/cargo/pull/7697).
+
+This is easiest to explain by example: let's say we're working on a command
+line project, simply named "cli". If we're writing an integration test, we want
+to invoke that `cli` binary and see what it does. When running tests and
+benchmarks, Cargo will set an environment variable named `CARGO_BIN_EXE_cli`,
+and I can use it inside my test:
+
+```rust
+let exe = env!("CARGO_BIN_EXE_cli");
+```
+
+This makes it easier to invoke `cli`, as we now have a path to it directly.
+
+### Library changes
+
+[You can now use associated constants on floats and integers directly][consts], rather
+than having to import the module. That is, you can now write `u32::MAX` or `f32::NAN`
+with no `use std::u32;` or `use std::f32;`.
+
+[consts]: https://github.com/rust-lang/rust/pull/68952/
+
+There is a [new `primitive`
+module](https://github.com/rust-lang/rust/pull/67637/) that re-exports Rust's
+primitive types. This can be useful when you're writing a macro and want to make
+sure that the types aren't shadowed.
+
+Additionally, we stabilized six new APIs:
+
+- [`Once::is_completed`]
+- [`f32::LOG10_2`]
+- [`f32::LOG2_10`]
+- [`f64::LOG10_2`]
+- [`f64::LOG2_10`]
+- [`iter::once_with`]
+
+[`Once::is_completed`]: https://doc.rust-lang.org/std/sync/struct.Once.html#method.is_completed
+[`f32::LOG10_2`]: https://doc.rust-lang.org/std/f32/consts/constant.LOG10_2.html
+[`f32::LOG2_10`]: https://doc.rust-lang.org/std/f32/consts/constant.LOG2_10.html
+[`f64::LOG10_2`]: https://doc.rust-lang.org/std/f64/consts/constant.LOG10_2.html
+[`f64::LOG2_10`]: https://doc.rust-lang.org/std/f64/consts/constant.LOG2_10.html
+[`iter::once_with`]: https://doc.rust-lang.org/std/iter/fn.once_with.html
+
+### Other changes
+
+[relnotes-cargo]: https://github.com/rust-lang/cargo/blob/master/CHANGELOG.md#cargo-143-2020-04-23
+[relnotes-clippy]: https://github.com/rust-lang/rust-clippy/blob/master/CHANGELOG.md#rust-143
+
+There are other changes in the Rust 1.43.0 release: check out what changed in
+[Rust][notes], [Cargo][relnotes-cargo], and [Clippy][relnotes-clippy].
+
+## Contributors to 1.43.0
+
+Many people came together to create Rust 1.43.0. We couldn't have done it
+without all of you. [Thanks!](https://thanks.rust-lang.org/rust/1.43.0/)