Blog post for Rust 1.58.0

Author: cuviper

posts/2022-01-13-Rust-1.58.0.md

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+---
+layout: post
+title: "Announcing Rust 1.58.0"
+author: The Rust Release Team
+release: true
+---
+
+The Rust team is happy to announce a new version of Rust, 1.58.0.
+Rust is a programming language empowering everyone to build reliable and efficient software.
+
+If you have a previous version of Rust installed via rustup, getting Rust 1.58.0 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 1.58.0][notes] on GitHub.
+
+[install]: https://www.rust-lang.org/install.html
+[notes]: https://github.com/rust-lang/rust/blob/master/RELEASES.md#version-1580-2022-01-13
+
+## What's in 1.58.0 stable
+
+Rust 1.58 brings captured identifiers in format strings, a change to the
+`Command` search path on Windows, more `#[must_use]` annotations in the
+standard library, and some new library stabilizations.
+
+### Captured identifiers in format strings
+
+Format strings can now capture arguments simply by writing `{ident}` in the
+string. Formats have long accepted positional arguments (optionally by index)
+and named arguments, for example:
+
+```rust
+println!("Hello, {}!", get_person());                // implicit position
+println!("Hello, {0}!", get_person());               // explicit index
+println!("Hello, {person}!", person = get_person()); // named
+```
+
+Now named arguments can also be captured from the surrounding scope, like:
+
+```rust
+let person = get_person();
+// ...
+println!("Hello, {person}!"); // captures the local `person`
+```
+
+This may also be used in formatting parameters:
+
+```rust
+let (width, precision) = get_format();
+for (name, score) in get_scores() {
+  println!("{name}: {score:width$.precision$}");
+}
+```
+
+Format strings can only capture plain identifiers, not arbitrary paths or
+expressions. For more complicated arguments, either assign them to a local name
+first, or use the older `name = expression` style of formatting arguments.
+
+This feature works in all macros accepting format strings. However, one corner
+case is the `panic!` macro in 2015 and 2018 editions, where `panic!("{ident}")`
+is still treated as an unformatted string -- the compiler will warn about this
+not having the intended effect.
+
+### Reduced Windows `Command` search path
+
+On Windows targets, `std::process::Command` will no longer search the current
+directory for executables. That effect was owed to historical behavior of the
+win32 [`CreateProcess`] API, so Rust was effectively searching in this order:
+
+1. (Rust specific) The directories that are listed in the child's `PATH`
+   environment variable, if it was explicitly changed from the parent.
+2. The directory from which the application loaded.
+3. The current directory for the parent process.
+4. The 32-bit Windows system directory.
+5. The 16-bit Windows system directory.
+6. The Windows directory.
+7. The directories that are listed in the `PATH` environment variable.
+
+However, using the current directory can lead to surprising results, or even
+malicious behavior when dealing with untrusted directories. For example,
+`ripgrep` published [CVE-2021-3013] when they learned that their child
+processes could be intercepted in this way. Even Microsoft's own PowerShell
+[documents][PS] that they do not use the current directory for security.
+
+Rust now performs its own search without the current directory, and the legacy
+16-bit directory is also not included, as there is no API to discover its
+location. So the new `Command` search order for Rust on Windows is:
+
+1. The directories that are listed in the child's `PATH` environment variable.
+2. The directory from which the application loaded.
+3. The 32-bit Windows system directory.
+4. The Windows directory.
+5. The directories that are listed in the `PATH` environment variable.
+
+Non-Windows targets continue to use their platform-specific behavior, most
+often only considering the child or parent `PATH` environment variable.
+
+[`CreateProcess`]: https://docs.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-processthreadsapi-createprocessa
+[CVE-2021-3013]: https://www.cve.org/CVERecord?id=CVE-2021-3013
+[PS]: https://docs.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_command_precedence?view=powershell-7.2
+
+### More `#[must_use]` in the standard library
+
+The `#[must_use]` attribute can be applied to types or functions when failing
+to explicitly consider them or their output is almost certainly a bug. This has
+long been used in the standard library for types like `Result`, which should be
+checked for error conditions. This also helps catch mistakes such as expecting
+a function to mutate a value in-place, when it actually returns a new value.
+
+Library [proposal 35] was approved in October 2021 to audit and expand the
+application of `#[must_use]` throughout the standard library, covering many
+more functions where the primary effect is the return value. This is similar
+to the idea of function purity, but looser than a true language feature. Some
+of these additions were present in release 1.57.0, and now in 1.58.0 the effort
+has completed.
+
+[proposal 35]: https://github.com/rust-lang/libs-team/issues/35
+
+### Stabilized APIs
+
+The following methods and trait implementations were stabilized.
+
+- [`Metadata::is_symlink`]
+- [`Path::is_symlink`]
+- [`{integer}::saturating_div`]
+- [`Option::unwrap_unchecked`]
+- [`Result::unwrap_unchecked`]
+- [`Result::unwrap_err_unchecked`]
+- [`NonZero{unsigned}::is_power_of_two`]
+
+The following previously stable functions are now `const`.
+
+- [`Duration::new`]
+- [`Duration::checked_add`]
+- [`Duration::saturating_add`]
+- [`Duration::checked_sub`]
+- [`Duration::saturating_sub`]
+- [`Duration::checked_mul`]
+- [`Duration::saturating_mul`]
+- [`Duration::checked_div`]
+- [`MaybeUninit::as_ptr`]
+- [`MaybeUninit::as_mut_ptr`]
+- [`MaybeUninit::assume_init`]
+- [`MaybeUninit::assume_init_ref`]
+
+[`Metadata::is_symlink`]: https://doc.rust-lang.org/stable/std/fs/struct.Metadata.html#method.is_symlink
+[`Path::is_symlink`]: https://doc.rust-lang.org/stable/std/path/struct.Path.html#method.is_symlink
+[`{integer}::saturating_div`]: https://doc.rust-lang.org/stable/std/primitive.i8.html#method.saturating_div
+[`Option::unwrap_unchecked`]: https://doc.rust-lang.org/stable/std/option/enum.Option.html#method.unwrap_unchecked
+[`Result::unwrap_unchecked`]: https://doc.rust-lang.org/stable/std/result/enum.Result.html#method.unwrap_unchecked
+[`Result::unwrap_err_unchecked`]: https://doc.rust-lang.org/stable/std/result/enum.Result.html#method.unwrap_err_unchecked
+[`NonZero{unsigned}::is_power_of_two`]: https://doc.rust-lang.org/stable/std/num/struct.NonZeroU8.html#method.is_power_of_two
+[`Duration::new`]: https://doc.rust-lang.org/stable/std/time/struct.Duration.html#method.new
+[`Duration::checked_add`]: https://doc.rust-lang.org/stable/std/time/struct.Duration.html#method.checked_add
+[`Duration::saturating_add`]: https://doc.rust-lang.org/stable/std/time/struct.Duration.html#method.saturating_add
+[`Duration::checked_sub`]: https://doc.rust-lang.org/stable/std/time/struct.Duration.html#method.checked_sub
+[`Duration::saturating_sub`]: https://doc.rust-lang.org/stable/std/time/struct.Duration.html#method.saturating_sub
+[`Duration::checked_mul`]: https://doc.rust-lang.org/stable/std/time/struct.Duration.html#method.checked_mul
+[`Duration::saturating_mul`]: https://doc.rust-lang.org/stable/std/time/struct.Duration.html#method.saturating_mul
+[`Duration::checked_div`]: https://doc.rust-lang.org/stable/std/time/struct.Duration.html#method.checked_div
+[`MaybeUninit::as_ptr`]: https://doc.rust-lang.org/stable/std/mem/union.MaybeUninit.html#method.as_ptr
+[`MaybeUninit::as_mut_ptr`]: https://doc.rust-lang.org/stable/std/mem/union.MaybeUninit.html#method.as_mut_ptr
+[`MaybeUninit::assume_init`]: https://doc.rust-lang.org/stable/std/mem/union.MaybeUninit.html#method.assume_init
+[`MaybeUninit::assume_init_ref`]: https://doc.rust-lang.org/stable/std/mem/union.MaybeUninit.html#method.assume_init_ref
+
+### Other changes
+
+There are other changes in the Rust 1.58.0 release: check out what changed in
+[Rust](https://github.com/rust-lang/rust/blob/master/RELEASES.md#version-1580-2022-01-13),
+[Cargo](https://github.com/rust-lang/cargo/blob/master/CHANGELOG.md#cargo-158-2022-01-13),
+and [Clippy](https://github.com/rust-lang/rust-clippy/blob/master/CHANGELOG.md#rust-158).
+
+### Contributors to 1.58.0
+
+Many people came together to create Rust 1.58.0.
+We couldn't have done it without all of you.
+[Thanks!](https://thanks.rust-lang.org/rust/1.58.0/)