$ rustup update stable

The Rust team is happy to announce a new version of Rust, 1.92.0. Rust is a programming language empowering everyone to build reliable and efficient software.

If you have a previous version of Rust installed via rustup, you can get 1.92.0 with:

$ rustup update stable

If you don’t have it already, you can get rustup from the appropriate page on our website, and check out the detailed release notes for 1.92.0.

If you’d like to help us out by testing future releases, you might consider updating locally to use the beta channel (rustup default beta) or the nightly channel (rustup default nightly). Please report any bugs you might come across!

What’s in 1.92.0 stable

Deny-by-default never type lints

The language and compiler teams continue to work on stabilization of the never type. In this release the never_type_fallback_flowing_into_unsafe and dependency_on_unit_never_type_fallback future compatibility lints were made deny-by-default, meaning they will cause a compilation error when detected.

It’s worth noting that while this can result in compilation errors, it is still a lint; these lints can all be #[allow]ed. These lints also will only fire when building the affected crates directly, not when they are built as dependencies (though a warning will be reported by Cargo in such cases).

These lints detect code which is likely to be broken by the never type stabilization. It is highly advised to fix them if they are reported in your crate graph.

We believe there to be approximately 500 crates affected by this lint. Despite that, we believe this to be acceptable, as lints are not a breaking change and it will allow for stabilizing the never type in the future. For more in-depth justification, see the Language Team’s assessment.

unused_must_use no longer warns about Result<(), UninhabitedType>

Rust’s unused_must_use lint warns when ignoring the return value of a function, if the function or its return type is annotated with #[must_use]. For instance, this warns if ignoring a return type of Result, to remind you to use ?, or something like .expect("...").

However, some functions return Result, but the error type they use is not actually "inhabited", meaning you cannot construct any values of that type (e.g. the ! or Infallible types).

The unused_must_use lint now no longer warns on Result<(), UninhabitedType>, or on ControlFlow<UninhabitedType, ()>. For instance, it will not warn on Result<(), Infallible>. This avoids having to check for an error that can never happen.

use core::convert::Infallible;
fn can_never_fail() -> Result<(), Infallible> {
Ok(())
}

fn main() {
can_never_fail();
}

This is particularly useful with the common pattern of a trait with an associated error type, where the error type may sometimes be infallible:

trait UsesAssocErrorType {
type Error;
fn method(&self) -> Result<(), Self::Error>;
}

struct CannotFail;
impl UsesAssocErrorType for CannotFail {
type Error = core::convert::Infallible;
fn method(&self) -> Result<(), Self::Error> {
Ok(())
}
}

struct CanFail;
impl UsesAssocErrorType for CanFail {
type Error = std::io::Error;
fn method(&self) -> Result<(), Self::Error> {
Err(std::io::Error::other("something went wrong"))
}
}

fn main() {
CannotFail.method();     CanFail.method(); }

Emit unwind tables even when -Cpanic=abort is enabled on linux

Backtraces with -Cpanic=abort previously worked in Rust 1.22 but were broken in Rust 1.23, as we stopped emitting unwind tables with -Cpanic=abort. In Rust 1.45 a workaround in the form of -Cforce-unwind-tables=yes was stabilized.

In Rust 1.92 unwind tables will be emitted by default even when -Cpanic=abort is specified, allowing for backtraces to work properly. If unwind tables are not desired then users should use -Cforce-unwind-tables=no to explicitly disable them being emitted.

Validate input to #[macro_export]

Over the past few releases, many changes were made to the way built-in attributes are processed in the compiler. This should greatly improve the error messages and warnings Rust gives for built-in attributes and especially make these diagnostics more consistent among all of the over 100 built-in attributes.

To give a small example, in this release specifically, Rust became stricter in checking what arguments are allowed to macro_export by upgrading that check to a "deny-by-default lint" that will be reported in dependencies.

Stabilized APIs

• NonZero<u{N}>::div_ceil
• Location::file_as_c_str
• RwLockWriteGuard::downgrade
• Box::new_zeroed
• Box::new_zeroed_slice
• Rc::new_zeroed
• Rc::new_zeroed_slice
• Arc::new_zeroed
• Arc::new_zeroed_slice
• btree_map::Entry::insert_entry
• btree_map::VacantEntry::insert_entry
• impl Extend<proc_macro::Group> for proc_macro::TokenStream
• impl Extend<proc_macro::Literal> for proc_macro::TokenStream
• impl Extend<proc_macro::Punct> for proc_macro::TokenStream
• impl Extend<proc_macro::Ident> for proc_macro::TokenStream

These previously stable APIs are now stable in const contexts:

• <[_]>::rotate_left
• <[_]>::rotate_right

Other changes

Check out everything that changed in Rust, Cargo, and Clippy.

Contributors to 1.92.0

Many people came together to create Rust 1.92.0. We couldn’t have done it without all of you. Thanks!