Announcing Rust 1.26

Routine minor release with standard library DX improvements and Cargo backend optimizations, lacking major language or milestone significance.

Breaking News

Changes that may make code or platforms move

Returning from main with impl Trait no longer works when Trait isn’t Termination

Previously, we only checked that the underlying type implemented the Termination trait. It is now only possible to return concrete types on stable, as nothing except for impl Termination will work, but that trait is currently unstable to import.

For example, this will no longer work on 1.26.1:

fn main() -> impl Copy {}

But this will keep working, as it doesn’t attempt to return any hidden types via impl Trait, but rather names types concretely.

fn main() -> Result<(), std::io::Error> {
    Ok(())
}

Turbofish no longer works for method arguments with impl Trait

Previously, we accidentally permitted code to specify the type of method arguments which use impl Trait. On 1.26.0, the code below would work, but how exactly turbofish (::<u32> below) should interact with impl Trait hasn’t yet been decided, so we’re preventing turbofish use until we can be sure the semantics are as we desire.

struct Foo;

impl Foo {
    fn bar(&self, _arg: impl Copy) {}
}

fn main() {
    Foo.bar::<u32>(0);
}

Library stabilizations

We stabilized fs::read_to_string, a convenience over File::open and io::Read::read_to_string for easily reading an entire file into memory at once:

use std::fs;
use std::net::SocketAddr;

let foo: SocketAddr = fs::read_to_string("address.txt")?.parse()?;

You can now format numbers as hexadecimal with Debug formatting:

assert!(format!("{:02x?}", b"Foo\0") == "[46, 6f, 6f, 00]")

Trailing commas are now supported by all macros in the standard library.

See the detailed release notes for more.

Cargo features

Cargo didn’t receive many big new features this release but rather saw a steady stream of stability and performance improvements. Cargo should now resolve lock files even faster, backtrack more intelligently, and require manual cargo update invocations less. Cargo’s binary now also shares the same version as rustc.

See the detailed release notes for more.

Errata · Point releases

Rust 1.26.1

29 May 2018 blog post

RLS no longer interferes with command line builds

The version of RLS shipped with 1.26.0 utilized the same target directory as Cargo from the command line, which meant that switching between the two would lead to everything being recompiled. This problem was made worse for Windows users due to a filesystem lock being left unreleased by either RLS or the compiler, leading to an increased error rate. This latter bug is not yet fixed, but it happens much less frequently with the first bug fixed.

Rustfmt bad formatting

Previously, rustfmt would overindent multi-line string literals, which is now fixed.

Returning from main with impl Trait no longer works when Trait isn’t Termination

For example, this will no longer work on 1.26.1:

fn main() -> impl Copy {}

But this will keep working, as it doesn’t attempt to return any hidden types via impl Trait, but rather names types concretely.

fn main() -> Result<(), std::io::Error> {
    Ok(())
}

Turbofish no longer works for method arguments with impl Trait

struct Foo;

impl Foo {
    fn bar(&self, _arg: impl Copy) {}
}

fn main() {
    Foo.bar::<u32>(0);
}

Floating point comparisons changed in constant contexts

Previously, comparing NaN as greater than other floating point numbers in a constant context would return true, which is a bug; now, this comparison returns false. In some cases that may mean that the behavior of code will change, but we expect this to be relatively unlikely.

use std::f64::NAN;
const FOO: bool = ::std::f64::NAN >= ::std::f64::NAN;
// On 1.26.0
assert_eq!(FOO, true);
// On 1.26.1
assert_eq!(FOO, false);

rustup should now work to install stable on platforms with missing docs

During the development cycle for 1.26, a change was made to how we build the documentation for the standard library, which made it so that we stopped producing the documentation component for a variety of tier 2 platforms. This led to breakage when running rustup update on those platforms, as rustup refused to partially install Rust. Some users will need to run rustup install stable instead of rustup update to make rustup avoid the missing docs component, but this should be a one-time problem.

This was unfortunately fixed too late to make it into 1.26 stable, so we added the patch for 1.26.1 to permit users to install Rust on these platforms.

$ rustup update
info: syncing channel updates for 'stable-x86_64-unknown-freebsd'
info: latest update on 2018-05-10, rust version 1.26.0 (a77568041 2018-05-07)
error: component 'rust-docs' for 'x86_64-unknown-freebsd' is unavailable for download

Rust 1.26.2

5 June 2018 blog post