Rust 1.8: what's new, what was stabilized

Short answerRust 1.8 was released on Apr 14, 2016: 9 compatibility notes that can affect existing code.

Apr 14, 2016release date

0language stabilizations

0APIs stabilized

-new edition

← Rust 1.7 All versions Rust 1.9 →

Can it break my build?

The release lists these compatibility notes. Most only affect rare code, but read them before you raise your toolchain in CI:

[Unstable compiler flags have been further restricted][1.8u]. Since
[It is no longer possible to match on empty enum variants using
The Unix-specific MetadataExt traits, including
[Modules sourced from the filesystem cannot appear within arbitrary
[--cfg compiler flags are parsed strictly as identifiers][1.8c].
On Unix, [stack overflow triggers a runtime abort instead of a
[Command::spawn and its equivalents return an error if any of
[Tuple and unit enum variants from other crates are in the type
[On Windows rustc emits .lib files for the staticlib library

Use it

rustup update stable        # get the newest release
rustup install 1.8          # or exactly this one
rustup override set 1.8     # pin a project to it

To require at least this version from users of your crate, set rust-version = "1.8" under [package] in Cargo.toml. Cargo then refuses to build it on older compilers with a clear message, and with resolver 3 (the default on the 2024 edition, Rust 1.85+) it also prefers dependency versions that support it.

Full release notes

Language

Rust supports overloading of compound assignment statements like += by implementing the [AddAssign], [SubAssign], [MulAssign], [DivAssign], [RemAssign], [BitAndAssign], [BitOrAssign], [BitXorAssign], [ShlAssign], or [ShrAssign] traits. [RFC 953].
Empty structs can be defined with braces, as in struct Foo { }, in addition to the non-braced form, struct Foo;. [RFC 218].

Libraries

Stabilized APIs:
[str::encode_utf16] (renamed from utf16_units)
[str::EncodeUtf16] (renamed from Utf16Units)
[Ref::map]
[RefMut::map]
[ptr::drop_in_place]
[time::Instant]
[time::SystemTime]
[Instant::now]
[Instant::duration_since] (renamed from duration_from_earlier)
[Instant::elapsed]
[SystemTime::now]
[SystemTime::duration_since] (renamed from duration_from_earlier)
[SystemTime::elapsed]
Various Add/Sub impls for Time and SystemTime
[SystemTimeError]
[SystemTimeError::duration]
Various impls for SystemTimeError
[UNIX_EPOCH]
[AddAssign], [SubAssign], [MulAssign], [DivAssign], [RemAssign], [BitAndAssign], [BitOrAssign], [BitXorAssign], [ShlAssign], [ShrAssign].
[The write! and writeln! macros correctly emit errors if any of their arguments can't be formatted][1.8w].
[Various I/O functions support large files on 32-bit Linux][1.8l].
[The Unix-specific raw modules, which contain a number of redefined C types are deprecated][1.8r], including os::raw::unix, os::raw::macos, and os::raw::linux. These modules defined types such as ino_t and dev_t. The inconsistency of these definitions across platforms was making it difficult to implement std correctly. Those that need these definitions should use the libc crate. [RFC 1415].
The Unix-specific MetadataExt traits, including os::unix::fs::MetadataExt, which expose values such as inode numbers [no longer return platform-specific types][1.8r], but instead return widened integers. [RFC 1415].
[btree_set::{IntoIter, Iter, Range} are covariant][1.8cv].
[Atomic loads and stores are not volatile][1.8a].
[All types in sync::mpsc implement fmt::Debug][1.8mp].

Performance

[Inlining hash functions lead to a 3% compile-time improvement in some workloads][1.8h].
When using jemalloc, its symbols are [unprefixed so that it overrides the libc malloc implementation][1.8h]. This means that for rustc, LLVM is now using jemalloc, which results in a 6% compile-time improvement on a specific workload.
[Avoid quadratic growth in function size due to cleanups][1.8cu].

Misc

[32-bit MSVC builds finally implement unwinding][1.8ms]. i686-pc-windows-msvc is now considered a tier-1 platform.
[The --print targets flag prints a list of supported targets][1.8t].
[The --print cfg flag prints the cfgs defined for the current target][1.8cf].
[rustc can be built with an new Cargo-based build system, written in Rust][1.8b]. It will eventually replace Rust's Makefile-based build system. To enable it configure with configure --rustbuild.
[Errors for non-exhaustive match patterns now list up to 3 missing variants while also indicating the total number of missing variants if more than 3][1.8m].
[Executable stacks are disabled on Linux and BSD][1.8nx].
The Rust Project now publishes binary releases of the standard library for a number of tier-2 targets: armv7-unknown-linux-gnueabihf, powerpc-unknown-linux-gnu, powerpc64-unknown-linux-gnu, powerpc64le-unknown-linux-gnu x86_64-rumprun-netbsd. These can be installed with tools such as [multirust][1.8mr].

Cargo

[cargo init creates a new Cargo project in the current directory][1.8ci]. It is otherwise like cargo new.
[Cargo has configuration keys for -v and --color][1.8cc]. verbose and color, respectively, go in the [term] section of .cargo/config.
[Configuration keys that evaluate to strings or integers can be set via environment variables][1.8ce]. For example the build.jobs key can be set via CARGO_BUILD_JOBS. Environment variables take precedence over config files.
[Target-specific dependencies support Rust cfg syntax for describing targets][1.8cfg] so that dependencies for multiple targets can be specified together. [RFC 1361].
[The environment variables CARGO_TARGET_ROOT, RUSTC, and RUSTDOC take precedence over the build.target-dir, build.rustc, and build.rustdoc configuration values][1.8cfv].
[The child process tree is killed on Windows when Cargo is killed][1.8ck].
[The build.target configuration value sets the target platform, like --target][1.8ct].

Compatibility Notes

Unstable compiler flags have been further restricted. Since 1.0 -Z flags have been considered unstable, and other flags that were considered unstable additionally required passing -Z unstable-options to access. Unlike unstable language and library features though, these options have been accessible on the stable release channel. Going forward, *new unstable flags will not be available on the stable release channel*, and old unstable flags will warn about their usage. In the future, all unstable flags will be unavailable on the stable release channel.
It is no longer possible to match on empty enum variants using the Variant(..) syntax. This has been a warning since 1.6.
The Unix-specific MetadataExt traits, including os::unix::fs::MetadataExt, which expose values such as inode numbers no longer return platform-specific types, but instead return widened integers. RFC 1415.
Modules sourced from the filesystem cannot appear within arbitrary blocks, but only within other modules.
--cfg compiler flags are parsed strictly as identifiers.
On Unix, stack overflow triggers a runtime abort instead of a SIGSEGV.
Command::spawn and its equivalents return an error if any of its command-line arguments contain interior NULs.
Tuple and unit enum variants from other crates are in the type namespace.
On Windows rustc emits .lib files for the staticlib library type instead of .a files. Additionally, for the MSVC toolchain, rustc emits import libraries named foo.dll.lib instead of foo.lib.

Release notes from the Rust project's RELEASES.md (MIT or Apache-2.0); summaries above are ours.

← Rust 1.7 All versions Rust 1.9 →

Up next

Next releaseRust 1.9Released May 26, 2016.Read it next →

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