Rust release · Feb 2, 2017

Rust 1.15: what's new, what was stabilized

Short answerRust 1.15 was released on Feb 2, 2017: 17 newly stable APIs (std::iter::Iterator::min_by, std::iter::Iterator::max_by, std::os::*::fs::FileExt, std::sync::atomic::Atomic*::get_mut, ...); 6 compatibility notes that can affect existing code. Point release: 1.15.1 (Feb 9, 2017).

Feb 2, 2017release date

0language stabilizations

17APIs stabilized

-new edition

← Rust 1.14 All versions Rust 1.16 →

17 APIs stabilized

std::iter::Iterator::min_by, std::iter::Iterator::max_by, std::os::*::fs::FileExt, std::sync::atomic::Atomic*::get_mut, std::sync::atomic::Atomic*::into_inner, std::vec::IntoIter::as_slice, std::vec::IntoIter::as_mut_slice, std::sync::mpsc::Receiver::try_iter, std::os::unix::process::CommandExt::before_exec, std::rc::Rc::strong_count, std::rc::Rc::weak_count, std::sync::Arc::strong_count, std::sync::Arc::weak_count, std::char::encode_utf8, std::char::encode_utf16, std::cell::Ref::clone, std::io::Take::into_inner

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:

[A number of minor changes to name resolution have been activated][37127].
[In this release, Cargo build scripts no longer have access to the OUT_DIR
[Higher-ranked lifetimes are no longer allowed to appear _only_ in associated
[The semantics relating modules to file system directories are changing in
[Rust-ABI symbols are no longer exported from cdylibs][38117]
[Once Peekable peeks a None it will return that None without re-querying

Use it

rustup update stable        # get the newest release
rustup install 1.15          # or exactly this one
rustup override set 1.15     # pin a project to it

To require at least this version from users of your crate, set rust-version = "1.15" 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

Basic procedural macros allowing custom #[derive], aka "macros 1.1", are stable. This allows popular code-generating crates like Serde and Diesel to work ergonomically. [RFC 1681].
[Tuple structs may be empty. Unary and empty tuple structs may be instantiated with curly braces][36868]. Part of [RFC 1506].
[A number of minor changes to name resolution have been activated][37127]. They add up to more consistent semantics, allowing for future evolution of Rust macros. Specified in [RFC 1560], see its section on ["changes"] for details of what is different. The breaking changes here have been transitioned through the [legacy_imports] lint since 1.14, with no known regressions.
[In macro_rules, path fragments can now be parsed as type parameter bounds][38279]
[?Sized can be used in where clauses][37791]
[There is now a limit on the size of monomorphized types and it can be modified with the #![type_size_limit] crate attribute, similarly to the #![recursion_limit] attribute][37789]

Compiler

[On Windows, the compiler will apply dllimport attributes when linking to extern functions][37973]. Additional attributes and flags can control which library kind is linked and its name. [RFC 1717].
[Rust-ABI symbols are no longer exported from cdylibs][38117]
[The --test flag works with procedural macro crates][38107]
[Fix extern "aapcs" fn ABI][37814]
[The -C no-stack-check flag is deprecated][37636]. It does nothing.
[The format! expander recognizes incorrect printf and shell-style formatting directives and suggests the correct format][37613].
[Only report one error for all unused imports in an import list][37456]

Compiler Performance

[Avoid unnecessary mk_ty calls in Ty::super_fold_with][37705]
[Avoid more unnecessary mk_ty calls in Ty::super_fold_with][37979]
[Don't clone in UnificationTable::probe][37848]
[Remove scope_auxiliary to cut RSS by 10%][37764]
[Use small vectors in type walker][37760]
[Macro expansion performance was improved][37701]
[Change HirVec<P<T>> to HirVec<T> in hir::Expr][37642]
[Replace FNV with a faster hash function][37229]

Stabilized APIs

[std::iter::Iterator::min_by]
[std::iter::Iterator::max_by]
[std::os::*::fs::FileExt]
[std::sync::atomic::Atomic*::get_mut]
[std::sync::atomic::Atomic*::into_inner]
[std::vec::IntoIter::as_slice]
[std::vec::IntoIter::as_mut_slice]
[std::sync::mpsc::Receiver::try_iter]
[std::os::unix::process::CommandExt::before_exec]
[std::rc::Rc::strong_count]
[std::rc::Rc::weak_count]
[std::sync::Arc::strong_count]
[std::sync::Arc::weak_count]
[std::char::encode_utf8]
[std::char::encode_utf16]
[std::cell::Ref::clone]
[std::io::Take::into_inner]

Libraries

[The standard sorting algorithm has been rewritten for dramatic performance improvements][38192]. It is a hybrid merge sort, drawing influences from Timsort. Previously it was a naive merge sort.
[Iterator::nth no longer has a Sized bound][38134]
[Extend<&T> is specialized for Vec where T: Copy][38182] to improve performance.
[chars().count() is much faster][37888] and so are [chars().last() and char_indices().last()][37882]
[Fix ARM Objective-C ABI in std::env::args][38146]
[Chinese characters display correctly in fmt::Debug][37855]
[Derive Default for Duration][37699]
[Support creation of anonymous pipes on WinXP/2k][37677]
[mpsc::RecvTimeoutError implements Error][37527]
[Don't pass overlapped handles to processes][38835]

Cargo

[In this release, Cargo build scripts no longer have access to the OUT_DIR environment variable at build time via env!("OUT_DIR")][cargo/3368]. They should instead check the variable at runtime with std::env. That the value was set at build time was a bug, and incorrect when cross-compiling. This change is known to cause breakage.
[Add --all flag to cargo test][cargo/3221]
[Compile statically against the MSVC CRT][cargo/3363]
[Mix feature flags into fingerprint/metadata shorthash][cargo/3102]
[Link OpenSSL statically on OSX][cargo/3311]
[Apply new fingerprinting to build dir outputs][cargo/3310]
[Test for bad path overrides with summaries][cargo/3336]
[Require cargo install --vers to take a semver version][cargo/3338]
[Fix retrying crate downloads for network errors][cargo/3348]
[Implement string lookup for build.rustflags config key][cargo/3356]
[Emit more info on --message-format=json][cargo/3319]
[Assume build.rs in the same directory as Cargo.toml is a build script][cargo/3361]
[Don't ignore errors in workspace manifest][cargo/3409]
[Fix --message-format JSON when rustc emits non-JSON warnings][cargo/3410]

Tooling

[Test runners (binaries built with --test) now support a --list argument that lists the tests it contains][38185]
[Test runners now support a --exact argument that makes the test filter match exactly, instead of matching only a substring of the test name][38181]
[rustdoc supports a --playground-url flag][37763]
[rustdoc provides more details about #[should_panic] errors][37749]

Misc

[The Rust build system is now written in Rust][37817]. The Makefiles may continue to be used in this release by passing --disable-rustbuild to the configure script, but they will be deleted soon. Note that the new build system uses a different on-disk layout that will likely affect any scripts building Rust.
[Rust supports i686-unknown-openbsd][38086]. Tier 3 support. No testing or releases.
[Rust supports the MSP430][37627]. Tier 3 support. No testing or releases.
[Rust supports the ARMv5TE architecture][37615]. Tier 3 support. No testing or releases.

Compatibility Notes

A number of minor changes to name resolution have been activated. They add up to more consistent semantics, allowing for future evolution of Rust macros. Specified in RFC 1560, see its section on "changes" for details of what is different. The breaking changes here have been transitioned through the legacy_imports lint since 1.14, with no known regressions.
In this release, Cargo build scripts no longer have access to the OUT_DIR environment variable at build time via env!("OUT_DIR"). They should instead check the variable at runtime with std::env. That the value was set at build time was a bug, and incorrect when cross-compiling. This change is known to cause breakage.
Higher-ranked lifetimes are no longer allowed to appear _only_ in associated types. The hr_lifetime_in_assoc_type lint has been a warning since 1.10 and is now an error by default. It will become a hard error in the near future.
The semantics relating modules to file system directories are changing in minor ways. This is captured in the new legacy_directory_ownership lint, which is a warning in this release, and will become a hard error in the future.
Rust-ABI symbols are no longer exported from cdylibs
Once Peekable peeks a None it will return that None without re-querying the underlying iterator

1.15.1 (Feb 9, 2017)

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