Rust release · Aug 31, 2017

Rust 1.20: what's new, what was stabilized

Short answerRust 1.20 was released on Aug 31, 2017: 34 newly stable APIs (CStr::into_c_string, CString::as_c_str, CString::into_boxed_c_str, Chain::get_mut, ...); 2 compatibility notes that can affect existing code.

Aug 31, 2017release date

0language stabilizations

34APIs stabilized

-new edition

← Rust 1.19 All versions Rust 1.21 →

34 APIs stabilized

CStr::into_c_string, CString::as_c_str, CString::into_boxed_c_str, Chain::get_mut, Chain::get_ref, Chain::into_inner, Option::get_or_insert_with, Option::get_or_insert, OsStr::into_os_string, OsString::into_boxed_os_str, Take::get_mut, Take::get_ref, Utf8Error::error_len, char::EscapeDebug, char::escape_debug, compile_error!, f32::from_bits, f32::to_bits, f64::from_bits, f64::to_bits, mem::ManuallyDrop, slice::sort_unstable_by_key, slice::sort_unstable_by, slice::sort_unstable, str::from_boxed_utf8_unchecked, str::as_bytes_mut, str::as_bytes_mut, str::from_utf8_mut, str::from_utf8_unchecked_mut, str::get_mut, str::get_unchecked_mut, str::get_unchecked, str::get, str::into_boxed_bytes

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:

[Functions with 'static in their return types will now not be as usable as
[The reimplementation of {f32, f64}::is_sign_{negative, positive} now

Use it

rustup update stable        # get the newest release
rustup install 1.20          # or exactly this one
rustup override set 1.20     # pin a project to it

To require at least this version from users of your crate, set rust-version = "1.20" 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

[Associated constants are now stabilised.][42809]
[A lot of macro bugs are now fixed.][42913]

Compiler

[Struct fields are now properly coerced to the expected field type.][42807]
[Enabled wasm LLVM backend][42571] WASM can now be built with the wasm32-experimental-emscripten target.
[Changed some of the error messages to be more helpful.][42033]
[Add support for RELRO(RELocation Read-Only) for platforms that support it.][43170]
[rustc now reports the total number of errors on compilation failure][43015] previously this was only the number of errors in the pass that failed.
[Expansion in rustc has been sped up 29x.][42533]
[added msp430-none-elf target.][43099]
[rustc will now suggest one-argument enum variant to fix type mismatch when applicable][43178]
[Fixes backtraces on Redox][43228]
[rustc now identifies different versions of same crate when absolute paths of different types match in an error message.][42826]

Libraries

[Relaxed Debug constraints on {HashMap,BTreeMap}::{Keys,Values}.][42854]
[Impl PartialEq, Eq, PartialOrd, Ord, Debug, Hash for unsized tuples.][43011]
[Impl fmt::{Display, Debug} for Ref, RefMut, MutexGuard, RwLockReadGuard, RwLockWriteGuard][42822]
[Impl Clone for DefaultHasher.][42799]
[Impl Sync for SyncSender.][42397]
[Impl FromStr for char][42271]
[Fixed how {f32, f64}::{is_sign_negative, is_sign_positive} handles NaN.][42431]
[allow messages in the unimplemented!() macro.][42155] ie. unimplemented!("Waiting for 1.21 to be stable")
[pub(restricted) is now supported in the thread_local! macro.][43185]
[Upgrade to Unicode 10.0.0][42999]
[Reimplemented {f32, f64}::{min, max} in Rust instead of using CMath.][42430]
[Skip the main thread's manual stack guard on Linux][43072]
[Iterator::nth for ops::{Range, RangeFrom} is now done in *O*(1) time][43077]
[#[repr(align(N))] attribute max number is now 2^31 - 1.][43097] This was previously 2^15.
[{OsStr, Path}::Display now avoids allocations where possible][42613]

Stabilized APIs

[CStr::into_c_string]
[CString::as_c_str]
[CString::into_boxed_c_str]
[Chain::get_mut]
[Chain::get_ref]
[Chain::into_inner]
[Option::get_or_insert_with]
[Option::get_or_insert]
[OsStr::into_os_string]
[OsString::into_boxed_os_str]
[Take::get_mut]
[Take::get_ref]
[Utf8Error::error_len]
[char::EscapeDebug]
[char::escape_debug]
[compile_error!]
[f32::from_bits]
[f32::to_bits]
[f64::from_bits]
[f64::to_bits]
[mem::ManuallyDrop]
[slice::sort_unstable_by_key]
[slice::sort_unstable_by]
[slice::sort_unstable]
[str::from_boxed_utf8_unchecked]
[str::as_bytes_mut]
[str::as_bytes_mut]
[str::from_utf8_mut]
[str::from_utf8_unchecked_mut]
[str::get_mut]
[str::get_unchecked_mut]
[str::get_unchecked]
[str::get]
[str::into_boxed_bytes]

Cargo

[Cargo API token location moved from ~/.cargo/config to ~/.cargo/credentials.][cargo/3978]
[Cargo will now build main.rs binaries that are in sub-directories of src/bin.][cargo/4214] ie. Having src/bin/server/main.rs and src/bin/client/main.rs generates target/debug/server and target/debug/client
[You can now specify version of a binary when installed through cargo install using --vers.][cargo/4229]
[Added --no-fail-fast flag to cargo to run all benchmarks regardless of failure.][cargo/4248]
[Changed the convention around which file is the crate root.][cargo/4259]

Compatibility Notes

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