Rust 1.31.0

Language

• 🎉 This version marks the release of the 2018 edition of Rust. 🎉
• New lifetime elision rules now allow for eliding lifetimes in functions and impl headers. E.g. impl<'a> Reader for BufReader<'a> {} can now be impl Reader for BufReader<'_> {}. Lifetimes are still required to be defined in structs.
• You can now define and use const functions. These are currently a strict minimal subset of the const fn RFC. Refer to the language reference for what exactly is available.
• You can now use tool lints, which allow you to scope lints from external tools using attributes. E.g. #[allow(clippy::filter_map)].
• #[no_mangle] and #[export_name] attributes can now be located anywhere in a crate, not just in exported functions.
• You can now use parentheses in pattern matches.

Compiler

• Updated musl to 1.1.20

Libraries

• You can now convert num::NonZero* types to their raw equivalents using the From trait. E.g. u8 now implements From<NonZeroU8>.
• You can now convert a &Option<T> into Option<&T> and &mut Option<T> into Option<&mut T> using the From trait.
• You can now multiply (*) a time::Duration by a u32.

Stabilized APIs

• slice::align_to
• slice::align_to_mut
• slice::chunks_exact
• slice::chunks_exact_mut
• slice::rchunks
• slice::rchunks_mut
• slice::rchunks_exact
• slice::rchunks_exact_mut
• Option::replace

Cargo

• Cargo will now download crates in parallel using HTTP/2.
• You can now rename packages in your Cargo.toml We have a guide on how to use the package key in your dependencies.

Rust 1.30.1

• Fixed overflow ICE in rustdoc
• Cap Cargo progress bar width at 60 in MSYS terminals

Rust 1.30.0

Language

• Procedural macros are now available. These kinds of macros allow for more powerful code generation. There is a new chapter available in the Rust Programming Language book that goes further in depth.
• You can now use keywords as identifiers using the raw identifiers syntax (r#), e.g. let r#for = true;
• Using anonymous parameters in traits is now deprecated with a warning and will be a hard error in the 2018 edition.
• You can now use crate in paths. This allows you to refer to the crate root in the path, e.g. use crate::foo; refers to foo in src/lib.rs.
• Using a external crate no longer requires being prefixed with ::. Previously, using a external crate in a module without a use statement required let json = ::serde_json::from_str(foo); but can now be written as let json = serde_json::from_str(foo);.
• You can now apply the #[used] attribute to static items to prevent the compiler from optimising them away, even if they appear to be unused, e.g. #[used] static FOO: u32 = 1;
• You can now import and reexport macros from other crates with the use syntax. Macros exported with #[macro_export] are now placed into the root module of the crate. If your macro relies on calling other local macros, it is recommended to export with the #[macro_export(local_inner_macros)] attribute so users won't have to import those macros.
• You can now catch visibility keywords (e.g. pub, pub(crate)) in macros using the vis specifier.
• Non-macro attributes now allow all forms of literals, not just strings. Previously, you would write #[attr("true")], and you can now write #[attr(true)].
• You can now specify a function to handle a panic in the Rust runtime with the #[panic_handler] attribute.

Compiler

• Added the riscv32imc-unknown-none-elf target.
• Added the aarch64-unknown-netbsd target
• Upgraded to LLVM 8.

Libraries

• ManuallyDrop now allows the inner type to be unsized.

Stabilized APIs

• Ipv4Addr::BROADCAST

• Ipv4Addr::LOCALHOST

• Ipv4Addr::UNSPECIFIED

• Ipv6Addr::LOCALHOST

• Ipv6Addr::UNSPECIFIED

• Iterator::find_map

  The following methods are replacement methods for trim_left, trim_right, trim_left_matches, and trim_right_matches, which will be deprecated in 1.33.0:

• str::trim_end_matches

• str::trim_end

• str::trim_start_matches

• str::trim_start

Cargo

• cargo run doesn't require specifying a package in workspaces.
• cargo doc now supports --message-format=json. This is equivalent to calling rustdoc --error-format=json.
• Cargo will now provide a progress bar for builds.

Misc

• rustdoc allows you to specify what edition to treat your code as with the --edition option.
• rustdoc now has the --color (specify whether to output color) and --error-format (specify error format, e.g. json) options.
• We now distribute a rust-gdbgui script that invokes gdbgui with Rust debug symbols.
• Attributes from Rust tools such as rustfmt or clippy are now available, e.g. #[rustfmt::skip] will skip formatting the next item.

Rust 1.29.2

• Workaround for an aliasing-related LLVM bug, which caused miscompilation.
• The rls-preview component on the windows-gnu targets has been restored.

Rust 1.29.1

Security Notes

• The standard library's str::repeat function contained an out of bounds write caused by an integer overflow. This has been fixed by deterministically panicking when an overflow happens.

  Thank you to Scott McMurray for responsibly disclosing this vulnerability to us.

Rust 1.29.0

Compiler

• Bumped minimum LLVM version to 5.0.
• Added powerpc64le-unknown-linux-musl target.
• Added aarch64-unknown-hermit and x86_64-unknown-hermit targets.
• Upgraded to LLVM 7.

Libraries

• Once::call_once no longer requires Once to be 'static.
• BuildHasherDefault now implements PartialEq and Eq.
• Box<CStr>, Box<OsStr>, and Box<Path> now implement Clone.
• Implemented PartialEq<&str> for OsString and PartialEq<OsString> for &str.
• Cell<T> now allows T to be unsized.
• SocketAddr is now stable on Redox.

Stabilized APIs

• Arc::downcast
• Iterator::flatten
• Rc::downcast

Cargo

• Cargo can silently fix some bad lockfiles. You can use --locked to disable this behavior.
• cargo-install will now allow you to cross compile an install using --target.
• Added the cargo-fix subcommand to automatically move project code from 2015 edition to 2018.
• cargo doc can now optionally document private types using the --document-private-items flag.

Misc

• rustdoc now has the --cap-lints option which demotes all lints above the specified level to that level. For example --cap-lints warn will demote deny and forbid lints to warn.
• rustc and rustdoc will now have the exit code of 1 if compilation fails and 101 if there is a panic.
• A preview of clippy has been made available through rustup. You can install the preview with rustup component add clippy-preview.

Compatibility Notes

• str::{slice_unchecked, slice_unchecked_mut} are now deprecated. Use str::get_unchecked(begin..end) instead.
• std::env::home_dir is now deprecated for its unintuitive behavior. Consider using the home_dir function from https://crates.io/crates/dirs instead.
• rustc will no longer silently ignore invalid data in target spec.
• cfg attributes and --cfg command line flags are now more strictly validated.

Rust 1.28.0

Language

• The #[repr(transparent)] attribute is now stable. This attribute allows a Rust newtype wrapper (struct NewType<T>(T);) to be represented as the inner type across Foreign Function Interface (FFI) boundaries.
• The keywords pure, sizeof, alignof, and offsetof have been unreserved and can now be used as identifiers.
• The GlobalAlloc trait and #[global_allocator] attribute are now stable. This will allow users to specify a global allocator for their program.
• Unit test functions marked with the #[test] attribute can now return Result<(), E: Debug> in addition to ().
• The lifetime specifier for macro_rules! is now stable. This allows macros to easily target lifetimes.

Compiler

• The s and z optimisation levels are now stable. These optimisations prioritise making smaller binary sizes. z is the same as s with the exception that it does not vectorise loops, which typically results in an even smaller binary.
• The short error format is now stable. Specified with --error-format=short this option will provide a more compressed output of rust error messages.
• Added a lint warning when you have duplicated macro_exports.
• Reduced the number of allocations in the macro parser. This can improve compile times of macro heavy crates on average by 5%.

Libraries

• Implemented Default for &mut str.
• Implemented From<bool> for all integer and unsigned number types.
• Implemented Extend for ().
• The Debug implementation of time::Duration should now be more easily human readable. Previously a Duration of one second would printed as Duration { secs: 1, nanos: 0 } and will now be printed as 1s.
• Implemented From<&String> for Cow<str>, From<&Vec<T>> for Cow<[T]>, From<Cow<CStr>> for CString, From<CString>, From<CStr>, From<&CString> for Cow<CStr>, From<OsString>, From<OsStr>, From<&OsString> for Cow<OsStr>, From<&PathBuf> for Cow<Path>, and From<Cow<Path>> for PathBuf.
• Implemented Shl and Shr for Wrapping<u128> and Wrapping<i128>.
• DirEntry::metadata now uses fstatat instead of lstat when possible. This can provide up to a 40% speed increase.
• Improved error messages when using format!.

Stabilized APIs

• Iterator::step_by
• Path::ancestors
• SystemTime::UNIX_EPOCH
• alloc::GlobalAlloc
• alloc::Layout
• alloc::LayoutErr
• alloc::System
• alloc::alloc
• alloc::alloc_zeroed
• alloc::dealloc
• alloc::realloc
• alloc::handle_alloc_error
• btree_map::Entry::or_default
• fmt::Alignment
• hash_map::Entry::or_default
• iter::repeat_with
• num::NonZeroUsize
• num::NonZeroU128
• num::NonZeroU16
• num::NonZeroU32
• num::NonZeroU64
• num::NonZeroU8
• ops::RangeBounds
• slice::SliceIndex
• slice::from_mut
• slice::from_ref
• {Any + Send + Sync}::downcast_mut
• {Any + Send + Sync}::downcast_ref
• {Any + Send + Sync}::is

Cargo

• Cargo will now no longer allow you to publish crates with build scripts that modify the src directory. The src directory in a crate should be considered to be immutable.

Misc

• The suggestion_applicability field in rustc's json output is now stable. This will allow dev tools to check whether a code suggestion would apply to them.

Compatibility Notes

• Rust will consider trait objects with duplicated constraints to be the same type as without the duplicated constraint. For example the below code will now fail to compile.

  trait Trait {}
  
  impl Trait + Send {
      fn test(&self) { println!("one"); } //~ ERROR duplicate definitions with name `test`
  }
  
  impl Trait + Send + Send {
      fn test(&self) { println!("two"); }
  }

Rust 1.27.2

Compatibility Notes

• The borrow checker was fixed to avoid potential unsoundness when using match ergonomics: #52213.

Rust 1.27.1

Security Notes

• rustdoc would execute plugins in the /tmp/rustdoc/plugins directory when running, which enabled executing code as some other user on a given machine. This release fixes that vulnerability; you can read more about this on the blog. The associated CVE is CVE-2018-1000622.

  Thank you to Red Hat for responsibly disclosing this vulnerability to us.

Compatibility Notes

• The borrow checker was fixed to avoid an additional potential unsoundness when using match ergonomics: #51415, #49534.

Rust 1.27.0

Language

• Removed 'proc' from the reserved keywords list. This allows proc to be used as an identifier.
• The dyn syntax is now available. This syntax is equivalent to the bare Trait syntax, and should make it clearer when being used in tandem with impl Trait because it is equivalent to the following syntax: &Trait == &dyn Trait, &mut Trait == &mut dyn Trait, and Box<Trait> == Box<dyn Trait>.
• Attributes on generic parameters such as types and lifetimes are now stable. e.g. fn foo<#[lifetime_attr] 'a, #[type_attr] T: 'a>() {}
• The #[must_use] attribute can now also be used on functions as well as types. It provides a lint that by default warns users when the value returned by a function has not been used.

Compiler

• Added the armv5te-unknown-linux-musleabi target.

Libraries

• SIMD (Single Instruction Multiple Data) on x86/x86_64 is now stable. This includes arch::x86 & arch::x86_64 modules which contain SIMD intrinsics, a new macro called is_x86_feature_detected!, the #[target_feature(enable="")] attribute, and adding target_feature = "" to the cfg attribute.
• A lot of methods for [u8], f32, and f64 previously only available in std are now available in core.
• The generic Rhs type parameter on ops::{Shl, ShlAssign, Shr} now defaults to Self.
• std::str::replace now has the #[must_use] attribute to clarify that the operation isn't done in place.
• Clone::clone, Iterator::collect, and ToOwned::to_owned now have the #[must_use] attribute to warn about unused potentially expensive allocations.

Stabilized APIs

• DoubleEndedIterator::rfind
• DoubleEndedIterator::rfold
• DoubleEndedIterator::try_rfold
• Duration::from_micros
• Duration::from_nanos
• Duration::subsec_micros
• Duration::subsec_millis
• HashMap::remove_entry
• Iterator::try_fold
• Iterator::try_for_each
• NonNull::cast
• Option::filter
• String::replace_range
• Take::set_limit
• hint::unreachable_unchecked
• os::unix::process::parent_id
• ptr::swap_nonoverlapping
• slice::rsplit_mut
• slice::rsplit
• slice::swap_with_slice

Cargo

• cargo-metadata now includes authors, categories, keywords, readme, and repository fields.
• cargo-metadata now includes a package's metadata table.
• Added the --target-dir optional argument. This allows you to specify a different directory than target for placing compilation artifacts.
• Cargo will be adding automatic target inference for binaries, benchmarks, examples, and tests in the Rust 2018 edition. If your project specifies specific targets, e.g. using [[bin]], and have other binaries in locations where cargo would infer a binary, Cargo will produce a warning. You can disable this feature ahead of time by setting any of the following to false: autobins, autobenches, autoexamples, autotests.
• Cargo will now cache compiler information. This can be disabled by setting CARGO_CACHE_RUSTC_INFO=0 in your environment.

Misc

• Added “The Rustc book” into the official documentation. “The Rustc book” documents and teaches how to use the rustc compiler.
• All books available on doc.rust-lang.org are now searchable.

Compatibility Notes

• Calling a CharExt or StrExt method directly on core will no longer work. e.g. ::core::prelude::v1::StrExt::is_empty("") will not compile, "".is_empty() will still compile.
• Debug output on atomic::{AtomicBool, AtomicIsize, AtomicPtr, AtomicUsize} will only print the inner type. E.g. print!("{:?}", AtomicBool::new(true)) will print true, not AtomicBool(true).
• The maximum number for repr(align(N)) is now 2²⁹. Previously you could enter higher numbers but they were not supported by LLVM. Up to 512MB alignment should cover all use cases.
• The .description() method on the std::error::Error trait has been soft-deprecated. It is no longer required to implement it.