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.

Rust 1.26.2

Compatibility Notes

• The borrow checker was fixed to avoid unsoundness when using match ergonomics.

Rust 1.26.1

Tools

• RLS now works on Windows.
• Rustfmt stopped badly formatting text in some cases.

Compatibility Notes

• fn main() -> impl Trait no longer works for non-Termination trait. This reverts an accidental stabilization.
• NaN > NaN no longer returns true in const-fn contexts.
• Prohibit using turbofish for impl Trait in method arguments.

Rust 1.26.0

Language

• Closures now implement Copy and/or Clone if all captured variables implement either or both traits.
• The inclusive range syntax e.g. for x in 0..=10 is now stable.
• The '_ lifetime is now stable. The underscore lifetime can be used anywhere a lifetime can be elided.
• impl Trait is now stable allowing you to have abstract types in returns or in function parameters. E.g. fn foo() -> impl Iterator<Item=u8> or fn open(path: impl AsRef<Path>).
• Pattern matching will now automatically apply dereferences.
• 128-bit integers in the form of u128 and i128 are now stable.
• main can now return Result<(), E: Debug> in addition to ().
• A lot of operations are now available in a const context. E.g. You can now index into constant arrays, reference and dereference into constants, and use tuple struct constructors.
• Fixed entry slice patterns are now stable. E.g.

  let points = [1, 2, 3, 4];
  match points {
      [1, 2, 3, 4] => println!("All points were sequential."),
      _ => println!("Not all points were sequential."),
  }

Compiler

• LLD is now used as the default linker for wasm32-unknown-unknown.
• Fixed exponential projection complexity on nested types. This can provide up to a ~12% reduction in compile times for certain crates.
• Added the --remap-path-prefix option to rustc. Allowing you to remap path prefixes outputted by the compiler.
• Added powerpc-unknown-netbsd target.

Libraries

• Implemented From<u16> for usize & From<{u8, i16}> for isize.
• Added hexadecimal formatting for integers with fmt::Debug e.g. assert!(format!("{:02x?}", b"Foo\0") == "[46, 6f, 6f, 00]")
• Implemented Default, Hash for cmp::Reverse.
• Optimized str::repeat being 8x faster in large cases.
• ascii::escape_default is now available in libcore.
• Trailing commas are now supported in std and core macros.
• Implemented Copy, Clone for cmp::Reverse
• Implemented Clone for char::{ToLowercase, ToUppercase}.

Stabilized APIs

• *const T::add
• *const T::copy_to_nonoverlapping
• *const T::copy_to
• *const T::read_unaligned
• *const T::read_volatile
• *const T::read
• *const T::sub
• *const T::wrapping_add
• *const T::wrapping_sub
• *mut T::add
• *mut T::copy_to_nonoverlapping
• *mut T::copy_to
• *mut T::read_unaligned
• *mut T::read_volatile
• *mut T::read
• *mut T::replace
• *mut T::sub
• *mut T::swap
• *mut T::wrapping_add
• *mut T::wrapping_sub
• *mut T::write_bytes
• *mut T::write_unaligned
• *mut T::write_volatile
• *mut T::write
• Box::leak
• FromUtf8Error::as_bytes
• LocalKey::try_with
• Option::cloned
• btree_map::Entry::and_modify
• fs::read_to_string
• fs::read
• fs::write
• hash_map::Entry::and_modify
• iter::FusedIterator
• ops::RangeInclusive
• ops::RangeToInclusive
• process::id
• slice::rotate_left
• slice::rotate_right
• String::retain

Cargo

• Cargo will now output path to custom commands when -v is passed with --list
• The Cargo binary version is now the same as the Rust version

Misc

• The second edition of "The Rust Programming Language" book is now recommended over the first.

Compatibility Notes

• aliasing a Fn trait as dyn no longer works. E.g. the following syntax is now invalid.
  use std::ops::Fn as dyn;
  fn g(_: Box<dyn(std::fmt::Debug)>) {}
• The result of dereferences are no longer promoted to 'static. e.g.

  fn main() {
      const PAIR: &(i32, i32) = &(0, 1);
      let _reversed_pair: &'static _ = &(PAIR.1, PAIR.0); // Doesn't work
  }

• Deprecate AsciiExt trait in favor of inherent methods.
• ".e0" will now no longer parse as 0.0 and will instead cause an error.
• Removed hoedown from rustdoc.
• Bounds on higher-kinded lifetimes a hard error.

Rust 1.25.0

Language

• The #[repr(align(x))] attribute is now stable. RFC 1358
• You can now use nested groups of imports. e.g. use std::{fs::File, io::Read, path::{Path, PathBuf}};
• You can now have | at the start of a match arm. e.g.

enum Foo { A, B, C }

fn main() {
    let x = Foo::A;
    match x {
        | Foo::A
        | Foo::B => println!("AB"),
        | Foo::C => println!("C"),
    }
}

Compiler

• Upgraded to LLVM 6.
• Added -C lto=val option.
• Added i586-unknown-linux-musl target

Libraries

• Impl Send for process::Command on Unix.
• Impl PartialEq and Eq for ParseCharError.
• UnsafeCell::into_inner is now safe.
• Implement libstd for CloudABI.
• Float::{from_bits, to_bits} is now available in libcore.
• Implement AsRef<Path> for Component
• Implemented Write for Cursor<&mut Vec<u8>>
• Moved Duration to libcore.

Stabilized APIs

• Location::column
• ptr::NonNull

The following functions can now be used in a constant expression. eg. static MINUTE: Duration = Duration::from_secs(60);

• Duration::new
• Duration::from_secs
• Duration::from_millis

Cargo

• cargo new no longer removes rust or rs prefixs/suffixs.
• cargo new now defaults to creating a binary crate, instead of a library crate.

Misc

• Rust by example is now shipped with new releases

Compatibility Notes

• Deprecated net::lookup_host.
• rustdoc has switched to pulldown as the default markdown renderer.
• The borrow checker was sometimes incorrectly permitting overlapping borrows around indexing operations (see #47349). This has been fixed (which also enabled some correct code that used to cause errors (e.g. #33903 and #46095).
• Removed deprecated unstable attribute #[simd].

Rust 1.24.1

• Do not abort when unwinding through FFI
• Emit UTF-16 files for linker arguments on Windows
• Make the error index generator work again
• Cargo will warn on Windows 7 if an update is needed.

Rust 1.24.0

Language

• External sysv64 ffi is now available. eg. extern "sysv64" fn foo () {}

Compiler

• rustc now uses 16 codegen units by default for release builds. For the fastest builds, utilize codegen-units=1.
• Added armv4t-unknown-linux-gnueabi target.
• Add aarch64-unknown-openbsd support

Libraries

• str::find::<char> now uses memchr. This should lead to a 10x improvement in performance in the majority of cases.
• OsStr's Debug implementation is now lossless and consistent with Windows.
• time::{SystemTime, Instant} now implement Hash.
• impl From<bool> for AtomicBool
• impl From<{CString, &CStr}> for {Arc<CStr>, Rc<CStr>}
• impl From<{OsString, &OsStr}> for {Arc<OsStr>, Rc<OsStr>}
• impl From<{PathBuf, &Path}> for {Arc<Path>, Rc<Path>}
• float::from_bits now just uses transmute. This provides some optimisations from LLVM.
• Copied AsciiExt methods onto char
• Remove T: Sized requirement on ptr::is_null()
• impl From<RecvError> for {TryRecvError, RecvTimeoutError}
• Optimised f32::{min, max} to generate more efficient x86 assembly
• [u8]::contains now uses memchr which provides a 3x speed improvement

Stabilized APIs

• RefCell::replace
• RefCell::swap
• atomic::spin_loop_hint

The following functions can now be used in a constant expression. eg. let buffer: [u8; size_of::<usize>()];, static COUNTER: AtomicUsize = AtomicUsize::new(1);

• AtomicBool::new
• AtomicUsize::new
• AtomicIsize::new
• AtomicPtr::new
• Cell::new
• {integer}::min_value
• {integer}::max_value
• mem::size_of
• mem::align_of
• ptr::null
• ptr::null_mut
• RefCell::new
• UnsafeCell::new

Cargo

• Added a workspace.default-members config that overrides implied --all in virtual workspaces.
• Enable incremental by default on development builds. Also added configuration keys to Cargo.toml and .cargo/config to disable on a per-project or global basis respectively.

Misc

Compatibility Notes

• Floating point types Debug impl now always prints a decimal point.
• Ipv6Addr now rejects superfluous ::'s in IPv6 addresses This is in accordance with IETF RFC 4291 §2.2.
• Unwinding will no longer go past FFI boundaries, and will instead abort.
• Formatter::flags method is now deprecated. The sign_plus, sign_minus, alternate, and sign_aware_zero_pad should be used instead.
• Leading zeros in tuple struct members is now an error
• column!() macro is one-based instead of zero-based
• fmt::Arguments can no longer be shared across threads
• Access to #[repr(packed)] struct fields is now unsafe
• Cargo sets a different working directory for the compiler

Rust 1.23.0

Language

• Arbitrary auto traits are now permitted in trait objects.
• rustc now uses subtyping on the left hand side of binary operations. Which should fix some confusing errors in some operations.

Compiler

• Enabled TrapUnreachable in LLVM which should mitigate the impact of undefined behavior.
• rustc now suggests renaming import if names clash.
• Display errors/warnings correctly when there are zero-width or wide characters.
• rustc now avoids unnecessary copies of arguments that are simple bindings This should improve memory usage on average by 5-10%.
• Updated musl used to build musl rustc to 1.1.17

Libraries

• Allow a trailing comma in assert_eq/ne macro
• Implement Hash for raw pointers to unsized types
• impl From<*mut T> for AtomicPtr<T>
• impl From<usize/isize> for AtomicUsize/AtomicIsize.
• Removed the T: Sync requirement for RwLock<T>: Send
• Removed T: Sized requirement for {<*const T>, <*mut T>}::as_ref and <*mut T>::as_mut
• Optimized Thread::{park, unpark} implementation
• Improved SliceExt::binary_search performance.
• impl FromIterator<()> for ()
• Copied AsciiExt trait methods to primitive types. Use of AsciiExt is now deprecated.

Stabilized APIs

Cargo

• Cargo now supports uninstallation of multiple packages eg. cargo uninstall foo bar uninstalls foo and bar.
• Added unit test checking to cargo check
• Cargo now lets you install a specific version using cargo install --version

Misc

• Releases now ship with the Cargo book documentation.
• rustdoc now prints rendering warnings on every run.

Compatibility Notes

• Changes have been made to type equality to make it more correct, in rare cases this could break some code. Tracking issue for further information
• char::escape_debug now uses Unicode 10 over 9.
• Upgraded Android SDK to 27, and NDK to r15c. This drops support for Android 9, the minimum supported version is Android 14.
• Bumped the minimum LLVM to 3.9