Rust 1.42.0

Language

• You can now use the slice pattern syntax with subslices. e.g.

  fn foo(words: &[&str]) {
      match words {
          ["Hello", "World", "!", ..] => println!("Hello World!"),
          ["Foo", "Bar", ..] => println!("Baz"),
          rest => println!("{:?}", rest),
      }
  }

• You can now use #[repr(transparent)] on univariant enums. Meaning that you can create an enum that has the exact layout and ABI of the type it contains.

• You can now use outer attribute procedural macros on inline modules.

• There are some syntax-only changes:

  • default is syntactically allowed before items in trait definitions.
  • Items in impls (i.e. consts, types, and fns) may syntactically leave out their bodies in favor of ;.
  • Bounds on associated types in impls are now syntactically allowed (e.g. type Foo: Ord;).
  • ... (the C-variadic type) may occur syntactically directly as the type of any function parameter.

  These are still rejected semantically, so you will likely receive an error but these changes can be seen and parsed by procedural macros and conditional compilation.

Compiler

• Added tier 2* support for armv7a-none-eabi.
• Added tier 2 support for riscv64gc-unknown-linux-gnu.
• Option::{expect,unwrap} and Result::{expect, expect_err, unwrap, unwrap_err} now produce panic messages pointing to the location where they were called, rather than core's internals.

* Refer to Rust's platform support page for more information on Rust's tiered platform support.

Libraries

• iter::Empty<T> now implements Send and Sync for any T.
• Pin::{map_unchecked, map_unchecked_mut} no longer require the return type to implement Sized.
• io::Cursor now derives PartialEq and Eq.
• Layout::new is now const.
• Added Standard Library support for riscv64gc-unknown-linux-gnu.

Stabilized APIs

• CondVar::wait_while
• CondVar::wait_timeout_while
• DebugMap::key
• DebugMap::value
• ManuallyDrop::take
• matches!
• ptr::slice_from_raw_parts_mut
• ptr::slice_from_raw_parts

Cargo

• You no longer need to include extern crate proc_macro; to be able to use proc_macro; in the 2018 edition.

Compatibility Notes

• Error::description has been deprecated, and its use will now produce a warning. It's recommended to use Display/to_string instead.

Rust 1.41.1

• Always check types of static items
• Always check lifetime bounds of Copy impls
• Fix miscompilation in callers of Layout::repeat
• Rust 1.41.0 was announced as the last Rust release with tier 1 or tier 2 support for 32-bit Apple targets. That announcement did not expect a patch release. 1.41.1 also includes release binaries for these targets.

Rust 1.41.0

Language

• You can now pass type parameters to foreign items when implementing traits. E.g. You can now write impl<T> From<Foo> for Vec<T> {}.
• You can now arbitrarily nest receiver types in the self position. E.g. you can now write fn foo(self: Box<Box<Self>>) {}. Previously only Self, &Self, &mut Self, Arc<Self>, Rc<Self>, and Box<Self> were allowed.
• You can now use any valid identifier in a format_args macro. Previously identifiers starting with an underscore were not allowed.
• Visibility modifiers (e.g. pub) are now syntactically allowed on trait items and enum variants. These are still rejected semantically, but can be seen and parsed by procedural macros and conditional compilation.
• You can now define a Rust extern "C" function with Box<T> and use T* as the corresponding type on the C side. Please see the documentation for more information, including the important caveat about preferring to avoid Box<T> in Rust signatures for functions defined in C.

Compiler

• Rustc will now warn if you have unused loop 'labels.
• Removed support for the i686-unknown-dragonfly target.
• Added tier 3 support* for the riscv64gc-unknown-linux-gnu target.
• You can now pass an arguments file passing the @path syntax to rustc. Note that the format differs somewhat from what is found in other tooling; please see the documentation for more information.
• You can now provide --extern flag without a path, indicating that it is available from the search path or specified with an -L flag.

* Refer to Rust's platform support page for more information on Rust's tiered platform support.

Libraries

• The core::panic module is now stable. It was already stable through std.
• NonZero* numerics now implement From<NonZero*> if it's a smaller integer width. E.g. NonZeroU16 now implements From<NonZeroU8>.
• MaybeUninit<T> now implements fmt::Debug.

Stabilized APIs

• Result::map_or
• Result::map_or_else
• std::rc::Weak::weak_count
• std::rc::Weak::strong_count
• std::sync::Weak::weak_count
• std::sync::Weak::strong_count

Cargo

• Cargo will now document all the private items for binary crates by default.
• cargo-install will now reinstall the package if it detects that it is out of date.
• Cargo.lock now uses a more git friendly format that should help to reduce merge conflicts.
• You can now override specific dependencies's build settings E.g. [profile.dev.package.image] opt-level = 2 sets the image crate's optimisation level to 2 for debug builds. You can also use [profile.<profile>.build-override] to override build scripts and their dependencies.

Misc

• You can now specify edition in documentation code blocks to compile the block for that edition. E.g. edition2018 tells rustdoc that the code sample should be compiled the 2018 edition of Rust.
• You can now provide custom themes to rustdoc with --theme, and check the current theme with --check-theme.
• You can use #[cfg(doc)] to compile an item when building documentation.

Compatibility Notes

• As previously announced 1.41 will be the last tier 1 release for 32-bit Apple targets. This means that the source code is still available to build, but the targets are no longer being tested and release binaries for those platforms will no longer be distributed by the Rust project. Please refer to the linked blog post for more information.

Rust 1.40.0

Language

• You can now use tuple structs and tuple enum variant's constructors in const contexts. e.g.

  pub struct Point(i32, i32);
  
  const ORIGIN: Point = {
      let constructor = Point;
  
      constructor(0, 0)
  };

• You can now mark structs, enums, and enum variants with the #[non_exhaustive] attribute to indicate that there may be variants or fields added in the future. For example this requires adding a wild-card branch (_ => {}) to any match statements on a non-exhaustive enum. (RFC 2008)

• You can now use function-like procedural macros in extern blocks and in type positions. e.g. type Generated = macro!();

• Function-like and attribute procedural macros can now emit macro_rules! items, so you can now have your macros generate macros.

• The meta pattern matcher in macro_rules! now correctly matches the modern attribute syntax. For example (#[$m:meta]) now matches #[attr], #[attr{tokens}], #[attr[tokens]], and #[attr(tokens)].

Compiler

• Added tier 3 support* for the thumbv7neon-unknown-linux-musleabihf target.
• Added tier 3 support for the aarch64-unknown-none-softfloat target.
• Added tier 3 support for the mips64-unknown-linux-muslabi64, and mips64el-unknown-linux-muslabi64 targets.

* Refer to Rust's platform support page for more information on Rust's tiered platform support.

Libraries

• The is_power_of_two method on unsigned numeric types is now a const function.

Stabilized APIs

• BTreeMap::get_key_value
• HashMap::get_key_value
• Option::as_deref_mut
• Option::as_deref
• Option::flatten
• UdpSocket::peer_addr
• f32::to_be_bytes
• f32::to_le_bytes
• f32::to_ne_bytes
• f64::to_be_bytes
• f64::to_le_bytes
• f64::to_ne_bytes
• f32::from_be_bytes
• f32::from_le_bytes
• f32::from_ne_bytes
• f64::from_be_bytes
• f64::from_le_bytes
• f64::from_ne_bytes
• mem::take
• slice::repeat
• todo!

Cargo

• Cargo will now always display warnings, rather than only on fresh builds.
• Feature flags (except --all-features) passed to a virtual workspace will now produce an error. Previously these flags were ignored.
• You can now publish dev-dependencies without including a version.

Misc

• You can now specify the #[cfg(doctest)] attribute to include an item only when running documentation tests with rustdoc.

Compatibility Notes

• As previously announced, any previous NLL warnings in the 2015 edition are now hard errors.
• The include! macro will now warn if it failed to include the entire file. The include! macro unintentionally only includes the first expression in a file, and this can be unintuitive. This will become either a hard error in a future release, or the behavior may be fixed to include all expressions as expected.
• Using #[inline] on function prototypes and consts now emits a warning under unused_attribute lint. Using #[inline] anywhere else inside traits or extern blocks now correctly emits a hard error.

Rust 1.39.0

Language

• You can now create async functions and blocks with async fn, async move {}, and async {} respectively, and you can now call .await on async expressions.
• You can now use certain attributes on function, closure, and function pointer parameters. These attributes include cfg, cfg_attr, allow, warn, deny, forbid as well as inert helper attributes used by procedural macro attributes applied to items. e.g.

  fn len(
      #[cfg(windows)] slice: &[u16],
      #[cfg(not(windows))] slice: &[u8],
  ) -> usize {
      slice.len()
  }

• You can now take shared references to bind-by-move patterns in the if guards of match arms. e.g.

  fn main() {
      let array: Box<[u8; 4]> = Box::new([1, 2, 3, 4]);
  
      match array {
          nums
  //      ---- `nums` is bound by move.
              if nums.iter().sum::<u8>() == 10
  //                 ^------ `.iter()` implicitly takes a reference to `nums`.
          => {
              drop(nums);
  //          ----------- Legal as `nums` was bound by move and so we have ownership.
          }
          _ => unreachable!(),
      }
  }

Compiler

• Added tier 3* support for the i686-unknown-uefi target.
• Added tier 3 support for the sparc64-unknown-openbsd target.
• rustc will now trim code snippets in diagnostics to fit in your terminal. Note Cargo currently doesn't use this feature. Refer to cargo#7315 to track this feature's progress.
• You can now pass --show-output argument to test binaries to print the output of successful tests.

* Refer to Rust's platform support page for more information on Rust's tiered platform support.

Libraries

• Vec::new and String::new are now const functions.
• LinkedList::new is now a const function.
• str::len, [T]::len and str::as_bytes are now const functions.
• The abs, wrapping_abs, and overflowing_abs numeric functions are now const.

Stabilized APIs

• Pin::into_inner
• Instant::checked_duration_since
• Instant::saturating_duration_since

Cargo

• You can now publish git dependencies if supplied with a version.
• The --all flag has been renamed to --workspace. Using --all is now deprecated.

Misc

• You can now pass -Clinker to rustdoc to control the linker used for compiling doctests.

Compatibility Notes

• Code that was previously accepted by the old borrow checker, but rejected by the NLL borrow checker is now a hard error in Rust 2018. This was previously a warning, and will also become a hard error in the Rust 2015 edition in the 1.40.0 release.
• rustdoc now requires rustc to be installed and in the same directory to run tests. This should improve performance when running a large amount of doctests.
• The try! macro will now issue a deprecation warning. It is recommended to use the ? operator instead.
• asinh(-0.0) now correctly returns -0.0. Previously this returned 0.0.

Rust 1.38.0

Language

• The #[global_allocator] attribute can now be used in submodules.
• The #[deprecated] attribute can now be used on macros.

Compiler

• Added pipelined compilation support to rustc. This will improve compilation times in some cases. For further information please refer to the "Evaluating pipelined rustc compilation" thread.
• Added tier 3* support for the aarch64-uwp-windows-msvc, i686-uwp-windows-gnu, i686-uwp-windows-msvc, x86_64-uwp-windows-gnu, and x86_64-uwp-windows-msvc targets.
• Added tier 3 support for the armv7-unknown-linux-gnueabi and armv7-unknown-linux-musleabi targets.
• Added tier 3 support for the hexagon-unknown-linux-musl target.
• Added tier 3 support for the riscv32i-unknown-none-elf target.
• Upgraded to LLVM 9.

* Refer to Rust's platform support page for more information on Rust's tiered platform support.

Libraries

• ascii::EscapeDefault now implements Clone and Display.
• Derive macros for prelude traits (e.g. Clone, Debug, Hash) are now available at the same path as the trait. (e.g. The Clone derive macro is available at std::clone::Clone). This also makes all built-in macros available in std/core root. e.g. std::include_bytes!.
• str::Chars now implements Debug.
• slice::{concat, connect, join} now accepts &[T] in addition to &T.
• *const T and *mut T now implement marker::Unpin.
• Arc<[T]> and Rc<[T]> now implement FromIterator<T>.
• Added euclidean remainder and division operations (div_euclid, rem_euclid) to all numeric primitives. Additionally checked, overflowing, and wrapping versions are available for all integer primitives.
• thread::AccessError now implements Clone, Copy, Eq, Error, and PartialEq.
• iter::{StepBy, Peekable, Take} now implement DoubleEndedIterator.

Stabilized APIs

• <*const T>::cast
• <*mut T>::cast
• Duration::as_secs_f32
• Duration::as_secs_f64
• Duration::div_f32
• Duration::div_f64
• Duration::from_secs_f32
• Duration::from_secs_f64
• Duration::mul_f32
• Duration::mul_f64
• any::type_name

Cargo

• Added pipelined compilation support to cargo.
• You can now pass the --features option multiple times to enable multiple features.

Rustdoc

• Documentation on pub use statements is prepended to the documentation of the re-exported item

Misc

• rustc will now warn about some incorrect uses of mem::{uninitialized, zeroed} that are known to cause undefined behaviour.

Compatibility Notes

• The x86_64-unknown-uefi platform can not be built with rustc 1.38.0.
• The armv7-unknown-linux-gnueabihf platform is known to have issues with certain crates such as libc.

Rust 1.37.0

Language

• #[must_use] will now warn if the type is contained in a tuple, Box, or an array and unused.
• You can now use the cfg and cfg_attr attributes on generic parameters.
• You can now use enum variants through type alias. e.g. You can write the following:

  type MyOption = Option<u8>;
  
  fn increment_or_zero(x: MyOption) -> u8 {
      match x {
          MyOption::Some(y) => y + 1,
          MyOption::None => 0,
      }
  }

• You can now use _ as an identifier for consts. e.g. You can write const _: u32 = 5;.
• You can now use #[repr(align(X)] on enums.
• The ? Kleene macro operator is now available in the 2015 edition.

Compiler

• You can now enable Profile-Guided Optimization with the -C profile-generate and -C profile-use flags. For more information on how to use profile guided optimization, please refer to the rustc book.
• The rust-lldb wrapper script should now work again.

Libraries

• mem::MaybeUninit<T> is now ABI-compatible with T.

Stabilized APIs

• BufReader::buffer
• BufWriter::buffer
• Cell::from_mut
• Cell<[T]>::as_slice_of_cells
• DoubleEndedIterator::nth_back
• Option::xor
• Wrapping::reverse_bits
• i128::reverse_bits
• i16::reverse_bits
• i32::reverse_bits
• i64::reverse_bits
• i8::reverse_bits
• isize::reverse_bits
• slice::copy_within
• u128::reverse_bits
• u16::reverse_bits
• u32::reverse_bits
• u64::reverse_bits
• u8::reverse_bits
• usize::reverse_bits

Cargo

• Cargo.lock files are now included by default when publishing executable crates with executables.
• You can now specify default-run="foo" in [package] to specify the default executable to use for cargo run.

Misc

Compatibility Notes

• Using ... for inclusive range patterns will now warn by default. Please transition your code to using the ..= syntax for inclusive ranges instead.
• Using a trait object without the dyn will now warn by default. Please transition your code to use dyn Trait for trait objects instead.

Rust 1.36.0

Language

• Non-Lexical Lifetimes are now enabled on the 2015 edition.
• The order of traits in trait objects no longer affects the semantics of that object. e.g. dyn Send + fmt::Debug is now equivalent to dyn fmt::Debug + Send, where this was previously not the case.

Libraries

• HashMap's implementation has been replaced with hashbrown::HashMap implementation.
• TryFromSliceError now implements From<Infallible>.
• mem::needs_drop is now available as a const fn.
• alloc::Layout::from_size_align_unchecked is now available as a const fn.
• String now implements BorrowMut<str>.
• io::Cursor now implements Default.
• Both NonNull::{dangling, cast} are now const fns.
• The alloc crate is now stable. alloc allows you to use a subset of std (e.g. Vec, Box, Arc) in #![no_std] environments if the environment has access to heap memory allocation.
• String now implements From<&String>.
• You can now pass multiple arguments to the dbg! macro. dbg! will return a tuple of each argument when there is multiple arguments.
• Result::{is_err, is_ok} are now #[must_use] and will produce a warning if not used.

Stabilized APIs

• VecDeque::rotate_left
• VecDeque::rotate_right
• Iterator::copied
• io::IoSlice
• io::IoSliceMut
• Read::read_vectored
• Write::write_vectored
• str::as_mut_ptr
• mem::MaybeUninit
• pointer::align_offset
• future::Future
• task::Context
• task::RawWaker
• task::RawWakerVTable
• task::Waker
• task::Poll

Cargo

• Cargo will now produce an error if you attempt to use the name of a required dependency as a feature.
• You can now pass the --offline flag to run cargo without accessing the network.

You can find further change's in Cargo's 1.36.0 release notes.

Clippy

There have been numerous additions and fixes to clippy, see Clippy's 1.36.0 release notes for more details.

Misc

Compatibility Notes

• With the stabilisation of mem::MaybeUninit, mem::uninitialized use is no longer recommended, and will be deprecated in 1.39.0.

Rust 1.35.0

Language

• FnOnce, FnMut, and the Fn traits are now implemented for Box<FnOnce>, Box<FnMut>, and Box<Fn> respectively.
• You can now coerce closures into unsafe function pointers. e.g.

  unsafe fn call_unsafe(func: unsafe fn()) {
      func()
  }
  
  pub fn main() {
      unsafe { call_unsafe(|| {}); }
  }

Compiler

• Added the armv6-unknown-freebsd-gnueabihf and armv7-unknown-freebsd-gnueabihf targets.
• Added the wasm32-unknown-wasi target.

Libraries

• Thread will now show its ID in Debug output.
• StdinLock, StdoutLock, and StderrLock now implement AsRawFd.
• alloc::System now implements Default.
• Expanded Debug output ({:#?}) for structs now has a trailing comma on the last field.
• char::{ToLowercase, ToUppercase} now implement ExactSizeIterator.
• All NonZero numeric types now implement FromStr.
• Removed the Read trait bounds on the BufReader::{get_ref, get_mut, into_inner} methods.
• You can now call the dbg! macro without any parameters to print the file and line where it is called.
• In place ASCII case conversions are now up to 4× faster. e.g. str::make_ascii_lowercase
• hash_map::{OccupiedEntry, VacantEntry} now implement Sync and Send.

Stabilized APIs

• f32::copysign
• f64::copysign
• RefCell::replace_with
• RefCell::map_split
• ptr::hash
• Range::contains
• RangeFrom::contains
• RangeTo::contains
• RangeInclusive::contains
• RangeToInclusive::contains
• Option::copied

Cargo

• You can now set cargo:rustc-cdylib-link-arg at build time to pass custom linker arguments when building a cdylib. Its usage is highly platform specific.

Misc

• The Rust toolchain is now available natively for musl based distros.

Rust 1.34.2

• Destabilize the Error::type_id function due to a security vulnerability (CVE-2019-12083)