Rust 1.50.0

Language

• You can now use const values for x in [x; N] array expressions. This has been technically possible since 1.38.0, as it was unintentionally stabilized.
• Assignments to ManuallyDrop<T> union fields are now considered safe.

Compiler

• Added tier 3* support for the armv5te-unknown-linux-uclibceabi target.
• Added tier 3 support for the aarch64-apple-ios-macabi target.
• The x86_64-unknown-freebsd is now built with the full toolset.
• Dropped support for all cloudabi targets.

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

Libraries

• proc_macro::Punct now implements PartialEq<char>.
• ops::{Index, IndexMut} are now implemented for fixed sized arrays of any length.
• On Unix platforms, the std::fs::File type now has a "niche" of -1. This value cannot be a valid file descriptor, and now means Option<File> takes up the same amount of space as File.

Stabilized APIs

• bool::then
• btree_map::Entry::or_insert_with_key
• f32::clamp
• f64::clamp
• hash_map::Entry::or_insert_with_key
• Ord::clamp
• RefCell::take
• slice::fill
• UnsafeCell::get_mut

The following previously stable methods are now const.

• IpAddr::is_ipv4
• IpAddr::is_ipv6
• IpAddr::is_unspecified
• IpAddr::is_loopback
• IpAddr::is_multicast
• Ipv4Addr::octets
• Ipv4Addr::is_loopback
• Ipv4Addr::is_private
• Ipv4Addr::is_link_local
• Ipv4Addr::is_multicast
• Ipv4Addr::is_broadcast
• Ipv4Addr::is_documentation
• Ipv4Addr::to_ipv6_compatible
• Ipv4Addr::to_ipv6_mapped
• Ipv6Addr::segments
• Ipv6Addr::is_unspecified
• Ipv6Addr::is_loopback
• Ipv6Addr::is_multicast
• Ipv6Addr::to_ipv4
• Layout::size
• Layout::align
• Layout::from_size_align
• pow for all integer types.
• checked_pow for all integer types.
• saturating_pow for all integer types.
• wrapping_pow for all integer types.
• next_power_of_two for all unsigned integer types.
• checked_next_power_of_two for all unsigned integer types.

Cargo

• Added the [build.rustc-workspace-wrapper] option. This option sets a wrapper to execute instead of rustc, for workspace members only.
• cargo:rerun-if-changed will now, if provided a directory, scan the entire contents of that directory for changes.
• Added the --workspace flag to the cargo update command.

Misc

• The search results tab and the help button are focusable with keyboard in rustdoc.
• Running tests will now print the total time taken to execute.

Compatibility Notes

• The compare_and_swap method on atomics has been deprecated. It's recommended to use the compare_exchange and compare_exchange_weak methods instead.
• Changes in how TokenStreams are checked have fixed some cases where you could write unhygenic macro_rules! macros.
• #![test] as an inner attribute is now considered unstable like other inner macro attributes, and reports an error by default through the soft_unstable lint.
• Overriding a forbid lint at the same level that it was set is now a hard error.
• You can no longer intercept panic! calls by supplying your own macro. It's recommended to use the #[panic_handler] attribute to provide your own implementation.
• Semi-colons after item statements (e.g. struct Foo {};) now produce a warning.

Rust 1.49.0

Language

• Unions can now implement Drop, and you can now have a field in a union with ManuallyDrop<T>.
• You can now cast uninhabited enums to integers.
• You can now bind by reference and by move in patterns. This allows you to selectively borrow individual components of a type. E.g.

  #[derive(Debug)]
  struct Person {
      name: String,
      age: u8,
  }
  
  let person = Person {
      name: String::from("Alice"),
      age: 20,
  };
  
  // `name` is moved out of person, but `age` is referenced.
  let Person { name, ref age } = person;
  println!("{} {}", name, age);

Compiler

• Added tier 1* support for aarch64-unknown-linux-gnu.
• Added tier 2 support for aarch64-apple-darwin.
• Added tier 2 support for aarch64-pc-windows-msvc.
• Added tier 3 support for mipsel-unknown-none.
• Raised the minimum supported LLVM version to LLVM 9.
• Output from threads spawned in tests is now captured.
• Change os and vendor values to "none" and "unknown" for some targets

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

Libraries

• RangeInclusive now checks for exhaustion when calling contains and indexing.
• ToString::to_string now no longer shrinks the internal buffer in the default implementation.

Stabilized APIs

• slice::select_nth_unstable
• slice::select_nth_unstable_by
• slice::select_nth_unstable_by_key

The following previously stable methods are now const.

• Poll::is_ready
• Poll::is_pending

Cargo

• Building a crate with cargo-package should now be independently reproducible.
• cargo-tree now marks proc-macro crates.
• Added CARGO_PRIMARY_PACKAGE build-time environment variable. This variable will be set if the crate being built is one the user selected to build, either with -p or through defaults.
• You can now use glob patterns when specifying packages & targets.

Compatibility Notes

• Demoted i686-unknown-freebsd from host tier 2 to target tier 2 support.
• Macros that end with a semi-colon are now treated as statements even if they expand to nothing.
• Rustc will now check for the validity of some built-in attributes on enum variants. Previously such invalid or unused attributes could be ignored.
• Leading whitespace is stripped more uniformly in documentation comments, which may change behavior. You read this post about the changes for more details.
• Trait bounds are no longer inferred for associated types.

Internal Only

These changes provide no direct user facing benefits, but represent significant improvements to the internals and overall performance of rustc and related tools.

• rustc's internal crates are now compiled using the initial-exec Thread Local Storage model.
• Calculate visibilities once in resolve.
• Added system to the llvm-libunwind bootstrap config option.
• Added --color for configuring terminal color support to bootstrap.

Rust 1.48.0

Language

• The unsafe keyword is now syntactically permitted on modules. This is still rejected semantically, but can now be parsed by procedural macros.

Compiler

• Stabilised the -C link-self-contained=<yes|no> compiler flag. This tells rustc whether to link its own C runtime and libraries or to rely on a external linker to find them. (Supported only on windows-gnu, linux-musl, and wasi platforms.)
• You can now use -C target-feature=+crt-static on linux-gnu targets. Note: If you're using cargo you must explicitly pass the --target flag.
• Added tier 2* support for aarch64-unknown-linux-musl.

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

Libraries

• io::Write is now implemented for &ChildStdin &Sink, &Stdout, and &Stderr.
• All arrays of any length now implement TryFrom<Vec<T>>.
• The matches! macro now supports having a trailing comma.
• Vec<A> now implements PartialEq<[B]> where A: PartialEq<B>.
• The RefCell::{replace, replace_with, clone} methods now all use #[track_caller].

Stabilized APIs

• slice::as_ptr_range
• slice::as_mut_ptr_range
• VecDeque::make_contiguous
• future::pending
• future::ready

The following previously stable methods are now const fn's:

• Option::is_some
• Option::is_none
• Option::as_ref
• Result::is_ok
• Result::is_err
• Result::as_ref
• Ordering::reverse
• Ordering::then

Cargo

Rustdoc

• You can now link to items in rustdoc using the intra-doc link syntax. E.g. /// Uses [`std::future`] will automatically generate a link to std::future's documentation. See "Linking to items by name" for more information.
• You can now specify #[doc(alias = "<alias>")] on items to add search aliases when searching through rustdoc's UI.

Compatibility Notes

• Promotion of references to 'static lifetime inside const fn now follows the same rules as inside a fn body. In particular, &foo() will not be promoted to 'static lifetime any more inside const fns.
• Associated type bindings on trait objects are now verified to meet the bounds declared on the trait when checking that they implement the trait.
• When trait bounds on associated types or opaque types are ambiguous, the compiler no longer makes an arbitrary choice on which bound to use.
• Fixed recursive nonterminals not being expanded in macros during pretty-print/reparse check. This may cause errors if your macro wasn't correctly handling recursive nonterminal tokens.
• &mut references to non zero-sized types are no longer promoted.
• rustc will now warn if you use attributes like #[link_name] or #[cold] in places where they have no effect.
• Updated _mm256_extract_epi8 and _mm256_extract_epi16 signatures in arch::{x86, x86_64} to return i32 to match the vendor signatures.
• mem::uninitialized will now panic if any inner types inside a struct or enum disallow zero-initialization.
• #[target_feature] will now error if used in a place where it has no effect.
• Foreign exceptions are now caught by catch_unwind and will cause an abort. Note: This behaviour is not guaranteed and is still considered undefined behaviour, see the catch_unwind documentation for further information.

Internal Only

These changes provide no direct user facing benefits, but represent significant improvements to the internals and overall performance of rustc and related tools.

• Building rustc from source now uses ninja by default over make. You can continue building with make by setting ninja=false in your config.toml.
• cg_llvm: fewer_names in uncached_llvm_type
• Made ensure_sufficient_stack() non-generic

Rust 1.47.0

Language

• Closures will now warn when not used.

Compiler

• Stabilized the -C control-flow-guard codegen option, which enables Control Flow Guard for Windows platforms, and is ignored on other platforms.
• Upgraded to LLVM 11.
• Added tier 3* support for the thumbv4t-none-eabi target.
• Upgrade the FreeBSD toolchain to version 11.4
• RUST_BACKTRACE's output is now more compact.

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

Libraries

• CStr now implements Index<RangeFrom<usize>>.
• Traits in std/core are now implemented for arrays of any length, not just those of length less than 33.
• ops::RangeFull and ops::Range now implement Default.
• panic::Location now implements Copy, Clone, Eq, Hash, Ord, PartialEq, and PartialOrd.

Stabilized APIs

• Ident::new_raw
• Range::is_empty
• RangeInclusive::is_empty
• Result::as_deref
• Result::as_deref_mut
• Vec::leak
• pointer::offset_from
• f32::TAU
• f64::TAU

The following previously stable APIs have now been made const.

• The new method for all NonZero integers.
• The checked_add,checked_sub,checked_mul,checked_neg, checked_shl, checked_shr, saturating_add, saturating_sub, and saturating_mul methods for all integers.
• The checked_abs, saturating_abs, saturating_neg, and signum for all signed integers.
• The is_ascii_alphabetic, is_ascii_uppercase, is_ascii_lowercase, is_ascii_alphanumeric, is_ascii_digit, is_ascii_hexdigit, is_ascii_punctuation, is_ascii_graphic, is_ascii_whitespace, and is_ascii_control methods for char and u8.

Cargo

• build-dependencies are now built with opt-level 0 by default. You can override this by setting the following in your Cargo.toml.

  [profile.release.build-override]
  opt-level = 3

• cargo-help will now display man pages for commands rather just the --help text.
• cargo-metadata now emits a test field indicating if a target has tests enabled.
• workspace.default-members now respects workspace.exclude.
• cargo-publish will now use an alternative registry by default if it's the only registry specified in package.publish.

Misc

• Added a help button beside Rustdoc's searchbar that explains rustdoc's type based search.
• Added the Ayu theme to rustdoc.

Compatibility Notes

• Bumped the minimum supported Emscripten version to 1.39.20.
• Fixed a regression parsing {} && false in tail expressions.
• Added changes to how proc-macros are expanded in macro_rules! that should help to preserve more span information. These changes may cause compilation errors if your macro was unhygenic or didn't correctly handle Delimiter::None.
• Moved support for the CloudABI target to tier 3.
• linux-gnu targets now require minimum kernel 2.6.32 and glibc 2.11.
• Added the rustc-docs component. This allows you to install and read the documentation for the compiler internal APIs. (Currently only available for x86_64-unknown-linux-gnu.)

Internal Only

• Improved default settings for bootstrapping in x.py. You can read details about this change in the "Changes to x.py defaults" post on the Inside Rust blog.

Rust 1.46.0

Language

• if, match, and loop expressions can now be used in const functions.
• Additionally you are now also able to coerce and cast to slices (&[T]) in const functions.
• The #[track_caller] attribute can now be added to functions to use the function's caller's location information for panic messages.
• Recursively indexing into tuples no longer needs parentheses. E.g. x.0.0 over (x.0).0.
• mem::transmute can now be used in statics and constants. Note You currently can't use mem::transmute in constant functions.

Compiler

• You can now use the cdylib target on Apple iOS and tvOS platforms.
• Enabled static "Position Independent Executables" by default for x86_64-unknown-linux-musl.

Libraries

• mem::forget is now a const fn.
• String now implements From<char>.
• The leading_ones, and trailing_ones methods have been stabilised for all integer types.
• vec::IntoIter<T> now implements AsRef<[T]>.
• All non-zero integer types (NonZeroU8) now implement TryFrom for their zero-able equivalent (e.g. TryFrom<u8>).
• &[T] and &mut [T] now implement PartialEq<Vec<T>>.
• (String, u16) now implements ToSocketAddrs.
• vec::Drain<'_, T> now implements AsRef<[T]>.

Stabilized APIs

• Option::zip
• vec::Drain::as_slice

Cargo

Added a number of new environment variables that are now available when compiling your crate.

• CARGO_BIN_NAME and CARGO_CRATE_NAME Providing the name of the specific binary being compiled and the name of the crate.
• CARGO_PKG_LICENSE The license from the manifest of the package.
• CARGO_PKG_LICENSE_FILE The path to the license file.

Compatibility Notes

• The target configuration option abi_blacklist has been renamed to unsupported_abis. The old name will still continue to work.
• Rustc will now warn if you cast a C-like enum that implements Drop. This was previously accepted but will become a hard error in a future release.
• Rustc will fail to compile if you have a struct with #[repr(i128)] or #[repr(u128)]. This representation is currently only allowed on enums.
• Tokens passed to macro_rules! are now always captured. This helps ensure that spans have the correct information, and may cause breakage if you were relying on receiving spans with dummy information.
• The InnoSetup installer for Windows is no longer available. This was a legacy installer that was replaced by a MSI installer a few years ago but was still being built.
• {f32, f64}::asinh now returns the correct values for negative numbers.
• Rustc will no longer accept overlapping trait implementations that only differ in how the lifetime was bound.
• Rustc now correctly relates the lifetime of an existential associated type. This fixes some edge cases where rustc would erroneously allow you to pass a shorter lifetime than expected.
• Rustc now dynamically links to libz (also called zlib) on Linux. The library will need to be installed for rustc to work, even though we expect it to be already available on most systems.
• Tests annotated with #[should_panic] are broken on ARMv7 while running under QEMU.
• Pretty printing of some tokens in procedural macros changed. The exact output returned by rustc's pretty printing is an unstable implementation detail: we recommend any macro relying on it to switch to a more robust parsing system.

Rust 1.45.2

• Fix bindings in tuple struct patterns
• Fix track_caller integration with trait objects

Rust 1.45.1

• Fix const propagation with references.
• rustfmt accepts rustfmt_skip in cfg_attr again.
• Avoid spurious implicit region bound.
• Install clippy on x.py install

Rust 1.45.0

Language

• Out of range float to int conversions using as has been defined as a saturating conversion. This was previously undefined behaviour, but you can use the {f64, f32}::to_int_unchecked methods to continue using the current behaviour, which may be desirable in rare performance sensitive situations.
• mem::Discriminant<T> now uses T's discriminant type instead of always using u64.
• Function like procedural macros can now be used in expression, pattern, and statement positions. This means you can now use a function-like procedural macro anywhere you can use a declarative (macro_rules!) macro.

Compiler

• You can now override individual target features through the target-feature flag. E.g. -C target-feature=+avx2 -C target-feature=+fma is now equivalent to -C target-feature=+avx2,+fma.
• Added the force-unwind-tables flag. This option allows rustc to always generate unwind tables regardless of panic strategy.
• Added the embed-bitcode flag. This codegen flag allows rustc to include LLVM bitcode into generated rlibs (this is on by default).
• Added the tiny value to the code-model codegen flag.
• Added tier 3 support* for the mipsel-sony-psp target.
• Added tier 3 support for the thumbv7a-uwp-windows-msvc target.
• Upgraded to LLVM 10.

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

Libraries

• net::{SocketAddr, SocketAddrV4, SocketAddrV6} now implements PartialOrd and Ord.
• proc_macro::TokenStream now implements Default.
• You can now use char with ops::{Range, RangeFrom, RangeFull, RangeInclusive, RangeTo} to iterate over a range of codepoints. E.g. you can now write the following;

  for ch in 'a'..='z' {
      print!("{}", ch);
  }
  println!();
  // Prints "abcdefghijklmnopqrstuvwxyz"

• OsString now implements FromStr.
• The saturating_neg method has been added to all signed integer primitive types, and the saturating_abs method has been added for all integer primitive types.
• Arc<T>, Rc<T> now implement From<Cow<'_, T>>, and Box now implements From<Cow> when T is [T: Copy], str, CStr, OsStr, or Path.
• Box<[T]> now implements From<[T; N]>.
• BitOr and BitOrAssign are implemented for all NonZero integer types.
• The fetch_min, and fetch_max methods have been added to all atomic integer types.
• The fetch_update method has been added to all atomic integer types.

Stabilized APIs

• Arc::as_ptr
• BTreeMap::remove_entry
• Rc::as_ptr
• rc::Weak::as_ptr
• rc::Weak::from_raw
• rc::Weak::into_raw
• str::strip_prefix
• str::strip_suffix
• sync::Weak::as_ptr
• sync::Weak::from_raw
• sync::Weak::into_raw
• char::UNICODE_VERSION
• Span::resolved_at
• Span::located_at
• Span::mixed_site
• unix::process::CommandExt::arg0

Cargo

• Cargo uses the embed-bitcode flag to optimize disk usage and build time.

Misc

• Rustdoc now supports strikethrough text in Markdown. E.g. ~~outdated information~~ becomes "outdated information".
• Added an emoji to Rustdoc's deprecated API message.

Compatibility Notes

• Trying to self initialize a static value (that is creating a value using itself) is unsound and now causes a compile error.
• {f32, f64}::powi now returns a slightly different value on Windows. This is due to changes in LLVM's intrinsics which {f32, f64}::powi uses.
• Rustdoc's CLI's extra error exit codes have been removed. These were previously undocumented and not intended for public use. Rustdoc still provides a non-zero exit code on errors.
• Rustc's lto flag is incompatible with the new embed-bitcode=no. This may cause issues if LTO is enabled through RUSTFLAGS or cargo rustc flags while cargo is adding embed-bitcode itself. The recommended way to control LTO is with Cargo profiles, either in Cargo.toml or .cargo/config, or by setting CARGO_PROFILE_<name>_LTO in the environment.

Internals Only

• Make clippy a git subtree instead of a git submodule
• Unify the undo log of all snapshot types

Rust 1.44.1

• rustfmt accepts rustfmt_skip in cfg_attr again.
• Don't hash executable filenames on apple platforms, fixing backtraces.
• Fix crashes when finding backtrace on macOS.
• Clippy applies lint levels into different files.

Rust 1.44.0

Language

• You can now use async/.await with #[no_std] enabled.
• Added the unused_braces lint.

Syntax-only changes

• Expansion-driven outline module parsing

#[cfg(FALSE)]
mod foo {
    mod bar {
        mod baz; // `foo/bar/baz.rs` doesn't exist, but no error!
    }
}

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

Compiler

• Rustc now respects the -C codegen-units flag in incremental mode. Additionally when in incremental mode rustc defaults to 256 codegen units.
• Refactored catch_unwind to have zero-cost, unless unwinding is enabled and a panic is thrown.
• Added tier 3* support for the aarch64-unknown-none and aarch64-unknown-none-softfloat targets.
• Added tier 3 support for arm64-apple-tvos and x86_64-apple-tvos targets.

Libraries

• Special cased vec![] to map directly to Vec::new(). This allows vec![] to be able to be used in const contexts.
• convert::Infallible now implements Hash.
• OsString now implements DerefMut and IndexMut returning a &mut OsStr.
• Unicode 13 is now supported.
• String now implements From<&mut str>.
• IoSlice now implements Copy.
• Vec<T> now implements From<[T; N]>. Where N is at most 32.
• proc_macro::LexError now implements fmt::Display and Error.
• from_le_bytes, to_le_bytes, from_be_bytes, to_be_bytes, from_ne_bytes, and to_ne_bytes methods are now const for all integer types.

Stabilized APIs

• PathBuf::with_capacity
• PathBuf::capacity
• PathBuf::clear
• PathBuf::reserve
• PathBuf::reserve_exact
• PathBuf::shrink_to_fit
• f32::to_int_unchecked
• f64::to_int_unchecked
• Layout::align_to
• Layout::pad_to_align
• Layout::array
• Layout::extend

Cargo

• Added the cargo tree command which will print a tree graph of your dependencies. E.g.

    mdbook v0.3.2 (/Users/src/rust/mdbook)
  ├── ammonia v3.0.0
  │   ├── html5ever v0.24.0
  │   │   ├── log v0.4.8
  │   │   │   └── cfg-if v0.1.9
  │   │   ├── mac v0.1.1
  │   │   └── markup5ever v0.9.0
  │   │       ├── log v0.4.8 (*)
  │   │       ├── phf v0.7.24
  │   │       │   └── phf_shared v0.7.24
  │   │       │       ├── siphasher v0.2.3
  │   │       │       └── unicase v1.4.2
  │   │       │           [build-dependencies]
  │   │       │           └── version_check v0.1.5
  ...
  

  You can also display dependencies on multiple versions of the same crate with cargo tree -d (short for cargo tree --duplicates).

Misc

• Rustdoc now allows you to specify --crate-version to have rustdoc include the version in the sidebar.

Compatibility Notes

• Rustc now correctly generates static libraries on Windows GNU targets with the .a extension, rather than the previous .lib.
• Removed the -C no_integrated_as flag from rustc.
• The file_name property in JSON output of macro errors now points the actual source file rather than the previous format of <NAME macros>. Note: this may not point to a file that actually exists on the user's system.
• The minimum required external LLVM version has been bumped to LLVM 8.
• mem::{zeroed, uninitialised} will now panic when used with types that do not allow zero initialization such as NonZeroU8. This was previously a warning.
• In 1.45.0 (the next release) converting a f64 to u32 using the as operator has been defined as a saturating operation. This was previously undefined behaviour, but you can use the {f64, f32}::to_int_unchecked methods to continue using the current behaviour, which may be desirable in rare performance sensitive situations.

Internal Only

These changes provide no direct user facing benefits, but represent significant improvements to the internals and overall performance of rustc and related tools.

• dep_graph Avoid allocating a set on when the number reads are small.
• Replace big JS dict with JSON parsing.