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Language

• Permit specifying explicit discriminants on all repr(Int) enums

  #[repr(u8)]
  enum Foo {
      A(u8) = 0,
      B(i8) = 1,
      C(bool) = 42,
  }
  

• Allow transmutes between the same type differing only in lifetimes
• Change constant evaluation errors from a deny-by-default lint to a hard error
• Trigger must_use on impl Trait for supertraits This makes impl ExactSizeIterator respect the existing #[must_use] annotation on Iterator.
• Allow ..=X in patterns
• Uplift clippy::for_loops_over_fallibles lint into rustc
• Stabilize sym operands in inline assembly
• Update to Unicode 15
• Opaque types no longer imply lifetime bounds This is a soundness fix which may break code that was erroneously relying on this behavior.

Compiler

• Add armv5te-none-eabi and thumbv5te-none-eabi tier 3 targets
  • Refer to Rust's platform support page for more information on Rust's tiered platform support.
• Add support for linking against macOS universal libraries

Libraries

• Fix #[derive(Default)] on a generic #[default] enum adding unnecessary Default bounds
• Update to Unicode 15

Stabilized APIs

• proc_macro::Span::source_text
• uX::{checked_add_signed, overflowing_add_signed, saturating_add_signed, wrapping_add_signed}
• iX::{checked_add_unsigned, overflowing_add_unsigned, saturating_add_unsigned, wrapping_add_unsigned}
• iX::{checked_sub_unsigned, overflowing_sub_unsigned, saturating_sub_unsigned, wrapping_sub_unsigned}
• BTreeSet::{first, last, pop_first, pop_last}
• BTreeMap::{first_key_value, last_key_value, first_entry, last_entry, pop_first, pop_last}
• Add AsFd implementations for stdio lock types on WASI.
• impl TryFrom<Vec<T>> for Box<[T; N]>
• core::hint::black_box
• Duration::try_from_secs_{f32,f64}
• Option::unzip
• std::os::fd

Rustdoc

• Add Rustdoc warning for invalid HTML tags in the documentation

Cargo

• Added cargo remove to remove dependencies from Cargo.toml
• cargo publish now waits for the new version to be downloadable before exiting

See detailed release notes for more.

Compatibility Notes

• Only apply ProceduralMasquerade hack to older versions of rental
• Don't export __heap_base and __data_end on wasm32-wasi.
• Don't export __wasm_init_memory on WebAssembly.
• Only export __tls_* on wasm32-unknown-unknown.
• Don't link to libresolv in libstd on Darwin
• Update libstd's libc to 0.2.135 (to make libstd no longer pull in libiconv.dylib on Darwin)
• Opaque types no longer imply lifetime bounds This is a soundness fix which may break code that was erroneously relying on this behavior.
• Make order_dependent_trait_objects show up in future-breakage reports
• Change std::process::Command spawning to default to inheriting the parent's signal mask

Internal Changes

These changes do not affect any public interfaces of Rust, but they represent significant improvements to the performance or internals of rustc and related tools.

• Enable BOLT for LLVM compilation
• Enable LTO for rustc_driver.so

Language

• Error on as casts of enums with #[non_exhaustive] variants
• Stabilize let else
• Stabilize generic associated types (GATs)
• Add lints let_underscore_drop and let_underscore_lock from Clippy
• Stabilize breaking from arbitrary labeled blocks ("label-break-value")
• Uninitialized integers, floats, and raw pointers are now considered immediate UB. Usage of MaybeUninit is the correct way to work with uninitialized memory.
• Stabilize raw-dylib for Windows x86_64, aarch64, and thumbv7a
• Do not allow Drop impl on foreign ADTs

Compiler

• Stabilize -Csplit-debuginfo on Linux
• Use niche-filling optimization even when multiple variants have data
• Associated type projections are now verified to be well-formed prior to resolving the underlying type
• Stringify non-shorthand visibility correctly
• Normalize struct field types when unsizing
• Update to LLVM 15
• Fix aarch64 call abi to correctly zeroext when needed
• debuginfo: Generalize C++-like encoding for enums
• Add special_module_name lint
• Add support for generating unique profraw files by default when using -C instrument-coverage
• Allow dynamic linking for iOS/tvOS targets

New targets:

• Add armv4t-none-eabi as a tier 3 target
• Add powerpc64-unknown-openbsd and riscv64-unknown-openbsd as tier 3 targets
  • Refer to Rust's platform support page for more information on Rust's tiered platform support.

Libraries

• Don't generate PartialEq::ne in derive(PartialEq)
• Windows RNG: Use BCRYPT_RNG_ALG_HANDLE by default
• Forbid mixing System with direct system allocator calls
• Document no support for writing to non-blocking stdio/stderr
• std::layout::Layout size must not overflow isize::MAX when rounded up to align This also changes the safety conditions on Layout::from_size_align_unchecked.

Stabilized APIs

• std::backtrace::Backtrace
• Bound::as_ref
• std::io::read_to_string
• <*const T>::cast_mut
• <*mut T>::cast_const

These APIs are now stable in const contexts:

• <*const T>::offset_from
• <*mut T>::offset_from

Cargo

• Apply GitHub fast path even for partial hashes
• Do not add home bin path to PATH if it's already there
• Take priority into account within the pending queue. This slightly optimizes job scheduling by Cargo, with typically small improvements on larger crate graph builds.

Compatibility Notes

• std::layout::Layout size must not overflow isize::MAX when rounded up to align. This also changes the safety conditions on Layout::from_size_align_unchecked.
• PollFn now only implements Unpin if the closure is Unpin. This is a possible breaking change if users were relying on the blanket unpin implementation. See discussion on the PR for details of why this change was made.
• Drop ExactSizeIterator impl from std::char::EscapeAscii This is a backwards-incompatible change to the standard library's surface area, but is unlikely to affect real world usage.
• Do not consider a single repeated lifetime eligible for elision in the return type This behavior was unintentionally changed in 1.64.0, and this release reverts that change by making this an error again.
• Reenable disabled early syntax gates as future-incompatibility lints
• Update the minimum external LLVM to 13
• Don't duplicate file descriptors into stdio fds
• Sunset RLS
• Deny usage of #![cfg_attr(..., crate_type = ...)] to set the crate type This strengthens the forward compatibility lint deprecated_cfg_attr_crate_type_name to deny.
• llvm-has-rust-patches allows setting the build system to treat the LLVM as having Rust-specific patches This option may need to be set for distributions that are building Rust with a patched LLVM via llvm-config, not the built-in LLVM.
• Combining three or more languages (e.g. Objective C, C++ and Rust) into one binary may hit linker limitations when using lld. For more information, see issue 102754.

Internal Changes

These changes do not affect any public interfaces of Rust, but they represent significant improvements to the performance or internals of rustc and related tools.

• Add x.sh and x.ps1 shell scripts
• compiletest: use target cfg instead of hard-coded tables
• Use object instead of LLVM for reading bitcode from rlibs
• Enable MIR inlining for optimized compilations This provides a 3-10% improvement in compiletimes for real world crates. See perf results.

Language

• Unions with mutable references or tuples of allowed types are now allowed
• It is now considered valid to deallocate memory pointed to by a shared reference &T if every byte in T is inside an UnsafeCell
• Unused tuple struct fields are now warned against in an allow-by-default lint, unused_tuple_struct_fields, similar to the existing warning for unused struct fields. This lint will become warn-by-default in the future.

Compiler

• Add Nintendo Switch as tier 3 target
  • Refer to Rust's platform support page for more information on Rust's tiered platform support.
• Only compile #[used] as llvm.compiler.used for ELF targets
• Add the --diagnostic-width compiler flag to define the terminal width.
• Add support for link-flavor rust-lld for iOS, tvOS and watchOS

Libraries

• Remove restrictions on compare-exchange memory ordering.
• You can now write! or writeln! into an OsString: Implement fmt::Write for OsString
• Make RwLockReadGuard covariant
• Implement FusedIterator for std::net::[Into]Incoming
• impl<T: AsRawFd> AsRawFd for {Arc,Box}<T>
• ptr::copy and ptr::swap are doing untyped copies
• Add cgroupv1 support to available_parallelism
• Mitigate many incorrect uses of mem::uninitialized

Stabilized APIs

• future::IntoFuture
• future::poll_fn
• task::ready!
• num::NonZero*::checked_mul
• num::NonZero*::checked_pow
• num::NonZero*::saturating_mul
• num::NonZero*::saturating_pow
• num::NonZeroI*::abs
• num::NonZeroI*::checked_abs
• num::NonZeroI*::overflowing_abs
• num::NonZeroI*::saturating_abs
• num::NonZeroI*::unsigned_abs
• num::NonZeroI*::wrapping_abs
• num::NonZeroU*::checked_add
• num::NonZeroU*::checked_next_power_of_two
• num::NonZeroU*::saturating_add
• os::unix::process::CommandExt::process_group
• os::windows::fs::FileTypeExt::is_symlink_dir
• os::windows::fs::FileTypeExt::is_symlink_file

These types were previously stable in std::ffi, but are now also available in core and alloc:

• core::ffi::CStr
• core::ffi::FromBytesWithNulError
• alloc::ffi::CString
• alloc::ffi::FromVecWithNulError
• alloc::ffi::IntoStringError
• alloc::ffi::NulError

These types were previously stable in std::os::raw, but are now also available in core::ffi and std::ffi:

• ffi::c_char
• ffi::c_double
• ffi::c_float
• ffi::c_int
• ffi::c_long
• ffi::c_longlong
• ffi::c_schar
• ffi::c_short
• ffi::c_uchar
• ffi::c_uint
• ffi::c_ulong
• ffi::c_ulonglong
• ffi::c_ushort

These APIs are now usable in const contexts:

• slice::from_raw_parts

Cargo

• Packages can now inherit settings from the workspace so that the settings can be centralized in one place. See workspace.package and workspace.dependencies for more details on how to define these common settings.
• Cargo commands can now accept multiple --target flags to build for multiple targets at once, and the build.target config option may now take an array of multiple targets.
• The --jobs argument can now take a negative number to count backwards from the max CPUs.
• cargo add will now update Cargo.lock.
• Added the --crate-type flag to cargo rustc to override the crate type.
• Significantly improved the performance fetching git dependencies from GitHub when using a hash in the rev field.

Misc

• The rust-analyzer rustup component is now available on the stable channel.

Compatibility Notes

• The minimum required versions for all -linux-gnu targets are now at least kernel 3.2 and glibc 2.17, for targets that previously supported older versions: Increase the minimum linux-gnu versions
• Network primitives are now implemented with the ideal Rust layout, not the C system layout. This can cause problems when transmuting the types.
• Add assertion that transmute_copy's U is not larger than T
• A soundness bug in BTreeMap was fixed that allowed data it was borrowing to be dropped before the container.
• The Drop behavior of C-like enums cast to ints has changed. These are already discouraged by a compiler warning.
• Relate late-bound closure lifetimes to parent fn in NLL
• Errors at const-eval time are now in future incompatibility reports
• On the thumbv6m-none-eabi target, some incorrect asm! statements were erroneously accepted if they used the high registers (r8 to r14) as an input/output operand. This is no longer accepted.
• impl Trait was accidentally accepted as the associated type value of return-position impl Trait, without fulfilling all the trait bounds of that associated type, as long as the hidden type satisfies said bounds. This has been fixed.

Internal Changes

These changes do not affect any public interfaces of Rust, but they represent significant improvements to the performance or internals of rustc and related tools.

• Windows builds now use profile-guided optimization, providing 10-20% improvements to compiler performance: Utilize PGO for windows x64 rustc dist builds
• Stop keeping metadata in memory before writing it to disk
• compiletest: strip debuginfo by default for mode=ui
• Many improvements to generated code for derives, including performance improvements:
  • Don't use match-destructuring for derived ops on structs.
  • Many small deriving cleanups
  • More derive output improvements
  • Clarify deriving code
  • Final derive output improvements
  • Stop injecting #[allow(unused_qualifications)] in generated derive implementations
  • Improve derive(Debug)
• Bump to clap 3
• fully move dropck to mir
• Optimize Vec::insert for the case where index == len.
• Convert rust-analyzer to an in-tree tool

Language

• Remove migrate borrowck mode for pre-NLL errors.
• Modify MIR building to drop repeat expressions with length zero.
• Remove label/lifetime shadowing warnings.
• Allow explicit generic arguments in the presence of impl Trait args.
• Make cenum_impl_drop_cast warnings deny-by-default.
• Prevent unwinding when -C panic=abort is used regardless of declared ABI.
• lub: don't bail out due to empty binders.

Compiler

• Stabilize the bundle native library modifier, also removing the deprecated static-nobundle linking kind.
• Add Apple WatchOS compile targets*.
• Add a Windows application manifest to rustc-main.

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

Libraries

• Implement Copy, Clone, PartialEq and Eq for core::fmt::Alignment.
• Extend ptr::null and null_mut to all thin (including extern) types.
• impl Read and Write for VecDeque<u8>.
• STD support for the Nintendo 3DS.
• Use rounding in float to Duration conversion methods.
• Make write/print macros eagerly drop temporaries.
• Implement internal traits that enable [OsStr]::join.
• Implement Hash for core::alloc::Layout.
• Add capacity documentation for OsString.
• Put a bound on collection misbehavior.
• Make std::mem::needs_drop accept ?Sized.
• impl Termination for Infallible and then make the Result impls of Termination more generic.
• Document Rust's stance on /proc/self/mem.

Stabilized APIs

• array::from_fn
• Box::into_pin
• BinaryHeap::try_reserve
• BinaryHeap::try_reserve_exact
• OsString::try_reserve
• OsString::try_reserve_exact
• PathBuf::try_reserve
• PathBuf::try_reserve_exact
• Path::try_exists
• Ref::filter_map
• RefMut::filter_map
• NonNull::<[T]>::len
• ToOwned::clone_into
• Ipv6Addr::to_ipv4_mapped
• unix::io::AsFd
• unix::io::BorrowedFd<'fd>
• unix::io::OwnedFd
• windows::io::AsHandle
• windows::io::BorrowedHandle<'handle>
• windows::io::OwnedHandle
• windows::io::HandleOrInvalid
• windows::io::HandleOrNull
• windows::io::InvalidHandleError
• windows::io::NullHandleError
• windows::io::AsSocket
• windows::io::BorrowedSocket<'handle>
• windows::io::OwnedSocket
• thread::scope
• thread::Scope
• thread::ScopedJoinHandle

These APIs are now usable in const contexts:

• array::from_ref
• slice::from_ref
• intrinsics::copy
• intrinsics::copy_nonoverlapping
• <*const T>::copy_to
• <*const T>::copy_to_nonoverlapping
• <*mut T>::copy_to
• <*mut T>::copy_to_nonoverlapping
• <*mut T>::copy_from
• <*mut T>::copy_from_nonoverlapping
• str::from_utf8
• Utf8Error::error_len
• Utf8Error::valid_up_to
• Condvar::new
• Mutex::new
• RwLock::new

Cargo

• Stabilize the --config path command-line argument.
• Expose rust-version in the environment as CARGO_PKG_RUST_VERSION.

Compatibility Notes

• #[link] attributes are now checked more strictly, which may introduce errors for invalid attribute arguments that were previously ignored.
• Rounding is now used when converting a float to a Duration. The converted duration can differ slightly from what it was.

Internal Changes

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

• Prepare Rust for LLVM opaque pointers.

Rust 1.62.1 addresses a few recent regressions in the compiler and standard library, and also mitigates a CPU vulnerability on Intel SGX.

• The compiler fixed unsound function coercions involving impl Trait return types.
• The compiler fixed an incremental compilation bug with async fn lifetimes.
• Windows added a fallback for overlapped I/O in synchronous reads and writes.
• The x86_64-fortanix-unknown-sgx target added a mitigation for the MMIO stale data vulnerability, advisory INTEL-SA-00615.

Language

• Stabilize #[derive(Default)] on enums with a #[default] variant
• Teach flow sensitive checks that visibly uninhabited call expressions never return
• Fix constants not getting dropped if part of a diverging expression
• Support unit struct/enum variant in destructuring assignment
• Remove mutable_borrow_reservation_conflict lint and allow the code pattern
• const functions may now specify extern "C" or extern "Rust"

Compiler

• linker: Stop using whole-archive on dependencies of dylibs
• Make unaligned_references lint deny-by-default This lint is also a future compatibility lint, and is expected to eventually become a hard error.
• Only add codegen backend to dep info if -Zbinary-dep-depinfo is used
• Reject #[thread_local] attribute on non-static items
• Add tier 3 aarch64-pc-windows-gnullvm and x86_64-pc-windows-gnullvm targets*
• Implement a lint to warn about unused macro rules
• Promote x86_64-unknown-none target to Tier 2*

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

Libraries

• Windows: Use a pipe relay for chaining pipes
• Replace Linux Mutex and Condvar with futex based ones.
• Replace RwLock by a futex based one on Linux
• std: directly use pthread in UNIX parker implementation

Stabilized APIs

• bool::then_some
• f32::total_cmp
• f64::total_cmp
• Stdin::lines
• windows::CommandExt::raw_arg
• impl<T: Default> Default for AssertUnwindSafe<T>
• From<Rc<str>> for Rc<[u8]>
• From<Arc<str>> for Arc<[u8]>
• FusedIterator for EncodeWide
• RDM intrinsics on aarch64

Clippy

• Create clippy lint against unexpectedly late drop for temporaries in match scrutinee expressions

Cargo

• Added the cargo add command for adding dependencies to Cargo.toml from the command-line. docs
• Package ID specs now support name@version syntax in addition to the previous name:version to align with the behavior in cargo add and other tools. cargo install and cargo yank also now support this syntax so the version does not need to passed as a separate flag.
• The git and registry directories in Cargo's home directory (usually ~/.cargo) are now marked as cache directories so that they are not included in backups or content indexing (on Windows).
• Added automatic @ argfile support, which will use "response files" if the command-line to rustc exceeds the operating system's limit.

Compatibility Notes

• cargo test now passes --target to rustdoc if the specified target is the same as the host target. #10594
• rustdoc: doctests are now run on unexported macro_rules! macros, matching other private items
• rustdoc: Remove .woff font files
• Enforce Copy bounds for repeat elements while considering lifetimes
• Windows: Fix potential unsoundness by aborting if File reads or writes cannot complete synchronously.

Internal Changes

• Unify ReentrantMutex implementations across all platforms

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

Language

• const fn signatures can now include generic trait bounds
• const fn signatures can now use impl Trait in argument and return position
• Function pointers can now be created, cast, and passed around in a const fn
• Recursive calls can now set the value of a function's opaque impl Trait return type

Compiler

• Linking modifier syntax in #[link] attributes and on the command line, as well as the whole-archive modifier specifically, are now supported
• The char type is now described as UTF-32 in debuginfo
• The #[target_feature] attribute can now be used with aarch64 features
• X86 #[target_feature = "adx"] is now stable

Libraries

• ManuallyDrop<T> is now documented to have the same layout as T
• #[ignore = "…"] messages are printed when running tests
• Consistently show absent stdio handles on Windows as NULL handles
• Make std::io::stdio::lock() return 'static handles. Previously, the creation of locked handles to stdin/stdout/stderr would borrow the handles being locked, which prevented writing let out = std::io::stdout().lock(); because out would outlive the return value of stdout(). Such code now works, eliminating a common pitfall that affected many Rust users.
• Vec::from_raw_parts is now less restrictive about its inputs
• std::thread::available_parallelism now takes cgroup quotas into account. Since available_parallelism is often used to create a thread pool for parallel computation, which may be CPU-bound for performance, available_parallelism will return a value consistent with the ability to use that many threads continuously, if possible. For instance, in a container with 8 virtual CPUs but quotas only allowing for 50% usage, available_parallelism will return 4.

Stabilized APIs

• Pin::static_mut
• Pin::static_ref
• Vec::retain_mut
• VecDeque::retain_mut
• Write for Cursor<[u8; N]>
• std::os::unix::net::SocketAddr::from_pathname
• std::process::ExitCode and std::process::Termination. The stabilization of these two APIs now makes it possible for programs to return errors from main with custom exit codes.
• std::thread::JoinHandle::is_finished

These APIs are now usable in const contexts:

• <*const T>::offset and <*mut T>::offset
• <*const T>::wrapping_offset and <*mut T>::wrapping_offset
• <*const T>::add and <*mut T>::add
• <*const T>::sub and <*mut T>::sub
• <*const T>::wrapping_add and <*mut T>::wrapping_add
• <*const T>::wrapping_sub and <*mut T>::wrapping_sub
• <[T]>::as_mut_ptr
• <[T]>::as_ptr_range
• <[T]>::as_mut_ptr_range

Cargo

No feature changes, but see compatibility notes.

Compatibility Notes

• Previously native static libraries were linked as whole-archive in some cases, but now rustc tries not to use whole-archive unless explicitly requested. This change may result in linking errors in some cases. To fix such errors, native libraries linked from the command line, build scripts, or #[link] attributes need to
  • (more common) either be reordered to respect dependencies between them (if a depends on b then a should go first and b second)
  • (less common) or be updated to use the +whole-archive modifier.
• Catching a second unwind from FFI code while cleaning up from a Rust panic now causes the process to abort
• Proc macros no longer see ident matchers wrapped in groups
• The number of # in r# raw string literals is now required to be less than 256
• When checking that a dyn type satisfies a trait bound, supertrait bounds are now enforced
• cargo vendor now only accepts one value for each --sync flag
• cfg predicates in all() and any() are always evaluated to detect errors, instead of short-circuiting. The compatibility considerations here arise in nightly-only code that used the short-circuiting behavior of all to write something like cfg(all(feature = "nightly", syntax-requiring-nightly)), which will now fail to compile. Instead, use either cfg_attr(feature = "nightly", ...) or nested uses of cfg.
• bootstrap: static-libstdcpp is now enabled by default, and can now be disabled when llvm-tools is enabled

Internal Changes

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

• debuginfo: Refactor debuginfo generation for types
• Remove the everybody loops pass

Language

• Stabilize #[cfg(panic = "...")] for either "unwind" or "abort".
• Stabilize #[cfg(target_has_atomic = "...")] for each integer size and "ptr".

Compiler

• Enable combining +crt-static and relocation-model=pic on x86_64-unknown-linux-gnu
• Fixes wrong unreachable_pub lints on nested and glob public reexport
• Stabilize -Z instrument-coverage as -C instrument-coverage
• Stabilize -Z print-link-args as --print link-args
• Add new Tier 3 target mips64-openwrt-linux-musl*
• Add new Tier 3 target armv7-unknown-linux-uclibceabi (softfloat)*
• Fix invalid removal of newlines from doc comments
• Add kernel target for RustyHermit
• Deny mixing bin crate type with lib crate types
• Make rustc use RUST_BACKTRACE=full by default
• Upgrade to LLVM 14

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

Libraries

• Guarantee call order for sort_by_cached_key
• Improve Duration::try_from_secs_f32/f64 accuracy by directly processing exponent and mantissa
• Make Instant::{duration_since, elapsed, sub} saturating
• Remove non-monotonic clocks workarounds in Instant::now
• Make BuildHasherDefault, iter::Empty and future::Pending covariant

Stabilized APIs

• Arc::new_cyclic
• Rc::new_cyclic
• slice::EscapeAscii
• <[u8]>::escape_ascii
• u8::escape_ascii
• Vec::spare_capacity_mut
• MaybeUninit::assume_init_drop
• MaybeUninit::assume_init_read
• i8::abs_diff
• i16::abs_diff
• i32::abs_diff
• i64::abs_diff
• i128::abs_diff
• isize::abs_diff
• u8::abs_diff
• u16::abs_diff
• u32::abs_diff
• u64::abs_diff
• u128::abs_diff
• usize::abs_diff
• Display for io::ErrorKind
• From<u8> for ExitCode
• Not for ! (the "never" type)
• _Op_Assign<$t> for Wrapping<$t>
• arch::is_aarch64_feature_detected!

Cargo

• Port cargo from toml-rs to toml_edit
• Stabilize -Ztimings as --timings
• Stabilize namespaced and weak dependency features.
• Accept more cargo:rustc-link-arg-* types from build script output.
• cargo-new should not add ignore rule on Cargo.lock inside subdirs

Misc

• Ship docs on Tier 2 platforms by reusing the closest Tier 1 platform docs
• Drop rustc-docs from complete profile
• bootstrap: tidy up flag handling for llvm build

Compatibility Notes

• Remove compiler-rt linking hack on Android
• Mitigations for platforms with non-monotonic clocks have been removed from Instant::now. On platforms that don't provide monotonic clocks, an instant is not guaranteed to be greater than an earlier instant anymore.
• Instant::{duration_since, elapsed, sub} do not panic anymore on underflow, saturating to 0 instead. In the real world the panic happened mostly on platforms with buggy monotonic clock implementations rather than catching programming errors like reversing the start and end times. Such programming errors will now results in 0 rather than a panic.
• In a future release we're planning to increase the baseline requirements for the Linux kernel to version 3.2, and for glibc to version 2.17. We'd love your feedback in PR #95026.

Internal Changes

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

• Switch all libraries to the 2021 edition

Language

• Stabilize default arguments for const parameters and remove the ordering restriction for type and const parameters
• Stabilize destructuring assignment
• Relax private in public lint on generic bounds and where clauses of trait impls
• Stabilize asm! and global_asm! for x86, x86_64, ARM, Aarch64, and RISC-V

Compiler

• Stabilize new symbol mangling format, leaving it opt-in (-Csymbol-mangling-version=v0)
• Emit LLVM optimization remarks when enabled with -Cremark
• Fix sparc64 ABI for aggregates with floating point members
• Warn when a #[test]-like built-in attribute macro is present multiple times.
• Add support for riscv64gc-unknown-freebsd
• Stabilize -Z emit-future-incompat as --json future-incompat
• Soft disable incremental compilation

This release disables incremental compilation, unless the user has explicitly opted in via the newly added RUSTC_FORCE_INCREMENTAL=1 environment variable. This is due to a known and relatively frequently occurring bug in incremental compilation, which causes builds to issue internal compiler errors. This particular bug is already fixed on nightly, but that fix has not yet rolled out to stable and is deemed too risky for a direct stable backport.

As always, we encourage users to test with nightly and report bugs so that we can track failures and fix issues earlier.

See 94124 for more details.

Libraries

• Remove unnecessary bounds for some Hash{Map,Set} methods

Stabilized APIs

• std::thread::available_parallelism
• Result::copied
• Result::cloned
• arch::asm!
• arch::global_asm!
• ops::ControlFlow::is_break
• ops::ControlFlow::is_continue
• TryFrom<char> for u8
• char::TryFromCharError implementing Clone, Debug, Display, PartialEq, Copy, Eq, Error
• iter::zip
• NonZeroU8::is_power_of_two
• NonZeroU16::is_power_of_two
• NonZeroU32::is_power_of_two
• NonZeroU64::is_power_of_two
• NonZeroU128::is_power_of_two
• NonZeroUsize::is_power_of_two
• DoubleEndedIterator for ToLowercase
• DoubleEndedIterator for ToUppercase
• TryFrom<&mut [T]> for [T; N]
• UnwindSafe for Once
• RefUnwindSafe for Once
• armv8 neon intrinsics for aarch64

Const-stable:

• mem::MaybeUninit::as_ptr
• mem::MaybeUninit::assume_init
• mem::MaybeUninit::assume_init_ref
• ffi::CStr::from_bytes_with_nul_unchecked

Cargo

• Stabilize the strip profile option
• Stabilize future-incompat-report
• Support abbreviating --release as -r
• Support term.quiet configuration
• Remove --host from cargo {publish,search,login}

Compatibility Notes

• Refactor weak symbols in std::sys::unix This may add new, versioned, symbols when building with a newer glibc, as the standard library uses weak linkage rather than dynamically attempting to load certain symbols at runtime.
• Deprecate crate_type and crate_name nested inside #![cfg_attr] This adds a future compatibility lint to supporting the use of cfg_attr wrapping either crate_type or crate_name specification within Rust files; it is recommended that users migrate to setting the equivalent command line flags.
• Remove effect of #[no_link] attribute on name resolution This may expose new names, leading to conflicts with preexisting names in a given namespace and a compilation failure.
• Cargo will document libraries before binaries.
• Respect doc=false in dependencies, not just the root crate
• Weaken guarantee around advancing underlying iterators in zip
• Make split_inclusive() on an empty slice yield an empty output
• Update std::env::temp_dir to use GetTempPath2 on Windows when available.
• unreachable! was updated to match other formatting macro behavior on Rust 2021

Internal Changes

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

• Fix many cases of normalization-related ICEs

• Replace dominators algorithm with simple Lengauer-Tarjan

• Store liveness in interval sets for region inference

• Remove in_band_lifetimes from the compiler and standard library, in preparation for removing this unstable feature.

• Fix race condition in std::fs::remove_dir_all (CVE-2022-21658)
• Handle captured arguments in the useless_format Clippy lint
• Move non_send_fields_in_send_ty Clippy lint to nursery
• Fix wrong error message displayed when some imports are missing
• Fix rustfmt not formatting generated files from stdin