Rust 1.80: what's new, what was stabilized

• rustfmt estimates line lengths differently when using non-ascii characters
• Type aliases are now handled correctly in orphan check
• Allow instructing rustdoc to read from stdin via -
• std::env::{set_var, remove_var} can no longer be converted to safe function pointers and no longer implement the Fn family of traits
• Warn (or error) when Self constructor from outer item is referenced in inner nested item
• Turn indirect_structural_match and pointer_structural_match lints into hard errors
• Make where_clause_object_safety lint a regular object safety violation
• Turn proc_macro_back_compat lint into a hard error.
• Detect unused structs even when implementing private traits
• std::sync::ReentrantLockGuard<T> is no longer Sync if T: !Sync which means std::io::StdoutLock and std::io::StderrLock are no longer Sync
• Type inference will fail in some cases due to new implementations of FromIterator for Box<str>.

Language

• Document maximum allocation size
• Allow zero-byte offsets and ZST read/writes on arbitrary pointers
• Support C23's variadics without a named parameter
• Stabilize exclusive_range_pattern feature
• Guarantee layout and ABI of Result in some scenarios

<a id="1.80-Compiler"></a>

Compiler

• Update cc crate to v1.0.97 allowing additional spectre mitigations on MSVC targets
• Allow field reordering on types marked repr(packed(1))
• Add a lint against never type fallback affecting unsafe code
• Disallow cast with trailing braced macro in let-else
• Expand for_loops_over_fallibles lint to lint on fallibles behind references.
• self-contained linker: retry linking without -fuse-ld=lld on CCs that don't support it
• Do not parse CVarArgs (...) as a type in trait bounds
• Improvements to LLDB formatting #124458 #124500
• For the wasm32-wasip2 target default to PIC and do not use -fuse-ld=lld
• Add x86_64-unknown-linux-none as a tier 3 target
• [Lint on foo.into_iter() resolving to &Box<[T]>: IntoIterator](https://github.com/rust-lang/rust/pull/124097/)

<a id="1.80-Libraries"></a>

Libraries

• Add size_of and size_of_val and align_of and align_of_val to the prelude
• Abort a process when FD ownership is violated
• io::Write::write_fmt: panic if the formatter fails when the stream does not fail
• Panic if PathBuf::set_extension would add a path separator
• Add assert_unsafe_precondition to unchecked_{add,sub,neg,mul,shl,shr} methods
• Update c_char on AIX to use the correct type
• offset_of! no longer returns a temporary
• Handle sigma in str.to_lowercase correctly
• Raise DEFAULT_MIN_STACK_SIZE to at least 64KiB

<a id="1.80-Stabilized-APIs"></a>

Stabilized APIs

• impl Default for Rc<CStr>
• impl Default for Rc<str>
• [impl Default for Rc<[T]>](https://doc.rust-lang.org/beta/alloc/rc/struct.Rc.html#impl-Default-for-Rc%3C%5BT%5D%3E)
• impl Default for Arc<str>
• impl Default for Arc<CStr>
• [impl Default for Arc<[T]>](https://doc.rust-lang.org/beta/alloc/sync/struct.Arc.html#impl-Default-for-Arc%3C%5BT%5D%3E)
• [impl IntoIterator for Box<[T]>](https://doc.rust-lang.org/beta/alloc/boxed/struct.Box.html#impl-IntoIterator-for-Box%3C%5BI%5D,+A%3E)
• impl FromIterator<String> for Box<str>
• impl FromIterator<char> for Box<str>
• LazyCell
• LazyLock
• Duration::div_duration_f32
• Duration::div_duration_f64
• Option::take_if
• Seek::seek_relative
• BinaryHeap::as_slice
• NonNull::offset
• NonNull::byte_offset
• NonNull::add
• NonNull::byte_add
• NonNull::sub
• NonNull::byte_sub
• NonNull::offset_from
• NonNull::byte_offset_from
• NonNull::read
• NonNull::read_volatile
• NonNull::read_unaligned
• NonNull::write
• NonNull::write_volatile
• NonNull::write_unaligned
• NonNull::write_bytes
• NonNull::copy_to
• NonNull::copy_to_nonoverlapping
• NonNull::copy_from
• NonNull::copy_from_nonoverlapping
• NonNull::replace
• NonNull::swap
• NonNull::drop_in_place
• NonNull::align_offset
• [<[T]>::split_at_checked](https://doc.rust-lang.org/beta/std/primitive.slice.html#method.split_at_checked)
• [<[T]>::split_at_mut_checked](https://doc.rust-lang.org/beta/std/primitive.slice.html#method.split_at_mut_checked)
• str::split_at_checked
• str::split_at_mut_checked
• str::trim_ascii
• str::trim_ascii_start
• str::trim_ascii_end
• [<[u8]>::trim_ascii](https://doc.rust-lang.org/beta/core/primitive.slice.html#method.trim_ascii)
• [<[u8]>::trim_ascii_start](https://doc.rust-lang.org/beta/core/primitive.slice.html#method.trim_ascii_start)
• [<[u8]>::trim_ascii_end](https://doc.rust-lang.org/beta/core/primitive.slice.html#method.trim_ascii_end)
• Ipv4Addr::BITS
• Ipv4Addr::to_bits
• Ipv4Addr::from_bits
• Ipv6Addr::BITS
• Ipv6Addr::to_bits
• Ipv6Addr::from_bits
• [Vec::<[T; N]>::into_flattened](https://doc.rust-lang.org/beta/alloc/vec/struct.Vec.html#method.into_flattened)
• [<[[T; N]]>::as_flattened](https://doc.rust-lang.org/beta/core/primitive.slice.html#method.as_flattened)
• [<[[T; N]]>::as_flattened_mut](https://doc.rust-lang.org/beta/core/primitive.slice.html#method.as_flattened_mut)

These APIs are now stable in const contexts:

• [<[T]>::last_chunk](https://doc.rust-lang.org/beta/core/primitive.slice.html#method.last_chunk)
• BinaryHeap::new

<a id="1.80-Cargo"></a>

Cargo

• Stabilize -Zcheck-cfg as always enabled
• Warn, rather than fail publish, if a target is excluded
• Add special check-cfg lint config for the unexpected_cfgs lint
• Stabilize cargo update --precise <yanked>
• Don't change file permissions on Cargo.toml when using cargo add
• Support using cargo fix on IPv6-only networks

<a id="1.80-Rustdoc"></a>

Rustdoc

• Allow searching for references
• Stabilize custom_code_classes_in_docs feature
• fix: In cross-crate scenarios show enum variants on type aliases of enums

<a id="1.80-Compatibility-Notes"></a>

Compatibility Notes

• rustfmt estimates line lengths differently when using non-ascii characters
• Type aliases are now handled correctly in orphan check
• Allow instructing rustdoc to read from stdin via -
• std::env::{set_var, remove_var} can no longer be converted to safe function pointers and no longer implement the Fn family of traits
• Warn (or error) when Self constructor from outer item is referenced in inner nested item
• Turn indirect_structural_match and pointer_structural_match lints into hard errors
• Make where_clause_object_safety lint a regular object safety violation
• Turn proc_macro_back_compat lint into a hard error.
• Detect unused structs even when implementing private traits
• std::sync::ReentrantLockGuard<T> is no longer Sync if T: !Sync which means std::io::StdoutLock and std::io::StderrLock are no longer Sync
• Type inference will fail in some cases due to new implementations of FromIterator for Box<str>. Notably, this breaks versions of the time crate before 0.3.35, due to no longer inferring the implementation for Box<[_]>.

<a id="1.80-Internal-Changes"></a>

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.

• Misc improvements to size of generated html by rustdoc e.g. #124738 and #123734
• MSVC targets no longer depend on libc

1.80.1 (Aug 8, 2024)

<a id="1.80.1"></a>

• Fix miscompilation in the jump threading MIR optimization when comparing floats
• Revert changes to the dead_code lint from 1.80.0