Rust 1.34.0

Language

• You can now use #[deprecated = "reason"] as a shorthand for #[deprecated(note = "reason")]. This was previously allowed by mistake but had no effect.
• You can now accept token streams in #[attr()],#[attr[]], and #[attr{}] procedural macros.
• You can now write extern crate self as foo; to import your crate's root into the extern prelude.

Compiler

• You can now target riscv64imac-unknown-none-elf and riscv64gc-unknown-none-elf.
• You can now enable linker plugin LTO optimisations with -C linker-plugin-lto. This allows rustc to compile your Rust code into LLVM bitcode allowing LLVM to perform LTO optimisations across C/C++ FFI boundaries.
• You can now target powerpc64-unknown-freebsd.

Libraries

• The trait bounds have been removed on some of HashMap<K, V, S>'s and HashSet<T, S>'s basic methods. Most notably you no longer require the Hash trait to create an iterator.
• The Ord trait bounds have been removed on some of BinaryHeap<T>'s basic methods. Most notably you no longer require the Ord trait to create an iterator.
• The methods overflowing_neg and wrapping_neg are now const functions for all numeric types.
• Indexing a str is now generic over all types that implement SliceIndex<str>.
• str::trim, str::trim_matches, str::trim_{start, end}, and str::trim_{start, end}_matches are now #[must_use] and will produce a warning if their returning type is unused.
• The methods checked_pow, saturating_pow, wrapping_pow, and overflowing_pow are now available for all numeric types. These are equivalent to methods such as wrapping_add for the pow operation.

Stabilized APIs

std & core

• Any::type_id
• Error::type_id
• atomic::AtomicI16
• atomic::AtomicI32
• atomic::AtomicI64
• atomic::AtomicI8
• atomic::AtomicU16
• atomic::AtomicU32
• atomic::AtomicU64
• atomic::AtomicU8
• convert::Infallible
• convert::TryFrom
• convert::TryInto
• iter::from_fn
• iter::successors
• num::NonZeroI128
• num::NonZeroI16
• num::NonZeroI32
• num::NonZeroI64
• num::NonZeroI8
• num::NonZeroIsize
• slice::sort_by_cached_key
• str::escape_debug
• str::escape_default
• str::escape_unicode
• str::split_ascii_whitespace

std

• Instant::checked_add
• Instant::checked_sub
• SystemTime::checked_add
• SystemTime::checked_sub

Cargo

• You can now use alternative registries to crates.io.

Misc

• You can now use the ? operator in your documentation tests without manually adding fn main() -> Result<(), _> {}.

Compatibility Notes

• Command::before_exec is being replaced by the unsafe method Command::pre_exec and will be deprecated with Rust 1.37.0.
• Use of ATOMIC_{BOOL, ISIZE, USIZE}_INIT is now deprecated as you can now use const functions in static variables.