Rust 1.61.0 — Rust - Product release notes & changelog tool

Language

Compiler

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:

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.