The Rust team is happy to announce a new version of Rust, 1.47.0. Rust is a
programming language that is empowering everyone to build reliable and
efficient software.
If you have a previous version of Rust installed via rustup, getting Rust
1.47.0 is as easy as:
rustup update stable
If you don't have it already, you can get rustup from the
appropriate page on our website, and check out the detailed release notes for
1.47.0 on GitHub.
What's in 1.47.0 stable
This release contains no new language features, though it does add one
long-awaited standard library feature. It is mostly quality of life
improvements, library stabilizations and const-ifications, and toolchain
improvements. See the detailed release notes to learn about other
changes not covered by this post.
Traits on larger arrays
Rust does not currently have a way to be generic over integer values. This
has long caused problems with arrays, because arrays have an integer as part
of their type; [T; N] is the type of an array of type T of N length.
Because there is no way to be generic over N, you have to manually implement
traits for arrays for every N you want to support. For the standard library,
it was decided to support up to N of 32.
We have been working on a feature called "const generics" that would allow
you to be generic over N. Fully explaining this feature is out of the scope
of this post, because we are not stabilizing const generics just yet.
However, the core of this feature has been implemented in the compiler, and
it has been decided that the feature is far enough along that we are okay
with the standard library using it to implement traits on arrays of any
length. What this means in
practice is that if you try to do something like this on Rust 1.46:
fn main() {
let xs = [0; 34];
println!("{:?}", xs);
}
you'd get this error:
error[E0277]: arrays only have std trait implementations for lengths 0..=32
--> src/main.rs:4:22
|
4 | println!("{:?}", xs);
| ^^ the trait `std::array::LengthAtMost32` is not implemented for `[{integer}; 34]`
|
= note: required because of the requirements on the impl of `std::fmt::Debug` for `[{integer}; 34]`
= note: required by `std::fmt::Debug::fmt`
= note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
But with Rust 1.47, it will properly print out the array.
This should make arrays significantly more useful to folks, though it will
take until the const generics feature stabilizes for libraries to be able to do
this kind of implementation for their own traits. We do not have a current
estimated date for the stabilization of const generics.
Shorter backtraces
Back in Rust 1.18, we made some changes to the backtraces rustc would
print on panic. There are a
number of things in a backtrace that aren't useful the majority of the time.
However, at some point, these
regressed. In Rust 1.47.0,
the culprit was found, and this has now been
fixed. Since the regression,
this program:
fn main() {
panic!();
}
would give you a backtrace that looks like this:
thread 'main' panicked at 'explicit panic', src/main.rs:2:5
stack backtrace:
0: backtrace::backtrace::libunwind::trace
at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.46/src/backtrace/libunwind.rs:86
1: backtrace::backtrace::trace_unsynchronized
at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.46/src/backtrace/mod.rs:66
2: std::sys_common::backtrace::_print_fmt
at src/libstd/sys_common/backtrace.rs:78
3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
at src/libstd/sys_common/backtrace.rs:59
4: core::fmt::write
at src/libcore/fmt/mod.rs:1076
5: std::io::Write::write_fmt
at src/libstd/io/mod.rs:1537
6: std::sys_common::backtrace::_print
at src/libstd/sys_common/backtrace.rs:62
7: std::sys_common::backtrace::print
at src/libstd/sys_common/backtrace.rs:49
8: std::panicking::default_hook::{{closure}}
at src/libstd/panicking.rs:198
9: std::panicking::default_hook
at src/libstd/panicking.rs:217
10: std::panicking::rust_panic_with_hook
at src/libstd/panicking.rs:526
11: std::panicking::begin_panic
at /rustc/04488afe34512aa4c33566eb16d8c912a3ae04f9/src/libstd/panicking.rs:456
12: playground::main
at src/main.rs:2
13: std::rt::lang_start::{{closure}}
at /rustc/04488afe34512aa4c33566eb16d8c912a3ae04f9/src/libstd/rt.rs:67
14: std::rt::lang_start_internal::{{closure}}
at src/libstd/rt.rs:52
15: std::panicking::try::do_call
at src/libstd/panicking.rs:348
16: std::panicking::try
at src/libstd/panicking.rs:325
17: std::panic::catch_unwind
at src/libstd/panic.rs:394
18: std::rt::lang_start_internal
at src/libstd/rt.rs:51
19: std::rt::lang_start
at /rustc/04488afe34512aa4c33566eb16d8c912a3ae04f9/src/libstd/rt.rs:67
20: main
21: __libc_start_main
22: _start
Now, in Rust 1.47.0, you'll see this instead:
thread 'main' panicked at 'explicit panic', src/main.rs:2:5
stack backtrace:
0: std::panicking::begin_panic
at /rustc/d6646f64790018719caebeafd352a92adfa1d75a/library/std/src/panicking.rs:497
1: playground::main
at ./src/main.rs:2
2: core::ops::function::FnOnce::call_once
at /rustc/d6646f64790018719caebeafd352a92adfa1d75a/library/core/src/ops/function.rs:227
This makes it much easier to see where the panic actually originated, and
you can still set RUST_BACKTRACE=full if you want to see everything.
LLVM 11
We have upgraded to LLVM 11.
The compiler still supports being compiled with LLVM versions as old as 8,
but by default, 11 is what you'll be getting.
Control Flow Guard on Windows
rustc now supports -C control-flow-guard, an option that will turn on Control Flow
Guard
on Windows. Other platforms ignore this flag.
Library changes
Additionally, nine new APIs were stabilized this release:
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.
See the detailed release notes for more.
Other changes
Rustdoc has gained support for the Ayu theme.
There are other changes in the Rust 1.47.0 release: check out what changed in
Rust, Cargo, and Clippy.
Contributors to 1.47.0
Many people came together to create Rust 1.47.0. We couldn't have done it
without all of you. Thanks!
