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Rust 1.48.0

Released on November 19, 2020

What's Changed

  • [The unsafe keyword is now syntactically permitted on modules.][75857] This

  • [Stabilised the -C link-self-contained= compiler flag.][76158] This tells
  • [You can now use -C target-feature=+crt-static on linux-gnu targets.][77386]
  • [Added tier 2\* support for aarch64-unknown-linux-musl.][76420]
Full Changelog

Language

--------

- [The unsafe keyword is now syntactically permitted on modules.][75857] This

is still rejected semantically, but can now be parsed by procedural macros.

Compiler

--------

- [Stabilised the -C link-self-contained= compiler flag.][76158] This tells

rustc whether to link its own C runtime and libraries or to rely on a external

linker to find them. (Supported only on windows-gnu, linux-musl, and wasi platforms.)

- [You can now use -C target-feature=+crt-static on linux-gnu targets.][77386]

Note: If you're using cargo you must explicitly pass the --target flag.

- [Added tier 2\* support for aarch64-unknown-linux-musl.][76420]

\* Refer to Rust's [platform support page][platform-support-doc] for more

information on Rust's tiered platform support.

Libraries

---------

- [io::Write is now implemented for &ChildStdin &Sink, &Stdout,

and &Stderr.][76275]

- [All arrays of any length now implement TryFrom>.][76310]

- [The matches! macro now supports having a trailing comma.][74880]

- [Vec now implements PartialEq<[B]> where A: PartialEq.][74194]

- [The RefCell::{replace, replace_with, clone} methods now all use #[track_caller].][77055]

Stabilized APIs

---------------

- [slice::as_ptr_range]

- [slice::as_mut_ptr_range]

- [VecDeque::make_contiguous]

- [future::pending]

- [future::ready]

The following previously stable methods are now const fn's:

- [Option::is_some]

- [Option::is_none]

- [Option::as_ref]

- [Result::is_ok]

- [Result::is_err]

- [Result::as_ref]

- [Ordering::reverse]

- [Ordering::then]

Cargo

-----

Rustdoc

-------

- [You can now link to items in rustdoc using the intra-doc link

syntax.][74430] E.g. `/// Uses [std::future] will automatically generate

a link to std::future's documentation. See ["Linking to items by

name"][intradoc-links] for more information.

- [You can now specify #[doc(alias = "")] on items to add search aliases

when searching through rustdoc's UI.][75740]

Compatibility Notes

-------------------

- [Promotion of references to 'static lifetime inside const fn now follows the

same rules as inside a fn body.][75502] In particular, &foo() will not be

promoted to 'static lifetime any more inside const fns.

- [Associated type bindings on trait objects are now verified to meet the bounds

declared on the trait when checking that they implement the trait.][27675]

- [When trait bounds on associated types or opaque types are ambiguous, the

compiler no longer makes an arbitrary choice on which bound to use.][54121]

- [Fixed recursive nonterminals not being expanded in macros during

pretty-print/reparse check.][77153] This may cause errors if your macro wasn't

correctly handling recursive nonterminal tokens.

- [&mut references to non zero-sized types are no longer promoted.][75585]

- [rustc will now warn if you use attributes like #[link_name] or #[cold]

in places where they have no effect.][73461]

- [Updated _mm256_extract_epi8 and _mm256_extract_epi16 signatures in

arch::{x86, x86_64} to return i32 to match the vendor signatures.][73166]

- [mem::uninitialized will now panic if any inner types inside a struct or enum

disallow zero-initialization.][71274]

- [#[target_feature] will now error if used in a place where it has no effect.][78143]

- [Foreign exceptions are now caught by catch_unwind and will cause an abort.][70212]

Note: This behaviour is not guaranteed and is still considered undefined behaviour,

see the [catch_unwind] documentation for further information.

Internal Only

-------------

These changes provide no direct user facing benefits, but represent significant

improvements to the internals and overall performance of rustc and

related tools.

- [Building rustc from source now uses ninja by default over make.][74922]

You can continue building with make by setting ninja=false in

your bootstrap.toml.

- [cg_llvm: fewer_names in uncached_llvm_type][76030]

- [Made ensure_sufficient_stack() non-generic][76680]

[78143]: https://github.com/rust-lang/rust/issues/78143

[76680]: https://github.com/rust-lang/rust/pull/76680/

[76030]: https://github.com/rust-lang/rust/pull/76030/

[70212]: https://github.com/rust-lang/rust/pull/70212/

[27675]: https://github.com/rust-lang/rust/issues/27675/

[54121]: https://github.com/rust-lang/rust/issues/54121/

[71274]: https://github.com/rust-lang/rust/pull/71274/

[77386]: https://github.com/rust-lang/rust/pull/77386/

[77153]: https://github.com/rust-lang/rust/pull/77153/

[77055]: https://github.com/rust-lang/rust/pull/77055/

[76275]: https://github.com/rust-lang/rust/pull/76275/

[76310]: https://github.com/rust-lang/rust/pull/76310/

[76420]: https://github.com/rust-lang/rust/pull/76420/

[76158]: https://github.com/rust-lang/rust/pull/76158/

[75857]: https://github.com/rust-lang/rust/pull/75857/

[75585]: https://github.com/rust-lang/rust/pull/75585/

[75740]: https://github.com/rust-lang/rust/pull/75740/

[75502]: https://github.com/rust-lang/rust/pull/75502/

[74880]: https://github.com/rust-lang/rust/pull/74880/

[74922]: https://github.com/rust-lang/rust/pull/74922/

[74430]: https://github.com/rust-lang/rust/pull/74430/

[74194]: https://github.com/rust-lang/rust/pull/74194/

[73461]: https://github.com/rust-lang/rust/pull/73461/

[73166]: https://github.com/rust-lang/rust/pull/73166/

[intradoc-links]: https://doc.rust-lang.org/rustdoc/linking-to-items-by-name.html

[catch_unwind]: https://doc.rust-lang.org/std/panic/fn.catch_unwind.html

[Option::is_some]: https://doc.rust-lang.org/std/option/enum.Option.html#method.is_some

[Option::is_none]: https://doc.rust-lang.org/std/option/enum.Option.html#method.is_none

[Option::as_ref]: https://doc.rust-lang.org/std/option/enum.Option.html#method.as_ref

[Result::is_ok]: https://doc.rust-lang.org/std/result/enum.Result.html#method.is_ok

[Result::is_err]: https://doc.rust-lang.org/std/result/enum.Result.html#method.is_err

[Result::as_ref]: https://doc.rust-lang.org/std/result/enum.Result.html#method.as_ref

[Ordering::reverse]: https://doc.rust-lang.org/std/cmp/enum.Ordering.html#method.reverse

[Ordering::then]: https://doc.rust-lang.org/std/cmp/enum.Ordering.html#method.then

[slice::as_ptr_range]: https://doc.rust-lang.org/std/primitive.slice.html#method.as_ptr_range

[slice::as_mut_ptr_range]: https://doc.rust-lang.org/std/primitive.slice.html#method.as_mut_ptr_range

[VecDeque::make_contiguous]: https://doc.rust-lang.org/std/collections/struct.VecDeque.html#method.make_contiguous

[future::pending]: https://doc.rust-lang.org/std/future/fn.pending.html

[future::ready`]: https://doc.rust-lang.org/std/future/fn.ready.html