Rust 1.49.0

Language

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

- [Unions can now implement Drop, and you can now have a field in a union

with ManuallyDrop.][77547]

- [You can now cast uninhabited enums to integers.][76199]

- [You can now bind by reference and by move in patterns.][76119] This

allows you to selectively borrow individual components of a type. E.g.

  #[derive(Debug)]
struct Person {
name: String,
age: u8,
}
let person = Person {
name: String::from("Alice"),
age: 20,
};
// name is moved out of person, but age is referenced.
let Person { name, ref age } = person;
println!("{} {}", name, age);

Compiler

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

- [Added tier 1\* support for aarch64-unknown-linux-gnu.][78228]

- [Added tier 2 support for aarch64-apple-darwin.][75991]

- [Added tier 2 support for aarch64-pc-windows-msvc.][75914]

- [Added tier 3 support for mipsel-unknown-none.][78676]

- [Raised the minimum supported LLVM version to LLVM 9.][78848]

- [Output from threads spawned in tests is now captured.][78227]

- [Change os and vendor values to "none" and "unknown" for some targets][78951]

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

information on Rust's tiered platform support.

Libraries

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

- [RangeInclusive now checks for exhaustion when calling contains and indexing.][78109]

- [ToString::to_string now no longer shrinks the internal buffer in the default implementation.][77997]

Stabilized APIs

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

- [slice::select_nth_unstable]

- [slice::select_nth_unstable_by]

- [slice::select_nth_unstable_by_key]

The following previously stable methods are now const.

- [Poll::is_ready]

- [Poll::is_pending]

Cargo

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

- [Building a crate with cargo-package should now be independently reproducible.][cargo/8864]

- [cargo-tree now marks proc-macro crates.][cargo/8765]

- [Added CARGO_PRIMARY_PACKAGE build-time environment variable.][cargo/8758] This

variable will be set if the crate being built is one the user selected to build, either

with -p or through defaults.

- [You can now use glob patterns when specifying packages & targets.][cargo/8752]

Compatibility Notes

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

- [Demoted i686-unknown-freebsd from host tier 2 to target tier 2 support.][78746]

- [Macros that end with a semi-colon are now treated as statements even if they expand to nothing.][78376]

- [Rustc will now check for the validity of some built-in attributes on enum variants.][77015]

Previously such invalid or unused attributes could be ignored.

- Leading whitespace is stripped more uniformly in documentation comments, which may change behavior. You

read [this post about the changes][rustdoc-ws-post] for more details.

- [Trait bounds are no longer inferred for associated types.][79904]

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.

- [rustc's internal crates are now compiled using the initial-exec Thread

Local Storage model.][78201]

- [Calculate visibilities once in resolve.][78077]

- [Added system to the llvm-libunwind bootstrap config option.][77703]

- [Added --color for configuring terminal color support to bootstrap.][79004]

[75991]: https://github.com/rust-lang/rust/pull/75991

[78951]: https://github.com/rust-lang/rust/pull/78951

[78848]: https://github.com/rust-lang/rust/pull/78848

[78746]: https://github.com/rust-lang/rust/pull/78746

[78376]: https://github.com/rust-lang/rust/pull/78376

[78228]: https://github.com/rust-lang/rust/pull/78228

[78227]: https://github.com/rust-lang/rust/pull/78227

[78201]: https://github.com/rust-lang/rust/pull/78201

[78109]: https://github.com/rust-lang/rust/pull/78109

[78077]: https://github.com/rust-lang/rust/pull/78077

[77997]: https://github.com/rust-lang/rust/pull/77997

[77703]: https://github.com/rust-lang/rust/pull/77703

[77547]: https://github.com/rust-lang/rust/pull/77547

[77015]: https://github.com/rust-lang/rust/pull/77015

[76199]: https://github.com/rust-lang/rust/pull/76199

[76119]: https://github.com/rust-lang/rust/pull/76119

[75914]: https://github.com/rust-lang/rust/pull/75914

[79004]: https://github.com/rust-lang/rust/pull/79004

[78676]: https://github.com/rust-lang/rust/pull/78676

[79904]: https://github.com/rust-lang/rust/issues/79904

[cargo/8864]: https://github.com/rust-lang/cargo/pull/8864

[cargo/8765]: https://github.com/rust-lang/cargo/pull/8765

[cargo/8758]: https://github.com/rust-lang/cargo/pull/8758

[cargo/8752]: https://github.com/rust-lang/cargo/pull/8752

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

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

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

[Poll::is_ready]: https://doc.rust-lang.org/stable/std/task/enum.Poll.html#method.is_ready

[Poll::is_pending]: https://doc.rust-lang.org/stable/std/task/enum.Poll.html#method.is_pending

[rustdoc-ws-post]: https://blog.guillaume-gomez.fr/articles/2020-11-11+New+doc+comment+handling+in+rustdoc