Log Message:
rust: Update to 1.40.0.

Version 1.40.0 (2019-12-19)
===========================

Language
--------
- [You can now use tuple `struct`s and tuple `enum` variant's constructors in
  `const` contexts.][65188] e.g.

  ```rust
  pub struct Point(i32, i32);

  const ORIGIN: Point = {
      let constructor = Point;

      constructor(0, 0)
  };
  ```

- [You can now mark `struct`s, `enum`s, and `enum` variants with the \ 
`#[non_exhaustive]` attribute to
  indicate that there may be variants or fields added in the future.][64639]
  For example this requires adding a wild-card branch (`_ => {}`) to any match
  statements on a non-exhaustive `enum`. [(RFC 2008)]
- [You can now use function-like procedural macros in `extern` blocks and in
  type positions.][63931] e.g. `type Generated = macro!();`
- [Function-like and attribute procedural macros can now emit
  `macro_rules!` items, so you can now have your macros generate macros.][64035]
- [The `meta` pattern matcher in `macro_rules!` now correctly matches the modern
  attribute syntax.][63674] For example `(#[$m:meta])` now matches `#[attr]`,
  `#[attr{tokens}]`, `#[attr[tokens]]`, and `#[attr(tokens)]`.

Compiler
--------
- [Added tier 3 support\* for the
  `thumbv7neon-unknown-linux-musleabihf` target.][66103]
- [Added tier 3 support for the
  `aarch64-unknown-none-softfloat` target.][64589]
- [Added tier 3 support for the `mips64-unknown-linux-muslabi64`, and
  `mips64el-unknown-linux-muslabi64` targets.][65843]

\* Refer to Rust's [platform support page][forge-platform-support] for more
  information on Rust's tiered platform support.

Libraries
---------
- [The `is_power_of_two` method on unsigned numeric types is now a `const` \ 
function.][65092]

Stabilized APIs
---------------
- [`BTreeMap::get_key_value`]
- [`HashMap::get_key_value`]
- [`Option::as_deref_mut`]
- [`Option::as_deref`]
- [`Option::flatten`]
- [`UdpSocket::peer_addr`]
- [`f32::to_be_bytes`]
- [`f32::to_le_bytes`]
- [`f32::to_ne_bytes`]
- [`f64::to_be_bytes`]
- [`f64::to_le_bytes`]
- [`f64::to_ne_bytes`]
- [`f32::from_be_bytes`]
- [`f32::from_le_bytes`]
- [`f32::from_ne_bytes`]
- [`f64::from_be_bytes`]
- [`f64::from_le_bytes`]
- [`f64::from_ne_bytes`]
- [`mem::take`]
- [`slice::repeat`]
- [`todo!`]

Cargo
-----
- [Cargo will now always display warnings, rather than only on
  fresh builds.][cargo/7450]
- [Feature flags (except `--all-features`) passed to a virtual workspace will
  now produce an error.][cargo/7507] Previously these flags were ignored.
- [You can now publish `dev-dependencies` without including
  a `version`.][cargo/7333]

Misc
----
- [You can now specify the `#[cfg(doctest)]` attribute to include an item only
  when running documentation tests with `rustdoc`.][63803]

Compatibility Notes
-------------------
- [As previously announced, any previous NLL warnings in the 2015 edition are
  now hard errors.][64221]
- [The `include!` macro will now warn if it failed to include the
  entire file.][64284] The `include!` macro unintentionally only includes the
  first _expression_ in a file, and this can be unintuitive. This will become
  either a hard error in a future release, or the behavior may be fixed to \ 
include all expressions as expected.
- [Using `#[inline]` on function prototypes and consts now emits a warning under
  `unused_attribute` lint.][65294] Using `#[inline]` anywhere else inside traits
  or `extern` blocks now correctly emits a hard error.

[65294]: https://github.com/rust-lang/rust/pull/65294/
[66103]: https://github.com/rust-lang/rust/pull/66103/
[65843]: https://github.com/rust-lang/rust/pull/65843/
[65188]: https://github.com/rust-lang/rust/pull/65188/
[65092]: https://github.com/rust-lang/rust/pull/65092/
[64589]: https://github.com/rust-lang/rust/pull/64589/
[64639]: https://github.com/rust-lang/rust/pull/64639/
[64221]: https://github.com/rust-lang/rust/pull/64221/
[64284]: https://github.com/rust-lang/rust/pull/64284/
[63931]: https://github.com/rust-lang/rust/pull/63931/
[64035]: https://github.com/rust-lang/rust/pull/64035/
[63674]: https://github.com/rust-lang/rust/pull/63674/
[63803]: https://github.com/rust-lang/rust/pull/63803/
[cargo/7450]: https://github.com/rust-lang/cargo/pull/7450/
[cargo/7507]: https://github.com/rust-lang/cargo/pull/7507/
[cargo/7525]: https://github.com/rust-lang/cargo/pull/7525/
[cargo/7333]: https://github.com/rust-lang/cargo/pull/7333/
[(rfc 2008)]: https://rust-lang.github.io/rfcs/2008-non-exhaustive.html
[`f32::to_be_bytes`]: \ 
https://doc.rust-lang.org/std/primitive.f32.html#method.to_be_bytes
[`f32::to_le_bytes`]: \ 
https://doc.rust-lang.org/std/primitive.f32.html#method.to_le_bytes
[`f32::to_ne_bytes`]: \ 
https://doc.rust-lang.org/std/primitive.f32.html#method.to_ne_bytes
[`f64::to_be_bytes`]: \ 
https://doc.rust-lang.org/std/primitive.f64.html#method.to_be_bytes
[`f64::to_le_bytes`]: \ 
https://doc.rust-lang.org/std/primitive.f64.html#method.to_le_bytes
[`f64::to_ne_bytes`]: \ 
https://doc.rust-lang.org/std/primitive.f64.html#method.to_ne_bytes
[`f32::from_be_bytes`]: \ 
https://doc.rust-lang.org/std/primitive.f32.html#method.from_be_bytes
[`f32::from_le_bytes`]: \ 
https://doc.rust-lang.org/std/primitive.f32.html#method.from_le_bytes
[`f32::from_ne_bytes`]: \ 
https://doc.rust-lang.org/std/primitive.f32.html#method.from_ne_bytes
[`f64::from_be_bytes`]: \ 
https://doc.rust-lang.org/std/primitive.f64.html#method.from_be_bytes
[`f64::from_le_bytes`]: \ 
https://doc.rust-lang.org/std/primitive.f64.html#method.from_le_bytes
[`f64::from_ne_bytes`]: \ 
https://doc.rust-lang.org/std/primitive.f64.html#method.from_ne_bytes
[`option::flatten`]: \ 
https://doc.rust-lang.org/std/option/enum.Option.html#method.flatten
[`option::as_deref`]: \ 
https://doc.rust-lang.org/std/option/enum.Option.html#method.as_deref
[`option::as_deref_mut`]: \ 
https://doc.rust-lang.org/std/option/enum.Option.html#method.as_deref_mut
[`hashmap::get_key_value`]: \ 
https://doc.rust-lang.org/std/collections/struct.HashMap.html#method.get_key_value
[`btreemap::get_key_value`]: \ 
https://doc.rust-lang.org/std/collections/struct.BTreeMap.html#method.get_key_value
[`slice::repeat`]: https://doc.rust-lang.org/std/primitive.slice.html#method.repeat
[`mem::take`]: https://doc.rust-lang.org/std/mem/fn.take.html
[`udpsocket::peer_addr`]: \ 
https://doc.rust-lang.org/std/net/struct.UdpSocket.html#method.peer_addr
[`todo!`]: https://doc.rust-lang.org/std/macro.todo.html