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Rust 1.43.0

Released on April 23, 2020

What's Changed

  • [Fixed using binary operations with &{number} (e.g. &1.0) not having
  • [Attributes such as #[cfg()] can now be used on if expressions.][69201]
  • [Allow type Foo: Ord syntactically.][69361]
  • [Fuse associated and extern items up to defaultness.][69194]
  • [Syntactically allow self in all fn contexts.][68764]
  • [Merge fn syntax + cleanup item parsing.][68728]
  • [item macro fragments can be interpolated into traits, impls, and extern blocks.][69366]

  • [You can now pass multiple lint flags to rustc to override the previous
  • [rustc will now prefer your system MinGW libraries over its bundled libraries
  • [rustc now buffers errors/warnings printed in JSON.][69227]

  • [Arc<[T; N]>, Box<[T; N]>, and Rc<[T; N]>, now implement
  • [You can now use associated constants on floats and integers directly, rather
  • [u8::is_ascii is now const.][68984]
  • [String now implements AsMut.][68742]
  • [Added the primitive module to std and core.][67637] This module
  • [Relaxed some of the trait bounds on HashMap and HashSet.][67642]
  • [string::FromUtf8Error now implements Clone + Eq.][68738]
  • [Once::is_completed]
  • [f32::LOG10_2]
  • [f32::LOG2_10]
  • [f64::LOG10_2]
  • [f64::LOG2_10]
  • [iter::once_with]

  • [You can now set config [profile]s in your .cargo/config, or through
  • [Cargo will now set CARGO_BIN_EXE_ pointing to a binary's

  • [Having trailing syntax in the assert! macro is now a hard error.][69548] This
  • [Fixed Self not having the correctly inferred type.][69340] This incorrectly

  • [Certain checks in the const_err lint were deemed unrelated to const
  • [All components are now built with opt-level=3 instead of 2.][67878]
  • [Improved how rustc generates drop code.][67332]
  • [Improved performance from #[inline]-ing certain hot functions.][69256]
  • [traits: preallocate 2 Vecs of known initial size][69022]
  • [Avoid exponential behaviour when relating types][68772]
  • [Skip Drop terminators for enum variants without drop glue][68943]
  • [Improve performance of coherence checks][68966]
  • [Deduplicate types in the generator witness][68672]
  • [Invert control in struct_lint_level.][68725]
Full Changelog

Language

--------

- [Fixed using binary operations with &{number} (e.g. &1.0) not having

the type inferred correctly.][68129]

- [Attributes such as #[cfg()] can now be used on if expressions.][69201]

Syntax only changes

- [Allow type Foo: Ord syntactically.][69361]

- [Fuse associated and extern items up to defaultness.][69194]

- [Syntactically allow self in all fn contexts.][68764]

- [Merge fn syntax + cleanup item parsing.][68728]

- [item macro fragments can be interpolated into traits, impls, and extern blocks.][69366]

For example, you may now write:

  macro_rules! mac_trait {

($i:item) => {


trait T { $i }


}


}


mac_trait! {


fn foo() {}


}

These are still rejected semantically, so you will likely receive an error but

these changes can be seen and parsed by macros and

conditional compilation.

Compiler

--------

- [You can now pass multiple lint flags to rustc to override the previous

flags.][67885] For example; rustc -D unused -A unused-variables denies

everything in the unused lint group except unused-variables which

is explicitly allowed. However, passing rustc -A unused-variables -D unused denies

everything in the unused lint group including unused-variables since

the allow flag is specified before the deny flag (and therefore overridden).

- [rustc will now prefer your system MinGW libraries over its bundled libraries

if they are available on windows-gnu.][67429]

- [rustc now buffers errors/warnings printed in JSON.][69227]

Libraries

---------

- [Arc<[T; N]>, Box<[T; N]>, and Rc<[T; N]>, now implement

TryFrom>,TryFrom>, and TryFrom>

respectively.][69538] Note These conversions are only available when N

is 0..=32.

- [You can now use associated constants on floats and integers directly, rather

than having to import the module.][68952] e.g. You can now write u32::MAX or

f32::NAN with no imports.

- [u8::is_ascii is now const.][68984]

- [String now implements AsMut.][68742]

- [Added the primitive module to std and core.][67637] This module

reexports Rust's primitive types. This is mainly useful in macros

where you want avoid these types being shadowed.

- [Relaxed some of the trait bounds on HashMap and HashSet.][67642]

- [string::FromUtf8Error now implements Clone + Eq.][68738]

Stabilized APIs

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

- [Once::is_completed]

- [f32::LOG10_2]

- [f32::LOG2_10]

- [f64::LOG10_2]

- [f64::LOG2_10]

- [iter::once_with]

Cargo

-----

- [You can now set config [profile]s in your .cargo/config, or through

your environment.][cargo/7823]

- [Cargo will now set CARGO_BIN_EXE_ pointing to a binary's

executable path when running integration tests or benchmarks.][cargo/7697]

is the name of your binary as-is e.g. If you wanted the executable

path for a binary named my-programyou would use env!("CARGO_BIN_EXE_my-program").

Misc

----

- [Certain checks in the const_err lint were deemed unrelated to const

evaluation][69185], and have been moved to the unconditional_panic and

arithmetic_overflow lints.

Compatibility Notes

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

- [Having trailing syntax in the assert! macro is now a hard error.][69548] This

has been a warning since 1.36.0.

- [Fixed Self not having the correctly inferred type.][69340] This incorrectly

led to some instances being accepted, and now correctly emits a hard error.

[69340]: https://github.com/rust-lang/rust/pull/69340

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.

- [All components are now built with opt-level=3 instead of 2.][67878]

- [Improved how rustc generates drop code.][67332]

- [Improved performance from #[inline]-ing certain hot functions.][69256]

- [traits: preallocate 2 Vecs of known initial size][69022]

- [Avoid exponential behaviour when relating types][68772]

- [Skip Drop terminators for enum variants without drop glue][68943]

- [Improve performance of coherence checks][68966]

- [Deduplicate types in the generator witness][68672]

- [Invert control in struct_lint_level.][68725]

[67332]: https://github.com/rust-lang/rust/pull/67332/

[67429]: https://github.com/rust-lang/rust/pull/67429/

[67637]: https://github.com/rust-lang/rust/pull/67637/

[67642]: https://github.com/rust-lang/rust/pull/67642/

[67878]: https://github.com/rust-lang/rust/pull/67878/

[67885]: https://github.com/rust-lang/rust/pull/67885/

[68129]: https://github.com/rust-lang/rust/pull/68129/

[68672]: https://github.com/rust-lang/rust/pull/68672/

[68725]: https://github.com/rust-lang/rust/pull/68725/

[68728]: https://github.com/rust-lang/rust/pull/68728/

[68738]: https://github.com/rust-lang/rust/pull/68738/

[68742]: https://github.com/rust-lang/rust/pull/68742/

[68764]: https://github.com/rust-lang/rust/pull/68764/

[68772]: https://github.com/rust-lang/rust/pull/68772/

[68943]: https://github.com/rust-lang/rust/pull/68943/

[68952]: https://github.com/rust-lang/rust/pull/68952/

[68966]: https://github.com/rust-lang/rust/pull/68966/

[68984]: https://github.com/rust-lang/rust/pull/68984/

[69022]: https://github.com/rust-lang/rust/pull/69022/

[69185]: https://github.com/rust-lang/rust/pull/69185/

[69194]: https://github.com/rust-lang/rust/pull/69194/

[69201]: https://github.com/rust-lang/rust/pull/69201/

[69227]: https://github.com/rust-lang/rust/pull/69227/

[69548]: https://github.com/rust-lang/rust/pull/69548/

[69256]: https://github.com/rust-lang/rust/pull/69256/

[69361]: https://github.com/rust-lang/rust/pull/69361/

[69366]: https://github.com/rust-lang/rust/pull/69366/

[69538]: https://github.com/rust-lang/rust/pull/69538/

[cargo/7823]: https://github.com/rust-lang/cargo/pull/7823

[cargo/7697]: https://github.com/rust-lang/cargo/pull/7697

[Once::is_completed]: https://doc.rust-lang.org/std/sync/struct.Once.html#method.is_completed

[f32::LOG10_2]: https://doc.rust-lang.org/std/f32/consts/constant.LOG10_2.html

[f32::LOG2_10]: https://doc.rust-lang.org/std/f32/consts/constant.LOG2_10.html

[f64::LOG10_2]: https://doc.rust-lang.org/std/f64/consts/constant.LOG10_2.html

[f64::LOG2_10]: https://doc.rust-lang.org/std/f64/consts/constant.LOG2_10.html

[iter::once_with]: https://doc.rust-lang.org/std/iter/fn.once_with.html