Updatify / Rust | Release notes

Language

• You can now use the cfg(target_vendor) attribute. E.g. #[cfg(target_vendor="apple")] fn main() { println!("Hello Apple!"); }
• Integer patterns such as in a match expression can now be exhaustive. E.g. You can have match statement on a u8 that covers 0..=255 and you would no longer be required to have a _ => unreachable!() case.
• You can now have multiple patterns in if let and while let expressions. You can do this with the same syntax as a match expression. E.g.

  enum Creature {
      Crab(String),
      Lobster(String),
      Person(String),
  }
  
  fn main() {
      let state = Creature::Crab("Ferris");
  
      if let Creature::Crab(name) | Creature::Person(name) = state {
          println!("This creature's name is: {}", name);
      }
  }

• You can now have irrefutable if let and while let patterns. Using this feature will by default produce a warning as this behaviour can be unintuitive. E.g. if let _ = 5 {}
• You can now use let bindings, assignments, expression statements, and irrefutable pattern destructuring in const functions.
• You can now call unsafe const functions. E.g.

  const unsafe fn foo() -> i32 { 5 }
  const fn bar() -> i32 {
      unsafe { foo() }
  }

• You can now specify multiple attributes in a cfg_attr attribute. E.g. #[cfg_attr(all(), must_use, optimize)]
• You can now specify a specific alignment with the #[repr(packed)] attribute. E.g. #[repr(packed(2))] struct Foo(i16, i32); is a struct with an alignment of 2 bytes and a size of 6 bytes.
• You can now import an item from a module as an _. This allows you to import a trait’s impls, and not have the name in the namespace. E.g.

  use std::io::Read as _;
  
  // Allowed as there is only one `Read` in the module.
  pub trait Read {}

• You may now use Rc, Arc, and Pin as method receivers.

Compiler

• You can now set a linker flavor for rustc with the -Clinker-flavor command line argument.
• The minimum required LLVM version has been bumped to 6.0.
• Added support for the PowerPC64 architecture on FreeBSD.
• The x86_64-fortanix-unknown-sgx target support has been upgraded to tier 2 support. Visit the platform support page for information on Rust’s platform support.
• Added support for the thumbv7neon-linux-androideabi and thumbv7neon-unknown-linux-gnueabihf targets.
• Added support for the x86_64-unknown-uefi target.

Libraries

• The methods overflowing_{add, sub, mul, shl, shr} are now const functions for all numeric types.
• The methods rotate_left, rotate_right, and wrapping_{add, sub, mul, shl, shr} are now const functions for all numeric types.
• The methods is_positive and is_negative are now const functions for all signed numeric types.
• The get method for all NonZero types is now const.
• The methods count_ones, count_zeros, leading_zeros, trailing_zeros, swap_bytes, from_be, from_le, to_be, to_le are now const for all numeric types.
• Ipv4Addr::new is now a const function

Stabilized APIs

• unix::FileExt::read_exact_at
• unix::FileExt::write_all_at
• Option::transpose
• Result::transpose
• convert::identity
• pin::Pin
• marker::Unpin
• marker::PhantomPinned
• Vec::resize_with
• VecDeque::resize_with
• Duration::as_millis
• Duration::as_micros
• Duration::as_nanos

Cargo

• You can now publish crates that require a feature flag to compile with cargo publish --features or cargo publish --all-features.
• Cargo should now rebuild a crate if a file was modified during the initial build.

Compatibility Notes

• The methods str::{trim_left, trim_right, trim_left_matches, trim_right_matches} are now deprecated in the standard library, and their usage will now produce a warning. Please use the str::{trim_start, trim_end, trim_start_matches, trim_end_matches} methods instead.
• The Error::cause method has been deprecated in favor of Error::source which supports downcasting.
• Libtest no longer creates a new thread for each test when --test-threads=1. It also runs the tests in deterministic order