1.37.0 #

• Released on: 15 August, 2019
• Branched from master on: 28 June, 2019

Language #

• #[must_use] will now warn if the type is contained in a tuple, Box, or an array and unused.
• You can now use the cfg and cfg_attr attributes on generic parameters.
• You can now use enum variants through type alias. e.g. You can write the following:

  type MyOption = Option<u8>;
  
  fn increment_or_zero(x: MyOption) -> u8 {
      match x {
          MyOption::Some(y) => y + 1,
          MyOption::None => 0,
      }
  }
  

• You can now use _ as an identifier for consts. e.g. You can write const _: u32 = 5;.
• You can now use #[repr(align(X)] on enums.
• The ? Kleene macro operator is now available in the 2015 edition.

Compiler #

• You can now enable Profile-Guided Optimization with the -C profile-generate and -C profile-use flags. For more information on how to use profile guided optimization, please refer to the rustc book.
• The rust-lldb wrapper script should now work again.

Libraries #

• mem::MaybeUninit<T> is now ABI-compatible with T.

Stabilized APIs #

• BufReader::buffer
• BufWriter::buffer
• Cell::from_mut
• Cell<[T]>::as_slice_of_cells
• DoubleEndedIterator::nth_back
• Option::xor
• Wrapping::reverse_bits
• i128::reverse_bits
• i16::reverse_bits
• i32::reverse_bits
• i64::reverse_bits
• i8::reverse_bits
• isize::reverse_bits
• slice::copy_within
• u128::reverse_bits
• u16::reverse_bits
• u32::reverse_bits
• u64::reverse_bits
• u8::reverse_bits
• usize::reverse_bits

Cargo #

• Cargo.lock files are now included by default when publishing executable crates with executables.
• You can now specify default-run="foo" in [package] to specify the default executable to use for cargo run.

Misc #

Compatibility Notes #

• Using ... for inclusive range patterns will now warn by default. Please transition your code to using the ..= syntax for inclusive ranges instead.
• Using a trait object without the dyn will now warn by default. Please transition your code to use dyn Trait for trait objects instead.