1.21.0 #

• Released on: 12 October, 2017
• Branched from master on: 25 August, 2017

Language #

• You can now use static references for literals. Example:

  fn main() {
      let x: &'static u32 = &0;
  }
  

• Relaxed path syntax. Optional :: before < is now allowed in all contexts. Example:

  my_macro!(Vec<i32>::new); // Always worked
  my_macro!(Vec::<i32>::new); // Now works
  

Compiler #

• Upgraded jemalloc to 4.5.0
• Enabled unwinding panics on Redox
• Now runs LLVM in parallel during translation phase. This should reduce peak memory usage.

Libraries #

• Generate builtin impls for Clone for all arrays and tuples that are T: Clone
• Stdin, Stdout, and Stderr now implement AsRawFd.
• Rc and Arc now implement From<&[T]> where T: Clone, From<str>, From<String>, From<Box<T>> where T: ?Sized, and From<Vec<T>>.

Stabilized APIs #

std::mem::discriminant

Cargo #

• You can now call cargo install with multiple package names
• Cargo commands inside a virtual workspace will now implicitly pass --all
• Added a [patch] section to Cargo.toml to handle prepublication dependencies RFC 1969
• include & exclude fields in Cargo.toml now accept gitignore like patterns
• Added the --all-targets option
• Using required dependencies as a feature is now deprecated and emits a warning

Misc #

• Cargo docs are moving to doc.rust-lang.org/cargo
• The rustdoc book is now available at doc.rust-lang.org/rustdoc
• Added a preview of RLS has been made available through rustup Install with rustup component add rls-preview
• std::os documentation for Unix, Linux, and Windows now appears on doc.rust-lang.org Previously only showed std::os::unix.

Compatibility Notes #

• Changes in method matching against higher-ranked types This may cause breakage in subtyping corner cases. A more in-depth explanation is available.
• rustc’s JSON error output’s byte position start at top of file. Was previously relative to the rustc’s internal CodeMap struct which required the unstable library libsyntax to correctly use.
• unused_results lint no longer ignores booleans