Language

• Out of range float to int conversions using as has been defined as a saturating conversion. This was previously undefined behaviour, but you can use the {f64, f32}::to_int_unchecked methods to continue using the current behaviour, which may be desirable in rare performance sensitive situations.
• mem::Discriminant<T> now uses T's discriminant type instead of always using u64.
• Function like procedural macros can now be used in expression, pattern, and statement positions. This means you can now use a function-like procedural macro anywhere you can use a declarative (macro_rules!) macro.

Compiler

• You can now override individual target features through the target-feature flag. E.g. -C target-feature=+avx2 -C target-feature=+fma is now equivalent to -C target-feature=+avx2,+fma.
• Added the force-unwind-tables flag. This option allows rustc to always generate unwind tables regardless of panic strategy.
• Added the embed-bitcode flag. This codegen flag allows rustc to include LLVM bitcode into generated rlibs (this is on by default).
• Added the tiny value to the code-model codegen flag.
• Added tier 3 support* for the mipsel-sony-psp target.
• Added tier 3 support for the thumbv7a-uwp-windows-msvc target.
• Upgraded to LLVM 10.

* Refer to Rust's platform support page for more information on Rust's tiered platform support.

Libraries

• net::{SocketAddr, SocketAddrV4, SocketAddrV6} now implements PartialOrd and Ord.
• proc_macro::TokenStream now implements Default.
• You can now use char with ops::{Range, RangeFrom, RangeFull, RangeInclusive, RangeTo} to iterate over a range of codepoints. E.g. you can now write the following;

  for ch in 'a'..='z' {
      print!("{}", ch);
  }
  println!();
  // Prints "abcdefghijklmnopqrstuvwxyz"
  

• OsString now implements FromStr.
• The saturating_neg method has been added to all signed integer primitive types, and the saturating_abs method has been added for all integer primitive types.
• Arc<T>, Rc<T> now implement From<Cow<'_, T>>, and Box now implements From<Cow> when T is [T: Copy], str, CStr, OsStr, or Path.
• Box<[T]> now implements From<[T; N]>.
• BitOr and BitOrAssign are implemented for all NonZero integer types.
• The fetch_min, and fetch_max methods have been added to all atomic integer types.
• The fetch_update method has been added to all atomic integer types.

Stabilized APIs

• Arc::as_ptr
• BTreeMap::remove_entry
• Rc::as_ptr
• rc::Weak::as_ptr
• rc::Weak::from_raw
• rc::Weak::into_raw
• str::strip_prefix
• str::strip_suffix
• sync::Weak::as_ptr
• sync::Weak::from_raw
• sync::Weak::into_raw
• char::UNICODE_VERSION
• Span::resolved_at
• Span::located_at
• Span::mixed_site
• unix::process::CommandExt::arg0

Cargo

• Cargo uses the embed-bitcode flag to optimize disk usage and build time.

Misc

• Rustdoc now supports strikethrough text in Markdown. E.g. ~~outdated information~~ becomes "outdated information".
• Added an emoji to Rustdoc's deprecated API message.

Compatibility Notes

• Trying to self initialize a static value (that is creating a value using itself) is unsound and now causes a compile error.
• {f32, f64}::powi now returns a slightly different value on Windows. This is due to changes in LLVM's intrinsics which {f32, f64}::powi uses.
• Rustdoc's CLI's extra error exit codes have been removed. These were previously undocumented and not intended for public use. Rustdoc still provides a non-zero exit code on errors.
• Rustc's lto flag is incompatible with the new embed-bitcode=no. This may cause issues if LTO is enabled through RUSTFLAGS or cargo rustc flags while cargo is adding embed-bitcode itself. The recommended way to control LTO is with Cargo profiles, either in Cargo.toml or .cargo/config, or by setting CARGO_PROFILE_<name>_LTO in the environment.

Internals Only

• Make clippy a git subtree instead of a git submodule
• Unify the undo log of all snapshot types