Compiler

• Bumped minimum LLVM version to 5.0.
• Added powerpc64le-unknown-linux-musl target.
• Added aarch64-unknown-hermit and x86_64-unknown-hermit targets.
• Upgraded to LLVM 7.

Libraries

• Once::call_once no longer requires Once to be 'static.
• BuildHasherDefault now implements PartialEq and Eq.
• Box<CStr>, Box<OsStr>, and Box<Path> now implement Clone.
• Implemented PartialEq<&str> for OsString and PartialEq<OsString> for &str.
• Cell<T> now allows T to be unsized.
• SocketAddr is now stable on Redox.

Stabilized APIs

• Arc::downcast
• Iterator::flatten
• Rc::downcast

Cargo

• Cargo can silently fix some bad lockfiles. You can use --locked to disable this behavior.
• cargo-install will now allow you to cross compile an install using --target.
• Added the cargo-fix subcommand to automatically move project code from 2015 edition to 2018.
• cargo doc can now optionally document private types using the --document-private-items flag.

Misc

• rustdoc now has the --cap-lints option which demotes all lints above the specified level to that level. For example --cap-lints warn will demote deny and forbid lints to warn.
• rustc and rustdoc will now have the exit code of 1 if compilation fails and 101 if there is a panic.
• A preview of clippy has been made available through rustup. You can install the preview with rustup component add clippy-preview.

Compatibility Notes

• str::{slice_unchecked, slice_unchecked_mut} are now deprecated. Use str::get_unchecked(begin..end) instead.
• std::env::home_dir is now deprecated for its unintuitive behavior. Consider using the home_dir function from https://crates.io/crates/dirs instead.
• rustc will no longer silently ignore invalid data in target spec.
• cfg attributes and --cfg command line flags are now more strictly validated.