Rust 1.30: what's new, what was stabilized

rustup update stable        # get the newest release
rustup install 1.30          # or exactly this one
rustup override set 1.30     # pin a project to it

Language

• [Procedural macros are now available.][52081] These kinds of macros allow for more powerful code generation. There is a [new chapter available][proc-macros] in the Rust Programming Language book that goes further in depth.
• [You can now use keywords as identifiers using the raw identifiers syntax (r#),][53236] e.g. let r#for = true;
• [Using anonymous parameters in traits is now deprecated with a warning and will be a hard error in the 2018 edition.][53272]
• [You can now use crate in paths.][54404] This allows you to refer to the crate root in the path, e.g. use crate::foo; refers to foo in src/lib.rs.
• [Using a external crate no longer requires being prefixed with ::.][54404] Previously, using a external crate in a module without a use statement required let json = ::serde_json::from_str(foo); but can now be written as let json = serde_json::from_str(foo);.
• [You can now apply the #[used] attribute to static items to prevent the compiler from optimising them away, even if they appear to be unused,][51363] e.g. #[used] static FOO: u32 = 1;
• [You can now import and reexport macros from other crates with the use syntax.][50911] Macros exported with #[macro_export] are now placed into the root module of the crate. If your macro relies on calling other local macros, it is recommended to export with the #[macro_export(local_inner_macros)] attribute so users won't have to import those macros.
• [You can now catch visibility keywords (e.g. pub, pub(crate)) in macros using the vis specifier.][53370]
• [Non-macro attributes now allow all forms of literals, not just strings.][53044] Previously, you would write #[attr("true")], and you can now write #[attr(true)].
• [You can now specify a function to handle a panic in the Rust runtime with the #[panic_handler] attribute.][51366]

Compiler

• [Added the riscv32imc-unknown-none-elf target.][53822]
• [Added the aarch64-unknown-netbsd target][53165]
• [Upgraded to LLVM 8.][53611]

Libraries

• [ManuallyDrop now allows the inner type to be unsized.][53033]

Stabilized APIs

• [Ipv4Addr::BROADCAST]
• [Ipv4Addr::LOCALHOST]
• [Ipv4Addr::UNSPECIFIED]
• [Ipv6Addr::LOCALHOST]
• [Ipv6Addr::UNSPECIFIED]
• [Iterator::find_map]

The following methods are replacement methods for trim_left, trim_right, trim_left_matches, and trim_right_matches, which will be deprecated in 1.33.0:

• [str::trim_end_matches]
• [str::trim_end]
• [str::trim_start_matches]
• [str::trim_start]

Cargo

• [cargo run doesn't require specifying a package in workspaces.][cargo/5877]
• [cargo doc now supports --message-format=json.][cargo/5878] This is equivalent to calling rustdoc --error-format=json.
• [Cargo will now provide a progress bar for builds.][cargo/5995]

Misc

• rustdoc allows you to specify what edition to treat your code as with the --edition option.
• rustdoc now has the --color (specify whether to output color) and --error-format (specify error format, e.g. json) options.
• We now distribute a rust-gdbgui script that invokes gdbgui with Rust debug symbols.
• Attributes from Rust tools such as rustfmt or clippy are now available, e.g. #[rustfmt::skip] will skip formatting the next item.

1.30.1 (Nov 8, 2018)

• Fixed overflow ICE in rustdoc
• Cap Cargo progress bar width at 60 in MSYS terminals