- Added slice pattern syntax with subslices, #[repr(transparent)] for univariant enums, outer‑attribute procedural macros on inline modules, and several syntax relaxations (default in traits, omitted bodies, associated‑type bounds, C‑varia...
- Compiler now includes tier‑2 support for armv7a and riscv64gc, improves panic messages for Option/Result expect/unwrap, and the standard library adds Send/Sync for iter::Empty, const Layout::new, Eq for io::Cursor, plus many stabilized A...
- Deprecated Error::description (produces a warning) and removed the need for extern crate proc_macro in the 2018 edition.
Rust 1.42.0
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Language: allow shortening lifetimes of &mut during unsize coercions and introduce new lints for invalid runtime symbols and c void return types.