- Added deprecation warnings for the #[deprecated] attribute and transformed transmuting function pointers into a breaking change, turning warnings into errors after a few cycles.
- Stabilized numerous new APIs and renamed panic functions; Cargo now supports concurrent runs and crate overrides, and std::sync::Once is poisoned on initialization failure.
- Reduced default BufReader/BufWriter buffer size to 8 KB, improved type‑unification performance, and introduced a quiet flag for test runners.
Rust 1.9.0
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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.