Rust 1.78 Released: New Linting, Stabilized APIs, and Performance Improvements

Rust 1.78 Released: New Linting, Stabilized APIs, and Performance Improvements

The Rust team has published version 1.78, continuing the six-week release cadence with a focus on developer experience and performance.

Highlights

New Clippy Lints

• redundant_closure_for_method_calls - catches unnecessary closures
• manual_map - suggests using .map() instead of manual matching
• unnecessary_lazy_evaluation - flags lazy eval where eager is fine

Stabilized APIs

#### HashMap::get_many_mut ````rust let mut map = HashMap::new(); map.insert("a", 1); map.insert("b", 2);

// Now stable! let [a, b] = map.get_many_mut(["a", "b"]).unwrap(); a += 10; b += 20; ````

#### Option::is_some_and / is_none_or Convenient predicates for Option handling: ```rust if opt.is_some_and(|x| x > 10) { ... } if opt.is_none_or(|x| x <= 10) { ... } ```

Compiler Performance

• 10-15% faster incremental compilation
• Improved parallel codegen utilization
• Reduced memory usage during type checking

Cargo Improvements

• cargo check --tests now checks test code
• Better error messages for feature unification
• cargo metadata includes edition info

Upgrade Guide

```bash rustup update stable ```

No breaking changes in this release.