clippy and rustfmt

Hundreds of lints, one format

cargo clippy runs hundreds of lints that catch non-idiomatic, inefficient or suspicious code and usually suggest the fix. cargo fmt formats code in the standard style; cargo fmt -- --check fails CI when files are not formatted. Run both in CI with warnings treated as errors (cargo clippy -- -D warnings) to keep a codebase consistent.

clippy suggestions on beginner code, run

I ran this with Rust 1.99.0 (cargo run, edition 2024, standard library only). clippy flags comparing len() to zero (use is_empty), total = total + x (use +=), a loop variable used only for indexing (iterate directly), and an unnecessary vec! (a plain array works). Output shows the warning titles.

fn main() {
    let items = vec![1, 2, 3];
    let mut total = 0;
    for i in 0..items.len() {
        total = total + items[i];
    }
    if total == 6 { println!("total is six") } else { println!("other") }
    let name = String::from("pen");
    let len = name.len() == 0;
    println!("{len}");
}

Output:

warning: length comparison to zero
warning: manual implementation of an assign operation
warning: the loop variable `i` is only used to index `items`
warning: useless use of `vec!`

rustfmt on a one-line program, run

I ran this with Rust 1.99.0 (cargo run, edition 2024, standard library only). cargo fmt --check shows the diff it would apply: the cramped line becomes properly indented, spaced code.

fn main(){let x=vec![1,2,3];for v in x.iter(){println!("{}",v);}}

Output:

-fn main(){let x=vec![1,2,3];for v in x.iter(){println!("{}",v);}}
+fn main() {
+    let x = vec![1, 2, 3];
+    for v in x.iter() {
+        println!("{}", v);
+    }
+}

Quick check: What does cargo clippy do?

• Downloads crates
• Formats code
• Lints code for common mistakes and non-idiomatic patterns
• Profiles performance