Crate complexity

Calculate cognitive complexity of Rust code.

Based on Cognitive Complexity by G. Ann Campbell.

Examples

Loops and branching increment the complexity by one each. Additionally, continue and break statements increment the complexity by one.

use complexity::Complexity;
use syn::{ItemFn, parse_str};

let code = r#"
fn sum_of_primes(max: u64) -> u64 {
    let mut total = 0;
    'outer: for i in 1..=max {
        for j in 2..i {
            if i % j == 0 {
                continue 'outer;
            }
        }
        total += i;
    }
}"#;

let func: ItemFn = parse_str(code)?;
assert_eq!(func.complexity(), 7);

However, a match only increases the complexity by one no matter how many branches there are.

use complexity::Complexity;
use syn::{ItemFn, parse_str};

let code = r#"
fn get_words(number: u64) -> &'static str {
    match number {
        1 => "one",
        2 => "a couple",
        3 => "a few",
        _ => "lots",
    }
}"#;

let func: ItemFn = parse_str(code)?;
assert_eq!(func.complexity(), 1);

Traits

Complexity

A trait for calculating the cognitive complexity of a Rust type.