Hideous knockaround in rust

main.rs

fn next_prime(given: &Vec<i32>) -> Option<i32> {
    fn is_prime(given: &Vec<i32>, i: i32) -> bool {
        given.iter().all(|&x| i % x != 0)
    }

    if let Some(next) = given.iter().last() {
        let mut next = next + 1;

        while !is_prime(given, next) {
            next += 1;
        }

        Some(next)
    } else {
        None
    }
}

fn main() {
    let mut primes = vec![2];

    for _ in 1..1000 {
        let np = next_prime(&primes);
        if let Some(np) = np {
            primes.push(np);
        }
    }

    println!("one obviously well and {:?}", primes);
}