rust/tests/ui/infinite_iter.rs

#![feature(iterator_for_each)]

use std::iter::repeat;

fn square_is_lower_64(x: &u32) -> bool { x * x < 64 }

#[allow(maybe_infinite_iter)]
#[deny(infinite_iter)]
fn infinite_iters() {
    repeat(0_u8).collect::<Vec<_>>(); // infinite iter
    (0..8_u32).take_while(square_is_lower_64).cycle().count(); // infinite iter
    (0..8_u64).chain(0..).max(); // infinite iter
    (0_usize..).chain([0usize, 1, 2].iter().cloned()).skip_while(|x| *x != 42).min(); // infinite iter
    (0..8_u32).rev().cycle().map(|x| x + 1_u32).for_each(|x| println!("{}", x)); // infinite iter
    (0..3_u32).flat_map(|x| x..).sum::<u32>(); // infinite iter
    (0_usize..).flat_map(|x| 0..x).product::<usize>();  // infinite iter
    (0_u64..).filter(|x| x % 2 == 0).last(); // infinite iter
    (0..42_u64).by_ref().last(); // not an infinite, because ranges are double-ended
    (0..).next(); // iterator is not exhausted
}

#[deny(maybe_infinite_iter)]
fn potential_infinite_iters() {
    (0..).zip((0..).take_while(square_is_lower_64)).count(); // maybe infinite iter
    repeat(42).take_while(|x| *x == 42).chain(0..42).max(); // maybe infinite iter
    (1..).scan(0, |state, x| { *state += x; Some(*state) }).min(); // maybe infinite iter
    (0..).find(|x| *x == 24); // maybe infinite iter
    (0..).position(|x| x == 24); // maybe infinite iter
    (0..).any(|x| x == 24); // maybe infinite iter
    (0..).all(|x| x == 24); // maybe infinite iter

    (0..).zip(0..42).take_while(|&(x, _)| x != 42).count(); // not infinite
    repeat(42).take_while(|x| *x == 42).next(); // iterator is not exhausted
}

fn main() {
    infinite_iters();
    potential_infinite_iters();
}