needless_range_loop suggests using iter on a value that do not have iter method

[malbarbo]

In this example:

use std::ops::Index;

struct S(Vec<u32>);

impl Index<usize> for S {
    type Output = u32;

    fn index(&self, index: usize) -> &u32 {
        &self.0[index]
    }
}

fn main() {
    let s = S(vec![1, 2, 3]);

    for i in 0..3 {
        println!("{:?}", s[i]);
    }
}

Clippy says "Consider using for item in s.iter().take(3), but s does not have iter method.

[mcarton]

I guess being indexable but not iterable is so uncommon no one ever noticed 😓

[llogiq]

Maybe we should suggest implementing an .iter() function for something that has a .len() and is Indexable?

[mcarton]

Why the len? Iterators need not to be finite.

[llogiq]

True. Perhaps we should only require Index<usize> then.

[tnielens]

The example isn't linted anymore.

The check early returns when the type has no .iter() method:

                // don't lint if the container that is indexed does not have .iter() method
                let has_iter = has_iter_method(cx, indexed_ty);
                if has_iter.is_none() {
                    return;
                }