new lint: warn if we match on index item and use wildcard pattern

[matthiaskrgr]

Inspired by #5499

pub fn main() {
    let x = vec![1,2,3];
    match_vec_idx(4 /*boom*/, x);
}

fn match_vec_idx(idx: usize, vec: Vec<u32>) -> bool {
    match vec[idx] {
        1 => return true,
        2 => return false,
        _ => {}
    }
return false
}

In this code we can see that we match on an item in a certain vector position, we only care about a limited number of cases and ignore the rest.

This code will panic if the idx is out of bounds, as it is the case here.
If we could lint the

match x[y] => {
   something => something_else,
   _  => {}
}

pattern where nothing happens anyway if we don't find any of the matched patterns in the vector position, we could suggest using .get() and avoid the panic:

pub fn main() {
    let x = vec![1,2,3];
    match_vec_idx(4/*no longer boom*/, x);
}

fn match_vec_idx(idx: usize, vec: Vec<u32>) -> bool {
    match vec.get(idx) { // use .get()
        Some(1) => return true, // wrapped in Some()
        Some(2) => return false, // wrapped in Some()
        _ => {}
    }
return false
}

[CrazyRoka]

I will try to do it as my first attempt to contribute to a project