New Lint for mutable for-loop counter variable

What it does

Given a program like so:

fn main() {
    for mut i in 0..10 {
        i = 10;
        println!("{}",i);
    }
}

Naively, the lint would warn on i being mutable and or suggest users do the following:

fn main() {
    for i in 0..10 {
        let k = 10;
        println!("{}",k);
    }
}

Advantage

• The original code gives the impression that the loop will only run once, whereas it will run 10 times.
• The new code does not use the variable i and so it is clear that the code will run 10 times.

Drawbacks

No response

Example

fn main() {
    for mut i in 0..10 {
        i = 10;
        println!("{}",i);
    }
}

Could be written as:

fn main() {
    for i in 0..10 {
        let k = 10;
        println!("{}",k);
    }
}

Start by reviewing the Rust examples in the issue and how the proposed lint should distinguish a mutable loop counter from an ordinary mutable binding. Done means the lint identifies the shown pattern and provides an appropriate diagnostic or suggestion without changing valid loop behavior.