`mut_range_bound` on immediately broken loop

[SNCPlay42]

I tried this code:

fn bytes_needed_for_level(_level: u32) -> usize {
    unimplemented!()
}

pub fn load(data: &[u8], mut level_count: u32) {
    let mut bytes_needed = 0;
    for level in 0..level_count {
        bytes_needed += bytes_needed_for_level(level);
        if bytes_needed > data.len() {
            eprintln!(
                "not enough bytes for the specified number of levels;
                loading only the first {} levels",
                level_count
            );
            level_count = level;
            break;
        }
    }

    // use level_count while loading the data...
    println!("level_count is {}", level_count);
}

I expected this to happen: no diagnostic. level_count is mutated for when it is used after the loop, and the loop is immediately broken, so the lack of effect changing the bound has on the number of iterations of the loop is moot.

Instead, this happened: the following diagnostic is emitted:

warning: attempt to mutate range bound within loop; note that the range of the loop is unchanged
  --> src/lib.rs:15:13
   |
15 |             level_count = level;
   |             ^^^^^^^^^^^
   |
   = note: `#[warn(clippy::mut_range_bound)]` on by default
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#mut_range_bound

warning: `playground` (lib) generated 1 warning

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clippy 0.1.56 (2021-08-03 a6ece56) on playground

[SNCPlay42]

I'm unsure to what extent this and #6072 are the same thing. In this code, the break provides a clear hint that the mutation was not expected to change the behaviour of the loop.

[dswij]

@rustbot claim