shadow_unrelated breaks when intermediary bindings are used

[gnzlbg]

Playground:

pub fn foo(a: i32) {
    let b = 3 * (3 + 1) / 2;
    let c = (f64::from(a) / f64::from(b)) as i32;

    let a = c + b;

    let _ = a;
}

produces

error: `a` is shadowed by `c + b`
 --> src/main.rs:8:9
  |
8 |     let a = c + b;
  |         ^
  |
note: lint level defined here
 --> src/main.rs:2:44
  |
2 | #![cfg_attr(feature = "cargo-clippy", deny(clippy::shadow_unrelated))]
  |                                            ^^^^^^^^^^^^^^^^^^^^^^^^
note: initialization happens here
 --> src/main.rs:8:13
  |
8 |     let a = c + b;
  |             ^^^^^
note: previous binding is here
 --> src/main.rs:4:12
  |
4 | pub fn foo(a: i32) {

The lint incorrectly errors that the new binding a is unrelated to the function argument a, but this is incorrect since these two bindings are related via c.

[detly]

Another example involving iterators:

fn decode() -> Option<Vec<u8>> {
    let message = b"prefix_message_goes_here";
    let mut iter = message.splitn(2, |&byte| byte == b'_');
    let prefix = iter.next()?;
    let message = iter.next()?;
    todo!()
}