Identify when buffer is being reused in `read_line` without clearing

Identify when a buffer is being reused without clearing in at least read_line, ideally in a general manner (might be impossible to do so), like in the following case:

use std::io;

fn main() {
    let mut guess = String::new();

    loop {
        println!("Enter a number");

        io::stdin().read_line(&mut guess).unwrap();

        println!("guess: {}", guess);
        let guess: u32 = match guess.trim().parse() {
            Ok(num) => num,
            Err(err) => {
                println!("{:?}", err);
                continue
            },
        };
}

CC https://github.com/rust-lang/rust/issues/56681#issuecomment-446431862

Start with the provided read_line example and investigate how Clippy could detect a reused buffer that is not cleared. Determine whether a general lint is feasible beyond this case, then define the diagnostic behavior and verify it with focused examples and tests.