Calling clone on argument in write! causes stackoverflow

[klingtnet]

I just stumbled across this issue in a small tool I'm developing.
At the moment I can't pinpoint what the cause of the stack overflow is but running the example below will result in this terminal output:

thread 'main' has overflowed its stack
fatal runtime error: stack overflow
timeout: the monitored command dumped core

This can be reproduced for stable (1.29), beta and nightly channels.

Here is a minimal example (playground):

use std::fmt::{Display, Formatter, Result};

#[derive(Clone)]
enum E {
    A,
}
impl Display for E {
    fn fmt(&self, f: &mut Formatter) -> Result {
        write!(f, "{}", self.clone())
    }
}

fn main() {
    let e = E::A;
    println!("{}", e);
}

[klingtnet]

Side note, this compiles without any warnings.

[sfackler]

write!(f, "{}", self.clone()) calls the Display implementation of E, which calls write(f, "{}", self.clone()), which calls the Display implementation of E, which...

[Havvy]

This also happens without the .clone(). It's entirely an expected stack overflow.

[klingtnet]

It's entirely an expected stack overflow.

With this context knowledge, then yes. This should be at least a clippy lint?

[sfackler]

This is basically a duplicate of #45838 I think.

[klingtnet]

Looks like it, a call to to_string() causes a stack overflow as well.

[sfackler]

Closing as a duplicate of that then.