derive(Error) hangs on invalid input in #[error] helper attribute

[zachs18]

use thiserror::Error;

#[derive(Error, Debug)]
pub enum ArgError {
    #[error("".yellow)]
    InvalidUrl,
}

causes the compiler to hang.

Specifically, it seems like this while loop https://github.com/dtolnay/thiserror/blob/master/impl/src/fmt.rs#L218-L229 is infinite if the input is not as expected; the if statement is skipped and input never changes, so the if statement is forever skipped.

[dtolnay]

Fixed in 2.0.2.