Duplicate labels when span length is 0 and preceded by a newline

[jmackie]

I'm seeing strange behaviour when my SourceSpan has length 0 and the byte before the offset is a newline 🤔

Minimal reproducible example:

use miette::{Diagnostic, NamedSource, Result, SourceSpan};
use thiserror::Error;

#[derive(Error, Debug, Diagnostic)]
#[error("oops!")]
#[diagnostic(severity(Error))]
struct MyBad {
    #[source_code]
    src: NamedSource,
    #[label("This bit here")]
    bad_bit: SourceSpan,
}

fn main() -> Result<()> {
    Err(MyBad {
        src: NamedSource::new("issue", "this is the first line\nthis is the second line"),
        bad_bit: (23, 0).into(),
    }
    .into())
}

Gives:

Error:
  × oops!
   ╭─[issue:1:1]
 1 │ this is the first line
   ·                        ▲
   ·                        ╰── This bit here
 2 │ this is the second line
   · ▲
   · ╰── This bit here
   ╰────

[zkat]

Interesting! I don't know what's going on, but I'd love some help with this one. :)