Unexpected behaviour on empty span

[indietyp]

I have been trying to model when an unexpected EOF occurs; the current behavior of empty spans in the fancy reporter is a bit puzzling to me.

In the example shown below, a span of 8..9 yields (which is expected):

Now my intuition (and AFAIK most tools) would say that the EOF of the string is at 9..9, setting 9..9 as the span yields:

Meanwhile, 8..8 yields:

I would've expected that 8..8 points before c (as c @ 8..9) and not after the character and 9..9 points to where 8..8 currently points to.

Do you know if this is expected behavior?

Minimal Reproducible Example

//! ```cargo
//! [dependencies]
//! miette = {version = "5.9.0", features = ["fancy"]}
//! ```
use miette::miette;
use miette::LabeledSpan;

fn main() {
    let report = miette!(
        labels = vec![LabeledSpan::at(8..8, "Unexpected EOF")],
        "Generic Error"
    ).with_source_code("a = b + c");
    
    println!("{report:?}");
}

[Benjamin-L]

This is effectively a bug, and the output for 9..9 should be:

  × Generic Error
   ╭────
 1 │ a = b + c
   ·          ▲
   ·          ╰── Unexpected EOF
   ╰────

I have a fix for this for the graphical report handler, but haven't successfully ported it over to the narratable handler yet. Ideally I'd like to keep the two in feature parity as much as possible, and I want to hold off on submitting a PR until I've got it working for both. I'll probably have time to take another shot at that later this week.

Longer term, the best path is probably to factor a lot of the duplicated logic between the graphical and narratable handlers into a central place. I have some ideas here, but it's gonna be more work than just fixing this one bug in both places.

[zkat]

@Benjamin-L I'll just assign it to you for now, since you're already on it.