Panic because of level overflow

[saecki]

The follwing code, with the input.txt file panics both on 0.3.18 and on the current main branch (3bf3403a74e4a73e15008001c81c09062e13f280).

use unicode_bidi::{BidiInfo, Level};

fn main() {
    let text = include_str!("input.txt");

    let range = 3071..3082;
    assert_eq!(&text[range.clone()], "@@@><”\03:");

    let bidi = BidiInfo::new(text, Some(Level::ltr()));
    let para = bidi.paragraphs.first().unwrap();
    assert_eq!(para.range, 0..3637);
    assert_eq!(para.level, Level::ltr());

    bidi.visual_runs(para, range);
}

input.txt

thread 'main' panicked at .../.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/unicode-bidi-0.3.18/src/lib.rs:956:47:
Level error: OutOfRangeNumber

[Manishearth]

Hmm, the level stack explicitly is supposed to cap out at 125 elements according to the spec, I'm surprised we dom't do that here, maybe we miss a spot?

[saecki]

I think due to implicit::resolve_levels the maximum is 126.

[asibahi]

Hah in the tagged release of zabadi (which is a port of this lib) hits a panic as well.

It panics at this line:

    min_level = min_level.new_lowest_ge_rtl() orelse @panic("Level number error");

in visual_runs_for_line.

apparently I just removed the panic and made overflow a noop in main. I am not sure if this is correct behaviour, tbh. I think I did that based on this discussion: Tehreer/SheenBidi#52 (reply in thread)