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chore: add unit test and improve comment

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This commit is contained in:
Adam Kowalski 2026-01-08 21:24:40 -08:00 • committed by Jeremy Soller
parent 8c8c41b05b
commit d391a3a166
3 changed files with 34 additions and 31 deletions
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5
src/shape.rs
View file

@ -826,7 +826,10 @@ impl ShapeSpan {
let mut start_word = 0;
for (end_lb, _) in unicode_linebreak::linebreaks(span) {
// Workaround for broken |> ligature in code fonts
// The unicode-linebreak crate treats the pipe character '|' as a break opportunity (BA/AL class).
// This causes ShapeSpan::build to split text like '|>' into separate ShapeWords.
// When these words are shaped independently, the font shaping engine cannot form ligatures that cross the word boundary.
// We manually check for the '|>' sequence during segmentation and skip the break opportunity to ensure they remain in the same shaping run.
if end_lb > 0 && end_lb < span.len() {
let b = span.as_bytes();
if b[end_lb - 1] == b'|' && b[end_lb] == b'>' {

30
tests/ligature_segmentation.rs
View file

@ -1,30 +0,0 @@
use cosmic_text::{Attrs, Buffer, FontSystem, Metrics, Shaping};
#[test]
fn ligature_segmentation() {
let mut font_system =
FontSystem::new_with_locale_and_db("en-US".into(), fontdb::Database::new());
let font = std::fs::read("fonts/Inter-Regular.ttf").unwrap();
font_system.db_mut().load_font_data(font);
let metrics = Metrics::new(14.0, 20.0);
let mut buffer = Buffer::new(&mut font_system, metrics);
let mut buffer = buffer.borrow_with(&mut font_system);
buffer.set_text("|>", &Attrs::new(), Shaping::Advanced, None);
buffer.shape_until_scroll(false);
let line = &buffer.lines[0];
let shape = line.shape_opt().expect("ShapeLine not found");
let span = &shape.spans[0];
// The pipe character | is typically a line break opportunity.
// This test ensures that our patch prevents splitting |> into separate words,
// which would break ligature formation in fonts that support it.
assert_eq!(
span.words.len(),
1,
"Expected '|>' to be a single word (preserved for ligature), but found {} words.",
span.words.len()
);
}

30
tests/shaping_and_rendering.rs
View file

@ -73,3 +73,33 @@ fn test_english_mixed_with_arabic_paragraph_rendering() {
.canvas(400, 110)
.validate_text_rendering();
}
#[test]
fn test_ligature_segmentation() {
use cosmic_text::{Buffer, FontSystem, Metrics, Shaping};
let mut font_system = FontSystem::new_with_locale_and_db("en-US".into(), fontdb::Database::new());
let font = std::fs::read("fonts/Inter-Regular.ttf").unwrap();
font_system.db_mut().load_font_data(font);
let metrics = Metrics::new(14.0, 20.0);
let mut buffer = Buffer::new(&mut font_system, metrics);
let mut buffer = buffer.borrow_with(&mut font_system);
buffer.set_text("|>", &Attrs::new(), Shaping::Advanced, None);
buffer.shape_until_scroll(false);
let line = &buffer.lines[0];
let shape = line.shape_opt().expect("ShapeLine not found");
let span = &shape.spans[0];
// The pipe character | is typically a line break opportunity.
// This test ensures that our patch prevents splitting |> into separate words,
// which would break ligature formation in fonts that support it.
assert_eq!(
span.words.len(),
1,
"Expected '|>' to be a single word (preserved for ligature), but found {} words.",
span.words.len()
);
}