From ec86a8fd3c29f2fa0061c4bf0a104333e6c7bb8e Mon Sep 17 00:00:00 2001
From: Youssef Azriouil <youssef.azriouil@gmail.com>
Date: Wed, 14 Oct 2026 18:57:44 +0200
Subject: [PATCH] Breaker: keep a page number's digits together

The emergency break inside a word wider than the measure could fall
between glyphs of one source character: an automatic page number wider
than its frame came out as "13" over "4". Glyphs sharing a cluster (the
generated digits of a page number, multi-glyph clusters) now stay together
and the number hangs out of its frame, as in InDesign.
---
 crates/compose/src/breaker.rs |  4 ++++
 crates/compose/src/tests.rs   | 17 +++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/crates/compose/src/breaker.rs b/crates/compose/src/breaker.rs
index c2db91fb..d5742f1d 100644
--- a/crates/compose/src/breaker.rs
+++ b/crates/compose/src/breaker.rs
@@ -462,7 +462,11 @@ fn overlong_words(items: &[Item], ig: &[usize], glyphs: &[Glyph], measure: f64)
                     let marks = out.get_or_insert_with(|| vec![false; glyphs.len()]);
                     for i in a..b {
                         let (Some(g), Some(next)) = (glyphs.get(i), glyphs.get(i + 1)) else { continue };
+                        // Glyphs of one source character (an automatic page number's digits, a
+                        // multi-glyph cluster) stay together, as InDesign keeps them.
+                        let one_char = next.byte == g.byte && (next.len == 0 || next.len == g.len);
                         let ok = !g.no_break
+                            && !one_char
                             && g.break_after != Some(false)
                             && next.ch != SOFT_HYPHEN
                             && !is_forced(next.ch)
diff --git a/crates/compose/src/tests.rs b/crates/compose/src/tests.rs
index 97eeb8cd..e1710cb8 100644
--- a/crates/compose/src/tests.rs
+++ b/crates/compose/src/tests.rs
@@ -358,6 +358,23 @@ fn jump_object_keeps_grid_aligned_lines_on_the_grid() {
     assert!((l.baseline - want).abs() < 1e-6, "{} vs {want}", l.baseline);
 }
 
+/// An automatic page number wider than its frame stays on one line and hangs out, as in InDesign
+/// ("136" in a frame made for two digits); breaking it put "13" over "4".
+#[test]
+fn page_number_wider_than_its_frame_stays_whole() {
+    let text = designcraft_doc::story::PAGE_NUMBER.to_string();
+    let (d, sid, _) = doc_with(&text, Rect::new(0.0, 0.0, 10.0, 40.0), ParaAttrs::default());
+    let mut specs = frame_specs(&d, sid);
+    specs[0].page_name = Some("136".into());
+    let cs = compose(&d, d.story(sid).unwrap(), &specs, &ComposeOptions::default());
+    let lines = all_lines(&cs);
+    assert_eq!(lines.len(), 1, "{lines:?}");
+    assert!(!cs.is_overset());
+    // A word of ordinary letters that doesn't fit still breaks where it must.
+    let (d, sid, _) = doc_with("Wordwiderthanframe", Rect::new(0.0, 0.0, 30.0, 200.0), ParaAttrs::default());
+    assert!(all_lines(&compose_story(&d, sid, &ComposeOptions::default())).len() > 1);
+}
+
 #[test]
 fn hostile_wrap_geometry_terminates() {
     let (d, sid) = wrap_doc(ParaAttrs { grid_align: Some(GridAlign::AllLines), ..Default::default() }, &[]);