From d5d5d93b91771e6f3bdeb00128c9c818b09507c0 Mon Sep 17 00:00:00 2001
From: Tobias Schmitz <tobiasschmitz2001@gmail.com>
Date: Mon, 5 May 2025 17:27:24 +0200
Subject: [PATCH] fix: prohibit some line break opportunities between
 LTR-ISOLATE and OBJECT-REPLACEMENT-CHARACTER

Don't provide a line breaking opportunity between and LTR-ISOLATE and an
OBJECT-REPLACEMENT-CHARACTER representing and inline item, if the LTR-ISOLATE
could end up as the only character on the previous line.
---
 crates/typst-layout/src/inline/linebreak.rs | 26 +++++++++++++++++++--
 1 file changed, 24 insertions(+), 2 deletions(-)

diff --git a/crates/typst-layout/src/inline/linebreak.rs b/crates/typst-layout/src/inline/linebreak.rs
index 31512604f..ef8159035 100644
--- a/crates/typst-layout/src/inline/linebreak.rs
+++ b/crates/typst-layout/src/inline/linebreak.rs
@@ -690,13 +690,35 @@ fn breakpoints(p: &Preparation, mut f: impl FnMut(usize, Breakpoint)) {
         let breakpoint = if point == text.len() {
             Breakpoint::Mandatory
         } else {
+            const LTR_ISOLATE: char = '\u{2066}';
+            const OBJ_REPLACE: char = '\u{FFFC}';
             match lb.get(c) {
-                // Fix for: https://github.com/unicode-org/icu4x/issues/4146
-                LineBreak::Glue | LineBreak::WordJoiner | LineBreak::ZWJ => continue,
                 LineBreak::MandatoryBreak
                 | LineBreak::CarriageReturn
                 | LineBreak::LineFeed
                 | LineBreak::NextLine => Breakpoint::Mandatory,
+
+                // https://github.com/typst/typst/issues/5489
+                //
+                // OBJECT-REPLACEMENT-CHARACTERs provide Contingent Break
+                // opportunities before and after by default. This behaviour
+                // is however tailorable, see:
+                // https://www.unicode.org/reports/tr14/#CB
+                // https://www.unicode.org/reports/tr14/#TailorableBreakingRules
+                // https://www.unicode.org/reports/tr14/#LB20
+                //
+                // Don't provide a line breaking opportunity between a LTR-
+                // ISOLATE and an OBJECT-REPLACEMENT-CHARACTER representing
+                // and inline item, if the LTR-ISOLATE could end up as the
+                // only character on the previous line.
+                LineBreak::CombiningMark
+                    if c == LTR_ISOLATE
+                        && text[point..].starts_with(OBJ_REPLACE)
+                        && last == (point - LTR_ISOLATE.len_utf8()) =>
+                {
+                    continue;
+                }
+
                 _ => Breakpoint::Normal,
             }
         };