From b59b8bfb352f57d50acd67a048baa8390d37e374 Mon Sep 17 00:00:00 2001
From: bluebear94 <uruwi@protonmail.com>
Date: Wed, 23 Aug 2023 07:39:22 -0400
Subject: linebreak_optimized: Handle breakpoints separated only by spaces
 (#1821)

---
 crates/typst-library/src/layout/par.rs |  17 +++++++++++++++--
 tests/ref/layout/par-justify.png       | Bin 19571 -> 27297 bytes
 tests/typ/layout/par-justify.typ       |  10 ++++++++++
 3 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/crates/typst-library/src/layout/par.rs b/crates/typst-library/src/layout/par.rs
index 9e5d4a97..23579105 100644
--- a/crates/typst-library/src/layout/par.rs
+++ b/crates/typst-library/src/layout/par.rs
@@ -929,9 +929,22 @@ fn linebreak_optimized<'a>(vt: &Vt, p: &'a Preparation<'a>, width: Abs) -> Vec<L
         let mut best: Option<Entry> = None;
 
         // Find the optimal predecessor.
-        for (i, pred) in table.iter_mut().enumerate().skip(active) {
+        for (i, pred) in table.iter().enumerate().skip(active) {
             // Layout the line.
             let start = pred.line.end;
+
+            // Fix for https://github.com/unicode-org/icu4x/issues/3811
+            if i > 0 {
+                if let Some(s_pred) = table.get(i + 1) {
+                    let next_start = s_pred.line.end;
+                    if !p.bidi.text[start..next_start]
+                        .contains(|c: char| !c.is_whitespace())
+                    {
+                        continue;
+                    }
+                }
+            }
+
             let attempt = line(vt, p, start..end, mandatory, hyphen);
 
             // Determine how much the line's spaces would need to be stretched
@@ -996,7 +1009,7 @@ fn linebreak_optimized<'a>(vt: &Vt, p: &'a Preparation<'a>, width: Abs) -> Vec<L
             }
 
             // In Knuth paper, cost = (1 + 100|r|^3 + p)^2 + a,
-            // where r is the ratio, p=50 is penaty, and a=3000 is consecutive penaty.
+            // where r is the ratio, p=50 is the penalty, and a=3000 is consecutive the penalty.
             // We divide the whole formula by 10, resulting (0.01 + |r|^3 + p)^2 + a,
             // where p=0.5 and a=300
             cost = (0.01 + cost).powi(2);
diff --git a/tests/ref/layout/par-justify.png b/tests/ref/layout/par-justify.png
index fd25c5b7..5745f081 100644
Binary files a/tests/ref/layout/par-justify.png and b/tests/ref/layout/par-justify.png differ
diff --git a/tests/typ/layout/par-justify.typ b/tests/typ/layout/par-justify.typ
index 2e5b4806..e72a2a07 100644
--- a/tests/typ/layout/par-justify.typ
+++ b/tests/typ/layout/par-justify.typ
@@ -40,3 +40,13 @@ This text can be fitted in one line.
 	"a b c "
 }
 #"d"
+
+---
+// Test that justification cannot lead to a leading space
+#set par(justify: true)
+#set text(size: 12pt)
+#set page(width: 45mm, height: auto)
+
+lorem ipsum 1234, lorem ipsum dolor sit amet
+
+#"  leading whitespace should still be displayed"
-- 
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