linebreak_optimized: Handle breakpoints separated only by spaces (#1821)

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);

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"