Fix CJ-Latin space at manual line breaks (#6700)

Co-authored-by: Laurenz Mädje <laurmaedje@gmail.com>

crates/typst-layout/src/inline/line.rs

@@ -149,6 +149,7 @@ pub fn line<'a>(
 
     // Trim the line at the end, if necessary for this breakpoint.
     let trim = range.start + breakpoint.trim(full).len();
+    let trimmed_range = range.start..trim;
 
     // Collect the items for the line.
     let mut items = Items::new();
@@ -179,7 +180,8 @@ pub fn line<'a>(
     trim_weak_spacing(&mut items);
 
     // Deal with CJ characters at line boundaries.
-    adjust_cj_at_line_boundaries(p, full, &mut items);
+    // Use the trimmed range for robust boundary checks.
+    adjust_cj_at_line_boundaries(p, trimmed_range, &mut items);
 
     // Compute the line's width.
     let width = items.iter().map(Item::natural_width).sum();
@@ -319,7 +321,11 @@ fn collect_range<'a>(
 ///
 /// See Requirements for Chinese Text Layout, Section 3.1.6.3 Compression of
 /// punctuation marks at line start or line end.
-fn adjust_cj_at_line_boundaries(p: &Preparation, text: &str, items: &mut Items) {
+///
+/// The `range` should only contain regular texts, with linebreaks trimmed.
+fn adjust_cj_at_line_boundaries(p: &Preparation, range: Range, items: &mut Items) {
+    let text = &p.text[range];
+
     if text.starts_with(BEGIN_PUNCT_PAT)
         || (p.config.cjk_latin_spacing && text.starts_with(is_of_cj_script))
     {

tests/suite/layout/inline/cjk.typ

@@ -84,6 +84,19 @@ abc字#linebreak()
 abc字\
 母
 
+--- issue-6539-cjk-latin-spacing-at-manual-linebreak ---
+// Issue #6539
+#set text(cjk-latin-spacing: auto)
+#set box(width: 2.3em, stroke: (x: green))
+
+#box(align(end)[甲国\ T国])
+
+#box(align(end)[乙国 \ T国])
+
+#box(align(end)[丙国 T国])
+
+#box(align(end)[丁国T国])
+
 --- issue-2650-cjk-latin-spacing-meta ---
 测a试