fix: Do not drop RTL-only text in a LTR buffer if width is None

Handles a specific case that wasn't happening before since we could only
have RTL-only text on an LTR line if the text was wrapping otherwise the
line would automatically be RTL

Author: hojjatabdollahi

src/shape.rs

@@ -1969,9 +1969,15 @@ impl ShapeLine {
                 } else {
                     (WordGlyphPos::ZERO, WordGlyphPos::new(span.words.len(), 0))
                 }
-            } else if span_index == start.span {
+            } else if span_index == start.span && (start.word, start.glyph) != (0, 0) {
+                // Continuation of an incongruent (reversed) span after a wrap:
+                // this visual line holds the logically-leading words [0, start).
                 (WordGlyphPos::ZERO, start.word_glyph_pos())
             } else {
+                // No continuation offset, so the whole incongruent span belongs to
+                // this line. Without this, a fully-RTL span under a forced-LTR base
+                // direction (start == 0) would collapse to an empty range and drop
+                // all of its glyphs.
                 (WordGlyphPos::ZERO, WordGlyphPos::new(span.words.len(), 0))
             };
 

tests/direction.rs

@@ -54,6 +54,22 @@ fn forced_ltr_overrides_rtl_content() {
     assert!(!first_run_rtl(&buffer),);
 }
 
+#[test]
+fn forced_ltr_keeps_rtl_glyphs() {
+    // a line whose content is entirely RTL must still produce glyphs
+    // when the base direction is forced to LTR (incongruent span on the no-wrap path)
+    let mut font_system = font_system();
+    let buffer = make_buffer(&mut font_system, "سلام", Direction::LeftToRight);
+    let run = buffer
+        .layout_runs()
+        .next()
+        .expect("expected at least one layout run");
+    assert!(
+        !run.glyphs.is_empty(),
+        "forced-LTR RTL line produced no glyphs"
+    );
+}
+
 #[test]
 fn force_ltr_overrides_first_strong_rtl() {
     let mut font_system = font_system();