[pango/fix-lig-carets-sinhala] Fix handling of ligature carets in some cases

[Matthias Clasen <matthiasc src gnome org>]

commit 7fa2dc0c69a1b1499913be65a20619e35b149ec5
Author: Matthias Clasen <mclasen redhat com>
Date:   Fri Jun 24 08:40:00 2022 -0400

    Fix handling of ligature carets in some cases
    
    With a text of "ර් ", we were accidentally producing
    a cursor position outside of the [start_xpos, end_xpos]
    range, which clearly makes no sense.
    
    Test included.
    
    Fixes: #684

 pango/glyphstring.c |  2 +-
 tests/test-bidi.c   | 39 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 40 insertions(+), 1 deletion(-)
---
diff --git a/pango/glyphstring.c b/pango/glyphstring.c
index ea9a63981..e52d41d4f 100644
--- a/pango/glyphstring.c
+++ b/pango/glyphstring.c
@@ -548,7 +548,7 @@ pango_glyph_string_index_to_x_full (PangoGlyphString *glyphs,
     }
 
   if (trailing)
-    cluster_offset += 1;
+    cluster_offset = MIN (cluster_offset + 1, cluster_chars);
 
   if (G_UNLIKELY (!cluster_chars)) /* pedantic */
      {
diff --git a/tests/test-bidi.c b/tests/test-bidi.c
index ba578ba8d..70e96543f 100644
--- a/tests/test-bidi.c
+++ b/tests/test-bidi.c
@@ -453,6 +453,44 @@ test_move_cursor_para (void)
   g_object_unref (layout);
 }
 
+static void
+test_sinhala_cursor (void)
+{
+  const char *text = "ර් á ";
+  PangoLayout *layout;
+  const char *p;
+  const PangoLogAttr *attrs;
+  int n, i;
+
+  layout = pango_layout_new (context);
+
+  pango_layout_set_text (layout, text, -1);
+
+  if (pango_layout_get_unknown_glyphs_count (layout) > 0)
+    {
+      g_object_unref (layout);
+      g_test_skip ("missing Sinhala fonts");
+      return;
+    }
+
+  attrs = pango_layout_get_log_attrs_readonly (layout, &n);
+
+  for (i = 0, p = text; *p; i++, p = g_utf8_next_char (p))
+    {
+      int index = p - text;
+      PangoRectangle strong, weak;
+
+      if (!attrs[i].is_cursor_position)
+        continue;
+
+      g_assert_true (pango_layout_get_direction (layout, index) == PANGO_DIRECTION_LTR);
+
+      pango_layout_get_cursor_pos (layout, index, &strong, &weak);
+      g_assert_true (strong.x == weak.x);
+      g_assert_true (strong.width == weak.width);
+    }
+}
+
 int
 main (int argc, char *argv[])
 {
@@ -471,6 +509,7 @@ main (int argc, char *argv[])
   g_test_add_func ("/bidi/embedding-levels", test_bidi_embedding_levels);
   g_test_add_func ("/bidi/move-cursor-line", test_move_cursor_line);
   g_test_add_func ("/bidi/move-cursor-para", test_move_cursor_para);
+  g_test_add_func ("/bidi/sinhala-cursor", test_sinhala_cursor);
 
   return g_test_run ();
 }