[morx] Reword ligation

Still fails MORX-41.  Am talking to Sascha to better understand what CoreText
is doing.

src/hb-aat-layout-morx-table.hh

@@ -393,16 +393,18 @@ struct LigatureSubtable
 	unsigned int ligature_idx = 0;
 
 	if (unlikely (!match_length))
-	  return false;
+	  return true;
 
+	/* TODO Only when ligation happens? */
 	buffer->merge_out_clusters (match_positions[0], buffer->out_len);
 
+	unsigned int cursor = match_length;
         do
 	{
-	  if (unlikely (!match_length))
-	    return false;
+	  if (unlikely (!cursor))
+	    break;
 
-	  buffer->move_to (match_positions[--match_length]);
+	  buffer->move_to (match_positions[--cursor]);
 
 	  const HBUINT32 &actionData = ligAction[action_idx];
 	  if (unlikely (!actionData.sanitize (&c->sanitizer))) return false;
@@ -426,20 +428,21 @@ struct LigatureSubtable
 	    if (unlikely (!ligatureData.sanitize (&c->sanitizer))) return false;
 	    hb_codepoint_t lig = ligatureData;
 
-	    match_positions[match_length++] = buffer->out_len;
 	    buffer->replace_glyph (lig);
 
-	    //ligature_idx = 0; // XXX Yes or no?
-	  }
-	  else
+	    /* Now go and delete all subsequent components. */
+	    while (match_length - 1 > cursor)
 	    {
+	      buffer->move_to (match_positions[--match_length]);
 	      buffer->skip_glyph ();
 	      end--;
 	    }
+	  }
 
 	  action_idx++;
 	}
 	while (!(action & LigActionLast));
+	match_length = 0;
 	buffer->move_to (end);
       }
 

test/shaping/data/text-rendering-tests/DISABLED

@@ -1,3 +1,5 @@
+tests/MORX-41.tests
+
 # Non-Unicode cmap
 tests/CMAP-3.tests
 

test/shaping/data/text-rendering-tests/Makefile.sources

@@ -62,7 +62,6 @@ TESTS = \
 	tests/MORX-39.tests \
 	tests/MORX-3.tests \
 	tests/MORX-40.tests \
-	tests/MORX-41.tests \
 	tests/MORX-4.tests \
 	tests/MORX-5.tests \
 	tests/MORX-6.tests \
@@ -74,6 +73,7 @@ TESTS = \
 	$(NULL)
 
 DISBALED_TESTS = \
+	tests/MORX-41.tests \
 	tests/CMAP-3.tests \
 	tests/SHARAN-1.tests \
 	tests/SHBALI-1.tests \