Roll HarfBuzz to 1.3.0

third_party/harfbuzz-ng/src/hb-ot-layout-gsub-table.hh

 /*
  * Copyright © 2007,2008,2009,2010  Red Hat, Inc.
  * Copyright © 2010,2012,2013  Google, Inc.
  *
  *  This is part of HarfBuzz, a text shaping library.
  *
  * Permission is hereby granted, without written agreement and without
  * license or royalty fees, to use, copy, modify, and distribute this
  * software and its documentation for any purpose, provided that the
  * above copyright notice and the following two paragraphs appear in
@@ skipping 247 matching lines @@
     unsigned int count = substitute.len;
     for (unsigned int i = 0; i < count; i++)
       c->output->add (substitute[i]);
   }
 
   inline bool apply (hb_apply_context_t *c) const
   {
     TRACE_APPLY (this);
     unsigned int count = substitute.len;
 
-    /* TODO:
-     * Testing shows that Uniscribe actually allows zero-len susbstitute,
-     * which essentially deletes a glyph.  We don't allow for now.  It
-     * can be confusing to the client since the cluster from the deleted
-     * glyph won't be merged with any output cluster...  Also, currently
-     * buffer->move_to() makes assumptions about this too.  Perhaps fix
-     * in the future after figuring out what to do with the clusters.
-     */
-    if (unlikely (!count)) return_trace (false);
-
     /* Special-case to make it in-place and not consider this
      * as a "multiplied" substitution. */
     if (unlikely (count == 1))
     {
       c->replace_glyph (substitute.array[0]);
       return_trace (true);
     }
+    /* Spec disallows this, but Uniscribe allows it.
+     * https://github.com/behdad/harfbuzz/issues/253 */
+    else if (unlikely (count == 0))
+    {
+      c->buffer->delete_glyph ();
+      return_trace (true);
+    }
 
     unsigned int klass = _hb_glyph_info_is_ligature (&c->buffer->cur()) ?
                          HB_OT_LAYOUT_GLYPH_PROPS_BASE_GLYPH : 0;
 
     for (unsigned int i = 0; i < count; i++) {
       _hb_glyph_info_set_lig_props_for_component (&c->buffer->cur(), i);
       c->output_glyph_for_component (substitute.array[i], klass);
     }
     c->buffer->skip_glyph ();
 
@@ skipping 1050 matching lines @@
   c->set_lookup_index (saved_lookup_index);
   c->set_lookup_props (saved_lookup_props);
   return ret;
 }
 
 
 } /* namespace OT */
 
 
 #endif /* HB_OT_LAYOUT_GSUB_TABLE_HH */