[GSUB/GPOS/Indic] Apply GSUB/GPOS within syllables only

This does not apply to the context matchings.

This regresses tests right now.  And we are not sure whether this is
the right thing to do for GPOS.  But we'll figure out.

src/hb-ot-layout-gsubgpos-private.hh

@@ -135,12 +135,14 @@ struct hb_apply_context_t
     inline mark_skipping_forward_iterator_t (hb_apply_context_t *c_,
 					     unsigned int start_index_,
 					     unsigned int num_items_,
-					     hb_mask_t mask_ = 0)
+					     hb_mask_t mask_ = 0,
+					     bool match_syllable_ = true)
     {
       c = c_;
       idx = start_index_;
       num_items = num_items_;
       mask = mask_ ? mask_ : c->lookup_mask;
+      syllable = match_syllable_ ? c->buffer->info[c->buffer->idx].syllable () : 0;
       end = MIN (c->buffer->len, c->buffer->idx + c->context_length);
     }
     inline bool has_no_chance (void) const
@@ -158,7 +160,7 @@ struct hb_apply_context_t
 	idx++;
       } while (_hb_ot_layout_skip_mark (c->face, &c->buffer->info[idx], lookup_props, property_out));
       num_items--;
-      return !!(c->buffer->info[idx].mask & mask);
+      return (c->buffer->info[idx].mask & mask) && (!syllable || syllable == c->buffer->info[idx].syllable ());
     }
     inline bool next (unsigned int *property_out = NULL)
     {
@@ -170,6 +172,7 @@ struct hb_apply_context_t
     hb_apply_context_t *c;
     unsigned int num_items;
     hb_mask_t mask;
+    uint8_t syllable;
     unsigned int end;
   };
 
@@ -178,12 +181,14 @@ struct hb_apply_context_t
     inline mark_skipping_backward_iterator_t (hb_apply_context_t *c_,
 					      unsigned int start_index_,
 					      unsigned int num_items_,
-					      hb_mask_t mask_ = 0)
+					      hb_mask_t mask_ = 0,
+					     bool match_syllable_ = true)
     {
       c = c_;
       idx = start_index_;
       num_items = num_items_;
       mask = mask_ ? mask_ : c->lookup_mask;
+      syllable = match_syllable_ ? c->buffer->info[c->buffer->idx].syllable () : 0;
     }
     inline bool has_no_chance (void) const
     {
@@ -200,7 +205,7 @@ struct hb_apply_context_t
 	idx--;
       } while (_hb_ot_layout_skip_mark (c->face, &c->buffer->out_info[idx], lookup_props, property_out));
       num_items--;
-      return !!(c->buffer->out_info[idx].mask & mask);
+      return (c->buffer->out_info[idx].mask & mask) && (!syllable || syllable == c->buffer->out_info[idx].syllable ());
     }
     inline bool prev (unsigned int *property_out = NULL)
     {
@@ -212,6 +217,7 @@ struct hb_apply_context_t
     hb_apply_context_t *c;
     unsigned int num_items;
     hb_mask_t mask;
+    uint8_t syllable;
   };
 
   inline bool should_mark_skip_current_glyph (void) const
@@ -341,7 +347,7 @@ static inline bool match_backtrack (hb_apply_context_t *c,
 				    match_func_t match_func,
 				    const void *match_data)
 {
-  hb_apply_context_t::mark_skipping_backward_iterator_t skippy_iter (c, c->buffer->backtrack_len (), count, (hb_mask_t) -1);
+  hb_apply_context_t::mark_skipping_backward_iterator_t skippy_iter (c, c->buffer->backtrack_len (), count, (hb_mask_t) -1, false);
   if (skippy_iter.has_no_chance ())
     return false;
 
@@ -364,7 +370,7 @@ static inline bool match_lookahead (hb_apply_context_t *c,
 				    const void *match_data,
 				    unsigned int offset)
 {
-  hb_apply_context_t::mark_skipping_forward_iterator_t skippy_iter (c, c->buffer->idx + offset - 1, count, (hb_mask_t) -1);
+  hb_apply_context_t::mark_skipping_forward_iterator_t skippy_iter (c, c->buffer->idx + offset - 1, count, (hb_mask_t) -1, false);
   if (skippy_iter.has_no_chance ())
     return false;