[repacker] correct lookup link insertion.

src/graph/gsubgpos-graph.hh

@@ -183,10 +183,13 @@ struct Lookup : public OT::Lookup
 
     Lookup* new_lookup = (Lookup*) buffer;
 
+    unsigned shift = 0;
     new_lookup->subTable.len = subTable.len + new_subtable_count;
     for (const auto& p : subtable_ids)
     {
-      unsigned offset_index = p.first + 1;
+      unsigned offset_index = p.first + shift + 1;
+      shift += p.second.length;
+
       for (unsigned subtable_id : p.second)
       {
         if (is_ext)
@@ -220,11 +223,13 @@ struct Lookup : public OT::Lookup
     auto& v = c.graph.vertices_[this_index];
     Lookup* lookup = (Lookup*) v.obj.head;
 
+    unsigned shift = 0;
     for (const auto& p : subtable_ids)
     {
-      unsigned insert_index = p.first;
+      unsigned insert_index = p.first + shift;
       unsigned pos_offset = p.second.length * OT::Offset16::static_size;
       unsigned insert_offset = (char*) &lookup->subTable[insert_index] - (char*) lookup;
+      shift += p.second.length;
 
       for (auto& l : v.obj.all_links_writer ())
       {

src/test-repacker.cc

@@ -1907,6 +1907,9 @@ main (int argc, char **argv)
   test_resolve_with_basic_pair_pos_2_split ();
   test_resolve_with_pair_pos_2_split_with_device_tables ();
 
+  // TODO(grieger): have run overflow tests compare graph equality not final packed binary.
+  // TODO(grieger): split test where multiple subtables in one lookup are split to test link ordering.
+  // TODO(grieger): split test where coverage table in subtable that is being split is shared.
   // TODO(grieger): test with extensions already mixed in as well.
   // TODO(grieger): test two layer ext promotion setup.
   // TODO(grieger): test sorting by subtables per byte in ext. promotion.