[repacker] WIP extension promotion implementation.

src/graph/graph.hh

diff --git a/src/graph/graph.hh b/src/graph/graph.hh
index 49638f3..ec3ee19 100644
--- a/src/graph/graph.hh
+++ b/src/graph/graph.hh
@@ -310,6 +310,57 @@
     }
   }
 
+
+  /*
+  void promote_extension_lookups (const hb_set_t& subtable_indices)
+  {
+    const OT::GSUBGPOS* gstar = (OT::GSUBGPOS*) root ().obj.head;
+
+    unsigned lookup_list_idx = index_for_offset (root_idx (), &(gstar->lookupList));
+    const OT::LookupList<SmallTypes>* lookupList =
+        (OT::LookupList<SmallTypes>*) object (lookup_list_idx).head;
+
+
+    for (unsigned i = 0; i < lookupList->len; i++)
+    {
+      unsigned lookup_idx = index_for_offset (lookup_list_idx, &(lookupList->arrayZ[i]));
+      const OT::Lookup* lookup = (OT::Lookup*) object (lookup_idx).head;
+
+      // TODO(grieger): use the correct type for GSUB vs GPOS
+      if (lookup->get_type () == 9) continue; // skip extensions
+
+      for (unsigned j = 0; j < lookup->subTable.len; j++)
+      {
+        unsigned subtable_idx = index_for_offset (lookup_idx, &(lookup->subTable.arrayZ[j]));
+        if (subtable_indices.has (subtable_idx))
+          promote_to_extension (lookup_idx);
+      }
+    }
+  }
+
+  void promote_to_extension (unsigned lookup_idx)
+  {
+    DEBUG_MSG (SUBSET_REPACK, nullptr, "Promoting %d to extension lookup.", lookup_idx);
+    // TODO(garretrieger): implement me.
+  }
+  */
+
+  unsigned index_for_offset(unsigned node_idx, const void* offset) const
+  {
+    const auto& node = object (node_idx);
+    if (offset < node.head || offset >= node.tail) return -1;
+
+    for (const auto& link : node.real_links)
+    {
+      if (offset != node.head + link.position)
+        continue;
+      return link.objidx;
+    }
+
+    return -1;
+  }
+
+
   /*
    * Assign unique space numbers to each connected subgraph of 24 bit and/or 32 bit offset(s).
    * Currently, this is implemented specifically tailored to the structure of a GPOS/GSUB

src/hb-ot-layout-common.hh

diff --git a/src/hb-ot-layout-common.hh b/src/hb-ot-layout-common.hh
index 9a4157b..e8cea60 100644
--- a/src/hb-ot-layout-common.hh
+++ b/src/hb-ot-layout-common.hh
@@ -1337,7 +1337,7 @@
     return_trace (true);
   }
 
-  private:
+  protected:
   HBUINT16	lookupType;		/* Different enumerations for GSUB and GPOS */
   HBUINT16	lookupFlag;		/* Lookup qualifiers */
   Array16Of<Offset16>

src/hb-ot-layout-gsubgpos.hh

diff --git a/src/hb-ot-layout-gsubgpos.hh b/src/hb-ot-layout-gsubgpos.hh
index 9f27705..62d5d15 100644
--- a/src/hb-ot-layout-gsubgpos.hh
+++ b/src/hb-ot-layout-gsubgpos.hh
@@ -4006,7 +4006,7 @@
 {
   friend struct GSUBGPOS;
 
-  protected:
+  public: // TODO
   FixedVersion<>version;	/* Version of the GSUB/GPOS table--initially set
 				 * to 0x00010000u */
   typename Types:: template OffsetTo<ScriptList>

src/hb-repacker.hh

diff --git a/src/hb-repacker.hh b/src/hb-repacker.hh
index 173fe4a..acfb686 100644
--- a/src/hb-repacker.hh
+++ b/src/hb-repacker.hh
@@ -33,6 +33,7 @@
 #include "hb-serialize.hh"
 #include "hb-vector.hh"
 #include "graph/graph.hh"
+#include "graph/gsubgpos-graph.hh"
 #include "graph/serialize.hh"
 
 using graph::graph_t;
@@ -43,6 +44,19 @@
  */
 
 static inline
+void _make_extensions (graph_t& sorted_graph)
+{
+  // TODO: Move this into graph or gsubgpos graph?
+  hb_hashmap_t<unsigned, graph::Lookup*> lookups;
+  find_lookups (sorted_graph, lookups);
+
+  for (auto p : lookups.iter ())
+  {
+    p.second->make_extension (sorted_graph, p.first);
+  }
+}
+
+static inline
 bool _try_isolating_subgraphs (const hb_vector_t<graph::overflow_record_t>& overflows,
                                graph_t& sorted_graph)
 {
@@ -158,6 +172,7 @@
 hb_resolve_overflows (const T& packed,
                       hb_tag_t table_tag,
                       unsigned max_rounds = 20) {
+  printf("Resolving overflows!\n");
   graph_t sorted_graph (packed);
   sorted_graph.sort_shortest_distance ();
 
@@ -172,6 +187,7 @@
       && will_overflow)
   {
     DEBUG_MSG (SUBSET_REPACK, nullptr, "Assigning spaces to 32 bit subgraphs.");
+    _make_extensions (sorted_graph);
     if (sorted_graph.assign_spaces ())
       sorted_graph.sort_shortest_distance ();
   }