Adding upstream version 110.0.1.upstream/110.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 4473 insertions, 0 deletions

diff --git a/gfx/harfbuzz/src/hb-ot-layout-gsubgpos.hh b/gfx/harfbuzz/src/hb-ot-layout-gsubgpos.hh
new file mode 100644
index 0000000000..04ccefd108
--- /dev/null
+++ b/gfx/harfbuzz/src/hb-ot-layout-gsubgpos.hh
@@ -0,0 +1,4473 @@
+/*
+ * Copyright © 2007,2008,2009,2010  Red Hat, Inc.
+ * Copyright © 2010,2012  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
+ * all copies of this software.
+ *
+ * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
+ * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
+ * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
+ * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
+ * DAMAGE.
+ *
+ * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
+ * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
+ * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
+ * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
+ *
+ * Red Hat Author(s): Behdad Esfahbod
+ * Google Author(s): Behdad Esfahbod
+ */
+
+#ifndef HB_OT_LAYOUT_GSUBGPOS_HH
+#define HB_OT_LAYOUT_GSUBGPOS_HH
+
+#include "hb.hh"
+#include "hb-buffer.hh"
+#include "hb-map.hh"
+#include "hb-set.hh"
+#include "hb-ot-map.hh"
+#include "hb-ot-layout-common.hh"
+#include "hb-ot-layout-gdef-table.hh"
+
+
+namespace OT {
+
+
+struct hb_intersects_context_t :
+       hb_dispatch_context_t<hb_intersects_context_t, bool>
+{
+  template <typename T>
+  return_t dispatch (const T &obj) { return obj.intersects (this->glyphs); }
+  static return_t default_return_value () { return false; }
+  bool stop_sublookup_iteration (return_t r) const { return r; }
+
+  const hb_set_t *glyphs;
+
+  hb_intersects_context_t (const hb_set_t *glyphs_) :
+                            glyphs (glyphs_) {}
+};
+
+struct hb_have_non_1to1_context_t :
+       hb_dispatch_context_t<hb_have_non_1to1_context_t, bool>
+{
+  template <typename T>
+  return_t dispatch (const T &obj) { return obj.may_have_non_1to1 (); }
+  static return_t default_return_value () { return false; }
+  bool stop_sublookup_iteration (return_t r) const { return r; }
+};
+
+struct hb_closure_context_t :
+       hb_dispatch_context_t<hb_closure_context_t>
+{
+  typedef return_t (*recurse_func_t) (hb_closure_context_t *c, unsigned lookup_index, hb_set_t *covered_seq_indicies, unsigned seq_index, unsigned end_index);
+  template <typename T>
+  return_t dispatch (const T &obj) { obj.closure (this); return hb_empty_t (); }
+  static return_t default_return_value () { return hb_empty_t (); }
+  void recurse (unsigned lookup_index, hb_set_t *covered_seq_indicies, unsigned seq_index, unsigned end_index)
+  {
+    if (unlikely (nesting_level_left == 0 || !recurse_func))
+      return;
+
+    nesting_level_left--;
+    recurse_func (this, lookup_index, covered_seq_indicies, seq_index, end_index);
+    nesting_level_left++;
+  }
+
+  void reset_lookup_visit_count ()
+  { lookup_count = 0; }
+
+  bool lookup_limit_exceeded ()
+  { return lookup_count > HB_MAX_LOOKUP_VISIT_COUNT; }
+
+  bool should_visit_lookup (unsigned int lookup_index)
+  {
+    if (lookup_count++ > HB_MAX_LOOKUP_VISIT_COUNT)
+      return false;
+
+    if (is_lookup_done (lookup_index))
+      return false;
+
+    return true;
+  }
+
+  bool is_lookup_done (unsigned int lookup_index)
+  {
+    if (unlikely (done_lookups_glyph_count->in_error () ||
+		  done_lookups_glyph_set->in_error ()))
+      return true;
+
+    /* Have we visited this lookup with the current set of glyphs? */
+    if (done_lookups_glyph_count->get (lookup_index) != glyphs->get_population ())
+    {
+      done_lookups_glyph_count->set (lookup_index, glyphs->get_population ());
+
+      if (!done_lookups_glyph_set->has (lookup_index))
+      {
+	if (unlikely (!done_lookups_glyph_set->set (lookup_index, hb::unique_ptr<hb_set_t> {hb_set_create ()})))
+	  return true;
+      }
+
+      hb_set_clear (done_lookups_glyph_set->get (lookup_index));
+    }
+
+    hb_set_t *covered_glyph_set = done_lookups_glyph_set->get (lookup_index);
+    if (unlikely (covered_glyph_set->in_error ()))
+      return true;
+    if (parent_active_glyphs ().is_subset (*covered_glyph_set))
+      return true;
+
+    covered_glyph_set->union_ (parent_active_glyphs ());
+    return false;
+  }
+
+  const hb_set_t& previous_parent_active_glyphs () {
+    if (active_glyphs_stack.length <= 1)
+      return *glyphs;
+
+    return active_glyphs_stack[active_glyphs_stack.length - 2];
+  }
+
+  const hb_set_t& parent_active_glyphs ()
+  {
+    if (!active_glyphs_stack)
+      return *glyphs;
+
+    return active_glyphs_stack.tail ();
+  }
+
+  hb_set_t& push_cur_active_glyphs ()
+  {
+    return *active_glyphs_stack.push ();
+  }
+
+  bool pop_cur_done_glyphs ()
+  {
+    if (!active_glyphs_stack)
+      return false;
+
+    active_glyphs_stack.pop ();
+    return true;
+  }
+
+  hb_face_t *face;
+  hb_set_t *glyphs;
+  hb_set_t output[1];
+  hb_vector_t<hb_set_t> active_glyphs_stack;
+  recurse_func_t recurse_func = nullptr;
+  unsigned int nesting_level_left;
+
+  hb_closure_context_t (hb_face_t *face_,
+			hb_set_t *glyphs_,
+			hb_map_t *done_lookups_glyph_count_,
+			hb_hashmap_t<unsigned, hb::unique_ptr<hb_set_t>> *done_lookups_glyph_set_,
+			unsigned int nesting_level_left_ = HB_MAX_NESTING_LEVEL) :
+			  face (face_),
+			  glyphs (glyphs_),
+			  nesting_level_left (nesting_level_left_),
+			  done_lookups_glyph_count (done_lookups_glyph_count_),
+			  done_lookups_glyph_set (done_lookups_glyph_set_)
+  {}
+
+  ~hb_closure_context_t () { flush (); }
+
+  void set_recurse_func (recurse_func_t func) { recurse_func = func; }
+
+  void flush ()
+  {
+    output->del_range (face->get_num_glyphs (), HB_SET_VALUE_INVALID);	/* Remove invalid glyphs. */
+    glyphs->union_ (*output);
+    output->clear ();
+    active_glyphs_stack.pop ();
+    active_glyphs_stack.reset ();
+  }
+
+  private:
+  hb_map_t *done_lookups_glyph_count;
+  hb_hashmap_t<unsigned, hb::unique_ptr<hb_set_t>> *done_lookups_glyph_set;
+  unsigned int lookup_count = 0;
+};
+
+
+
+struct hb_closure_lookups_context_t :
+       hb_dispatch_context_t<hb_closure_lookups_context_t>
+{
+  typedef return_t (*recurse_func_t) (hb_closure_lookups_context_t *c, unsigned lookup_index);
+  template <typename T>
+  return_t dispatch (const T &obj) { obj.closure_lookups (this); return hb_empty_t (); }
+  static return_t default_return_value () { return hb_empty_t (); }
+  void recurse (unsigned lookup_index)
+  {
+    if (unlikely (nesting_level_left == 0 || !recurse_func))
+      return;
+
+    /* Return if new lookup was recursed to before. */
+    if (lookup_limit_exceeded ()
+        || visited_lookups->in_error ()
+        || visited_lookups->has (lookup_index))
+      // Don't increment lookup count here, that will be done in the call to closure_lookups()
+      // made by recurse_func.
+      return;
+
+    nesting_level_left--;
+    recurse_func (this, lookup_index);
+    nesting_level_left++;
+  }
+
+  void set_lookup_visited (unsigned lookup_index)
+  { visited_lookups->add (lookup_index); }
+
+  void set_lookup_inactive (unsigned lookup_index)
+  { inactive_lookups->add (lookup_index); }
+
+  bool lookup_limit_exceeded ()
+  {
+    bool ret = lookup_count > HB_MAX_LOOKUP_VISIT_COUNT;
+    if (ret)
+      DEBUG_MSG (SUBSET, nullptr, "lookup visit count limit exceeded in lookup closure!");
+    return ret; }
+
+  bool is_lookup_visited (unsigned lookup_index)
+  {
+    if (unlikely (lookup_count++ > HB_MAX_LOOKUP_VISIT_COUNT))
+    {
+      DEBUG_MSG (SUBSET, nullptr, "total visited lookup count %u exceeds max limit, lookup %u is dropped.",
+                 lookup_count, lookup_index);
+      return true;
+    }
+
+    if (unlikely (visited_lookups->in_error ()))
+      return true;
+
+    return visited_lookups->has (lookup_index);
+  }
+
+  hb_face_t *face;
+  const hb_set_t *glyphs;
+  recurse_func_t recurse_func;
+  unsigned int nesting_level_left;
+
+  hb_closure_lookups_context_t (hb_face_t *face_,
+				const hb_set_t *glyphs_,
+				hb_set_t *visited_lookups_,
+				hb_set_t *inactive_lookups_,
+				unsigned nesting_level_left_ = HB_MAX_NESTING_LEVEL) :
+				face (face_),
+				glyphs (glyphs_),
+				recurse_func (nullptr),
+				nesting_level_left (nesting_level_left_),
+				visited_lookups (visited_lookups_),
+				inactive_lookups (inactive_lookups_),
+				lookup_count (0) {}
+
+  void set_recurse_func (recurse_func_t func) { recurse_func = func; }
+
+  private:
+  hb_set_t *visited_lookups;
+  hb_set_t *inactive_lookups;
+  unsigned int lookup_count;
+};
+
+struct hb_would_apply_context_t :
+       hb_dispatch_context_t<hb_would_apply_context_t, bool>
+{
+  template <typename T>
+  return_t dispatch (const T &obj) { return obj.would_apply (this); }
+  static return_t default_return_value () { return false; }
+  bool stop_sublookup_iteration (return_t r) const { return r; }
+
+  hb_face_t *face;
+  const hb_codepoint_t *glyphs;
+  unsigned int len;
+  bool zero_context;
+
+  hb_would_apply_context_t (hb_face_t *face_,
+			    const hb_codepoint_t *glyphs_,
+			    unsigned int len_,
+			    bool zero_context_) :
+			      face (face_),
+			      glyphs (glyphs_),
+			      len (len_),
+			      zero_context (zero_context_) {}
+};
+
+struct hb_collect_glyphs_context_t :
+       hb_dispatch_context_t<hb_collect_glyphs_context_t>
+{
+  typedef return_t (*recurse_func_t) (hb_collect_glyphs_context_t *c, unsigned int lookup_index);
+  template <typename T>
+  return_t dispatch (const T &obj) { obj.collect_glyphs (this); return hb_empty_t (); }
+  static return_t default_return_value () { return hb_empty_t (); }
+  void recurse (unsigned int lookup_index)
+  {
+    if (unlikely (nesting_level_left == 0 || !recurse_func))
+      return;
+
+    /* Note that GPOS sets recurse_func to nullptr already, so it doesn't get
+     * past the previous check.  For GSUB, we only want to collect the output
+     * glyphs in the recursion.  If output is not requested, we can go home now.
+     *
+     * Note further, that the above is not exactly correct.  A recursed lookup
+     * is allowed to match input that is not matched in the context, but that's
+     * not how most fonts are built.  It's possible to relax that and recurse
+     * with all sets here if it proves to be an issue.
+     */
+
+    if (output == hb_set_get_empty ())
+      return;
+
+    /* Return if new lookup was recursed to before. */
+    if (recursed_lookups->has (lookup_index))
+      return;
+
+    hb_set_t *old_before = before;
+    hb_set_t *old_input  = input;
+    hb_set_t *old_after  = after;
+    before = input = after = hb_set_get_empty ();
+
+    nesting_level_left--;
+    recurse_func (this, lookup_index);
+    nesting_level_left++;
+
+    before = old_before;
+    input  = old_input;
+    after  = old_after;
+
+    recursed_lookups->add (lookup_index);
+  }
+
+  hb_face_t *face;
+  hb_set_t *before;
+  hb_set_t *input;
+  hb_set_t *after;
+  hb_set_t *output;
+  recurse_func_t recurse_func;
+  hb_set_t *recursed_lookups;
+  unsigned int nesting_level_left;
+
+  hb_collect_glyphs_context_t (hb_face_t *face_,
+			       hb_set_t  *glyphs_before, /* OUT.  May be NULL */
+			       hb_set_t  *glyphs_input,  /* OUT.  May be NULL */
+			       hb_set_t  *glyphs_after,  /* OUT.  May be NULL */
+			       hb_set_t  *glyphs_output, /* OUT.  May be NULL */
+			       unsigned int nesting_level_left_ = HB_MAX_NESTING_LEVEL) :
+			      face (face_),
+			      before (glyphs_before ? glyphs_before : hb_set_get_empty ()),
+			      input  (glyphs_input  ? glyphs_input  : hb_set_get_empty ()),
+			      after  (glyphs_after  ? glyphs_after  : hb_set_get_empty ()),
+			      output (glyphs_output ? glyphs_output : hb_set_get_empty ()),
+			      recurse_func (nullptr),
+			      recursed_lookups (hb_set_create ()),
+			      nesting_level_left (nesting_level_left_) {}
+  ~hb_collect_glyphs_context_t () { hb_set_destroy (recursed_lookups); }
+
+  void set_recurse_func (recurse_func_t func) { recurse_func = func; }
+};
+
+
+
+template <typename set_t>
+struct hb_collect_coverage_context_t :
+       hb_dispatch_context_t<hb_collect_coverage_context_t<set_t>, const Coverage &>
+{
+  typedef const Coverage &return_t; // Stoopid that we have to dupe this here.
+  template <typename T>
+  return_t dispatch (const T &obj) { return obj.get_coverage (); }
+  static return_t default_return_value () { return Null (Coverage); }
+  bool stop_sublookup_iteration (return_t r) const
+  {
+    r.collect_coverage (set);
+    return false;
+  }
+
+  hb_collect_coverage_context_t (set_t *set_) :
+				   set (set_) {}
+
+  set_t *set;
+};
+
+struct hb_ot_apply_context_t :
+       hb_dispatch_context_t<hb_ot_apply_context_t, bool, HB_DEBUG_APPLY>
+{
+  struct matcher_t
+  {
+    matcher_t () :
+	     lookup_props (0),
+	     mask (-1),
+	     ignore_zwnj (false),
+	     ignore_zwj (false),
+	     per_syllable (false),
+	     syllable {0},
+	     match_func (nullptr),
+	     match_data (nullptr) {}
+
+    typedef bool (*match_func_t) (hb_glyph_info_t &info, unsigned value, const void *data);
+
+    void set_ignore_zwnj (bool ignore_zwnj_) { ignore_zwnj = ignore_zwnj_; }
+    void set_ignore_zwj (bool ignore_zwj_) { ignore_zwj = ignore_zwj_; }
+    void set_lookup_props (unsigned int lookup_props_) { lookup_props = lookup_props_; }
+    void set_mask (hb_mask_t mask_) { mask = mask_; }
+    void set_per_syllable (bool per_syllable_) { per_syllable = per_syllable_; }
+    void set_syllable (uint8_t syllable_)  { syllable = per_syllable ? syllable_ : 0; }
+    void set_match_func (match_func_t match_func_,
+			 const void *match_data_)
+    { match_func = match_func_; match_data = match_data_; }
+
+    enum may_match_t {
+      MATCH_NO,
+      MATCH_YES,
+      MATCH_MAYBE
+    };
+
+    may_match_t may_match (hb_glyph_info_t &info,
+			   hb_codepoint_t glyph_data) const
+    {
+      if (!(info.mask & mask) ||
+	  (syllable && syllable != info.syllable ()))
+	return MATCH_NO;
+
+      if (match_func)
+	return match_func (info, glyph_data, match_data) ? MATCH_YES : MATCH_NO;
+
+      return MATCH_MAYBE;
+    }
+
+    enum may_skip_t {
+      SKIP_NO,
+      SKIP_YES,
+      SKIP_MAYBE
+    };
+
+    may_skip_t may_skip (const hb_ot_apply_context_t *c,
+			 const hb_glyph_info_t       &info) const
+    {
+      if (!c->check_glyph_property (&info, lookup_props))
+	return SKIP_YES;
+
+      if (unlikely (_hb_glyph_info_is_default_ignorable_and_not_hidden (&info) &&
+		    (ignore_zwnj || !_hb_glyph_info_is_zwnj (&info)) &&
+		    (ignore_zwj || !_hb_glyph_info_is_zwj (&info))))
+	return SKIP_MAYBE;
+
+      return SKIP_NO;
+    }
+
+    protected:
+    unsigned int lookup_props;
+    hb_mask_t mask;
+    bool ignore_zwnj;
+    bool ignore_zwj;
+    bool per_syllable;
+    uint8_t syllable;
+    match_func_t match_func;
+    const void *match_data;
+  };
+
+  struct skipping_iterator_t
+  {
+    void init (hb_ot_apply_context_t *c_, bool context_match = false)
+    {
+      c = c_;
+      match_glyph_data16 = nullptr;
+#ifndef HB_NO_BEYOND_64K
+      match_glyph_data24 = nullptr;
+#endif
+      matcher.set_match_func (nullptr, nullptr);
+      matcher.set_lookup_props (c->lookup_props);
+      /* Ignore ZWNJ if we are matching GPOS, or matching GSUB context and asked to. */
+      matcher.set_ignore_zwnj (c->table_index == 1 || (context_match && c->auto_zwnj));
+      /* Ignore ZWJ if we are matching context, or asked to. */
+      matcher.set_ignore_zwj  (context_match || c->auto_zwj);
+      matcher.set_mask (context_match ? -1 : c->lookup_mask);
+      matcher.set_per_syllable (c->per_syllable);
+    }
+    void set_lookup_props (unsigned int lookup_props)
+    {
+      matcher.set_lookup_props (lookup_props);
+    }
+    void set_match_func (matcher_t::match_func_t match_func_,
+			 const void *match_data_)
+    {
+      matcher.set_match_func (match_func_, match_data_);
+    }
+    void set_glyph_data (const HBUINT16 glyph_data[])
+    {
+      match_glyph_data16 = glyph_data;
+#ifndef HB_NO_BEYOND_64K
+      match_glyph_data24 = nullptr;
+#endif
+    }
+#ifndef HB_NO_BEYOND_64K
+    void set_glyph_data (const HBUINT24 glyph_data[])
+    {
+      match_glyph_data16 = nullptr;
+      match_glyph_data24 = glyph_data;
+    }
+#endif
+
+    void reset (unsigned int start_index_,
+		unsigned int num_items_)
+    {
+      idx = start_index_;
+      num_items = num_items_;
+      end = c->buffer->len;
+      matcher.set_syllable (start_index_ == c->buffer->idx ? c->buffer->cur().syllable () : 0);
+    }
+
+    void reject ()
+    {
+      num_items++;
+      backup_glyph_data ();
+    }
+
+    matcher_t::may_skip_t
+    may_skip (const hb_glyph_info_t &info) const
+    { return matcher.may_skip (c, info); }
+
+    bool next (unsigned *unsafe_to = nullptr)
+    {
+      assert (num_items > 0);
+      /* The alternate condition below is faster at string boundaries,
+       * but produces subpar "unsafe-to-concat" values. */
+      signed stop = (signed) end - (signed) num_items;
+      if (c->buffer->flags & HB_BUFFER_FLAG_PRODUCE_UNSAFE_TO_CONCAT)
+        stop = (signed) end - 1;
+      while ((signed) idx < stop)
+      {
+	idx++;
+	hb_glyph_info_t &info = c->buffer->info[idx];
+
+	matcher_t::may_skip_t skip = matcher.may_skip (c, info);
+	if (unlikely (skip == matcher_t::SKIP_YES))
+	  continue;
+
+	matcher_t::may_match_t match = matcher.may_match (info, get_glyph_data ());
+	if (match == matcher_t::MATCH_YES ||
+	    (match == matcher_t::MATCH_MAYBE &&
+	     skip == matcher_t::SKIP_NO))
+	{
+	  num_items--;
+	  advance_glyph_data ();
+	  return true;
+	}
+
+	if (skip == matcher_t::SKIP_NO)
+	{
+	  if (unsafe_to)
+	    *unsafe_to = idx + 1;
+	  return false;
+	}
+      }
+      if (unsafe_to)
+        *unsafe_to = end;
+      return false;
+    }
+    bool prev (unsigned *unsafe_from = nullptr)
+    {
+      assert (num_items > 0);
+      /* The alternate condition below is faster at string boundaries,
+       * but produces subpar "unsafe-to-concat" values. */
+      unsigned stop = num_items - 1;
+      if (c->buffer->flags & HB_BUFFER_FLAG_PRODUCE_UNSAFE_TO_CONCAT)
+        stop = 1 - 1;
+      while (idx > stop)
+      {
+	idx--;
+	hb_glyph_info_t &info = c->buffer->out_info[idx];
+
+	matcher_t::may_skip_t skip = matcher.may_skip (c, info);
+	if (unlikely (skip == matcher_t::SKIP_YES))
+	  continue;
+
+	matcher_t::may_match_t match = matcher.may_match (info, get_glyph_data ());
+	if (match == matcher_t::MATCH_YES ||
+	    (match == matcher_t::MATCH_MAYBE &&
+	     skip == matcher_t::SKIP_NO))
+	{
+	  num_items--;
+	  advance_glyph_data ();
+	  return true;
+	}
+
+	if (skip == matcher_t::SKIP_NO)
+	{
+	  if (unsafe_from)
+	    *unsafe_from = hb_max (1u, idx) - 1u;
+	  return false;
+	}
+      }
+      if (unsafe_from)
+        *unsafe_from = 0;
+      return false;
+    }
+
+    hb_codepoint_t
+    get_glyph_data ()
+    {
+      if (match_glyph_data16) return *match_glyph_data16;
+#ifndef HB_NO_BEYOND_64K
+      else
+      if (match_glyph_data24) return *match_glyph_data24;
+#endif
+      return 0;
+    }
+    void
+    advance_glyph_data ()
+    {
+      if (match_glyph_data16) match_glyph_data16++;
+#ifndef HB_NO_BEYOND_64K
+      else
+      if (match_glyph_data24) match_glyph_data24++;
+#endif
+    }
+    void
+    backup_glyph_data ()
+    {
+      if (match_glyph_data16) match_glyph_data16--;
+#ifndef HB_NO_BEYOND_64K
+      else
+      if (match_glyph_data24) match_glyph_data24--;
+#endif
+    }
+
+    unsigned int idx;
+    protected:
+    hb_ot_apply_context_t *c;
+    matcher_t matcher;
+    const HBUINT16 *match_glyph_data16;
+#ifndef HB_NO_BEYOND_64K
+    const HBUINT24 *match_glyph_data24;
+#endif
+
+    unsigned int num_items;
+    unsigned int end;
+  };
+
+
+  const char *get_name () { return "APPLY"; }
+  typedef return_t (*recurse_func_t) (hb_ot_apply_context_t *c, unsigned int lookup_index);
+  template <typename T>
+  return_t dispatch (const T &obj) { return obj.apply (this); }
+  static return_t default_return_value () { return false; }
+  bool stop_sublookup_iteration (return_t r) const { return r; }
+  return_t recurse (unsigned int sub_lookup_index)
+  {
+    if (unlikely (nesting_level_left == 0 || !recurse_func || buffer->max_ops-- <= 0))
+    {
+      buffer->shaping_failed = true;
+      return default_return_value ();
+    }
+
+    nesting_level_left--;
+    bool ret = recurse_func (this, sub_lookup_index);
+    nesting_level_left++;
+    return ret;
+  }
+
+  skipping_iterator_t iter_input, iter_context;
+
+  unsigned int table_index; /* GSUB/GPOS */
+  hb_font_t *font;
+  hb_face_t *face;
+  hb_buffer_t *buffer;
+  recurse_func_t recurse_func = nullptr;
+  const GDEF &gdef;
+  const VariationStore &var_store;
+  VariationStore::cache_t *var_store_cache;
+  hb_set_digest_t digest;
+
+  hb_direction_t direction;
+  hb_mask_t lookup_mask = 1;
+  unsigned int lookup_index = (unsigned) -1;
+  unsigned int lookup_props = 0;
+  unsigned int nesting_level_left = HB_MAX_NESTING_LEVEL;
+
+  bool has_glyph_classes;
+  bool auto_zwnj = true;
+  bool auto_zwj = true;
+  bool per_syllable = false;
+  bool random = false;
+  uint32_t random_state = 1;
+  unsigned new_syllables = (unsigned) -1;
+
+  hb_ot_apply_context_t (unsigned int table_index_,
+			 hb_font_t *font_,
+			 hb_buffer_t *buffer_) :
+			table_index (table_index_),
+			font (font_), face (font->face), buffer (buffer_),
+			gdef (
+#ifndef HB_NO_OT_LAYOUT
+			      *face->table.GDEF->table
+#else
+			      Null (GDEF)
+#endif
+			     ),
+			var_store (gdef.get_var_store ()),
+			var_store_cache (
+#ifndef HB_NO_VAR
+					 table_index == 1 && font->num_coords ? var_store.create_cache () : nullptr
+#else
+					 nullptr
+#endif
+					),
+			digest (buffer_->digest ()),
+			direction (buffer_->props.direction),
+			has_glyph_classes (gdef.has_glyph_classes ())
+  { init_iters (); }
+
+  ~hb_ot_apply_context_t ()
+  {
+#ifndef HB_NO_VAR
+    VariationStore::destroy_cache (var_store_cache);
+#endif
+  }
+
+  void init_iters ()
+  {
+    iter_input.init (this, false);
+    iter_context.init (this, true);
+  }
+
+  void set_lookup_mask (hb_mask_t mask) { lookup_mask = mask; init_iters (); }
+  void set_auto_zwj (bool auto_zwj_) { auto_zwj = auto_zwj_; init_iters (); }
+  void set_auto_zwnj (bool auto_zwnj_) { auto_zwnj = auto_zwnj_; init_iters (); }
+  void set_per_syllable (bool per_syllable_) { per_syllable = per_syllable_; init_iters (); }
+  void set_random (bool random_) { random = random_; }
+  void set_recurse_func (recurse_func_t func) { recurse_func = func; }
+  void set_lookup_index (unsigned int lookup_index_) { lookup_index = lookup_index_; }
+  void set_lookup_props (unsigned int lookup_props_) { lookup_props = lookup_props_; init_iters (); }
+
+  uint32_t random_number ()
+  {
+    /* http://www.cplusplus.com/reference/random/minstd_rand/ */
+    random_state = random_state * 48271 % 2147483647;
+    return random_state;
+  }
+
+  bool match_properties_mark (hb_codepoint_t  glyph,
+			      unsigned int    glyph_props,
+			      unsigned int    match_props) const
+  {
+    /* If using mark filtering sets, the high short of
+     * match_props has the set index.
+     */
+    if (match_props & LookupFlag::UseMarkFilteringSet)
+      return gdef.mark_set_covers (match_props >> 16, glyph);
+
+    /* The second byte of match_props has the meaning
+     * "ignore marks of attachment type different than
+     * the attachment type specified."
+     */
+    if (match_props & LookupFlag::MarkAttachmentType)
+      return (match_props & LookupFlag::MarkAttachmentType) == (glyph_props & LookupFlag::MarkAttachmentType);
+
+    return true;
+  }
+
+  bool check_glyph_property (const hb_glyph_info_t *info,
+			     unsigned int  match_props) const
+  {
+    hb_codepoint_t glyph = info->codepoint;
+    unsigned int glyph_props = _hb_glyph_info_get_glyph_props (info);
+
+    /* Not covered, if, for example, glyph class is ligature and
+     * match_props includes LookupFlags::IgnoreLigatures
+     */
+    if (glyph_props & match_props & LookupFlag::IgnoreFlags)
+      return false;
+
+    if (unlikely (glyph_props & HB_OT_LAYOUT_GLYPH_PROPS_MARK))
+      return match_properties_mark (glyph, glyph_props, match_props);
+
+    return true;
+  }
+
+  void _set_glyph_class (hb_codepoint_t glyph_index,
+			  unsigned int class_guess = 0,
+			  bool ligature = false,
+			  bool component = false)
+  {
+    digest.add (glyph_index);
+
+    if (new_syllables != (unsigned) -1)
+      buffer->cur().syllable() = new_syllables;
+
+    unsigned int props = _hb_glyph_info_get_glyph_props (&buffer->cur());
+    props |= HB_OT_LAYOUT_GLYPH_PROPS_SUBSTITUTED;
+    if (ligature)
+    {
+      props |= HB_OT_LAYOUT_GLYPH_PROPS_LIGATED;
+      /* In the only place that the MULTIPLIED bit is used, Uniscribe
+       * seems to only care about the "last" transformation between
+       * Ligature and Multiple substitutions.  Ie. if you ligate, expand,
+       * and ligate again, it forgives the multiplication and acts as
+       * if only ligation happened.  As such, clear MULTIPLIED bit.
+       */
+      props &= ~HB_OT_LAYOUT_GLYPH_PROPS_MULTIPLIED;
+    }
+    if (component)
+      props |= HB_OT_LAYOUT_GLYPH_PROPS_MULTIPLIED;
+    if (likely (has_glyph_classes))
+    {
+      props &= HB_OT_LAYOUT_GLYPH_PROPS_PRESERVE;
+      _hb_glyph_info_set_glyph_props (&buffer->cur(), props | gdef.get_glyph_props (glyph_index));
+    }
+    else if (class_guess)
+    {
+      props &= HB_OT_LAYOUT_GLYPH_PROPS_PRESERVE;
+      _hb_glyph_info_set_glyph_props (&buffer->cur(), props | class_guess);
+    }
+    else
+      _hb_glyph_info_set_glyph_props (&buffer->cur(), props);
+  }
+
+  void replace_glyph (hb_codepoint_t glyph_index)
+  {
+    _set_glyph_class (glyph_index);
+    (void) buffer->replace_glyph (glyph_index);
+  }
+  void replace_glyph_inplace (hb_codepoint_t glyph_index)
+  {
+    _set_glyph_class (glyph_index);
+    buffer->cur().codepoint = glyph_index;
+  }
+  void replace_glyph_with_ligature (hb_codepoint_t glyph_index,
+				    unsigned int class_guess)
+  {
+    _set_glyph_class (glyph_index, class_guess, true);
+    (void) buffer->replace_glyph (glyph_index);
+  }
+  void output_glyph_for_component (hb_codepoint_t glyph_index,
+				   unsigned int class_guess)
+  {
+    _set_glyph_class (glyph_index, class_guess, false, true);
+    (void) buffer->output_glyph (glyph_index);
+  }
+};
+
+
+struct hb_accelerate_subtables_context_t :
+       hb_dispatch_context_t<hb_accelerate_subtables_context_t>
+{
+  template <typename Type>
+  static inline bool apply_to (const void *obj, hb_ot_apply_context_t *c)
+  {
+    const Type *typed_obj = (const Type *) obj;
+    return typed_obj->apply (c);
+  }
+
+#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
+  template <typename T>
+  static inline auto apply_cached_ (const T *obj, hb_ot_apply_context_t *c, hb_priority<1>) HB_RETURN (bool, obj->apply (c, true) )
+  template <typename T>
+  static inline auto apply_cached_ (const T *obj, hb_ot_apply_context_t *c, hb_priority<0>) HB_RETURN (bool, obj->apply (c) )
+  template <typename Type>
+  static inline bool apply_cached_to (const void *obj, hb_ot_apply_context_t *c)
+  {
+    const Type *typed_obj = (const Type *) obj;
+    return apply_cached_ (typed_obj, c, hb_prioritize);
+  }
+
+  template <typename T>
+  static inline auto cache_func_ (const T *obj, hb_ot_apply_context_t *c, bool enter, hb_priority<1>) HB_RETURN (bool, obj->cache_func (c, enter) )
+  template <typename T>
+  static inline bool cache_func_ (const T *obj, hb_ot_apply_context_t *c, bool enter, hb_priority<0>) { return false; }
+  template <typename Type>
+  static inline bool cache_func_to (const void *obj, hb_ot_apply_context_t *c, bool enter)
+  {
+    const Type *typed_obj = (const Type *) obj;
+    return cache_func_ (typed_obj, c, enter, hb_prioritize);
+  }
+#endif
+
+  typedef bool (*hb_apply_func_t) (const void *obj, hb_ot_apply_context_t *c);
+  typedef bool (*hb_cache_func_t) (const void *obj, hb_ot_apply_context_t *c, bool enter);
+
+  struct hb_applicable_t
+  {
+    friend struct hb_accelerate_subtables_context_t;
+    friend struct hb_ot_layout_lookup_accelerator_t;
+
+    template <typename T>
+    void init (const T &obj_,
+	       hb_apply_func_t apply_func_
+#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
+	       , hb_apply_func_t apply_cached_func_
+	       , hb_cache_func_t cache_func_
+#endif
+		)
+    {
+      obj = &obj_;
+      apply_func = apply_func_;
+#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
+      apply_cached_func = apply_cached_func_;
+      cache_func = cache_func_;
+#endif
+      digest.init ();
+      obj_.get_coverage ().collect_coverage (&digest);
+    }
+
+    bool apply (hb_ot_apply_context_t *c) const
+    {
+      return digest.may_have (c->buffer->cur().codepoint) && apply_func (obj, c);
+    }
+#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
+    bool apply_cached (hb_ot_apply_context_t *c) const
+    {
+      return digest.may_have (c->buffer->cur().codepoint) &&  apply_cached_func (obj, c);
+    }
+    bool cache_enter (hb_ot_apply_context_t *c) const
+    {
+      return cache_func (obj, c, true);
+    }
+    void cache_leave (hb_ot_apply_context_t *c) const
+    {
+      cache_func (obj, c, false);
+    }
+#endif
+
+    private:
+    const void *obj;
+    hb_apply_func_t apply_func;
+#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
+    hb_apply_func_t apply_cached_func;
+    hb_cache_func_t cache_func;
+#endif
+    hb_set_digest_t digest;
+  };
+
+  typedef hb_vector_t<hb_applicable_t> array_t;
+
+#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
+  template <typename T>
+  auto cache_cost (const T &obj, hb_priority<1>) HB_AUTO_RETURN ( obj.cache_cost () )
+  template <typename T>
+  auto cache_cost (const T &obj, hb_priority<0>) HB_AUTO_RETURN ( 0u )
+#endif
+
+  /* Dispatch interface. */
+  template <typename T>
+  return_t dispatch (const T &obj)
+  {
+    hb_applicable_t entry;
+
+    entry.init (obj,
+		apply_to<T>
+#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
+		, apply_cached_to<T>
+		, cache_func_to<T>
+#endif
+		);
+
+    array.push (entry);
+
+#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
+    /* Cache handling
+     *
+     * We allow one subtable from each lookup to use a cache. The assumption
+     * being that multiple subtables of the same lookup cannot use a cache
+     * because the resources they would use will collide.  As such, we ask
+     * each subtable to tell us how much it costs (which a cache would avoid),
+     * and we allocate the cache opportunity to the costliest subtable.
+     */
+    unsigned cost = cache_cost (obj, hb_prioritize);
+    if (cost > cache_user_cost && !array.in_error ())
+    {
+      cache_user_idx = array.length - 1;
+      cache_user_cost = cost;
+    }
+#endif
+
+    return hb_empty_t ();
+  }
+  static return_t default_return_value () { return hb_empty_t (); }
+
+  hb_accelerate_subtables_context_t (array_t &array_) :
+				     array (array_) {}
+
+  array_t &array;
+
+#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
+  unsigned cache_user_idx = (unsigned) -1;
+  unsigned cache_user_cost = 0;
+#endif
+};
+
+
+typedef bool (*intersects_func_t) (const hb_set_t *glyphs, unsigned value, const void *data, void *cache);
+typedef void (*intersected_glyphs_func_t) (const hb_set_t *glyphs, const void *data, unsigned value, hb_set_t *intersected_glyphs, void *cache);
+typedef void (*collect_glyphs_func_t) (hb_set_t *glyphs, unsigned value, const void *data);
+typedef bool (*match_func_t) (hb_glyph_info_t &info, unsigned value, const void *data);
+
+struct ContextClosureFuncs
+{
+  intersects_func_t intersects;
+  intersected_glyphs_func_t intersected_glyphs;
+};
+struct ContextCollectGlyphsFuncs
+{
+  collect_glyphs_func_t collect;
+};
+struct ContextApplyFuncs
+{
+  match_func_t match;
+};
+struct ChainContextApplyFuncs
+{
+  match_func_t match[3];
+};
+
+
+static inline bool intersects_glyph (const hb_set_t *glyphs, unsigned value, const void *data HB_UNUSED, void *cache HB_UNUSED)
+{
+  return glyphs->has (value);
+}
+static inline bool intersects_class (const hb_set_t *glyphs, unsigned value, const void *data, void *cache)
+{
+  const ClassDef &class_def = *reinterpret_cast<const ClassDef *>(data);
+  hb_map_t *map = (hb_map_t *) cache;
+
+  hb_codepoint_t *cached_v;
+  if (map->has (value, &cached_v))
+    return *cached_v;
+
+  bool v = class_def.intersects_class (glyphs, value);
+  map->set (value, v);
+
+  return v;
+}
+static inline bool intersects_coverage (const hb_set_t *glyphs, unsigned value, const void *data, void *cache HB_UNUSED)
+{
+  Offset16To<Coverage> coverage;
+  coverage = value;
+  return (data+coverage).intersects (glyphs);
+}
+
+
+static inline void intersected_glyph (const hb_set_t *glyphs HB_UNUSED, const void *data, unsigned value, hb_set_t *intersected_glyphs, HB_UNUSED void *cache)
+{
+  unsigned g = reinterpret_cast<const HBUINT16 *>(data)[value];
+  intersected_glyphs->add (g);
+}
+
+using intersected_class_cache_t = hb_hashmap_t<unsigned, hb_set_t>;
+
+static inline void intersected_class_glyphs (const hb_set_t *glyphs, const void *data, unsigned value, hb_set_t *intersected_glyphs, void *cache)
+{
+  const ClassDef &class_def = *reinterpret_cast<const ClassDef *>(data);
+
+  intersected_class_cache_t *map = (intersected_class_cache_t *) cache;
+
+  hb_set_t *cached_v;
+  if (map->has (value, &cached_v))
+  {
+    intersected_glyphs->union_ (*cached_v);
+    return;
+  }
+
+  hb_set_t v;
+  class_def.intersected_class_glyphs (glyphs, value, &v);
+
+  intersected_glyphs->union_ (v);
+
+  map->set (value, std::move (v));
+}
+
+static inline void intersected_coverage_glyphs (const hb_set_t *glyphs, const void *data, unsigned value, hb_set_t *intersected_glyphs, HB_UNUSED void *cache)
+{
+  Offset16To<Coverage> coverage;
+  coverage = value;
+  (data+coverage).intersect_set (*glyphs, *intersected_glyphs);
+}
+
+
+template <typename HBUINT>
+static inline bool array_is_subset_of (const hb_set_t *glyphs,
+				       unsigned int count,
+				       const HBUINT values[],
+				       intersects_func_t intersects_func,
+				       const void *intersects_data,
+				       void *cache)
+{
+  for (const auto &_ : + hb_iter (values, count))
+    if (!intersects_func (glyphs, _, intersects_data, cache)) return false;
+  return true;
+}
+
+
+static inline void collect_glyph (hb_set_t *glyphs, unsigned value, const void *data HB_UNUSED)
+{
+  glyphs->add (value);
+}
+static inline void collect_class (hb_set_t *glyphs, unsigned value, const void *data)
+{
+  const ClassDef &class_def = *reinterpret_cast<const ClassDef *>(data);
+  class_def.collect_class (glyphs, value);
+}
+static inline void collect_coverage (hb_set_t *glyphs, unsigned value, const void *data)
+{
+  Offset16To<Coverage> coverage;
+  coverage = value;
+  (data+coverage).collect_coverage (glyphs);
+}
+template <typename HBUINT>
+static inline void collect_array (hb_collect_glyphs_context_t *c HB_UNUSED,
+				  hb_set_t *glyphs,
+				  unsigned int count,
+				  const HBUINT values[],
+				  collect_glyphs_func_t collect_func,
+				  const void *collect_data)
+{
+  return
+  + hb_iter (values, count)
+  | hb_apply ([&] (const HBUINT &_) { collect_func (glyphs, _, collect_data); })
+  ;
+}
+
+
+static inline bool match_glyph (hb_glyph_info_t &info, unsigned value, const void *data HB_UNUSED)
+{
+  return info.codepoint == value;
+}
+static inline bool match_class (hb_glyph_info_t &info, unsigned value, const void *data)
+{
+  const ClassDef &class_def = *reinterpret_cast<const ClassDef *>(data);
+  return class_def.get_class (info.codepoint) == value;
+}
+static inline bool match_class_cached (hb_glyph_info_t &info, unsigned value, const void *data)
+{
+  unsigned klass = info.syllable();
+  if (klass < 255)
+    return klass == value;
+  const ClassDef &class_def = *reinterpret_cast<const ClassDef *>(data);
+  klass = class_def.get_class (info.codepoint);
+  if (likely (klass < 255))
+    info.syllable() = klass;
+  return klass == value;
+}
+static inline bool match_coverage (hb_glyph_info_t &info, unsigned value, const void *data)
+{
+  Offset16To<Coverage> coverage;
+  coverage = value;
+  return (data+coverage).get_coverage (info.codepoint) != NOT_COVERED;
+}
+
+template <typename HBUINT>
+static inline bool would_match_input (hb_would_apply_context_t *c,
+				      unsigned int count, /* Including the first glyph (not matched) */
+				      const HBUINT input[], /* Array of input values--start with second glyph */
+				      match_func_t match_func,
+				      const void *match_data)
+{
+  if (count != c->len)
+    return false;
+
+  for (unsigned int i = 1; i < count; i++)
+  {
+    hb_glyph_info_t info;
+    info.codepoint = c->glyphs[i];
+    if (likely (!match_func (info, input[i - 1], match_data)))
+      return false;
+  }
+
+  return true;
+}
+template <typename HBUINT>
+static inline bool match_input (hb_ot_apply_context_t *c,
+				unsigned int count, /* Including the first glyph (not matched) */
+				const HBUINT input[], /* Array of input values--start with second glyph */
+				match_func_t match_func,
+				const void *match_data,
+				unsigned int *end_position,
+				unsigned int match_positions[HB_MAX_CONTEXT_LENGTH],
+				unsigned int *p_total_component_count = nullptr)
+{
+  TRACE_APPLY (nullptr);
+
+  if (unlikely (count > HB_MAX_CONTEXT_LENGTH)) return_trace (false);
+
+  hb_buffer_t *buffer = c->buffer;
+
+  hb_ot_apply_context_t::skipping_iterator_t &skippy_iter = c->iter_input;
+  skippy_iter.reset (buffer->idx, count - 1);
+  skippy_iter.set_match_func (match_func, match_data);
+  skippy_iter.set_glyph_data (input);
+
+  /*
+   * This is perhaps the trickiest part of OpenType...  Remarks:
+   *
+   * - If all components of the ligature were marks, we call this a mark ligature.
+   *
+   * - If there is no GDEF, and the ligature is NOT a mark ligature, we categorize
+   *   it as a ligature glyph.
+   *
+   * - Ligatures cannot be formed across glyphs attached to different components
+   *   of previous ligatures.  Eg. the sequence is LAM,SHADDA,LAM,FATHA,HEH, and
+   *   LAM,LAM,HEH form a ligature, leaving SHADDA,FATHA next to eachother.
+   *   However, it would be wrong to ligate that SHADDA,FATHA sequence.
+   *   There are a couple of exceptions to this:
+   *
+   *   o If a ligature tries ligating with marks that belong to it itself, go ahead,
+   *     assuming that the font designer knows what they are doing (otherwise it can
+   *     break Indic stuff when a matra wants to ligate with a conjunct,
+   *
+   *   o If two marks want to ligate and they belong to different components of the
+   *     same ligature glyph, and said ligature glyph is to be ignored according to
+   *     mark-filtering rules, then allow.
+   *     https://github.com/harfbuzz/harfbuzz/issues/545
+   */
+
+  unsigned int total_component_count = 0;
+  total_component_count += _hb_glyph_info_get_lig_num_comps (&buffer->cur());
+
+  unsigned int first_lig_id = _hb_glyph_info_get_lig_id (&buffer->cur());
+  unsigned int first_lig_comp = _hb_glyph_info_get_lig_comp (&buffer->cur());
+
+  enum {
+    LIGBASE_NOT_CHECKED,
+    LIGBASE_MAY_NOT_SKIP,
+    LIGBASE_MAY_SKIP
+  } ligbase = LIGBASE_NOT_CHECKED;
+
+  match_positions[0] = buffer->idx;
+  for (unsigned int i = 1; i < count; i++)
+  {
+    unsigned unsafe_to;
+    if (!skippy_iter.next (&unsafe_to))
+    {
+      *end_position = unsafe_to;
+      return_trace (false);
+    }
+
+    match_positions[i] = skippy_iter.idx;
+
+    unsigned int this_lig_id = _hb_glyph_info_get_lig_id (&buffer->info[skippy_iter.idx]);
+    unsigned int this_lig_comp = _hb_glyph_info_get_lig_comp (&buffer->info[skippy_iter.idx]);
+
+    if (first_lig_id && first_lig_comp)
+    {
+      /* If first component was attached to a previous ligature component,
+       * all subsequent components should be attached to the same ligature
+       * component, otherwise we shouldn't ligate them... */
+      if (first_lig_id != this_lig_id || first_lig_comp != this_lig_comp)
+      {
+	/* ...unless, we are attached to a base ligature and that base
+	 * ligature is ignorable. */
+	if (ligbase == LIGBASE_NOT_CHECKED)
+	{
+	  bool found = false;
+	  const auto *out = buffer->out_info;
+	  unsigned int j = buffer->out_len;
+	  while (j && _hb_glyph_info_get_lig_id (&out[j - 1]) == first_lig_id)
+	  {
+	    if (_hb_glyph_info_get_lig_comp (&out[j - 1]) == 0)
+	    {
+	      j--;
+	      found = true;
+	      break;
+	    }
+	    j--;
+	  }
+
+	  if (found && skippy_iter.may_skip (out[j]) == hb_ot_apply_context_t::matcher_t::SKIP_YES)
+	    ligbase = LIGBASE_MAY_SKIP;
+	  else
+	    ligbase = LIGBASE_MAY_NOT_SKIP;
+	}
+
+	if (ligbase == LIGBASE_MAY_NOT_SKIP)
+	  return_trace (false);
+      }
+    }
+    else
+    {
+      /* If first component was NOT attached to a previous ligature component,
+       * all subsequent components should also NOT be attached to any ligature
+       * component, unless they are attached to the first component itself! */
+      if (this_lig_id && this_lig_comp && (this_lig_id != first_lig_id))
+	return_trace (false);
+    }
+
+    total_component_count += _hb_glyph_info_get_lig_num_comps (&buffer->info[skippy_iter.idx]);
+  }
+
+  *end_position = skippy_iter.idx + 1;
+
+  if (p_total_component_count)
+    *p_total_component_count = total_component_count;
+
+  return_trace (true);
+}
+static inline bool ligate_input (hb_ot_apply_context_t *c,
+				 unsigned int count, /* Including the first glyph */
+				 const unsigned int match_positions[HB_MAX_CONTEXT_LENGTH], /* Including the first glyph */
+				 unsigned int match_end,
+				 hb_codepoint_t lig_glyph,
+				 unsigned int total_component_count)
+{
+  TRACE_APPLY (nullptr);
+
+  hb_buffer_t *buffer = c->buffer;
+
+  buffer->merge_clusters (buffer->idx, match_end);
+
+  /* - If a base and one or more marks ligate, consider that as a base, NOT
+   *   ligature, such that all following marks can still attach to it.
+   *   https://github.com/harfbuzz/harfbuzz/issues/1109
+   *
+   * - If all components of the ligature were marks, we call this a mark ligature.
+   *   If it *is* a mark ligature, we don't allocate a new ligature id, and leave
+   *   the ligature to keep its old ligature id.  This will allow it to attach to
+   *   a base ligature in GPOS.  Eg. if the sequence is: LAM,LAM,SHADDA,FATHA,HEH,
+   *   and LAM,LAM,HEH for a ligature, they will leave SHADDA and FATHA with a
+   *   ligature id and component value of 2.  Then if SHADDA,FATHA form a ligature
+   *   later, we don't want them to lose their ligature id/component, otherwise
+   *   GPOS will fail to correctly position the mark ligature on top of the
+   *   LAM,LAM,HEH ligature.  See:
+   *     https://bugzilla.gnome.org/show_bug.cgi?id=676343
+   *
+   * - If a ligature is formed of components that some of which are also ligatures
+   *   themselves, and those ligature components had marks attached to *their*
+   *   components, we have to attach the marks to the new ligature component
+   *   positions!  Now *that*'s tricky!  And these marks may be following the
+   *   last component of the whole sequence, so we should loop forward looking
+   *   for them and update them.
+   *
+   *   Eg. the sequence is LAM,LAM,SHADDA,FATHA,HEH, and the font first forms a
+   *   'calt' ligature of LAM,HEH, leaving the SHADDA and FATHA with a ligature
+   *   id and component == 1.  Now, during 'liga', the LAM and the LAM-HEH ligature
+   *   form a LAM-LAM-HEH ligature.  We need to reassign the SHADDA and FATHA to
+   *   the new ligature with a component value of 2.
+   *
+   *   This in fact happened to a font...  See:
+   *   https://bugzilla.gnome.org/show_bug.cgi?id=437633
+   */
+
+  bool is_base_ligature = _hb_glyph_info_is_base_glyph (&buffer->info[match_positions[0]]);
+  bool is_mark_ligature = _hb_glyph_info_is_mark (&buffer->info[match_positions[0]]);
+  for (unsigned int i = 1; i < count; i++)
+    if (!_hb_glyph_info_is_mark (&buffer->info[match_positions[i]]))
+    {
+      is_base_ligature = false;
+      is_mark_ligature = false;
+      break;
+    }
+  bool is_ligature = !is_base_ligature && !is_mark_ligature;
+
+  unsigned int klass = is_ligature ? HB_OT_LAYOUT_GLYPH_PROPS_LIGATURE : 0;
+  unsigned int lig_id = is_ligature ? _hb_allocate_lig_id (buffer) : 0;
+  unsigned int last_lig_id = _hb_glyph_info_get_lig_id (&buffer->cur());
+  unsigned int last_num_components = _hb_glyph_info_get_lig_num_comps (&buffer->cur());
+  unsigned int components_so_far = last_num_components;
+
+  if (is_ligature)
+  {
+    _hb_glyph_info_set_lig_props_for_ligature (&buffer->cur(), lig_id, total_component_count);
+    if (_hb_glyph_info_get_general_category (&buffer->cur()) == HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK)
+    {
+      _hb_glyph_info_set_general_category (&buffer->cur(), HB_UNICODE_GENERAL_CATEGORY_OTHER_LETTER);
+    }
+  }
+  c->replace_glyph_with_ligature (lig_glyph, klass);
+
+  for (unsigned int i = 1; i < count; i++)
+  {
+    while (buffer->idx < match_positions[i] && buffer->successful)
+    {
+      if (is_ligature)
+      {
+	unsigned int this_comp = _hb_glyph_info_get_lig_comp (&buffer->cur());
+	if (this_comp == 0)
+	  this_comp = last_num_components;
+	unsigned int new_lig_comp = components_so_far - last_num_components +
+				    hb_min (this_comp, last_num_components);
+	  _hb_glyph_info_set_lig_props_for_mark (&buffer->cur(), lig_id, new_lig_comp);
+      }
+      (void) buffer->next_glyph ();
+    }
+
+    last_lig_id = _hb_glyph_info_get_lig_id (&buffer->cur());
+    last_num_components = _hb_glyph_info_get_lig_num_comps (&buffer->cur());
+    components_so_far += last_num_components;
+
+    /* Skip the base glyph */
+    buffer->idx++;
+  }
+
+  if (!is_mark_ligature && last_lig_id)
+  {
+    /* Re-adjust components for any marks following. */
+    for (unsigned i = buffer->idx; i < buffer->len; ++i)
+    {
+      if (last_lig_id != _hb_glyph_info_get_lig_id (&buffer->info[i])) break;
+
+      unsigned this_comp = _hb_glyph_info_get_lig_comp (&buffer->info[i]);
+      if (!this_comp) break;
+
+      unsigned new_lig_comp = components_so_far - last_num_components +
+			      hb_min (this_comp, last_num_components);
+      _hb_glyph_info_set_lig_props_for_mark (&buffer->info[i], lig_id, new_lig_comp);
+    }
+  }
+  return_trace (true);
+}
+
+template <typename HBUINT>
+static inline bool match_backtrack (hb_ot_apply_context_t *c,
+				    unsigned int count,
+				    const HBUINT backtrack[],
+				    match_func_t match_func,
+				    const void *match_data,
+				    unsigned int *match_start)
+{
+  TRACE_APPLY (nullptr);
+
+  hb_ot_apply_context_t::skipping_iterator_t &skippy_iter = c->iter_context;
+  skippy_iter.reset (c->buffer->backtrack_len (), count);
+  skippy_iter.set_match_func (match_func, match_data);
+  skippy_iter.set_glyph_data (backtrack);
+
+  for (unsigned int i = 0; i < count; i++)
+  {
+    unsigned unsafe_from;
+    if (!skippy_iter.prev (&unsafe_from))
+    {
+      *match_start = unsafe_from;
+      return_trace (false);
+    }
+  }
+
+  *match_start = skippy_iter.idx;
+  return_trace (true);
+}
+
+template <typename HBUINT>
+static inline bool match_lookahead (hb_ot_apply_context_t *c,
+				    unsigned int count,
+				    const HBUINT lookahead[],
+				    match_func_t match_func,
+				    const void *match_data,
+				    unsigned int start_index,
+				    unsigned int *end_index)
+{
+  TRACE_APPLY (nullptr);
+
+  hb_ot_apply_context_t::skipping_iterator_t &skippy_iter = c->iter_context;
+  skippy_iter.reset (start_index - 1, count);
+  skippy_iter.set_match_func (match_func, match_data);
+  skippy_iter.set_glyph_data (lookahead);
+
+  for (unsigned int i = 0; i < count; i++)
+  {
+    unsigned unsafe_to;
+    if (!skippy_iter.next (&unsafe_to))
+    {
+      *end_index = unsafe_to;
+      return_trace (false);
+    }
+  }
+
+  *end_index = skippy_iter.idx + 1;
+  return_trace (true);
+}
+
+
+
+struct LookupRecord
+{
+  bool serialize (hb_serialize_context_t *c,
+		  const hb_map_t         *lookup_map) const
+  {
+    TRACE_SERIALIZE (this);
+    auto *out = c->embed (*this);
+    if (unlikely (!out)) return_trace (false);
+
+    return_trace (c->check_assign (out->lookupListIndex, lookup_map->get (lookupListIndex), HB_SERIALIZE_ERROR_INT_OVERFLOW));
+  }
+
+  bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    return_trace (c->check_struct (this));
+  }
+
+  HBUINT16	sequenceIndex;		/* Index into current glyph
+					 * sequence--first glyph = 0 */
+  HBUINT16	lookupListIndex;	/* Lookup to apply to that
+					 * position--zero--based */
+  public:
+  DEFINE_SIZE_STATIC (4);
+};
+
+static unsigned serialize_lookuprecord_array (hb_serialize_context_t *c,
+					      const hb_array_t<const LookupRecord> lookupRecords,
+					      const hb_map_t *lookup_map)
+{
+  unsigned count = 0;
+  for (const LookupRecord& r : lookupRecords)
+  {
+    if (!lookup_map->has (r.lookupListIndex))
+      continue;
+
+    if (!r.serialize (c, lookup_map))
+      return 0;
+
+    count++;
+  }
+  return count;
+}
+
+enum ContextFormat { SimpleContext = 1, ClassBasedContext = 2, CoverageBasedContext = 3 };
+
+template <typename HBUINT>
+static void context_closure_recurse_lookups (hb_closure_context_t *c,
+					     unsigned inputCount, const HBUINT input[],
+					     unsigned lookupCount,
+					     const LookupRecord lookupRecord[] /* Array of LookupRecords--in design order */,
+					     unsigned value,
+					     ContextFormat context_format,
+					     const void *data,
+					     intersected_glyphs_func_t intersected_glyphs_func,
+					     void *cache)
+{
+  hb_set_t *covered_seq_indicies = hb_set_create ();
+  for (unsigned int i = 0; i < lookupCount; i++)
+  {
+    unsigned seqIndex = lookupRecord[i].sequenceIndex;
+    if (seqIndex >= inputCount) continue;
+
+    bool has_pos_glyphs = false;
+    hb_set_t pos_glyphs;
+
+    if (!hb_set_has (covered_seq_indicies, seqIndex))
+    {
+      has_pos_glyphs = true;
+      if (seqIndex == 0)
+      {
+        switch (context_format) {
+        case ContextFormat::SimpleContext:
+          pos_glyphs.add (value);
+          break;
+        case ContextFormat::ClassBasedContext:
+          intersected_glyphs_func (&c->parent_active_glyphs (), data, value, &pos_glyphs, cache);
+          break;
+        case ContextFormat::CoverageBasedContext:
+          pos_glyphs.set (c->parent_active_glyphs ());
+          break;
+        }
+      }
+      else
+      {
+        const void *input_data = input;
+        unsigned input_value = seqIndex - 1;
+        if (context_format != ContextFormat::SimpleContext)
+        {
+          input_data = data;
+          input_value = input[seqIndex - 1];
+        }
+
+        intersected_glyphs_func (c->glyphs, input_data, input_value, &pos_glyphs, cache);
+      }
+    }
+
+    covered_seq_indicies->add (seqIndex);
+    if (has_pos_glyphs) {
+      c->push_cur_active_glyphs () = std::move (pos_glyphs);
+    } else {
+      c->push_cur_active_glyphs ().set (*c->glyphs);
+    }
+
+    unsigned endIndex = inputCount;
+    if (context_format == ContextFormat::CoverageBasedContext)
+      endIndex += 1;
+
+    c->recurse (lookupRecord[i].lookupListIndex, covered_seq_indicies, seqIndex, endIndex);
+
+    c->pop_cur_done_glyphs ();
+  }
+
+  hb_set_destroy (covered_seq_indicies);
+}
+
+template <typename context_t>
+static inline void recurse_lookups (context_t *c,
+                                    unsigned int lookupCount,
+                                    const LookupRecord lookupRecord[] /* Array of LookupRecords--in design order */)
+{
+  for (unsigned int i = 0; i < lookupCount; i++)
+    c->recurse (lookupRecord[i].lookupListIndex);
+}
+
+static inline void apply_lookup (hb_ot_apply_context_t *c,
+				 unsigned int count, /* Including the first glyph */
+				 unsigned int match_positions[HB_MAX_CONTEXT_LENGTH], /* Including the first glyph */
+				 unsigned int lookupCount,
+				 const LookupRecord lookupRecord[], /* Array of LookupRecords--in design order */
+				 unsigned int match_end)
+{
+  hb_buffer_t *buffer = c->buffer;
+  int end;
+
+  /* All positions are distance from beginning of *output* buffer.
+   * Adjust. */
+  {
+    unsigned int bl = buffer->backtrack_len ();
+    end = bl + match_end - buffer->idx;
+
+    int delta = bl - buffer->idx;
+    /* Convert positions to new indexing. */
+    for (unsigned int j = 0; j < count; j++)
+      match_positions[j] += delta;
+  }
+
+  for (unsigned int i = 0; i < lookupCount && buffer->successful; i++)
+  {
+    unsigned int idx = lookupRecord[i].sequenceIndex;
+    if (idx >= count)
+      continue;
+
+    unsigned int orig_len = buffer->backtrack_len () + buffer->lookahead_len ();
+
+    /* This can happen if earlier recursed lookups deleted many entries. */
+    if (unlikely (match_positions[idx] >= orig_len))
+      continue;
+
+    if (unlikely (!buffer->move_to (match_positions[idx])))
+      break;
+
+    if (unlikely (buffer->max_ops <= 0))
+      break;
+
+    if (HB_BUFFER_MESSAGE_MORE && c->buffer->messaging ())
+    {
+      if (buffer->have_output)
+        c->buffer->sync_so_far ();
+      c->buffer->message (c->font,
+			  "recursing to lookup %u at %d",
+			  (unsigned) lookupRecord[i].lookupListIndex,
+			  buffer->idx);
+    }
+
+    if (!c->recurse (lookupRecord[i].lookupListIndex))
+      continue;
+
+    if (HB_BUFFER_MESSAGE_MORE && c->buffer->messaging ())
+    {
+      if (buffer->have_output)
+        c->buffer->sync_so_far ();
+      c->buffer->message (c->font,
+			  "recursed to lookup %u",
+			  (unsigned) lookupRecord[i].lookupListIndex);
+    }
+
+    unsigned int new_len = buffer->backtrack_len () + buffer->lookahead_len ();
+    int delta = new_len - orig_len;
+
+    if (!delta)
+      continue;
+
+    /* Recursed lookup changed buffer len.  Adjust.
+     *
+     * TODO:
+     *
+     * Right now, if buffer length increased by n, we assume n new glyphs
+     * were added right after the current position, and if buffer length
+     * was decreased by n, we assume n match positions after the current
+     * one where removed.  The former (buffer length increased) case is
+     * fine, but the decrease case can be improved in at least two ways,
+     * both of which are significant:
+     *
+     *   - If recursed-to lookup is MultipleSubst and buffer length
+     *     decreased, then it's current match position that was deleted,
+     *     NOT the one after it.
+     *
+     *   - If buffer length was decreased by n, it does not necessarily
+     *     mean that n match positions where removed, as there recursed-to
+     *     lookup might had a different LookupFlag.  Here's a constructed
+     *     case of that:
+     *     https://github.com/harfbuzz/harfbuzz/discussions/3538
+     *
+     * It should be possible to construct tests for both of these cases.
+     */
+
+    end += delta;
+    if (end < int (match_positions[idx]))
+    {
+      /* End might end up being smaller than match_positions[idx] if the recursed
+       * lookup ended up removing many items.
+       * Just never rewind end beyond start of current position, since that is
+       * not possible in the recursed lookup.  Also adjust delta as such.
+       *
+       * https://bugs.chromium.org/p/chromium/issues/detail?id=659496
+       * https://github.com/harfbuzz/harfbuzz/issues/1611
+       */
+      delta += match_positions[idx] - end;
+      end = match_positions[idx];
+    }
+
+    unsigned int next = idx + 1; /* next now is the position after the recursed lookup. */
+
+    if (delta > 0)
+    {
+      if (unlikely (delta + count > HB_MAX_CONTEXT_LENGTH))
+	break;
+    }
+    else
+    {
+      /* NOTE: delta is non-positive. */
+      delta = hb_max (delta, (int) next - (int) count);
+      next -= delta;
+    }
+
+    /* Shift! */
+    memmove (match_positions + next + delta, match_positions + next,
+	     (count - next) * sizeof (match_positions[0]));
+    next += delta;
+    count += delta;
+
+    /* Fill in new entries. */
+    for (unsigned int j = idx + 1; j < next; j++)
+      match_positions[j] = match_positions[j - 1] + 1;
+
+    /* And fixup the rest. */
+    for (; next < count; next++)
+      match_positions[next] += delta;
+  }
+
+  (void) buffer->move_to (end);
+}
+
+
+
+/* Contextual lookups */
+
+struct ContextClosureLookupContext
+{
+  ContextClosureFuncs funcs;
+  ContextFormat context_format;
+  const void *intersects_data;
+  void *intersects_cache;
+  void *intersected_glyphs_cache;
+};
+
+struct ContextCollectGlyphsLookupContext
+{
+  ContextCollectGlyphsFuncs funcs;
+  const void *collect_data;
+};
+
+struct ContextApplyLookupContext
+{
+  ContextApplyFuncs funcs;
+  const void *match_data;
+};
+
+template <typename HBUINT>
+static inline bool context_intersects (const hb_set_t *glyphs,
+				       unsigned int inputCount, /* Including the first glyph (not matched) */
+				       const HBUINT input[], /* Array of input values--start with second glyph */
+				       ContextClosureLookupContext &lookup_context)
+{
+  return array_is_subset_of (glyphs,
+			     inputCount ? inputCount - 1 : 0, input,
+			     lookup_context.funcs.intersects,
+			     lookup_context.intersects_data,
+			     lookup_context.intersects_cache);
+}
+
+template <typename HBUINT>
+static inline void context_closure_lookup (hb_closure_context_t *c,
+					   unsigned int inputCount, /* Including the first glyph (not matched) */
+					   const HBUINT input[], /* Array of input values--start with second glyph */
+					   unsigned int lookupCount,
+					   const LookupRecord lookupRecord[],
+					   unsigned value, /* Index of first glyph in Coverage or Class value in ClassDef table */
+					   ContextClosureLookupContext &lookup_context)
+{
+  if (context_intersects (c->glyphs,
+			  inputCount, input,
+			  lookup_context))
+    context_closure_recurse_lookups (c,
+				     inputCount, input,
+				     lookupCount, lookupRecord,
+				     value,
+				     lookup_context.context_format,
+				     lookup_context.intersects_data,
+				     lookup_context.funcs.intersected_glyphs,
+				     lookup_context.intersected_glyphs_cache);
+}
+
+template <typename HBUINT>
+static inline void context_collect_glyphs_lookup (hb_collect_glyphs_context_t *c,
+						  unsigned int inputCount, /* Including the first glyph (not matched) */
+						  const HBUINT input[], /* Array of input values--start with second glyph */
+						  unsigned int lookupCount,
+						  const LookupRecord lookupRecord[],
+						  ContextCollectGlyphsLookupContext &lookup_context)
+{
+  collect_array (c, c->input,
+		 inputCount ? inputCount - 1 : 0, input,
+		 lookup_context.funcs.collect, lookup_context.collect_data);
+  recurse_lookups (c,
+		   lookupCount, lookupRecord);
+}
+
+template <typename HBUINT>
+static inline bool context_would_apply_lookup (hb_would_apply_context_t *c,
+					       unsigned int inputCount, /* Including the first glyph (not matched) */
+					       const HBUINT input[], /* Array of input values--start with second glyph */
+					       unsigned int lookupCount HB_UNUSED,
+					       const LookupRecord lookupRecord[] HB_UNUSED,
+					       const ContextApplyLookupContext &lookup_context)
+{
+  return would_match_input (c,
+			    inputCount, input,
+			    lookup_context.funcs.match, lookup_context.match_data);
+}
+
+template <typename HBUINT>
+static inline bool context_apply_lookup (hb_ot_apply_context_t *c,
+					 unsigned int inputCount, /* Including the first glyph (not matched) */
+					 const HBUINT input[], /* Array of input values--start with second glyph */
+					 unsigned int lookupCount,
+					 const LookupRecord lookupRecord[],
+					 const ContextApplyLookupContext &lookup_context)
+{
+  unsigned match_end = 0;
+  unsigned match_positions[HB_MAX_CONTEXT_LENGTH];
+  if (match_input (c,
+		   inputCount, input,
+		   lookup_context.funcs.match, lookup_context.match_data,
+		   &match_end, match_positions))
+  {
+    c->buffer->unsafe_to_break (c->buffer->idx, match_end);
+    apply_lookup (c,
+		  inputCount, match_positions,
+		  lookupCount, lookupRecord,
+		  match_end);
+    return true;
+  }
+  else
+  {
+    c->buffer->unsafe_to_concat (c->buffer->idx, match_end);
+    return false;
+  }
+}
+
+template <typename Types>
+struct Rule
+{
+  bool intersects (const hb_set_t *glyphs, ContextClosureLookupContext &lookup_context) const
+  {
+    return context_intersects (glyphs,
+			       inputCount, inputZ.arrayZ,
+			       lookup_context);
+  }
+
+  void closure (hb_closure_context_t *c, unsigned value, ContextClosureLookupContext &lookup_context) const
+  {
+    if (unlikely (c->lookup_limit_exceeded ())) return;
+
+    const auto &lookupRecord = StructAfter<UnsizedArrayOf<LookupRecord>>
+					   (inputZ.as_array ((inputCount ? inputCount - 1 : 0)));
+    context_closure_lookup (c,
+			    inputCount, inputZ.arrayZ,
+			    lookupCount, lookupRecord.arrayZ,
+			    value, lookup_context);
+  }
+
+  void closure_lookups (hb_closure_lookups_context_t *c,
+                        ContextClosureLookupContext &lookup_context) const
+  {
+    if (unlikely (c->lookup_limit_exceeded ())) return;
+    if (!intersects (c->glyphs, lookup_context)) return;
+
+    const auto &lookupRecord = StructAfter<UnsizedArrayOf<LookupRecord>>
+					   (inputZ.as_array (inputCount ? inputCount - 1 : 0));
+    recurse_lookups (c, lookupCount, lookupRecord.arrayZ);
+  }
+
+  void collect_glyphs (hb_collect_glyphs_context_t *c,
+		       ContextCollectGlyphsLookupContext &lookup_context) const
+  {
+    const auto &lookupRecord = StructAfter<UnsizedArrayOf<LookupRecord>>
+					   (inputZ.as_array (inputCount ? inputCount - 1 : 0));
+    context_collect_glyphs_lookup (c,
+				   inputCount, inputZ.arrayZ,
+				   lookupCount, lookupRecord.arrayZ,
+				   lookup_context);
+  }
+
+  bool would_apply (hb_would_apply_context_t *c,
+		    const ContextApplyLookupContext &lookup_context) const
+  {
+    const auto &lookupRecord = StructAfter<UnsizedArrayOf<LookupRecord>>
+					   (inputZ.as_array (inputCount ? inputCount - 1 : 0));
+    return context_would_apply_lookup (c,
+				       inputCount, inputZ.arrayZ,
+				       lookupCount, lookupRecord.arrayZ,
+				       lookup_context);
+  }
+
+  bool apply (hb_ot_apply_context_t *c,
+	      const ContextApplyLookupContext &lookup_context) const
+  {
+    TRACE_APPLY (this);
+    const auto &lookupRecord = StructAfter<UnsizedArrayOf<LookupRecord>>
+					   (inputZ.as_array (inputCount ? inputCount - 1 : 0));
+    return_trace (context_apply_lookup (c, inputCount, inputZ.arrayZ, lookupCount, lookupRecord.arrayZ, lookup_context));
+  }
+
+  bool serialize (hb_serialize_context_t *c,
+		  const hb_map_t *input_mapping, /* old->new glyphid or class mapping */
+		  const hb_map_t *lookup_map) const
+  {
+    TRACE_SERIALIZE (this);
+    auto *out = c->start_embed (this);
+    if (unlikely (!c->extend_min (out))) return_trace (false);
+
+    out->inputCount = inputCount;
+    const auto input = inputZ.as_array (inputCount - 1);
+    for (const auto org : input)
+    {
+      HBUINT16 d;
+      d = input_mapping->get (org);
+      c->copy (d);
+    }
+
+    const auto &lookupRecord = StructAfter<UnsizedArrayOf<LookupRecord>>
+					   (inputZ.as_array ((inputCount ? inputCount - 1 : 0)));
+
+    unsigned count = serialize_lookuprecord_array (c, lookupRecord.as_array (lookupCount), lookup_map);
+    return_trace (c->check_assign (out->lookupCount, count, HB_SERIALIZE_ERROR_INT_OVERFLOW));
+  }
+
+  bool subset (hb_subset_context_t *c,
+	       const hb_map_t *lookup_map,
+	       const hb_map_t *klass_map = nullptr) const
+  {
+    TRACE_SUBSET (this);
+    if (unlikely (!inputCount)) return_trace (false);
+    const auto input = inputZ.as_array (inputCount - 1);
+
+    const hb_map_t *mapping = klass_map == nullptr ? c->plan->glyph_map : klass_map;
+    if (!hb_all (input, mapping)) return_trace (false);
+    return_trace (serialize (c->serializer, mapping, lookup_map));
+  }
+
+  public:
+  bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    return_trace (inputCount.sanitize (c) &&
+		  lookupCount.sanitize (c) &&
+		  c->check_range (inputZ.arrayZ,
+				  inputZ.item_size * (inputCount ? inputCount - 1 : 0) +
+				  LookupRecord::static_size * lookupCount));
+  }
+
+  protected:
+  HBUINT16	inputCount;		/* Total number of glyphs in input
+					 * glyph sequence--includes the first
+					 * glyph */
+  HBUINT16	lookupCount;		/* Number of LookupRecords */
+  UnsizedArrayOf<typename Types::HBUINT>
+		inputZ;			/* Array of match inputs--start with
+					 * second glyph */
+/*UnsizedArrayOf<LookupRecord>
+		lookupRecordX;*/	/* Array of LookupRecords--in
+					 * design order */
+  public:
+  DEFINE_SIZE_ARRAY (4, inputZ);
+};
+
+template <typename Types>
+struct RuleSet
+{
+  using Rule = OT::Rule<Types>;
+
+  bool intersects (const hb_set_t *glyphs,
+		   ContextClosureLookupContext &lookup_context) const
+  {
+    return
+    + hb_iter (rule)
+    | hb_map (hb_add (this))
+    | hb_map ([&] (const Rule &_) { return _.intersects (glyphs, lookup_context); })
+    | hb_any
+    ;
+  }
+
+  void closure (hb_closure_context_t *c, unsigned value,
+		ContextClosureLookupContext &lookup_context) const
+  {
+    if (unlikely (c->lookup_limit_exceeded ())) return;
+
+    return
+    + hb_iter (rule)
+    | hb_map (hb_add (this))
+    | hb_apply ([&] (const Rule &_) { _.closure (c, value, lookup_context); })
+    ;
+  }
+
+  void closure_lookups (hb_closure_lookups_context_t *c,
+                        ContextClosureLookupContext &lookup_context) const
+  {
+    if (unlikely (c->lookup_limit_exceeded ())) return;
+    + hb_iter (rule)
+    | hb_map (hb_add (this))
+    | hb_apply ([&] (const Rule &_) { _.closure_lookups (c, lookup_context); })
+    ;
+  }
+
+  void collect_glyphs (hb_collect_glyphs_context_t *c,
+		       ContextCollectGlyphsLookupContext &lookup_context) const
+  {
+    return
+    + hb_iter (rule)
+    | hb_map (hb_add (this))
+    | hb_apply ([&] (const Rule &_) { _.collect_glyphs (c, lookup_context); })
+    ;
+  }
+
+  bool would_apply (hb_would_apply_context_t *c,
+		    const ContextApplyLookupContext &lookup_context) const
+  {
+    return
+    + hb_iter (rule)
+    | hb_map (hb_add (this))
+    | hb_map ([&] (const Rule &_) { return _.would_apply (c, lookup_context); })
+    | hb_any
+    ;
+  }
+
+  bool apply (hb_ot_apply_context_t *c,
+	      const ContextApplyLookupContext &lookup_context) const
+  {
+    TRACE_APPLY (this);
+    return_trace (
+    + hb_iter (rule)
+    | hb_map (hb_add (this))
+    | hb_map ([&] (const Rule &_) { return _.apply (c, lookup_context); })
+    | hb_any
+    )
+    ;
+  }
+
+  bool subset (hb_subset_context_t *c,
+	       const hb_map_t *lookup_map,
+	       const hb_map_t *klass_map = nullptr) const
+  {
+    TRACE_SUBSET (this);
+
+    auto snap = c->serializer->snapshot ();
+    auto *out = c->serializer->start_embed (*this);
+    if (unlikely (!c->serializer->extend_min (out))) return_trace (false);
+
+    for (const Offset16To<Rule>& _ : rule)
+    {
+      if (!_) continue;
+      auto o_snap = c->serializer->snapshot ();
+      auto *o = out->rule.serialize_append (c->serializer);
+      if (unlikely (!o)) continue;
+
+      if (!o->serialize_subset (c, _, this, lookup_map, klass_map))
+      {
+	out->rule.pop ();
+	c->serializer->revert (o_snap);
+      }
+    }
+
+    bool ret = bool (out->rule);
+    if (!ret) c->serializer->revert (snap);
+
+    return_trace (ret);
+  }
+
+  bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    return_trace (rule.sanitize (c, this));
+  }
+
+  protected:
+  Array16OfOffset16To<Rule>
+		rule;			/* Array of Rule tables
+					 * ordered by preference */
+  public:
+  DEFINE_SIZE_ARRAY (2, rule);
+};
+
+
+template <typename Types>
+struct ContextFormat1_4
+{
+  using RuleSet = OT::RuleSet<Types>;
+
+  bool intersects (const hb_set_t *glyphs) const
+  {
+    struct ContextClosureLookupContext lookup_context = {
+      {intersects_glyph, intersected_glyph},
+      ContextFormat::SimpleContext,
+      nullptr
+    };
+
+    return
+    + hb_zip (this+coverage, ruleSet)
+    | hb_filter (*glyphs, hb_first)
+    | hb_map (hb_second)
+    | hb_map (hb_add (this))
+    | hb_map ([&] (const RuleSet &_) { return _.intersects (glyphs, lookup_context); })
+    | hb_any
+    ;
+  }
+
+  bool may_have_non_1to1 () const
+  { return true; }
+
+  void closure (hb_closure_context_t *c) const
+  {
+    hb_set_t& cur_active_glyphs = c->push_cur_active_glyphs ();
+    get_coverage ().intersect_set (c->previous_parent_active_glyphs (), cur_active_glyphs);
+
+    struct ContextClosureLookupContext lookup_context = {
+      {intersects_glyph, intersected_glyph},
+      ContextFormat::SimpleContext,
+      nullptr
+    };
+
+    + hb_zip (this+coverage, hb_range ((unsigned) ruleSet.len))
+    | hb_filter ([&] (hb_codepoint_t _) {
+      return c->previous_parent_active_glyphs ().has (_);
+    }, hb_first)
+    | hb_map ([&](const hb_pair_t<hb_codepoint_t, unsigned> _) { return hb_pair_t<unsigned, const RuleSet&> (_.first, this+ruleSet[_.second]); })
+    | hb_apply ([&] (const hb_pair_t<unsigned, const RuleSet&>& _) { _.second.closure (c, _.first, lookup_context); })
+    ;
+
+    c->pop_cur_done_glyphs ();
+  }
+
+  void closure_lookups (hb_closure_lookups_context_t *c) const
+  {
+    struct ContextClosureLookupContext lookup_context = {
+      {intersects_glyph, nullptr},
+      ContextFormat::SimpleContext,
+      nullptr
+    };
+
+    + hb_zip (this+coverage, ruleSet)
+    | hb_filter (*c->glyphs, hb_first)
+    | hb_map (hb_second)
+    | hb_map (hb_add (this))
+    | hb_apply ([&] (const RuleSet &_) { _.closure_lookups (c, lookup_context); })
+    ;
+  }
+
+  void collect_variation_indices (hb_collect_variation_indices_context_t *c) const {}
+
+  void collect_glyphs (hb_collect_glyphs_context_t *c) const
+  {
+    (this+coverage).collect_coverage (c->input);
+
+    struct ContextCollectGlyphsLookupContext lookup_context = {
+      {collect_glyph},
+      nullptr
+    };
+
+    + hb_iter (ruleSet)
+    | hb_map (hb_add (this))
+    | hb_apply ([&] (const RuleSet &_) { _.collect_glyphs (c, lookup_context); })
+    ;
+  }
+
+  bool would_apply (hb_would_apply_context_t *c) const
+  {
+    const RuleSet &rule_set = this+ruleSet[(this+coverage).get_coverage (c->glyphs[0])];
+    struct ContextApplyLookupContext lookup_context = {
+      {match_glyph},
+      nullptr
+    };
+    return rule_set.would_apply (c, lookup_context);
+  }
+
+  const Coverage &get_coverage () const { return this+coverage; }
+
+  bool apply (hb_ot_apply_context_t *c) const
+  {
+    TRACE_APPLY (this);
+    unsigned int index = (this+coverage).get_coverage (c->buffer->cur().codepoint);
+    if (likely (index == NOT_COVERED))
+      return_trace (false);
+
+    const RuleSet &rule_set = this+ruleSet[index];
+    struct ContextApplyLookupContext lookup_context = {
+      {match_glyph},
+      nullptr
+    };
+    return_trace (rule_set.apply (c, lookup_context));
+  }
+
+  bool subset (hb_subset_context_t *c) const
+  {
+    TRACE_SUBSET (this);
+    const hb_set_t &glyphset = *c->plan->glyphset_gsub ();
+    const hb_map_t &glyph_map = *c->plan->glyph_map;
+
+    auto *out = c->serializer->start_embed (*this);
+    if (unlikely (!c->serializer->extend_min (out))) return_trace (false);
+    out->format = format;
+
+    const hb_map_t *lookup_map = c->table_tag == HB_OT_TAG_GSUB ? c->plan->gsub_lookups : c->plan->gpos_lookups;
+    hb_sorted_vector_t<hb_codepoint_t> new_coverage;
+    + hb_zip (this+coverage, ruleSet)
+    | hb_filter (glyphset, hb_first)
+    | hb_filter (subset_offset_array (c, out->ruleSet, this, lookup_map), hb_second)
+    | hb_map (hb_first)
+    | hb_map (glyph_map)
+    | hb_sink (new_coverage)
+    ;
+
+    out->coverage.serialize_serialize (c->serializer, new_coverage.iter ());
+    return_trace (bool (new_coverage));
+  }
+
+  bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    return_trace (coverage.sanitize (c, this) && ruleSet.sanitize (c, this));
+  }
+
+  protected:
+  HBUINT16	format;			/* Format identifier--format = 1 */
+  typename Types::template OffsetTo<Coverage>
+		coverage;		/* Offset to Coverage table--from
+					 * beginning of table */
+  Array16Of<typename Types::template OffsetTo<RuleSet>>
+		ruleSet;		/* Array of RuleSet tables
+					 * ordered by Coverage Index */
+  public:
+  DEFINE_SIZE_ARRAY (2 + 2 * Types::size, ruleSet);
+};
+
+
+template <typename Types>
+struct ContextFormat2_5
+{
+  using RuleSet = OT::RuleSet<SmallTypes>;
+
+  bool intersects (const hb_set_t *glyphs) const
+  {
+    if (!(this+coverage).intersects (glyphs))
+      return false;
+
+    const ClassDef &class_def = this+classDef;
+
+    hb_map_t cache;
+    struct ContextClosureLookupContext lookup_context = {
+      {intersects_class, nullptr},
+      ContextFormat::ClassBasedContext,
+      &class_def,
+      &cache
+    };
+
+    hb_set_t retained_coverage_glyphs;
+    (this+coverage).intersect_set (*glyphs, retained_coverage_glyphs);
+
+    hb_set_t coverage_glyph_classes;
+    class_def.intersected_classes (&retained_coverage_glyphs, &coverage_glyph_classes);
+
+
+    return
+    + hb_iter (ruleSet)
+    | hb_map (hb_add (this))
+    | hb_enumerate
+    | hb_map ([&] (const hb_pair_t<unsigned, const RuleSet &> p)
+	      { return class_def.intersects_class (glyphs, p.first) &&
+		       coverage_glyph_classes.has (p.first) &&
+		       p.second.intersects (glyphs, lookup_context); })
+    | hb_any
+    ;
+  }
+
+  bool may_have_non_1to1 () const
+  { return true; }
+
+  void closure (hb_closure_context_t *c) const
+  {
+    if (!(this+coverage).intersects (c->glyphs))
+      return;
+
+    hb_set_t& cur_active_glyphs = c->push_cur_active_glyphs ();
+    get_coverage ().intersect_set (c->previous_parent_active_glyphs (),
+                                                 cur_active_glyphs);
+
+    const ClassDef &class_def = this+classDef;
+
+    hb_map_t cache;
+    intersected_class_cache_t intersected_cache;
+    struct ContextClosureLookupContext lookup_context = {
+      {intersects_class, intersected_class_glyphs},
+      ContextFormat::ClassBasedContext,
+      &class_def,
+      &cache,
+      &intersected_cache
+    };
+
+    + hb_enumerate (ruleSet)
+    | hb_filter ([&] (unsigned _)
+    { return class_def.intersects_class (&c->parent_active_glyphs (), _); },
+		 hb_first)
+    | hb_apply ([&] (const hb_pair_t<unsigned, const typename Types::template OffsetTo<RuleSet>&> _)
+                {
+                  const RuleSet& rule_set = this+_.second;
+                  rule_set.closure (c, _.first, lookup_context);
+                })
+    ;
+
+    c->pop_cur_done_glyphs ();
+  }
+
+  void closure_lookups (hb_closure_lookups_context_t *c) const
+  {
+    if (!(this+coverage).intersects (c->glyphs))
+      return;
+
+    const ClassDef &class_def = this+classDef;
+
+    hb_map_t cache;
+    struct ContextClosureLookupContext lookup_context = {
+      {intersects_class, nullptr},
+      ContextFormat::ClassBasedContext,
+      &class_def,
+      &cache
+    };
+
+    + hb_iter (ruleSet)
+    | hb_map (hb_add (this))
+    | hb_enumerate
+    | hb_filter ([&] (const hb_pair_t<unsigned, const RuleSet &> p)
+    { return class_def.intersects_class (c->glyphs, p.first); })
+    | hb_map (hb_second)
+    | hb_apply ([&] (const RuleSet & _)
+    { _.closure_lookups (c, lookup_context); });
+  }
+
+  void collect_variation_indices (hb_collect_variation_indices_context_t *c) const {}
+
+  void collect_glyphs (hb_collect_glyphs_context_t *c) const
+  {
+    (this+coverage).collect_coverage (c->input);
+
+    const ClassDef &class_def = this+classDef;
+    struct ContextCollectGlyphsLookupContext lookup_context = {
+      {collect_class},
+      &class_def
+    };
+
+    + hb_iter (ruleSet)
+    | hb_map (hb_add (this))
+    | hb_apply ([&] (const RuleSet &_) { _.collect_glyphs (c, lookup_context); })
+    ;
+  }
+
+  bool would_apply (hb_would_apply_context_t *c) const
+  {
+    const ClassDef &class_def = this+classDef;
+    unsigned int index = class_def.get_class (c->glyphs[0]);
+    const RuleSet &rule_set = this+ruleSet[index];
+    struct ContextApplyLookupContext lookup_context = {
+      {match_class},
+      &class_def
+    };
+    return rule_set.would_apply (c, lookup_context);
+  }
+
+  const Coverage &get_coverage () const { return this+coverage; }
+
+  unsigned cache_cost () const
+  {
+    unsigned c = (this+classDef).cost () * ruleSet.len;
+    return c >= 4 ? c : 0;
+  }
+  bool cache_func (hb_ot_apply_context_t *c, bool enter) const
+  {
+    if (enter)
+    {
+      if (!HB_BUFFER_TRY_ALLOCATE_VAR (c->buffer, syllable))
+	return false;
+      auto &info = c->buffer->info;
+      unsigned count = c->buffer->len;
+      for (unsigned i = 0; i < count; i++)
+	info[i].syllable() = 255;
+      c->new_syllables = 255;
+      return true;
+    }
+    else
+    {
+      c->new_syllables = (unsigned) -1;
+      HB_BUFFER_DEALLOCATE_VAR (c->buffer, syllable);
+      return true;
+    }
+  }
+
+  bool apply (hb_ot_apply_context_t *c, bool cached = false) const
+  {
+    TRACE_APPLY (this);
+    unsigned int index = (this+coverage).get_coverage (c->buffer->cur().codepoint);
+    if (likely (index == NOT_COVERED)) return_trace (false);
+
+    const ClassDef &class_def = this+classDef;
+
+    struct ContextApplyLookupContext lookup_context = {
+      {cached ? match_class_cached : match_class},
+      &class_def
+    };
+
+    if (cached && c->buffer->cur().syllable() < 255)
+      index = c->buffer->cur().syllable ();
+    else
+    {
+      index = class_def.get_class (c->buffer->cur().codepoint);
+      if (cached && index < 255)
+	c->buffer->cur().syllable() = index;
+    }
+    const RuleSet &rule_set = this+ruleSet[index];
+    return_trace (rule_set.apply (c, lookup_context));
+  }
+
+  bool subset (hb_subset_context_t *c) const
+  {
+    TRACE_SUBSET (this);
+    auto *out = c->serializer->start_embed (*this);
+    if (unlikely (!c->serializer->extend_min (out))) return_trace (false);
+    out->format = format;
+    if (unlikely (!out->coverage.serialize_subset (c, coverage, this)))
+      return_trace (false);
+
+    hb_map_t klass_map;
+    out->classDef.serialize_subset (c, classDef, this, &klass_map);
+
+    const hb_set_t* glyphset = c->plan->glyphset_gsub ();
+    hb_set_t retained_coverage_glyphs;
+    (this+coverage).intersect_set (*glyphset, retained_coverage_glyphs);
+
+    hb_set_t coverage_glyph_classes;
+    (this+classDef).intersected_classes (&retained_coverage_glyphs, &coverage_glyph_classes);
+
+    const hb_map_t *lookup_map = c->table_tag == HB_OT_TAG_GSUB ? c->plan->gsub_lookups : c->plan->gpos_lookups;
+    bool ret = true;
+    int non_zero_index = -1, index = 0;
+    auto snapshot = c->serializer->snapshot();
+    for (const auto& _ : + hb_enumerate (ruleSet)
+			 | hb_filter (klass_map, hb_first))
+    {
+      auto *o = out->ruleSet.serialize_append (c->serializer);
+      if (unlikely (!o))
+      {
+	ret = false;
+	break;
+      }
+
+      if (coverage_glyph_classes.has (_.first) &&
+	  o->serialize_subset (c, _.second, this, lookup_map, &klass_map)) {
+	non_zero_index = index;
+        snapshot = c->serializer->snapshot();
+      }
+
+      index++;
+    }
+
+    if (!ret || non_zero_index == -1) return_trace (false);
+
+    //prune empty trailing ruleSets
+    --index;
+    while (index > non_zero_index)
+    {
+      out->ruleSet.pop ();
+      index--;
+    }
+    c->serializer->revert (snapshot);
+
+    return_trace (bool (out->ruleSet));
+  }
+
+  bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    return_trace (coverage.sanitize (c, this) && classDef.sanitize (c, this) && ruleSet.sanitize (c, this));
+  }
+
+  protected:
+  HBUINT16	format;			/* Format identifier--format = 2 */
+  typename Types::template OffsetTo<Coverage>
+		coverage;		/* Offset to Coverage table--from
+					 * beginning of table */
+  typename Types::template OffsetTo<ClassDef>
+		classDef;		/* Offset to glyph ClassDef table--from
+					 * beginning of table */
+  Array16Of<typename Types::template OffsetTo<RuleSet>>
+		ruleSet;		/* Array of RuleSet tables
+					 * ordered by class */
+  public:
+  DEFINE_SIZE_ARRAY (4 + 2 * Types::size, ruleSet);
+};
+
+
+struct ContextFormat3
+{
+  using RuleSet = OT::RuleSet<SmallTypes>;
+
+  bool intersects (const hb_set_t *glyphs) const
+  {
+    if (!(this+coverageZ[0]).intersects (glyphs))
+      return false;
+
+    struct ContextClosureLookupContext lookup_context = {
+      {intersects_coverage, nullptr},
+      ContextFormat::CoverageBasedContext,
+      this
+    };
+    return context_intersects (glyphs,
+			       glyphCount, (const HBUINT16 *) (coverageZ.arrayZ + 1),
+			       lookup_context);
+  }
+
+  bool may_have_non_1to1 () const
+  { return true; }
+
+  void closure (hb_closure_context_t *c) const
+  {
+    if (!(this+coverageZ[0]).intersects (c->glyphs))
+      return;
+
+    hb_set_t& cur_active_glyphs = c->push_cur_active_glyphs ();
+    get_coverage ().intersect_set (c->previous_parent_active_glyphs (),
+                                                 cur_active_glyphs);
+
+
+    const LookupRecord *lookupRecord = &StructAfter<LookupRecord> (coverageZ.as_array (glyphCount));
+    struct ContextClosureLookupContext lookup_context = {
+      {intersects_coverage, intersected_coverage_glyphs},
+      ContextFormat::CoverageBasedContext,
+      this
+    };
+    context_closure_lookup (c,
+			    glyphCount, (const HBUINT16 *) (coverageZ.arrayZ + 1),
+			    lookupCount, lookupRecord,
+			    0, lookup_context);
+
+    c->pop_cur_done_glyphs ();
+  }
+
+  void closure_lookups (hb_closure_lookups_context_t *c) const
+  {
+    if (!intersects (c->glyphs))
+      return;
+    const LookupRecord *lookupRecord = &StructAfter<LookupRecord> (coverageZ.as_array (glyphCount));
+    recurse_lookups (c, lookupCount, lookupRecord);
+  }
+
+  void collect_variation_indices (hb_collect_variation_indices_context_t *c) const {}
+
+  void collect_glyphs (hb_collect_glyphs_context_t *c) const
+  {
+    (this+coverageZ[0]).collect_coverage (c->input);
+
+    const LookupRecord *lookupRecord = &StructAfter<LookupRecord> (coverageZ.as_array (glyphCount));
+    struct ContextCollectGlyphsLookupContext lookup_context = {
+      {collect_coverage},
+      this
+    };
+
+    context_collect_glyphs_lookup (c,
+				   glyphCount, (const HBUINT16 *) (coverageZ.arrayZ + 1),
+				   lookupCount, lookupRecord,
+				   lookup_context);
+  }
+
+  bool would_apply (hb_would_apply_context_t *c) const
+  {
+    const LookupRecord *lookupRecord = &StructAfter<LookupRecord> (coverageZ.as_array (glyphCount));
+    struct ContextApplyLookupContext lookup_context = {
+      {match_coverage},
+      this
+    };
+    return context_would_apply_lookup (c,
+				       glyphCount, (const HBUINT16 *) (coverageZ.arrayZ + 1),
+				       lookupCount, lookupRecord,
+				       lookup_context);
+  }
+
+  const Coverage &get_coverage () const { return this+coverageZ[0]; }
+
+  bool apply (hb_ot_apply_context_t *c) const
+  {
+    TRACE_APPLY (this);
+    unsigned int index = (this+coverageZ[0]).get_coverage (c->buffer->cur().codepoint);
+    if (likely (index == NOT_COVERED)) return_trace (false);
+
+    const LookupRecord *lookupRecord = &StructAfter<LookupRecord> (coverageZ.as_array (glyphCount));
+    struct ContextApplyLookupContext lookup_context = {
+      {match_coverage},
+      this
+    };
+    return_trace (context_apply_lookup (c, glyphCount, (const HBUINT16 *) (coverageZ.arrayZ + 1), lookupCount, lookupRecord, lookup_context));
+  }
+
+  bool subset (hb_subset_context_t *c) const
+  {
+    TRACE_SUBSET (this);
+    auto *out = c->serializer->start_embed (this);
+    if (unlikely (!c->serializer->extend_min (out))) return_trace (false);
+
+    out->format = format;
+    out->glyphCount = glyphCount;
+
+    auto coverages = coverageZ.as_array (glyphCount);
+
+    for (const Offset16To<Coverage>& offset : coverages)
+    {
+      /* TODO(subset) This looks like should not be necessary to write this way. */
+      auto *o = c->serializer->allocate_size<Offset16To<Coverage>> (Offset16To<Coverage>::static_size);
+      if (unlikely (!o)) return_trace (false);
+      if (!o->serialize_subset (c, offset, this)) return_trace (false);
+    }
+
+    const auto& lookupRecord = StructAfter<UnsizedArrayOf<LookupRecord>> (coverageZ.as_array (glyphCount));
+    const hb_map_t *lookup_map = c->table_tag == HB_OT_TAG_GSUB ? c->plan->gsub_lookups : c->plan->gpos_lookups;
+
+
+    unsigned count = serialize_lookuprecord_array (c->serializer, lookupRecord.as_array (lookupCount), lookup_map);
+    return_trace (c->serializer->check_assign (out->lookupCount, count, HB_SERIALIZE_ERROR_INT_OVERFLOW));
+  }
+
+  bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    if (!c->check_struct (this)) return_trace (false);
+    unsigned int count = glyphCount;
+    if (!count) return_trace (false); /* We want to access coverageZ[0] freely. */
+    if (!c->check_array (coverageZ.arrayZ, count)) return_trace (false);
+    for (unsigned int i = 0; i < count; i++)
+      if (!coverageZ[i].sanitize (c, this)) return_trace (false);
+    const LookupRecord *lookupRecord = &StructAfter<LookupRecord> (coverageZ.as_array (glyphCount));
+    return_trace (c->check_array (lookupRecord, lookupCount));
+  }
+
+  protected:
+  HBUINT16	format;			/* Format identifier--format = 3 */
+  HBUINT16	glyphCount;		/* Number of glyphs in the input glyph
+					 * sequence */
+  HBUINT16	lookupCount;		/* Number of LookupRecords */
+  UnsizedArrayOf<Offset16To<Coverage>>
+		coverageZ;		/* Array of offsets to Coverage
+					 * table in glyph sequence order */
+/*UnsizedArrayOf<LookupRecord>
+		lookupRecordX;*/	/* Array of LookupRecords--in
+					 * design order */
+  public:
+  DEFINE_SIZE_ARRAY (6, coverageZ);
+};
+
+struct Context
+{
+  template <typename context_t, typename ...Ts>
+  typename context_t::return_t dispatch (context_t *c, Ts&&... ds) const
+  {
+    TRACE_DISPATCH (this, u.format);
+    if (unlikely (!c->may_dispatch (this, &u.format))) return_trace (c->no_dispatch_return_value ());
+    switch (u.format) {
+    case 1: return_trace (c->dispatch (u.format1, std::forward<Ts> (ds)...));
+    case 2: return_trace (c->dispatch (u.format2, std::forward<Ts> (ds)...));
+    case 3: return_trace (c->dispatch (u.format3, std::forward<Ts> (ds)...));
+#ifndef HB_NO_BEYOND_64K
+    case 4: return_trace (c->dispatch (u.format4, std::forward<Ts> (ds)...));
+    case 5: return_trace (c->dispatch (u.format5, std::forward<Ts> (ds)...));
+#endif
+    default:return_trace (c->default_return_value ());
+    }
+  }
+
+  protected:
+  union {
+  HBUINT16			format;		/* Format identifier */
+  ContextFormat1_4<SmallTypes>	format1;
+  ContextFormat2_5<SmallTypes>	format2;
+  ContextFormat3		format3;
+#ifndef HB_NO_BEYOND_64K
+  ContextFormat1_4<MediumTypes>	format4;
+  ContextFormat2_5<MediumTypes>	format5;
+#endif
+  } u;
+};
+
+
+/* Chaining Contextual lookups */
+
+struct ChainContextClosureLookupContext
+{
+  ContextClosureFuncs funcs;
+  ContextFormat context_format;
+  const void *intersects_data[3];
+  void *intersects_cache[3];
+  void *intersected_glyphs_cache;
+};
+
+struct ChainContextCollectGlyphsLookupContext
+{
+  ContextCollectGlyphsFuncs funcs;
+  const void *collect_data[3];
+};
+
+struct ChainContextApplyLookupContext
+{
+  ChainContextApplyFuncs funcs;
+  const void *match_data[3];
+};
+
+template <typename HBUINT>
+static inline bool chain_context_intersects (const hb_set_t *glyphs,
+					     unsigned int backtrackCount,
+					     const HBUINT backtrack[],
+					     unsigned int inputCount, /* Including the first glyph (not matched) */
+					     const HBUINT input[], /* Array of input values--start with second glyph */
+					     unsigned int lookaheadCount,
+					     const HBUINT lookahead[],
+					     ChainContextClosureLookupContext &lookup_context)
+{
+  return array_is_subset_of (glyphs,
+			     backtrackCount, backtrack,
+			     lookup_context.funcs.intersects,
+			     lookup_context.intersects_data[0],
+			     lookup_context.intersects_cache[0])
+      && array_is_subset_of (glyphs,
+			     inputCount ? inputCount - 1 : 0, input,
+			     lookup_context.funcs.intersects,
+			     lookup_context.intersects_data[1],
+			     lookup_context.intersects_cache[1])
+      && array_is_subset_of (glyphs,
+			     lookaheadCount, lookahead,
+			     lookup_context.funcs.intersects,
+			     lookup_context.intersects_data[2],
+			     lookup_context.intersects_cache[2]);
+}
+
+template <typename HBUINT>
+static inline void chain_context_closure_lookup (hb_closure_context_t *c,
+						 unsigned int backtrackCount,
+						 const HBUINT backtrack[],
+						 unsigned int inputCount, /* Including the first glyph (not matched) */
+						 const HBUINT input[], /* Array of input values--start with second glyph */
+						 unsigned int lookaheadCount,
+						 const HBUINT lookahead[],
+						 unsigned int lookupCount,
+						 const LookupRecord lookupRecord[],
+						 unsigned value,
+						 ChainContextClosureLookupContext &lookup_context)
+{
+  if (chain_context_intersects (c->glyphs,
+				backtrackCount, backtrack,
+				inputCount, input,
+				lookaheadCount, lookahead,
+				lookup_context))
+    context_closure_recurse_lookups (c,
+		     inputCount, input,
+		     lookupCount, lookupRecord,
+		     value,
+		     lookup_context.context_format,
+		     lookup_context.intersects_data[1],
+		     lookup_context.funcs.intersected_glyphs,
+		     lookup_context.intersected_glyphs_cache);
+}
+
+template <typename HBUINT>
+static inline void chain_context_collect_glyphs_lookup (hb_collect_glyphs_context_t *c,
+							unsigned int backtrackCount,
+							const HBUINT backtrack[],
+							unsigned int inputCount, /* Including the first glyph (not matched) */
+							const HBUINT input[], /* Array of input values--start with second glyph */
+							unsigned int lookaheadCount,
+							const HBUINT lookahead[],
+							unsigned int lookupCount,
+							const LookupRecord lookupRecord[],
+							ChainContextCollectGlyphsLookupContext &lookup_context)
+{
+  collect_array (c, c->before,
+		 backtrackCount, backtrack,
+		 lookup_context.funcs.collect, lookup_context.collect_data[0]);
+  collect_array (c, c->input,
+		 inputCount ? inputCount - 1 : 0, input,
+		 lookup_context.funcs.collect, lookup_context.collect_data[1]);
+  collect_array (c, c->after,
+		 lookaheadCount, lookahead,
+		 lookup_context.funcs.collect, lookup_context.collect_data[2]);
+  recurse_lookups (c,
+		   lookupCount, lookupRecord);
+}
+
+template <typename HBUINT>
+static inline bool chain_context_would_apply_lookup (hb_would_apply_context_t *c,
+						     unsigned int backtrackCount,
+						     const HBUINT backtrack[] HB_UNUSED,
+						     unsigned int inputCount, /* Including the first glyph (not matched) */
+						     const HBUINT input[], /* Array of input values--start with second glyph */
+						     unsigned int lookaheadCount,
+						     const HBUINT lookahead[] HB_UNUSED,
+						     unsigned int lookupCount HB_UNUSED,
+						     const LookupRecord lookupRecord[] HB_UNUSED,
+						     const ChainContextApplyLookupContext &lookup_context)
+{
+  return (c->zero_context ? !backtrackCount && !lookaheadCount : true)
+      && would_match_input (c,
+			    inputCount, input,
+			    lookup_context.funcs.match[1], lookup_context.match_data[1]);
+}
+
+template <typename HBUINT>
+static inline bool chain_context_apply_lookup (hb_ot_apply_context_t *c,
+					       unsigned int backtrackCount,
+					       const HBUINT backtrack[],
+					       unsigned int inputCount, /* Including the first glyph (not matched) */
+					       const HBUINT input[], /* Array of input values--start with second glyph */
+					       unsigned int lookaheadCount,
+					       const HBUINT lookahead[],
+					       unsigned int lookupCount,
+					       const LookupRecord lookupRecord[],
+					       const ChainContextApplyLookupContext &lookup_context)
+{
+  unsigned end_index = c->buffer->idx;
+  unsigned match_end = 0;
+  unsigned match_positions[HB_MAX_CONTEXT_LENGTH];
+  if (!(match_input (c,
+		     inputCount, input,
+		     lookup_context.funcs.match[1], lookup_context.match_data[1],
+		     &match_end, match_positions) && (end_index = match_end)
+       && match_lookahead (c,
+			   lookaheadCount, lookahead,
+			   lookup_context.funcs.match[2], lookup_context.match_data[2],
+			   match_end, &end_index)))
+  {
+    c->buffer->unsafe_to_concat (c->buffer->idx, end_index);
+    return false;
+  }
+
+  unsigned start_index = c->buffer->out_len;
+  if (!match_backtrack (c,
+			backtrackCount, backtrack,
+			lookup_context.funcs.match[0], lookup_context.match_data[0],
+			&start_index))
+  {
+    c->buffer->unsafe_to_concat_from_outbuffer (start_index, end_index);
+    return false;
+  }
+
+  c->buffer->unsafe_to_break_from_outbuffer (start_index, end_index);
+  apply_lookup (c,
+		inputCount, match_positions,
+		lookupCount, lookupRecord,
+		match_end);
+  return true;
+}
+
+template <typename Types>
+struct ChainRule
+{
+  bool intersects (const hb_set_t *glyphs, ChainContextClosureLookupContext &lookup_context) const
+  {
+    const auto &input = StructAfter<decltype (inputX)> (backtrack);
+    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
+    return chain_context_intersects (glyphs,
+				     backtrack.len, backtrack.arrayZ,
+				     input.lenP1, input.arrayZ,
+				     lookahead.len, lookahead.arrayZ,
+				     lookup_context);
+  }
+
+  void closure (hb_closure_context_t *c, unsigned value,
+		ChainContextClosureLookupContext &lookup_context) const
+  {
+    if (unlikely (c->lookup_limit_exceeded ())) return;
+
+    const auto &input = StructAfter<decltype (inputX)> (backtrack);
+    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
+    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
+    chain_context_closure_lookup (c,
+				  backtrack.len, backtrack.arrayZ,
+				  input.lenP1, input.arrayZ,
+				  lookahead.len, lookahead.arrayZ,
+				  lookup.len, lookup.arrayZ,
+				  value,
+				  lookup_context);
+  }
+
+  void closure_lookups (hb_closure_lookups_context_t *c,
+                        ChainContextClosureLookupContext &lookup_context) const
+  {
+    if (unlikely (c->lookup_limit_exceeded ())) return;
+    if (!intersects (c->glyphs, lookup_context)) return;
+
+    const auto &input = StructAfter<decltype (inputX)> (backtrack);
+    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
+    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
+    recurse_lookups (c, lookup.len, lookup.arrayZ);
+  }
+
+  void collect_glyphs (hb_collect_glyphs_context_t *c,
+		       ChainContextCollectGlyphsLookupContext &lookup_context) const
+  {
+    const auto &input = StructAfter<decltype (inputX)> (backtrack);
+    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
+    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
+    chain_context_collect_glyphs_lookup (c,
+					 backtrack.len, backtrack.arrayZ,
+					 input.lenP1, input.arrayZ,
+					 lookahead.len, lookahead.arrayZ,
+					 lookup.len, lookup.arrayZ,
+					 lookup_context);
+  }
+
+  bool would_apply (hb_would_apply_context_t *c,
+		    const ChainContextApplyLookupContext &lookup_context) const
+  {
+    const auto &input = StructAfter<decltype (inputX)> (backtrack);
+    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
+    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
+    return chain_context_would_apply_lookup (c,
+					     backtrack.len, backtrack.arrayZ,
+					     input.lenP1, input.arrayZ,
+					     lookahead.len, lookahead.arrayZ, lookup.len,
+					     lookup.arrayZ, lookup_context);
+  }
+
+  bool apply (hb_ot_apply_context_t *c,
+	      const ChainContextApplyLookupContext &lookup_context) const
+  {
+    TRACE_APPLY (this);
+    const auto &input = StructAfter<decltype (inputX)> (backtrack);
+    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
+    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
+    return_trace (chain_context_apply_lookup (c,
+					      backtrack.len, backtrack.arrayZ,
+					      input.lenP1, input.arrayZ,
+					      lookahead.len, lookahead.arrayZ, lookup.len,
+					      lookup.arrayZ, lookup_context));
+  }
+
+  template<typename Iterator,
+	   hb_requires (hb_is_iterator (Iterator))>
+  void serialize_array (hb_serialize_context_t *c,
+			HBUINT16 len,
+			Iterator it) const
+  {
+    c->copy (len);
+    for (const auto g : it)
+      c->copy ((HBUINT16) g);
+  }
+
+  bool serialize (hb_serialize_context_t *c,
+		  const hb_map_t *lookup_map,
+		  const hb_map_t *backtrack_map,
+		  const hb_map_t *input_map = nullptr,
+		  const hb_map_t *lookahead_map = nullptr) const
+  {
+    TRACE_SERIALIZE (this);
+    auto *out = c->start_embed (this);
+    if (unlikely (!out)) return_trace (false);
+
+    const hb_map_t *mapping = backtrack_map;
+    serialize_array (c, backtrack.len, + backtrack.iter ()
+				       | hb_map (mapping));
+
+    const auto &input = StructAfter<decltype (inputX)> (backtrack);
+    if (input_map) mapping = input_map;
+    serialize_array (c, input.lenP1, + input.iter ()
+				     | hb_map (mapping));
+
+    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
+    if (lookahead_map) mapping = lookahead_map;
+    serialize_array (c, lookahead.len, + lookahead.iter ()
+				       | hb_map (mapping));
+
+    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
+
+    HBUINT16* lookupCount = c->embed (&(lookup.len));
+    if (!lookupCount) return_trace (false);
+
+    unsigned count = serialize_lookuprecord_array (c, lookup.as_array (), lookup_map);
+    return_trace (c->check_assign (*lookupCount, count, HB_SERIALIZE_ERROR_INT_OVERFLOW));
+  }
+
+  bool subset (hb_subset_context_t *c,
+	       const hb_map_t *lookup_map,
+	       const hb_map_t *backtrack_map = nullptr,
+	       const hb_map_t *input_map = nullptr,
+	       const hb_map_t *lookahead_map = nullptr) const
+  {
+    TRACE_SUBSET (this);
+
+    const auto &input = StructAfter<decltype (inputX)> (backtrack);
+    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
+
+    if (!backtrack_map)
+    {
+      const hb_set_t &glyphset = *c->plan->glyphset_gsub ();
+      if (!hb_all (backtrack, glyphset) ||
+	  !hb_all (input, glyphset) ||
+	  !hb_all (lookahead, glyphset))
+	return_trace (false);
+
+      serialize (c->serializer, lookup_map, c->plan->glyph_map);
+    }
+    else
+    {
+      if (!hb_all (backtrack, backtrack_map) ||
+	  !hb_all (input, input_map) ||
+	  !hb_all (lookahead, lookahead_map))
+	return_trace (false);
+
+      serialize (c->serializer, lookup_map, backtrack_map, input_map, lookahead_map);
+    }
+
+    return_trace (true);
+  }
+
+  bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    if (!backtrack.sanitize (c)) return_trace (false);
+    const auto &input = StructAfter<decltype (inputX)> (backtrack);
+    if (!input.sanitize (c)) return_trace (false);
+    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
+    if (!lookahead.sanitize (c)) return_trace (false);
+    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
+    return_trace (lookup.sanitize (c));
+  }
+
+  protected:
+  Array16Of<typename Types::HBUINT>
+		backtrack;		/* Array of backtracking values
+					 * (to be matched before the input
+					 * sequence) */
+  HeadlessArrayOf<typename Types::HBUINT>
+		inputX;			/* Array of input values (start with
+					 * second glyph) */
+  Array16Of<typename Types::HBUINT>
+		lookaheadX;		/* Array of lookahead values's (to be
+					 * matched after the input sequence) */
+  Array16Of<LookupRecord>
+		lookupX;		/* Array of LookupRecords--in
+					 * design order) */
+  public:
+  DEFINE_SIZE_MIN (8);
+};
+
+template <typename Types>
+struct ChainRuleSet
+{
+  using ChainRule = OT::ChainRule<Types>;
+
+  bool intersects (const hb_set_t *glyphs, ChainContextClosureLookupContext &lookup_context) const
+  {
+    return
+    + hb_iter (rule)
+    | hb_map (hb_add (this))
+    | hb_map ([&] (const ChainRule &_) { return _.intersects (glyphs, lookup_context); })
+    | hb_any
+    ;
+  }
+  void closure (hb_closure_context_t *c, unsigned value, ChainContextClosureLookupContext &lookup_context) const
+  {
+    if (unlikely (c->lookup_limit_exceeded ())) return;
+
+    return
+    + hb_iter (rule)
+    | hb_map (hb_add (this))
+    | hb_apply ([&] (const ChainRule &_) { _.closure (c, value, lookup_context); })
+    ;
+  }
+
+  void closure_lookups (hb_closure_lookups_context_t *c,
+                        ChainContextClosureLookupContext &lookup_context) const
+  {
+    if (unlikely (c->lookup_limit_exceeded ())) return;
+
+    + hb_iter (rule)
+    | hb_map (hb_add (this))
+    | hb_apply ([&] (const ChainRule &_) { _.closure_lookups (c, lookup_context); })
+    ;
+  }
+
+  void collect_glyphs (hb_collect_glyphs_context_t *c, ChainContextCollectGlyphsLookupContext &lookup_context) const
+  {
+    return
+    + hb_iter (rule)
+    | hb_map (hb_add (this))
+    | hb_apply ([&] (const ChainRule &_) { _.collect_glyphs (c, lookup_context); })
+    ;
+  }
+
+  bool would_apply (hb_would_apply_context_t *c,
+		    const ChainContextApplyLookupContext &lookup_context) const
+  {
+    return
+    + hb_iter (rule)
+    | hb_map (hb_add (this))
+    | hb_map ([&] (const ChainRule &_) { return _.would_apply (c, lookup_context); })
+    | hb_any
+    ;
+  }
+
+  bool apply (hb_ot_apply_context_t *c,
+	      const ChainContextApplyLookupContext &lookup_context) const
+  {
+    TRACE_APPLY (this);
+    return_trace (
+    + hb_iter (rule)
+    | hb_map (hb_add (this))
+    | hb_map ([&] (const ChainRule &_) { return _.apply (c, lookup_context); })
+    | hb_any
+    )
+    ;
+  }
+
+  bool subset (hb_subset_context_t *c,
+	       const hb_map_t *lookup_map,
+	       const hb_map_t *backtrack_klass_map = nullptr,
+	       const hb_map_t *input_klass_map = nullptr,
+	       const hb_map_t *lookahead_klass_map = nullptr) const
+  {
+    TRACE_SUBSET (this);
+
+    auto snap = c->serializer->snapshot ();
+    auto *out = c->serializer->start_embed (*this);
+    if (unlikely (!c->serializer->extend_min (out))) return_trace (false);
+
+    for (const Offset16To<ChainRule>& _ : rule)
+    {
+      if (!_) continue;
+      auto o_snap = c->serializer->snapshot ();
+      auto *o = out->rule.serialize_append (c->serializer);
+      if (unlikely (!o)) continue;
+
+      if (!o->serialize_subset (c, _, this,
+				lookup_map,
+				backtrack_klass_map,
+				input_klass_map,
+				lookahead_klass_map))
+      {
+	out->rule.pop ();
+	c->serializer->revert (o_snap);
+      }
+    }
+
+    bool ret = bool (out->rule);
+    if (!ret) c->serializer->revert (snap);
+
+    return_trace (ret);
+  }
+
+  bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    return_trace (rule.sanitize (c, this));
+  }
+
+  protected:
+  Array16OfOffset16To<ChainRule>
+		rule;			/* Array of ChainRule tables
+					 * ordered by preference */
+  public:
+  DEFINE_SIZE_ARRAY (2, rule);
+};
+
+template <typename Types>
+struct ChainContextFormat1_4
+{
+  using ChainRuleSet = OT::ChainRuleSet<Types>;
+
+  bool intersects (const hb_set_t *glyphs) const
+  {
+    struct ChainContextClosureLookupContext lookup_context = {
+      {intersects_glyph, intersected_glyph},
+      ContextFormat::SimpleContext,
+      {nullptr, nullptr, nullptr}
+    };
+
+    return
+    + hb_zip (this+coverage, ruleSet)
+    | hb_filter (*glyphs, hb_first)
+    | hb_map (hb_second)
+    | hb_map (hb_add (this))
+    | hb_map ([&] (const ChainRuleSet &_) { return _.intersects (glyphs, lookup_context); })
+    | hb_any
+    ;
+  }
+
+  bool may_have_non_1to1 () const
+  { return true; }
+
+  void closure (hb_closure_context_t *c) const
+  {
+    hb_set_t& cur_active_glyphs = c->push_cur_active_glyphs ();
+    get_coverage ().intersect_set (c->previous_parent_active_glyphs (),
+                                                 cur_active_glyphs);
+
+    struct ChainContextClosureLookupContext lookup_context = {
+      {intersects_glyph, intersected_glyph},
+      ContextFormat::SimpleContext,
+      {nullptr, nullptr, nullptr}
+    };
+
+    + hb_zip (this+coverage, hb_range ((unsigned) ruleSet.len))
+    | hb_filter ([&] (hb_codepoint_t _) {
+      return c->previous_parent_active_glyphs ().has (_);
+    }, hb_first)
+    | hb_map ([&](const hb_pair_t<hb_codepoint_t, unsigned> _) { return hb_pair_t<unsigned, const ChainRuleSet&> (_.first, this+ruleSet[_.second]); })
+    | hb_apply ([&] (const hb_pair_t<unsigned, const ChainRuleSet&>& _) { _.second.closure (c, _.first, lookup_context); })
+    ;
+
+    c->pop_cur_done_glyphs ();
+  }
+
+  void closure_lookups (hb_closure_lookups_context_t *c) const
+  {
+    struct ChainContextClosureLookupContext lookup_context = {
+      {intersects_glyph, nullptr},
+      ContextFormat::SimpleContext,
+      {nullptr, nullptr, nullptr}
+    };
+
+    + hb_zip (this+coverage, ruleSet)
+    | hb_filter (*c->glyphs, hb_first)
+    | hb_map (hb_second)
+    | hb_map (hb_add (this))
+    | hb_apply ([&] (const ChainRuleSet &_) { _.closure_lookups (c, lookup_context); })
+    ;
+  }
+
+  void collect_variation_indices (hb_collect_variation_indices_context_t *c) const {}
+
+  void collect_glyphs (hb_collect_glyphs_context_t *c) const
+  {
+    (this+coverage).collect_coverage (c->input);
+
+    struct ChainContextCollectGlyphsLookupContext lookup_context = {
+      {collect_glyph},
+      {nullptr, nullptr, nullptr}
+    };
+
+    + hb_iter (ruleSet)
+    | hb_map (hb_add (this))
+    | hb_apply ([&] (const ChainRuleSet &_) { _.collect_glyphs (c, lookup_context); })
+    ;
+  }
+
+  bool would_apply (hb_would_apply_context_t *c) const
+  {
+    const ChainRuleSet &rule_set = this+ruleSet[(this+coverage).get_coverage (c->glyphs[0])];
+    struct ChainContextApplyLookupContext lookup_context = {
+      {{match_glyph, match_glyph, match_glyph}},
+      {nullptr, nullptr, nullptr}
+    };
+    return rule_set.would_apply (c, lookup_context);
+  }
+
+  const Coverage &get_coverage () const { return this+coverage; }
+
+  bool apply (hb_ot_apply_context_t *c) const
+  {
+    TRACE_APPLY (this);
+    unsigned int index = (this+coverage).get_coverage (c->buffer->cur().codepoint);
+    if (likely (index == NOT_COVERED)) return_trace (false);
+
+    const ChainRuleSet &rule_set = this+ruleSet[index];
+    struct ChainContextApplyLookupContext lookup_context = {
+      {{match_glyph, match_glyph, match_glyph}},
+      {nullptr, nullptr, nullptr}
+    };
+    return_trace (rule_set.apply (c, lookup_context));
+  }
+
+  bool subset (hb_subset_context_t *c) const
+  {
+    TRACE_SUBSET (this);
+    const hb_set_t &glyphset = *c->plan->glyphset_gsub ();
+    const hb_map_t &glyph_map = *c->plan->glyph_map;
+
+    auto *out = c->serializer->start_embed (*this);
+    if (unlikely (!c->serializer->extend_min (out))) return_trace (false);
+    out->format = format;
+
+    const hb_map_t *lookup_map = c->table_tag == HB_OT_TAG_GSUB ? c->plan->gsub_lookups : c->plan->gpos_lookups;
+    hb_sorted_vector_t<hb_codepoint_t> new_coverage;
+    + hb_zip (this+coverage, ruleSet)
+    | hb_filter (glyphset, hb_first)
+    | hb_filter (subset_offset_array (c, out->ruleSet, this, lookup_map), hb_second)
+    | hb_map (hb_first)
+    | hb_map (glyph_map)
+    | hb_sink (new_coverage)
+    ;
+
+    out->coverage.serialize_serialize (c->serializer, new_coverage.iter ());
+    return_trace (bool (new_coverage));
+  }
+
+  bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    return_trace (coverage.sanitize (c, this) && ruleSet.sanitize (c, this));
+  }
+
+  protected:
+  HBUINT16	format;			/* Format identifier--format = 1 */
+  typename Types::template OffsetTo<Coverage>
+		coverage;		/* Offset to Coverage table--from
+					 * beginning of table */
+  Array16Of<typename Types::template OffsetTo<ChainRuleSet>>
+		ruleSet;		/* Array of ChainRuleSet tables
+					 * ordered by Coverage Index */
+  public:
+  DEFINE_SIZE_ARRAY (2 + 2 * Types::size, ruleSet);
+};
+
+template <typename Types>
+struct ChainContextFormat2_5
+{
+  using ChainRuleSet = OT::ChainRuleSet<SmallTypes>;
+
+  bool intersects (const hb_set_t *glyphs) const
+  {
+    if (!(this+coverage).intersects (glyphs))
+      return false;
+
+    const ClassDef &backtrack_class_def = this+backtrackClassDef;
+    const ClassDef &input_class_def = this+inputClassDef;
+    const ClassDef &lookahead_class_def = this+lookaheadClassDef;
+
+    hb_map_t caches[3] = {};
+    struct ChainContextClosureLookupContext lookup_context = {
+      {intersects_class, nullptr},
+      ContextFormat::ClassBasedContext,
+      {&backtrack_class_def,
+       &input_class_def,
+       &lookahead_class_def},
+      {&caches[0], &caches[1], &caches[2]}
+    };
+
+    hb_set_t retained_coverage_glyphs;
+    (this+coverage).intersect_set (*glyphs, retained_coverage_glyphs);
+
+    hb_set_t coverage_glyph_classes;
+    input_class_def.intersected_classes (&retained_coverage_glyphs, &coverage_glyph_classes);
+
+    return
+    + hb_iter (ruleSet)
+    | hb_map (hb_add (this))
+    | hb_enumerate
+    | hb_map ([&] (const hb_pair_t<unsigned, const ChainRuleSet &> p)
+	      { return input_class_def.intersects_class (glyphs, p.first) &&
+		       coverage_glyph_classes.has (p.first) &&
+		       p.second.intersects (glyphs, lookup_context); })
+    | hb_any
+    ;
+  }
+
+  bool may_have_non_1to1 () const
+  { return true; }
+
+  void closure (hb_closure_context_t *c) const
+  {
+    if (!(this+coverage).intersects (c->glyphs))
+      return;
+
+    hb_set_t& cur_active_glyphs = c->push_cur_active_glyphs ();
+    get_coverage ().intersect_set (c->previous_parent_active_glyphs (),
+                                                 cur_active_glyphs);
+
+
+    const ClassDef &backtrack_class_def = this+backtrackClassDef;
+    const ClassDef &input_class_def = this+inputClassDef;
+    const ClassDef &lookahead_class_def = this+lookaheadClassDef;
+
+    hb_map_t caches[3] = {};
+    intersected_class_cache_t intersected_cache;
+    struct ChainContextClosureLookupContext lookup_context = {
+      {intersects_class, intersected_class_glyphs},
+      ContextFormat::ClassBasedContext,
+      {&backtrack_class_def,
+       &input_class_def,
+       &lookahead_class_def},
+      {&caches[0], &caches[1], &caches[2]},
+      &intersected_cache
+    };
+
+    + hb_enumerate (ruleSet)
+    | hb_filter ([&] (unsigned _)
+    { return input_class_def.intersects_class (&c->parent_active_glyphs (), _); },
+		 hb_first)
+    | hb_apply ([&] (const hb_pair_t<unsigned, const typename Types::template OffsetTo<ChainRuleSet>&> _)
+                {
+                  const ChainRuleSet& chainrule_set = this+_.second;
+                  chainrule_set.closure (c, _.first, lookup_context);
+                })
+    ;
+
+    c->pop_cur_done_glyphs ();
+  }
+
+  void closure_lookups (hb_closure_lookups_context_t *c) const
+  {
+    if (!(this+coverage).intersects (c->glyphs))
+      return;
+
+    const ClassDef &backtrack_class_def = this+backtrackClassDef;
+    const ClassDef &input_class_def = this+inputClassDef;
+    const ClassDef &lookahead_class_def = this+lookaheadClassDef;
+
+    hb_map_t caches[3] = {};
+    struct ChainContextClosureLookupContext lookup_context = {
+      {intersects_class, nullptr},
+      ContextFormat::ClassBasedContext,
+      {&backtrack_class_def,
+       &input_class_def,
+       &lookahead_class_def},
+      {&caches[0], &caches[1], &caches[2]}
+    };
+
+    + hb_iter (ruleSet)
+    | hb_map (hb_add (this))
+    | hb_enumerate
+    | hb_filter([&] (unsigned klass)
+    { return input_class_def.intersects_class (c->glyphs, klass); }, hb_first)
+    | hb_map (hb_second)
+    | hb_apply ([&] (const ChainRuleSet &_)
+    { _.closure_lookups (c, lookup_context); })
+    ;
+  }
+
+  void collect_variation_indices (hb_collect_variation_indices_context_t *c) const {}
+
+  void collect_glyphs (hb_collect_glyphs_context_t *c) const
+  {
+    (this+coverage).collect_coverage (c->input);
+
+    const ClassDef &backtrack_class_def = this+backtrackClassDef;
+    const ClassDef &input_class_def = this+inputClassDef;
+    const ClassDef &lookahead_class_def = this+lookaheadClassDef;
+
+    struct ChainContextCollectGlyphsLookupContext lookup_context = {
+      {collect_class},
+      {&backtrack_class_def,
+       &input_class_def,
+       &lookahead_class_def}
+    };
+
+    + hb_iter (ruleSet)
+    | hb_map (hb_add (this))
+    | hb_apply ([&] (const ChainRuleSet &_) { _.collect_glyphs (c, lookup_context); })
+    ;
+  }
+
+  bool would_apply (hb_would_apply_context_t *c) const
+  {
+    const ClassDef &backtrack_class_def = this+backtrackClassDef;
+    const ClassDef &input_class_def = this+inputClassDef;
+    const ClassDef &lookahead_class_def = this+lookaheadClassDef;
+
+    unsigned int index = input_class_def.get_class (c->glyphs[0]);
+    const ChainRuleSet &rule_set = this+ruleSet[index];
+    struct ChainContextApplyLookupContext lookup_context = {
+      {{match_class, match_class, match_class}},
+      {&backtrack_class_def,
+       &input_class_def,
+       &lookahead_class_def}
+    };
+    return rule_set.would_apply (c, lookup_context);
+  }
+
+  const Coverage &get_coverage () const { return this+coverage; }
+
+  unsigned cache_cost () const
+  {
+    unsigned c = (this+lookaheadClassDef).cost () * ruleSet.len;
+    return c >= 4 ? c : 0;
+  }
+  bool cache_func (hb_ot_apply_context_t *c, bool enter) const
+  {
+    if (enter)
+    {
+      if (!HB_BUFFER_TRY_ALLOCATE_VAR (c->buffer, syllable))
+	return false;
+      auto &info = c->buffer->info;
+      unsigned count = c->buffer->len;
+      for (unsigned i = 0; i < count; i++)
+	info[i].syllable() = 255;
+      c->new_syllables = 255;
+      return true;
+    }
+    else
+    {
+      c->new_syllables = (unsigned) -1;
+      HB_BUFFER_DEALLOCATE_VAR (c->buffer, syllable);
+      return true;
+    }
+  }
+
+  bool apply (hb_ot_apply_context_t *c, bool cached = false) const
+  {
+    TRACE_APPLY (this);
+    unsigned int index = (this+coverage).get_coverage (c->buffer->cur().codepoint);
+    if (likely (index == NOT_COVERED)) return_trace (false);
+
+    const ClassDef &backtrack_class_def = this+backtrackClassDef;
+    const ClassDef &input_class_def = this+inputClassDef;
+    const ClassDef &lookahead_class_def = this+lookaheadClassDef;
+
+    /* For ChainContextFormat2_5 we cache the LookaheadClassDef instead of InputClassDef.
+     * The reason is that most heavy fonts want to identify a glyph in context and apply
+     * a lookup to it. In this scenario, the length of the input sequence is one, whereas
+     * the lookahead / backtrack are typically longer.  The one glyph in input sequence is
+     * looked-up below and no input glyph is looked up in individual rules, whereas the
+     * lookahead and backtrack glyphs are tried.  Since we match lookahead before backtrack,
+     * we should cache lookahead.  This decisions showed a 20% improvement in shaping of
+     * the Gulzar font.
+     */
+
+    struct ChainContextApplyLookupContext lookup_context = {
+      {{cached && &backtrack_class_def == &input_class_def ? match_class_cached : match_class,
+        cached && &input_class_def == &lookahead_class_def ? match_class_cached : match_class,
+        cached ? match_class_cached : match_class}},
+      {&backtrack_class_def,
+       &input_class_def,
+       &lookahead_class_def}
+    };
+
+    index = input_class_def.get_class (c->buffer->cur().codepoint);
+    const ChainRuleSet &rule_set = this+ruleSet[index];
+    return_trace (rule_set.apply (c, lookup_context));
+  }
+
+  bool subset (hb_subset_context_t *c) const
+  {
+    TRACE_SUBSET (this);
+    auto *out = c->serializer->start_embed (*this);
+    if (unlikely (!c->serializer->extend_min (out))) return_trace (false);
+    out->format = format;
+    out->coverage.serialize_subset (c, coverage, this);
+
+    hb_map_t backtrack_klass_map;
+    hb_map_t input_klass_map;
+    hb_map_t lookahead_klass_map;
+
+    out->backtrackClassDef.serialize_subset (c, backtrackClassDef, this, &backtrack_klass_map);
+    // TODO: subset inputClassDef based on glyphs survived in Coverage subsetting
+    out->inputClassDef.serialize_subset (c, inputClassDef, this, &input_klass_map);
+    out->lookaheadClassDef.serialize_subset (c, lookaheadClassDef, this, &lookahead_klass_map);
+
+    if (unlikely (!c->serializer->propagate_error (backtrack_klass_map,
+						   input_klass_map,
+						   lookahead_klass_map)))
+      return_trace (false);
+
+    const hb_set_t* glyphset = c->plan->glyphset_gsub ();
+    hb_set_t retained_coverage_glyphs;
+    (this+coverage).intersect_set (*glyphset, retained_coverage_glyphs);
+
+    hb_set_t coverage_glyph_classes;
+    (this+inputClassDef).intersected_classes (&retained_coverage_glyphs, &coverage_glyph_classes);
+
+    int non_zero_index = -1, index = 0;
+    bool ret = true;
+    const hb_map_t *lookup_map = c->table_tag == HB_OT_TAG_GSUB ? c->plan->gsub_lookups : c->plan->gpos_lookups;
+    auto last_non_zero = c->serializer->snapshot ();
+    for (const auto& _ : + hb_enumerate (ruleSet)
+			 | hb_filter (input_klass_map, hb_first))
+    {
+      auto *o = out->ruleSet.serialize_append (c->serializer);
+      if (unlikely (!o))
+      {
+	ret = false;
+	break;
+      }
+      if (coverage_glyph_classes.has (_.first) &&
+          o->serialize_subset (c, _.second, this,
+			       lookup_map,
+			       &backtrack_klass_map,
+			       &input_klass_map,
+			       &lookahead_klass_map))
+      {
+        last_non_zero = c->serializer->snapshot ();
+	non_zero_index = index;
+      }
+
+      index++;
+    }
+
+    if (!ret || non_zero_index == -1) return_trace (false);
+
+    // prune empty trailing ruleSets
+    if (index > non_zero_index) {
+      c->serializer->revert (last_non_zero);
+      out->ruleSet.len = non_zero_index + 1;
+    }
+
+    return_trace (bool (out->ruleSet));
+  }
+
+  bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    return_trace (coverage.sanitize (c, this) &&
+		  backtrackClassDef.sanitize (c, this) &&
+		  inputClassDef.sanitize (c, this) &&
+		  lookaheadClassDef.sanitize (c, this) &&
+		  ruleSet.sanitize (c, this));
+  }
+
+  protected:
+  HBUINT16	format;			/* Format identifier--format = 2 */
+  typename Types::template OffsetTo<Coverage>
+		coverage;		/* Offset to Coverage table--from
+					 * beginning of table */
+  typename Types::template OffsetTo<ClassDef>
+		backtrackClassDef;	/* Offset to glyph ClassDef table
+					 * containing backtrack sequence
+					 * data--from beginning of table */
+  typename Types::template OffsetTo<ClassDef>
+		inputClassDef;		/* Offset to glyph ClassDef
+					 * table containing input sequence
+					 * data--from beginning of table */
+  typename Types::template OffsetTo<ClassDef>
+		lookaheadClassDef;	/* Offset to glyph ClassDef table
+					 * containing lookahead sequence
+					 * data--from beginning of table */
+  Array16Of<typename Types::template OffsetTo<ChainRuleSet>>
+		ruleSet;		/* Array of ChainRuleSet tables
+					 * ordered by class */
+  public:
+  DEFINE_SIZE_ARRAY (4 + 4 * Types::size, ruleSet);
+};
+
+struct ChainContextFormat3
+{
+  using RuleSet = OT::RuleSet<SmallTypes>;
+
+  bool intersects (const hb_set_t *glyphs) const
+  {
+    const auto &input = StructAfter<decltype (inputX)> (backtrack);
+
+    if (!(this+input[0]).intersects (glyphs))
+      return false;
+
+    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
+    struct ChainContextClosureLookupContext lookup_context = {
+      {intersects_coverage, nullptr},
+      ContextFormat::CoverageBasedContext,
+      {this, this, this}
+    };
+    return chain_context_intersects (glyphs,
+				     backtrack.len, (const HBUINT16 *) backtrack.arrayZ,
+				     input.len, (const HBUINT16 *) input.arrayZ + 1,
+				     lookahead.len, (const HBUINT16 *) lookahead.arrayZ,
+				     lookup_context);
+  }
+
+  bool may_have_non_1to1 () const
+  { return true; }
+
+  void closure (hb_closure_context_t *c) const
+  {
+    const auto &input = StructAfter<decltype (inputX)> (backtrack);
+
+    if (!(this+input[0]).intersects (c->glyphs))
+      return;
+
+    hb_set_t& cur_active_glyphs = c->push_cur_active_glyphs ();
+    get_coverage ().intersect_set (c->previous_parent_active_glyphs (),
+                                                 cur_active_glyphs);
+
+
+    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
+    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
+    struct ChainContextClosureLookupContext lookup_context = {
+      {intersects_coverage, intersected_coverage_glyphs},
+      ContextFormat::CoverageBasedContext,
+      {this, this, this}
+    };
+    chain_context_closure_lookup (c,
+				  backtrack.len, (const HBUINT16 *) backtrack.arrayZ,
+				  input.len, (const HBUINT16 *) input.arrayZ + 1,
+				  lookahead.len, (const HBUINT16 *) lookahead.arrayZ,
+				  lookup.len, lookup.arrayZ,
+				  0, lookup_context);
+
+    c->pop_cur_done_glyphs ();
+  }
+
+  void closure_lookups (hb_closure_lookups_context_t *c) const
+  {
+    if (!intersects (c->glyphs))
+      return;
+
+    const auto &input = StructAfter<decltype (inputX)> (backtrack);
+    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
+    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
+    recurse_lookups (c, lookup.len, lookup.arrayZ);
+  }
+
+  void collect_variation_indices (hb_collect_variation_indices_context_t *c) const {}
+
+  void collect_glyphs (hb_collect_glyphs_context_t *c) const
+  {
+    const auto &input = StructAfter<decltype (inputX)> (backtrack);
+
+    (this+input[0]).collect_coverage (c->input);
+
+    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
+    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
+
+    struct ChainContextCollectGlyphsLookupContext lookup_context = {
+      {collect_coverage},
+      {this, this, this}
+    };
+    chain_context_collect_glyphs_lookup (c,
+					 backtrack.len, (const HBUINT16 *) backtrack.arrayZ,
+					 input.len, (const HBUINT16 *) input.arrayZ + 1,
+					 lookahead.len, (const HBUINT16 *) lookahead.arrayZ,
+					 lookup.len, lookup.arrayZ,
+					 lookup_context);
+  }
+
+  bool would_apply (hb_would_apply_context_t *c) const
+  {
+    const auto &input = StructAfter<decltype (inputX)> (backtrack);
+    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
+    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
+    struct ChainContextApplyLookupContext lookup_context = {
+      {{match_coverage, match_coverage, match_coverage}},
+      {this, this, this}
+    };
+    return chain_context_would_apply_lookup (c,
+					     backtrack.len, (const HBUINT16 *) backtrack.arrayZ,
+					     input.len, (const HBUINT16 *) input.arrayZ + 1,
+					     lookahead.len, (const HBUINT16 *) lookahead.arrayZ,
+					     lookup.len, lookup.arrayZ, lookup_context);
+  }
+
+  const Coverage &get_coverage () const
+  {
+    const auto &input = StructAfter<decltype (inputX)> (backtrack);
+    return this+input[0];
+  }
+
+  bool apply (hb_ot_apply_context_t *c) const
+  {
+    TRACE_APPLY (this);
+    const auto &input = StructAfter<decltype (inputX)> (backtrack);
+
+    unsigned int index = (this+input[0]).get_coverage (c->buffer->cur().codepoint);
+    if (likely (index == NOT_COVERED)) return_trace (false);
+
+    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
+    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
+    struct ChainContextApplyLookupContext lookup_context = {
+      {{match_coverage, match_coverage, match_coverage}},
+      {this, this, this}
+    };
+    return_trace (chain_context_apply_lookup (c,
+					      backtrack.len, (const HBUINT16 *) backtrack.arrayZ,
+					      input.len, (const HBUINT16 *) input.arrayZ + 1,
+					      lookahead.len, (const HBUINT16 *) lookahead.arrayZ,
+					      lookup.len, lookup.arrayZ, lookup_context));
+  }
+
+  template<typename Iterator,
+	   hb_requires (hb_is_iterator (Iterator))>
+  bool serialize_coverage_offsets (hb_subset_context_t *c, Iterator it, const void* base) const
+  {
+    TRACE_SERIALIZE (this);
+    auto *out = c->serializer->start_embed<Array16OfOffset16To<Coverage>> ();
+
+    if (unlikely (!c->serializer->allocate_size<HBUINT16> (HBUINT16::static_size)))
+      return_trace (false);
+
+    for (auto& offset : it) {
+      auto *o = out->serialize_append (c->serializer);
+      if (unlikely (!o) || !o->serialize_subset (c, offset, base))
+        return_trace (false);
+    }
+
+    return_trace (true);
+  }
+
+  bool subset (hb_subset_context_t *c) const
+  {
+    TRACE_SUBSET (this);
+
+    auto *out = c->serializer->start_embed (this);
+    if (unlikely (!out)) return_trace (false);
+    if (unlikely (!c->serializer->embed (this->format))) return_trace (false);
+
+    if (!serialize_coverage_offsets (c, backtrack.iter (), this))
+      return_trace (false);
+
+    const auto &input = StructAfter<decltype (inputX)> (backtrack);
+    if (!serialize_coverage_offsets (c, input.iter (), this))
+      return_trace (false);
+
+    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
+    if (!serialize_coverage_offsets (c, lookahead.iter (), this))
+      return_trace (false);
+
+    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
+    const hb_map_t *lookup_map = c->table_tag == HB_OT_TAG_GSUB ? c->plan->gsub_lookups : c->plan->gpos_lookups;
+
+    HBUINT16 *lookupCount = c->serializer->copy<HBUINT16> (lookup.len);
+    if (!lookupCount) return_trace (false);
+
+    unsigned count = serialize_lookuprecord_array (c->serializer, lookup.as_array (), lookup_map);
+    return_trace (c->serializer->check_assign (*lookupCount, count, HB_SERIALIZE_ERROR_INT_OVERFLOW));
+  }
+
+  bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    if (!backtrack.sanitize (c, this)) return_trace (false);
+    const auto &input = StructAfter<decltype (inputX)> (backtrack);
+    if (!input.sanitize (c, this)) return_trace (false);
+    if (!input.len) return_trace (false); /* To be consistent with Context. */
+    const auto &lookahead = StructAfter<decltype (lookaheadX)> (input);
+    if (!lookahead.sanitize (c, this)) return_trace (false);
+    const auto &lookup = StructAfter<decltype (lookupX)> (lookahead);
+    return_trace (lookup.sanitize (c));
+  }
+
+  protected:
+  HBUINT16	format;			/* Format identifier--format = 3 */
+  Array16OfOffset16To<Coverage>
+		backtrack;		/* Array of coverage tables
+					 * in backtracking sequence, in  glyph
+					 * sequence order */
+  Array16OfOffset16To<Coverage>
+		inputX		;	/* Array of coverage
+					 * tables in input sequence, in glyph
+					 * sequence order */
+  Array16OfOffset16To<Coverage>
+		lookaheadX;		/* Array of coverage tables
+					 * in lookahead sequence, in glyph
+					 * sequence order */
+  Array16Of<LookupRecord>
+		lookupX;		/* Array of LookupRecords--in
+					 * design order) */
+  public:
+  DEFINE_SIZE_MIN (10);
+};
+
+struct ChainContext
+{
+  template <typename context_t, typename ...Ts>
+  typename context_t::return_t dispatch (context_t *c, Ts&&... ds) const
+  {
+    TRACE_DISPATCH (this, u.format);
+    if (unlikely (!c->may_dispatch (this, &u.format))) return_trace (c->no_dispatch_return_value ());
+    switch (u.format) {
+    case 1: return_trace (c->dispatch (u.format1, std::forward<Ts> (ds)...));
+    case 2: return_trace (c->dispatch (u.format2, std::forward<Ts> (ds)...));
+    case 3: return_trace (c->dispatch (u.format3, std::forward<Ts> (ds)...));
+#ifndef HB_NO_BEYOND_64K
+    case 4: return_trace (c->dispatch (u.format4, std::forward<Ts> (ds)...));
+    case 5: return_trace (c->dispatch (u.format5, std::forward<Ts> (ds)...));
+#endif
+    default:return_trace (c->default_return_value ());
+    }
+  }
+
+  protected:
+  union {
+  HBUINT16				format;	/* Format identifier */
+  ChainContextFormat1_4<SmallTypes>	format1;
+  ChainContextFormat2_5<SmallTypes>	format2;
+  ChainContextFormat3			format3;
+#ifndef HB_NO_BEYOND_64K
+  ChainContextFormat1_4<MediumTypes>	format4;
+  ChainContextFormat2_5<MediumTypes>	format5;
+#endif
+  } u;
+};
+
+
+template <typename T>
+struct ExtensionFormat1
+{
+  unsigned int get_type () const { return extensionLookupType; }
+
+  template <typename X>
+  const X& get_subtable () const
+  { return this + reinterpret_cast<const Offset32To<typename T::SubTable> &> (extensionOffset); }
+
+  template <typename context_t, typename ...Ts>
+  typename context_t::return_t dispatch (context_t *c, Ts&&... ds) const
+  {
+    TRACE_DISPATCH (this, format);
+    if (unlikely (!c->may_dispatch (this, this))) return_trace (c->no_dispatch_return_value ());
+    return_trace (get_subtable<typename T::SubTable> ().dispatch (c, get_type (), std::forward<Ts> (ds)...));
+  }
+
+  void collect_variation_indices (hb_collect_variation_indices_context_t *c) const
+  { dispatch (c); }
+
+  /* This is called from may_dispatch() above with hb_sanitize_context_t. */
+  bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    return_trace (c->check_struct (this) &&
+		  extensionLookupType != T::SubTable::Extension);
+  }
+
+  bool subset (hb_subset_context_t *c) const
+  {
+    TRACE_SUBSET (this);
+
+    auto *out = c->serializer->start_embed (this);
+    if (unlikely (!out || !c->serializer->extend_min (out))) return_trace (false);
+
+    out->format = format;
+    out->extensionLookupType = extensionLookupType;
+
+    const auto& src_offset =
+        reinterpret_cast<const Offset32To<typename T::SubTable> &> (extensionOffset);
+    auto& dest_offset =
+        reinterpret_cast<Offset32To<typename T::SubTable> &> (out->extensionOffset);
+
+    return_trace (dest_offset.serialize_subset (c, src_offset, this, get_type ()));
+  }
+
+  protected:
+  HBUINT16	format;			/* Format identifier. Set to 1. */
+  HBUINT16	extensionLookupType;	/* Lookup type of subtable referenced
+					 * by ExtensionOffset (i.e. the
+					 * extension subtable). */
+  Offset32	extensionOffset;	/* Offset to the extension subtable,
+					 * of lookup type subtable. */
+  public:
+  DEFINE_SIZE_STATIC (8);
+};
+
+template <typename T>
+struct Extension
+{
+  unsigned int get_type () const
+  {
+    switch (u.format) {
+    case 1: return u.format1.get_type ();
+    default:return 0;
+    }
+  }
+  template <typename X>
+  const X& get_subtable () const
+  {
+    switch (u.format) {
+    case 1: return u.format1.template get_subtable<typename T::SubTable> ();
+    default:return Null (typename T::SubTable);
+    }
+  }
+
+  // Specialization of dispatch for subset. dispatch() normally just
+  // dispatches to the sub table this points too, but for subset
+  // we need to run subset on this subtable too.
+  template <typename ...Ts>
+  typename hb_subset_context_t::return_t dispatch (hb_subset_context_t *c, Ts&&... ds) const
+  {
+    switch (u.format) {
+    case 1: return u.format1.subset (c);
+    default: return c->default_return_value ();
+    }
+  }
+
+  template <typename context_t, typename ...Ts>
+  typename context_t::return_t dispatch (context_t *c, Ts&&... ds) const
+  {
+    TRACE_DISPATCH (this, u.format);
+    if (unlikely (!c->may_dispatch (this, &u.format))) return_trace (c->no_dispatch_return_value ());
+    switch (u.format) {
+    case 1: return_trace (u.format1.dispatch (c, std::forward<Ts> (ds)...));
+    default:return_trace (c->default_return_value ());
+    }
+  }
+
+  protected:
+  union {
+  HBUINT16		format;		/* Format identifier */
+  ExtensionFormat1<T>	format1;
+  } u;
+};
+
+
+/*
+ * GSUB/GPOS Common
+ */
+
+struct hb_ot_layout_lookup_accelerator_t
+{
+  template <typename TLookup>
+  void init (const TLookup &lookup)
+  {
+    subtables.init ();
+    hb_accelerate_subtables_context_t c_accelerate_subtables (subtables);
+    lookup.dispatch (&c_accelerate_subtables);
+
+    digest.init ();
+    for (auto& subtable : hb_iter (subtables))
+      digest.add (subtable.digest);
+
+#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
+    cache_user_idx = c_accelerate_subtables.cache_user_idx;
+    for (unsigned i = 0; i < subtables.length; i++)
+      if (i != cache_user_idx)
+	subtables[i].apply_cached_func = subtables[i].apply_func;
+#endif
+  }
+  void fini () { subtables.fini (); }
+
+  bool may_have (hb_codepoint_t g) const
+  { return digest.may_have (g); }
+
+  bool apply (hb_ot_apply_context_t *c, bool use_cache) const
+  {
+#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
+    if (use_cache)
+    {
+      return
+      + hb_iter (subtables)
+      | hb_map ([&c] (const hb_accelerate_subtables_context_t::hb_applicable_t &_) { return _.apply_cached (c); })
+      | hb_any
+      ;
+    }
+    else
+#endif
+    {
+      return
+      + hb_iter (subtables)
+      | hb_map ([&c] (const hb_accelerate_subtables_context_t::hb_applicable_t &_) { return _.apply (c); })
+      | hb_any
+      ;
+    }
+    return false;
+  }
+
+  bool cache_enter (hb_ot_apply_context_t *c) const
+  {
+#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
+    return cache_user_idx != (unsigned) -1 &&
+	   subtables[cache_user_idx].cache_enter (c);
+#else
+    return false;
+#endif
+  }
+  void cache_leave (hb_ot_apply_context_t *c) const
+  {
+#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
+    subtables[cache_user_idx].cache_leave (c);
+#endif
+  }
+
+
+  hb_set_digest_t digest;
+  private:
+  hb_accelerate_subtables_context_t::array_t subtables;
+#ifndef HB_NO_OT_LAYOUT_LOOKUP_CACHE
+  unsigned cache_user_idx = (unsigned) -1;
+#endif
+};
+
+template <typename Types>
+struct GSUBGPOSVersion1_2
+{
+  friend struct GSUBGPOS;
+
+  protected:
+  FixedVersion<>version;	/* Version of the GSUB/GPOS table--initially set
+				 * to 0x00010000u */
+  typename Types:: template OffsetTo<ScriptList>
+		scriptList;	/* ScriptList table */
+  typename Types::template OffsetTo<FeatureList>
+		featureList;	/* FeatureList table */
+  typename Types::template OffsetTo<LookupList<Types>>
+		lookupList;	/* LookupList table */
+  Offset32To<FeatureVariations>
+		featureVars;	/* Offset to Feature Variations
+				   table--from beginning of table
+				 * (may be NULL).  Introduced
+				 * in version 0x00010001. */
+  public:
+  DEFINE_SIZE_MIN (4 + 3 * Types::size);
+
+  unsigned int get_size () const
+  {
+    return min_size +
+	   (version.to_int () >= 0x00010001u ? featureVars.static_size : 0);
+  }
+
+  const typename Types::template OffsetTo<LookupList<Types>>* get_lookup_list_offset () const
+  {
+    return &lookupList;
+  }
+
+  template <typename TLookup>
+  bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    typedef List16OfOffsetTo<TLookup, typename Types::HBUINT> TLookupList;
+    if (unlikely (!(scriptList.sanitize (c, this) &&
+		    featureList.sanitize (c, this) &&
+		    reinterpret_cast<const typename Types::template OffsetTo<TLookupList> &> (lookupList).sanitize (c, this))))
+      return_trace (false);
+
+#ifndef HB_NO_VAR
+    if (unlikely (!(version.to_int () < 0x00010001u || featureVars.sanitize (c, this))))
+      return_trace (false);
+#endif
+
+    return_trace (true);
+  }
+
+  template <typename TLookup>
+  bool subset (hb_subset_layout_context_t *c) const
+  {
+    TRACE_SUBSET (this);
+    auto *out = c->subset_context->serializer->embed (*this);
+    if (unlikely (!out)) return_trace (false);
+
+    typedef LookupOffsetList<TLookup, typename Types::HBUINT> TLookupList;
+    reinterpret_cast<typename Types::template OffsetTo<TLookupList> &> (out->lookupList)
+	.serialize_subset (c->subset_context,
+			   reinterpret_cast<const typename Types::template OffsetTo<TLookupList> &> (lookupList),
+			   this,
+			   c);
+
+    reinterpret_cast<typename Types::template OffsetTo<RecordListOfFeature> &> (out->featureList)
+	.serialize_subset (c->subset_context,
+			   reinterpret_cast<const typename Types::template OffsetTo<RecordListOfFeature> &> (featureList),
+			   this,
+			   c);
+
+    out->scriptList.serialize_subset (c->subset_context,
+				      scriptList,
+				      this,
+				      c);
+
+#ifndef HB_NO_VAR
+    if (version.to_int () >= 0x00010001u)
+    {
+      bool ret = out->featureVars.serialize_subset (c->subset_context, featureVars, this, c);
+      if (!ret && version.major == 1)
+      {
+	out->version.major = 1;
+	out->version.minor = 0;
+      }
+    }
+#endif
+
+    return_trace (true);
+  }
+};
+
+struct GSUBGPOS
+{
+  unsigned int get_size () const
+  {
+    switch (u.version.major) {
+    case 1: return u.version1.get_size ();
+#ifndef HB_NO_BEYOND_64K
+    case 2: return u.version2.get_size ();
+#endif
+    default: return u.version.static_size;
+    }
+  }
+
+  template <typename TLookup>
+  bool sanitize (hb_sanitize_context_t *c) const
+  {
+    TRACE_SANITIZE (this);
+    if (unlikely (!u.version.sanitize (c))) return_trace (false);
+    switch (u.version.major) {
+    case 1: return_trace (u.version1.sanitize<TLookup> (c));
+#ifndef HB_NO_BEYOND_64K
+    case 2: return_trace (u.version2.sanitize<TLookup> (c));
+#endif
+    default: return_trace (true);
+    }
+  }
+
+  template <typename TLookup>
+  bool subset (hb_subset_layout_context_t *c) const
+  {
+    switch (u.version.major) {
+    case 1: return u.version1.subset<TLookup> (c);
+#ifndef HB_NO_BEYOND_64K
+    case 2: return u.version2.subset<TLookup> (c);
+#endif
+    default: return false;
+    }
+  }
+
+  const ScriptList &get_script_list () const
+  {
+    switch (u.version.major) {
+    case 1: return this+u.version1.scriptList;
+#ifndef HB_NO_BEYOND_64K
+    case 2: return this+u.version2.scriptList;
+#endif
+    default: return Null (ScriptList);
+    }
+  }
+  const FeatureList &get_feature_list () const
+  {
+    switch (u.version.major) {
+    case 1: return this+u.version1.featureList;
+#ifndef HB_NO_BEYOND_64K
+    case 2: return this+u.version2.featureList;
+#endif
+    default: return Null (FeatureList);
+    }
+  }
+  unsigned int get_lookup_count () const
+  {
+    switch (u.version.major) {
+    case 1: return (this+u.version1.lookupList).len;
+#ifndef HB_NO_BEYOND_64K
+    case 2: return (this+u.version2.lookupList).len;
+#endif
+    default: return 0;
+    }
+  }
+  const Lookup& get_lookup (unsigned int i) const
+  {
+    switch (u.version.major) {
+    case 1: return (this+u.version1.lookupList)[i];
+#ifndef HB_NO_BEYOND_64K
+    case 2: return (this+u.version2.lookupList)[i];
+#endif
+    default: return Null (Lookup);
+    }
+  }
+  const FeatureVariations &get_feature_variations () const
+  {
+    switch (u.version.major) {
+    case 1: return (u.version.to_int () >= 0x00010001u ? this+u.version1.featureVars : Null (FeatureVariations));
+#ifndef HB_NO_BEYOND_64K
+    case 2: return this+u.version2.featureVars;
+#endif
+    default: return Null (FeatureVariations);
+    }
+  }
+
+  bool has_data () const { return u.version.to_int (); }
+  unsigned int get_script_count () const
+  { return get_script_list ().len; }
+  const Tag& get_script_tag (unsigned int i) const
+  { return get_script_list ().get_tag (i); }
+  unsigned int get_script_tags (unsigned int start_offset,
+				unsigned int *script_count /* IN/OUT */,
+				hb_tag_t     *script_tags /* OUT */) const
+  { return get_script_list ().get_tags (start_offset, script_count, script_tags); }
+  const Script& get_script (unsigned int i) const
+  { return get_script_list ()[i]; }
+  bool find_script_index (hb_tag_t tag, unsigned int *index) const
+  { return get_script_list ().find_index (tag, index); }
+
+  unsigned int get_feature_count () const
+  { return get_feature_list ().len; }
+  hb_tag_t get_feature_tag (unsigned int i) const
+  { return i == Index::NOT_FOUND_INDEX ? HB_TAG_NONE : get_feature_list ().get_tag (i); }
+  unsigned int get_feature_tags (unsigned int start_offset,
+				 unsigned int *feature_count /* IN/OUT */,
+				 hb_tag_t     *feature_tags /* OUT */) const
+  { return get_feature_list ().get_tags (start_offset, feature_count, feature_tags); }
+  const Feature& get_feature (unsigned int i) const
+  { return get_feature_list ()[i]; }
+  bool find_feature_index (hb_tag_t tag, unsigned int *index) const
+  { return get_feature_list ().find_index (tag, index); }
+
+  bool find_variations_index (const int *coords, unsigned int num_coords,
+			      unsigned int *index) const
+  {
+#ifdef HB_NO_VAR
+    *index = FeatureVariations::NOT_FOUND_INDEX;
+    return false;
+#endif
+    return get_feature_variations ().find_index (coords, num_coords, index);
+  }
+  const Feature& get_feature_variation (unsigned int feature_index,
+					unsigned int variations_index) const
+  {
+#ifndef HB_NO_VAR
+    if (FeatureVariations::NOT_FOUND_INDEX != variations_index &&
+	u.version.to_int () >= 0x00010001u)
+    {
+      const Feature *feature = get_feature_variations ().find_substitute (variations_index,
+									  feature_index);
+      if (feature)
+	return *feature;
+    }
+#endif
+    return get_feature (feature_index);
+  }
+
+  void feature_variation_collect_lookups (const hb_set_t *feature_indexes,
+					  const hb_hashmap_t<unsigned, const Feature*> *feature_substitutes_map,
+					  hb_set_t       *lookup_indexes /* OUT */) const
+  {
+#ifndef HB_NO_VAR
+    get_feature_variations ().collect_lookups (feature_indexes, feature_substitutes_map, lookup_indexes);
+#endif
+  }
+
+#ifndef HB_NO_VAR
+  void collect_feature_substitutes_with_variations (hb_collect_feature_substitutes_with_var_context_t *c) const
+  { get_feature_variations ().collect_feature_substitutes_with_variations (c); }
+#endif
+
+  template <typename TLookup>
+  void closure_lookups (hb_face_t      *face,
+			const hb_set_t *glyphs,
+			hb_set_t       *lookup_indexes /* IN/OUT */) const
+  {
+    hb_set_t visited_lookups, inactive_lookups;
+    hb_closure_lookups_context_t c (face, glyphs, &visited_lookups, &inactive_lookups);
+
+    c.set_recurse_func (TLookup::template dispatch_recurse_func<hb_closure_lookups_context_t>);
+
+    for (unsigned lookup_index : *lookup_indexes)
+      reinterpret_cast<const TLookup &> (get_lookup (lookup_index)).closure_lookups (&c, lookup_index);
+
+    hb_set_union (lookup_indexes, &visited_lookups);
+    hb_set_subtract (lookup_indexes, &inactive_lookups);
+  }
+
+  void prune_langsys (const hb_map_t *duplicate_feature_map,
+                      const hb_set_t *layout_scripts,
+                      hb_hashmap_t<unsigned, hb::unique_ptr<hb_set_t>> *script_langsys_map,
+                      hb_set_t       *new_feature_indexes /* OUT */) const
+  {
+    hb_prune_langsys_context_t c (this, script_langsys_map, duplicate_feature_map, new_feature_indexes);
+
+    unsigned count = get_script_count ();
+    for (unsigned script_index = 0; script_index < count; script_index++)
+    {
+      const Tag& tag = get_script_tag (script_index);
+      if (!layout_scripts->has (tag)) continue;
+      const Script& s = get_script (script_index);
+      s.prune_langsys (&c, script_index);
+    }
+  }
+
+  void prune_features (const hb_map_t *lookup_indices, /* IN */
+		       const hb_hashmap_t<unsigned, hb::shared_ptr<hb_set_t>> *feature_record_cond_idx_map, /* IN */
+		       const hb_hashmap_t<unsigned, const Feature*> *feature_substitutes_map, /* IN */
+		       hb_set_t       *feature_indices /* IN/OUT */) const
+  {
+#ifndef HB_NO_VAR
+    // This is the set of feature indices which have alternate versions defined
+    // if the FeatureVariation's table and the alternate version(s) intersect the
+    // set of lookup indices.
+    hb_set_t alternate_feature_indices;
+    get_feature_variations ().closure_features (lookup_indices, feature_record_cond_idx_map, &alternate_feature_indices);
+    if (unlikely (alternate_feature_indices.in_error()))
+    {
+      feature_indices->err ();
+      return;
+    }
+#endif
+
+    for (unsigned i : hb_iter (feature_indices))
+    {
+      hb_tag_t tag =  get_feature_tag (i);
+      if (tag == HB_TAG ('p', 'r', 'e', 'f'))
+        // Note: Never ever drop feature 'pref', even if it's empty.
+        // HarfBuzz chooses shaper for Khmer based on presence of this
+        // feature.	See thread at:
+	// http://lists.freedesktop.org/archives/harfbuzz/2012-November/002660.html
+        continue;
+
+
+      const Feature *f = &(get_feature (i));
+      const Feature** p = nullptr;
+      if (feature_substitutes_map->has (i, &p))
+        f = *p;
+
+      if (!f->featureParams.is_null () &&
+          tag == HB_TAG ('s', 'i', 'z', 'e'))
+        continue;
+
+      if (!f->intersects_lookup_indexes (lookup_indices)
+#ifndef HB_NO_VAR
+          && !alternate_feature_indices.has (i)
+#endif
+	  )
+	feature_indices->del (i);
+    }
+  }
+
+  template <typename T>
+  struct accelerator_t
+  {
+    accelerator_t (hb_face_t *face)
+    {
+      this->table = hb_sanitize_context_t ().reference_table<T> (face);
+      if (unlikely (this->table->is_blocklisted (this->table.get_blob (), face)))
+      {
+	hb_blob_destroy (this->table.get_blob ());
+	this->table = hb_blob_get_empty ();
+      }
+
+      this->lookup_count = table->get_lookup_count ();
+
+      this->accels = (hb_ot_layout_lookup_accelerator_t *) hb_calloc (this->lookup_count, sizeof (hb_ot_layout_lookup_accelerator_t));
+      if (unlikely (!this->accels))
+      {
+	this->lookup_count = 0;
+	this->table.destroy ();
+	this->table = hb_blob_get_empty ();
+      }
+
+      for (unsigned int i = 0; i < this->lookup_count; i++)
+	this->accels[i].init (table->get_lookup (i));
+    }
+    ~accelerator_t ()
+    {
+      for (unsigned int i = 0; i < this->lookup_count; i++)
+	this->accels[i].fini ();
+      hb_free (this->accels);
+      this->table.destroy ();
+    }
+
+    hb_blob_ptr_t<T> table;
+    unsigned int lookup_count;
+    hb_ot_layout_lookup_accelerator_t *accels;
+  };
+
+  protected:
+  union {
+  FixedVersion<>			version;	/* Version identifier */
+  GSUBGPOSVersion1_2<SmallTypes>	version1;
+#ifndef HB_NO_BEYOND_64K
+  GSUBGPOSVersion1_2<MediumTypes>	version2;
+#endif
+  } u;
+  public:
+  DEFINE_SIZE_MIN (4);
+};
+
+
+} /* namespace OT */
+
+
+#endif /* HB_OT_LAYOUT_GSUBGPOS_HH */