[aat] Fix unsafe-to-break

At any position, if state is not zero, mark unsafe-to-break before,
unless we can reason it safe.

At any position, if there's an action entry for end-of-text, mark
unsafe to break.

Also changes buffer diff impl to allow for flag differences as long
as the buffer glyph flags are superset of reference glyph flags.

With this, all MORX tests pass.

src/hb-aat-layout-common-private.hh

@@ -614,8 +614,7 @@ struct StateTableDriver
 			   hb_face_t *face_) :
 	      machine (machine_),
 	      buffer (buffer_),
-	      num_glyphs (face_->get_num_glyphs ()),
-	      last_zero (0) {}
+	      num_glyphs (face_->get_num_glyphs ()) {}
 
   template <typename context_t>
   inline void drive (context_t *c)
@@ -629,9 +628,6 @@ struct StateTableDriver
     bool last_was_dont_advance = false;
     for (buffer->idx = 0;;)
     {
-      if (!state)
-	last_zero = buffer->idx;
-
       unsigned int klass = buffer->idx < buffer->len ?
 			   machine.get_class (info[buffer->idx].codepoint, num_glyphs) :
 			   0 /* End of text */;
@@ -639,6 +635,30 @@ struct StateTableDriver
       if (unlikely (!entry))
 	break;
 
+      /* Unsafe-to-break before this if not in state 0, as things might
+       * go differently if we start from state 0 here. */
+      if (state && buffer->idx)
+      {
+	/* Special-case easy cases: if starting here at state 0 is not
+	 * actionable, and leads to the same next state, then it's safe.
+	 * Let's hope...  Maybe disable the conditional later, if proves
+	 * insufficient. */
+	const Entry<EntryData> *start_entry = machine.get_entryZ (0, klass);
+	if (start_entry->newState != entry->newState ||
+	    (start_entry->flags & context_t::DontAdvance) != (entry->flags & context_t::DontAdvance) ||
+	    c->is_actionable (this, entry) ||
+	    c->is_actionable (this, start_entry))
+	  buffer->unsafe_to_break (buffer->idx - 1, buffer->idx + 1);
+      }
+
+      /* Unsafe-to-break if end-of-text would kick in here. */
+      if (buffer->idx + 2 <= buffer->len)
+      {
+	const Entry<EntryData> *end_entry = machine.get_entryZ (state, 0);
+	if (c->is_actionable (this, end_entry))
+	  buffer->unsafe_to_break (buffer->idx, buffer->idx + 2);
+      }
+
       if (unlikely (!c->transition (this, entry)))
         break;
 
@@ -665,7 +685,6 @@ struct StateTableDriver
   const StateTable<EntryData> &machine;
   hb_buffer_t *buffer;
   unsigned int num_glyphs;
-  unsigned int last_zero;
 };
 
 

src/hb-aat-layout-morx-table.hh

@@ -58,9 +58,13 @@ struct RearrangementSubtable
 
     inline driver_context_t (const RearrangementSubtable *table) :
 	ret (false),
-	start (0), end (0),
-	last_zero_before_start (0) {}
+	start (0), end (0) {}
 
+    inline bool is_actionable (StateTableDriver<void> *driver,
+			       const Entry<void> *entry)
+    {
+      return (entry->flags & Verb) && start < end;
+    }
     inline bool transition (StateTableDriver<void> *driver,
 			    const Entry<void> *entry)
     {
@@ -68,10 +72,7 @@ struct RearrangementSubtable
       unsigned int flags = entry->flags;
 
       if (flags & MarkFirst)
-      {
 	start = buffer->idx;
-	last_zero_before_start = driver->last_zero;
-      }
 
       if (flags & MarkLast)
 	end = MIN (buffer->idx + 1, buffer->len);
@@ -110,7 +111,7 @@ struct RearrangementSubtable
 
 	if (end - start >= l + r)
 	{
-	  buffer->unsafe_to_break (last_zero_before_start, MIN (buffer->idx + 1, buffer->len));
+	  buffer->merge_clusters (start, MIN (buffer->idx + 1, buffer->len));
 	  buffer->merge_clusters (start, end);
 
 	  hb_glyph_info_t *info = buffer->info;
@@ -147,7 +148,6 @@ struct RearrangementSubtable
     private:
     unsigned int start;
     unsigned int end;
-    unsigned int last_zero_before_start;
   };
 
   inline bool apply (hb_aat_apply_context_t *c) const
@@ -200,9 +200,18 @@ struct ContextualSubtable
 	ret (false),
 	mark_set (false),
 	mark (0),
-	last_zero_before_mark (0),
 	subs (table+table->substitutionTables) {}
 
+    inline bool is_actionable (StateTableDriver<EntryData> *driver,
+			       const Entry<EntryData> *entry)
+    {
+      hb_buffer_t *buffer = driver->buffer;
+
+      if (buffer->idx == buffer->len && !mark_set)
+        return false;
+
+      return entry->data.markIndex != 0xFFFF || entry->data.currentIndex != 0xFFFF;
+    }
     inline bool transition (StateTableDriver<EntryData> *driver,
 			    const Entry<EntryData> *entry)
     {
@@ -220,7 +229,7 @@ struct ContextualSubtable
 	const GlyphID *replacement = lookup.get_value (info[mark].codepoint, driver->num_glyphs);
 	if (replacement)
 	{
-	  buffer->unsafe_to_break (last_zero_before_mark, MIN (buffer->idx + 1, buffer->len));
+	  buffer->unsafe_to_break (mark, MIN (buffer->idx + 1, buffer->len));
 	  info[mark].codepoint = *replacement;
 	  ret = true;
 	}
@@ -233,7 +242,6 @@ struct ContextualSubtable
 	const GlyphID *replacement = lookup.get_value (info[idx].codepoint, driver->num_glyphs);
 	if (replacement)
 	{
-	  buffer->unsafe_to_break (driver->last_zero, idx + 1);
 	  info[idx].codepoint = *replacement;
 	  ret = true;
 	}
@@ -243,7 +251,6 @@ struct ContextualSubtable
       {
 	mark_set = true;
 	mark = buffer->idx;
-	last_zero_before_mark = driver->last_zero;
       }
 
       return true;
@@ -254,7 +261,6 @@ struct ContextualSubtable
     private:
     bool mark_set;
     unsigned int mark;
-    unsigned int last_zero_before_mark;
     const UnsizedOffsetListOf<Lookup<GlyphID>, HBUINT32> &subs;
   };
 
@@ -344,6 +350,11 @@ struct LigatureSubtable
 	ligature (table+table->ligature),
 	match_length (0) {}
 
+    inline bool is_actionable (StateTableDriver<EntryData> *driver,
+			       const Entry<EntryData> *entry)
+    {
+      return !!(entry->flags & PerformAction);
+    }
     inline bool transition (StateTableDriver<EntryData> *driver,
 			    const Entry<EntryData> *entry)
     {

src/hb-buffer.cc

@@ -1933,7 +1933,7 @@ hb_buffer_diff (hb_buffer_t *buffer,
       result |= HB_BUFFER_DIFF_FLAG_CODEPOINT_MISMATCH;
     if (buf_info->cluster != ref_info->cluster)
       result |= HB_BUFFER_DIFF_FLAG_CLUSTER_MISMATCH;
-    if ((buf_info->mask & HB_GLYPH_FLAG_DEFINED) != (ref_info->mask & HB_GLYPH_FLAG_DEFINED))
+    if ((buf_info->mask & HB_GLYPH_FLAG_DEFINED) & (ref_info->mask & HB_GLYPH_FLAG_DEFINED) != (ref_info->mask & HB_GLYPH_FLAG_DEFINED))
       result |= HB_BUFFER_DIFF_FLAG_GLYPH_FLAGS_MISMATCH;
     if (contains && ref_info->codepoint == dottedcircle_glyph)
       result |= HB_BUFFER_DIFF_FLAG_DOTTED_CIRCLE_PRESENT;