[OTLayout] Respect lookup-flags skipping over non-mark glyphs

Before, when matching ligatures, we never skipping over base / liga
glyphs even if that was what the LookupFlags asked for.

Fixed now.  We carefully reviewed all instances of this, and tested with
Amiri as well as some Indic scripts, and are confident that this should
NOT break anyone's fonts.  It's also how Uniscribe does it, from what
we can tell.

src/hb-ot-layout-gpos-table.hh

@@ -1250,7 +1250,7 @@ struct MarkMarkPosFormat1
     /* now we search backwards for a suitable mark glyph until a non-mark glyph */
     unsigned int property;
     hb_apply_context_t::skipping_backward_iterator_t skippy_iter (c, c->buffer->idx, 1);
-    if (!skippy_iter.prev (&property)) return TRACE_RETURN (false);
+    if (!skippy_iter.prev (&property, c->lookup_props & ~LookupFlag::IgnoreFlags)) return TRACE_RETURN (false);
 
     if (!(property & HB_OT_LAYOUT_GLYPH_PROPS_MARK)) return TRACE_RETURN (false);
 

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

@@ -317,7 +317,7 @@ struct hb_apply_context_t
 	if (has_no_chance ())
 	  return false;
 	idx++;
-      } while (c->should_skip_mark (&c->buffer->info[idx], lookup_props, property_out));
+      } while (c->should_skip (&c->buffer->info[idx], lookup_props, property_out));
       num_items--;
       return (c->buffer->info[idx].mask & mask) && (!syllable || syllable == c->buffer->info[idx].syllable ());
     }
@@ -366,7 +366,7 @@ struct hb_apply_context_t
 	if (has_no_chance ())
 	  return false;
 	idx--;
-      } while (c->should_skip_mark (&c->buffer->out_info[idx], lookup_props, property_out));
+      } while (c->should_skip (&c->buffer->out_info[idx], lookup_props, property_out));
       num_items--;
       return (c->buffer->out_info[idx].mask & mask) && (!syllable || syllable == c->buffer->out_info[idx].syllable ());
     }
@@ -435,9 +435,9 @@ struct hb_apply_context_t
   }
 
   inline bool
-  should_skip_mark (hb_glyph_info_t *info,
-		   unsigned int  lookup_props,
-		   unsigned int *property_out) const
+  should_skip (hb_glyph_info_t *info,
+	       unsigned int  lookup_props,
+	       unsigned int *property_out) const
   {
     unsigned int property;
 
@@ -445,18 +445,13 @@ struct hb_apply_context_t
     if (property_out)
       *property_out = property;
 
-    /* If it's a mark, skip it if we don't accept it. */
-    if (unlikely (property & HB_OT_LAYOUT_GLYPH_PROPS_MARK))
-      return !match_properties (info->codepoint, property, lookup_props);
-
-    /* If not a mark, don't skip. */
-    return false;
+    return !match_properties (info->codepoint, property, lookup_props);
   }
 
 
-  inline bool should_mark_skip_current_glyph (void) const
+  inline bool should_skip_current_glyph (void) const
   {
-    return should_skip_mark (&buffer->cur(), lookup_props, NULL);
+    return should_skip (&buffer->cur(), lookup_props, NULL);
   }
 
   inline void set_class (hb_codepoint_t glyph_index, unsigned int class_guess) const
@@ -720,7 +715,7 @@ static inline void ligate_input (hb_apply_context_t *c,
 
   for (unsigned int i = 1; i < count; i++)
   {
-    while (c->should_mark_skip_current_glyph ())
+    while (c->should_skip_current_glyph ())
     {
       if (!is_mark_ligature) {
 	unsigned int new_lig_comp = components_so_far - last_num_components +
@@ -849,7 +844,7 @@ static inline bool apply_lookup (hb_apply_context_t *c,
   {
     if (unlikely (c->buffer->idx == end))
       return TRACE_RETURN (true);
-    while (c->should_mark_skip_current_glyph ())
+    while (c->should_skip_current_glyph ())
     {
       /* No lookup applied for this index */
       c->buffer->next_glyph ();