[subset] fix find_duplicate_features

We should check each feature against all other features with the same
tag for duplicates.

src/hb-ot-layout-gsubgpos.hh

@@ -3678,55 +3678,57 @@ struct GSUBGPOS
                                 const hb_set_t *feature_indices,
                                 hb_map_t *duplicate_feature_map /* OUT */) const
   {
+    hb_set_t unique_features;
+    hb_tag_t prev_t = get_feature_tag (feature_indices->get_min ());
     //find out duplicate features after subset
-    unsigned prev = 0xFFFFu;
     for (unsigned i : feature_indices->iter ())
     {
-      if (prev == 0xFFFFu)
-      {
-        duplicate_feature_map->set (i, i);
-        prev = i;
-        continue;
-      }
-
       hb_tag_t t = get_feature_tag (i);
-      hb_tag_t prev_t = get_feature_tag (prev);
       if (t != prev_t)
       {
+        prev_t = t;
+        unique_features.clear ();
+        unique_features.add (i);
         duplicate_feature_map->set (i, i);
-        prev = i;
         continue;
       }
 
-      const Feature& f = get_feature (i);
-      const Feature& prev_f = get_feature (prev);
+      bool found = false;
 
-      auto f_iter =
-      + hb_iter (f.lookupIndex)
-      | hb_filter (lookup_indices)
-      ;
-
-      auto prev_iter =
-      + hb_iter (prev_f.lookupIndex)
-      | hb_filter (lookup_indices)
-      ;
-
-      if (f_iter.len () != prev_iter.len ())
+      for (unsigned other_f_index : unique_features.iter ())
       {
-        duplicate_feature_map->set (i, i);
-        prev = i;
-        continue;
+        const Feature& f = get_feature (i);
+        const Feature& other_f = get_feature (other_f_index);
+
+        auto f_iter =
+        + hb_iter (f.lookupIndex)
+        | hb_filter (lookup_indices)
+        ;
+  
+        auto other_f_iter =
+        + hb_iter (other_f.lookupIndex)
+        | hb_filter (lookup_indices)
+        ;
+  
+        bool is_equal = true;
+        for (; f_iter && other_f_iter; f_iter++, other_f_iter++)
+        {
+          unsigned a = *f_iter;
+          unsigned b = *other_f_iter;
+          if (a != b) { is_equal = false; break; }
+        }
+
+        if (is_equal == false || f_iter || other_f_iter) continue;
+        
+        found = true;
+        duplicate_feature_map->set (i, other_f_index);
+        break;
       }
-
-      bool is_equal = true;
-      for (auto _ : + hb_zip (f_iter, prev_iter))
-        if (_.first != _.second) { is_equal = false; break; }
-
-      if (is_equal == true) duplicate_feature_map->set (i, prev);
-      else
+      
+      if (found == false)
       {
+        unique_features.add (i);
         duplicate_feature_map->set (i, i);
-        prev = i;
       }
     }
   }

test/subset/data/Makefile.am

@@ -35,6 +35,7 @@ EXTRA_DIST += \
 	expected/layout.gdef-attachlist \
 	expected/layout.notonastaliqurdu \
 	expected/layout.tinos \
+	expected/layout.duplicate_features \
 	expected/cmap \
 	expected/cmap14 \
 	expected/sbix \

test/subset/data/Makefile.sources

@@ -32,6 +32,7 @@ TESTS = \
 	tests/layout.notonastaliqurdu.tests \
 	tests/layout.tests \
 	tests/layout.tinos.tests \
+	tests/layout.duplicate_features.tests \
 	tests/sbix.tests \
 	tests/variable.tests \
 	tests/glyph_names.tests \

test/subset/data/tests/layout.duplicate_features.tests

@@ -0,0 +1,11 @@
+FONTS:
+AlegreyaSans-BlackItalic.ttf
+
+PROFILES:
+default.txt
+glyph-names.txt
+notdef-outline.txt
+
+SUBSETS:
+U+20,U+2f,U+38,U+49,U+4c,U+51,U+53,U+66,U+67,U+6f,U+b4,U+2044
+*

test/subset/meson.build

@@ -27,6 +27,7 @@ tests = [
   'layout.gdef-attachlist',
   'layout.notonastaliqurdu',
   'layout.tinos',
+  'layout.duplicate_features',
   'cmap',
   'cmap14',
   'sbix',