[subset] avoid writing out duplicate extra glyph names in post table

Add check for possible duplicate with other name index

src/hb-ot-post-table-v2subset.hh

@@ -79,6 +79,7 @@ HB_INTERNAL bool postV2Tail::subset (hb_subset_context_t *c) const
   post::accelerator_t _post;
   _post.init (c->plan->source);
 
+  hb_hashmap_t<hb_bytes_t, unsigned, std::nullptr_t, unsigned, nullptr, (unsigned)-1> glyph_name_to_new_index;
   for (hb_codepoint_t new_gid = 0; new_gid < num_glyphs; new_gid++)
   {
     hb_codepoint_t old_gid = reverse_glyph_map.get (new_gid);
@@ -90,22 +91,28 @@ HB_INTERNAL bool postV2Tail::subset (hb_subset_context_t *c) const
     else
     {
       hb_bytes_t s = _post.find_glyph_name (old_gid);
-      int standard_glyph_index = -1;
-      for (unsigned i = 0; i < format1_names_length; i++)
+      new_index = glyph_name_to_new_index.get (s);
+      if (new_index == (unsigned)-1)
       {
-        if (s == format1_names (i))
+        int standard_glyph_index = -1;
+        for (unsigned i = 0; i < format1_names_length; i++)
         {
-          standard_glyph_index = i;
-          break;
+          if (s == format1_names (i))
+          {
+            standard_glyph_index = i;
+            break;
+          }
         }
+
+        if (standard_glyph_index == -1)
+        {
+          new_index = 258 + i;
+          i++;
+        }
+        else
+        { new_index = standard_glyph_index; }
+        glyph_name_to_new_index.set (s, new_index);
       }
-      if (standard_glyph_index == -1)
-      {
-        new_index = 258 + i;
-        i++;
-      }
-      else
-      { new_index = standard_glyph_index; }
       old_new_index_map.set (old_index, new_index);
     }
     old_gid_new_index_map.set (old_gid, new_index);

test/subset/data/Makefile.am

@@ -51,6 +51,7 @@ EXTRA_DIST += \
 	expected/variable \
 	expected/glyph_names \
 	expected/math \
+	expected/post \
 	fonts \
 	profiles \
 	$(NULL)

test/subset/data/Makefile.sources

@@ -43,6 +43,7 @@ TESTS = \
 	tests/variable.tests \
 	tests/glyph_names.tests \
 	tests/math.tests \
+	tests/post.tests \
 	$(NULL)
 
 # TODO: re-enable once colrv1 subsetting is stabilized.

test/subset/data/tests/post.tests

@@ -0,0 +1,12 @@
+FONTS:
+SreeKrushnadevaraya-Regular.ttf
+
+PROFILES:
+default.txt
+retain-gids.txt
+glyph-names.txt
+notdef-outline.txt
+
+SUBSETS:
+U+c30,U+c36,U+c40,U+c4d
+*

test/subset/meson.build

@@ -45,6 +45,7 @@ tests = [
   'cbdt',
   'variable',
   'glyph_names',
+  'post',
 ]
 
 repack_tests = [