[instancer] bug fix in post table applying mvar deltas

src/hb-ot-post-table.hh

@@ -99,6 +99,10 @@ struct post
     post *post_prime = c->serializer->start_embed<post> ();
     if (unlikely (!post_prime)) return_trace (false);
 
+    bool glyph_names = c->plan->flags & HB_SUBSET_FLAGS_GLYPH_NAMES;
+    if (!serialize (c->serializer, glyph_names))
+      return_trace (false);
+
 #ifndef HB_NO_VAR
     if (c->plan->normalized_coords)
     {
@@ -110,10 +114,6 @@ struct post
     }
 #endif
 
-    bool glyph_names = c->plan->flags & HB_SUBSET_FLAGS_GLYPH_NAMES;
-    if (!serialize (c->serializer, glyph_names))
-      return_trace (false);
-
     if (c->plan->user_axes_location.has (HB_TAG ('s','l','n','t')) &&
         !c->plan->pinned_at_default)
     {

test/subset/data/Makefile.am

@@ -65,6 +65,7 @@ EXTRA_DIST += \
 	expected/instance_no_double_free \
 	expected/mvar_full_instance \
 	expected/instance_comp_glyph_empty_child \
+	expected/post_apply_mvar_delta \
 	fonts \
 	profiles \
 	$(NULL)

test/subset/data/Makefile.sources

@@ -56,6 +56,7 @@ TESTS = \
 	tests/instance_no_double_free.tests \
 	tests/mvar_full_instance.tests \
 	tests/instance_comp_glyph_empty_child.tests \
+	tests/post_apply_mvar_delta.tests \
 	$(NULL)
 
 # TODO: re-enable once colrv1 subsetting is stabilized.

test/subset/data/tests/post_apply_mvar_delta.tests

@@ -0,0 +1,11 @@
+FONTS:
+Recursive-ABC.ttf
+
+PROFILES:
+no-layout.txt
+
+SUBSETS:
+*
+
+INSTANCES:
+wght=400,CASL=0,CRSV=0,MONO=0,slnt=0

test/subset/meson.build

@@ -58,6 +58,7 @@ tests = [
   'instance_no_double_free',
   'mvar_full_instance',
   'instance_comp_glyph_empty_child',
+  'post_apply_mvar_delta',
 ]
 
 repack_tests = [