[subset] Always place CFF1/2 char strings at the end of the packed table.

Makes the behaviour from HB_SUBSET_FLAGS_IFTB_REQUIREMENTS the default.

src/hb-subset-cff1.cc

@@ -621,10 +621,8 @@ struct cff1_subset_plan
     desubroutinize = plan->flags & HB_SUBSET_FLAGS_DESUBROUTINIZE;
 
  #ifdef HB_EXPERIMENTAL_API
-    charstrings_last = plan->flags & HB_SUBSET_FLAGS_IFTB_REQUIREMENTS;
     min_charstrings_off_size = (plan->flags & HB_SUBSET_FLAGS_IFTB_REQUIREMENTS) ? 4 : 0;
  #else
-    charstrings_last = false;
     min_charstrings_off_size = 0;
  #endif
 
@@ -786,7 +784,6 @@ struct cff1_subset_plan
   unsigned int	topDictModSIDs[name_dict_values_t::ValCount];
 
   bool		desubroutinize = false;
-  bool		charstrings_last = false;
 
   unsigned	min_charstrings_off_size = 0;
 };
@@ -817,10 +814,12 @@ bool
 OT::cff1::accelerator_subset_t::serialize (hb_serialize_context_t *c,
 					   struct OT::cff1_subset_plan &plan) const
 {
-  if (plan.charstrings_last) {
-    if (!_serialize_cff1_charstrings(c, plan, *this))
-      return false;
-  }
+  /* push charstrings onto the object stack first which will ensure it packs as the last
+     object in the table. Keeping the chastrings last satisfies the requirements for patching
+     via IFTB. If this ordering needs to be changed in the future, charstrings should be left
+     at the end whenever HB_SUBSET_FLAGS_ITFB_REQUIREMENTS is enabled. */
+  if (!_serialize_cff1_charstrings(c, plan, *this))
+    return false;
 
   /* private dicts & local subrs */
   for (int i = (int) privateDicts.length; --i >= 0 ;)
@@ -860,11 +859,6 @@ OT::cff1::accelerator_subset_t::serialize (hb_serialize_context_t *c,
   if (!is_CID ())
     plan.info.privateDictInfo = plan.fontdicts_mod[0].privateDictInfo;
 
-  if (!plan.charstrings_last) {
-    if (!_serialize_cff1_charstrings(c, plan, *this))
-      return false;
-  }
-
   /* FDArray (FD Index) */
   if (fdArray != &Null (CFF1FDArray))
   {

src/hb-subset-cff2.cc

@@ -440,10 +440,8 @@ struct cff2_subset_plan
 		     pinned; // For instancing we need this path
 
  #ifdef HB_EXPERIMENTAL_API
-    charstrings_last = plan->flags & HB_SUBSET_FLAGS_IFTB_REQUIREMENTS;
     min_charstrings_off_size = (plan->flags & HB_SUBSET_FLAGS_IFTB_REQUIREMENTS) ? 4 : 0;
  #else
-    charstrings_last = false;
     min_charstrings_off_size = 0;
  #endif
 
@@ -518,7 +516,6 @@ struct cff2_subset_plan
 
   bool	    drop_hints = false;
   bool	    desubroutinize = false;
-  bool	    charstrings_last = false;
 
   unsigned  min_charstrings_off_size = 0;
 };
@@ -551,10 +548,12 @@ OT::cff2::accelerator_subset_t::serialize (hb_serialize_context_t *c,
 					   struct cff2_subset_plan &plan,
 					   hb_array_t<int> normalized_coords) const
 {
-  if (plan.charstrings_last) {
-    if (!_serialize_cff2_charstrings(c, plan, *this))
-      return false;
-  }
+  /* push charstrings onto the object stack first which will ensure it packs as the last
+     object in the table. Keeping the chastrings last satisfies the requirements for patching
+     via IFTB. If this ordering needs to be changed in the future, charstrings should be left
+     at the end whenever HB_SUBSET_FLAGS_ITFB_REQUIREMENTS is enabled. */
+  if (!_serialize_cff2_charstrings(c, plan, *this))
+    return false;
 
   /* private dicts & local subrs */
   hb_vector_t<table_info_t>  private_dict_infos;
@@ -594,11 +593,6 @@ OT::cff2::accelerator_subset_t::serialize (hb_serialize_context_t *c,
     }
   }
 
-  if (!plan.charstrings_last) {
-    if (!_serialize_cff2_charstrings(c, plan, *this))
-      return false;
-  }
-
   /* FDSelect */
   if (fdSelect != &Null (CFF2FDSelect))
   {