upb: Update _upb_map_next signature to return a boolean and remove the _nextmutable Map iterator API.

PiperOrigin-RevId: 730964212

Author: adazh

upb/message/internal/map.h

@@ -102,14 +102,13 @@ UPB_INLINE void _upb_map_fromvalue(upb_value val, void* out, size_t size) {
   }
 }
 
-UPB_INLINE void* _upb_map_next(const struct upb_Map* map, size_t* iter) {
+UPB_INLINE bool _upb_map_next(const struct upb_Map* map, size_t* iter) {
   upb_strtable_iter it;
   it.t = &map->t.strtable;
   it.index = *iter;
   upb_strtable_next(&it);
   *iter = it.index;
-  if (upb_strtable_done(&it)) return NULL;
-  return (void*)str_tabent(&it);
+  return !upb_strtable_done(&it);
 }
 
 UPB_INLINE void _upb_Map_Clear(struct upb_Map* map) {

upb_generator/c/generator.cc

@@ -676,17 +676,6 @@ void GenerateMapSetters(upb::FieldDefPtr field, const DefPoolPair& pools,
       )cc",
       msg_name, resolved_name, MapKeyCType(field),
       FieldInitializer(pools, field, options), MapKeySize(field, "key"));
-  output(
-      R"cc(
-        UPB_INLINE $0 $1_$2_nextmutable($1* msg, size_t* iter) {
-          const upb_MiniTableField field = $3;
-          upb_Map* map = (upb_Map*)upb_Message_GetMap(UPB_UPCAST(msg), &field);
-          if (!map) return NULL;
-          return ($0)_upb_map_next(map, iter);
-        }
-      )cc",
-      CType(field), msg_name, resolved_name,
-      FieldInitializerStrong(pools, field, options));
 }
 
 void GenerateRepeatedSetters(upb::FieldDefPtr field, const DefPoolPair& pools,