Index type name should returned if index type is not supported

Signed-off-by: Nfishpenguin <kun.yu@zilliz.com>

CHANGELOG.md

@@ -21,6 +21,7 @@ Please mark all changes in change log and use the issue from GitHub
 -   \#2696 Check the validity of the parameters of creating collection: segment_size
 -   \#2697 Index can not be created
 -   \#2698 Count entities got wrong result with binary vectors
+-   \#2728 Index type name should returned if index type is not supported
 -   \#2731 No entity returned with `get_entity_by_id`
 
 ## Feature

core/src/server/ValidationUtil.cpp

@@ -193,8 +193,14 @@ Status
 ValidateCollectionIndexType(int32_t index_type) {
     int engine_type = static_cast<int>(engine::EngineType(index_type));
     if (engine_type <= 0 || engine_type > static_cast<int>(engine::EngineType::MAX_VALUE)) {
-        std::string msg = "Invalid index type: " + std::to_string(index_type) + ". " +
-                          "Make sure the index type is in IndexType list.";
+        std::string index_type_str;
+        for (auto it = engine::s_map_engine_type.begin(); it != engine::s_map_engine_type.end(); it++) {
+            if (it->second == (engine::EngineType)index_type) {
+                index_type_str = it->first;
+            }
+        }
+        std::string msg =
+            "Invalid index type: " + index_type_str + ". " + "Make sure the index type is in IndexType list.";
         LOG_SERVER_ERROR_ << msg;
         return Status(SERVER_INVALID_INDEX_TYPE, msg);
     }