Add typing.overload for convert_ids_tokens (huggingface#6637)

* add overload for type checker

* black

src/transformers/tokenization_utils.py

@@ -20,7 +20,7 @@
 import logging
 import re
 import unicodedata
-from typing import Any, Dict, List, Optional, Tuple, Union
+from typing import Any, Dict, List, Optional, Tuple, Union, overload
 
 from .file_utils import add_end_docstrings
 from .tokenization_utils_base import (
@@ -657,6 +657,14 @@ def get_special_tokens_mask(
         """
         return [0] * ((len(token_ids_1) if token_ids_1 else 0) + len(token_ids_0))
 
+    @overload
+    def convert_ids_to_tokens(self, ids: int, skip_special_tokens: bool = False) -> str:
+        ...
+
+    @overload
+    def convert_ids_to_tokens(self, ids: List[int], skip_special_tokens: bool = False) -> List[str]:
+        ...
+
     def convert_ids_to_tokens(
         self, ids: Union[int, List[int]], skip_special_tokens: bool = False
     ) -> Union[str, List[str]]: