Add tokenizers class mismatch detection between cls and checkpoint

src/transformers/models/bert_japanese/tokenization_bert_japanese.py

@@ -132,7 +132,7 @@ def __init__(
         if not os.path.isfile(vocab_file):
             raise ValueError(
                 f"Can't find a vocabulary file at path '{vocab_file}'. To load the vocabulary from a Google pretrained "
-                "model use `tokenizer = BertTokenizer.from_pretrained(PRETRAINED_MODEL_NAME)`"
+                "model use `tokenizer = AutoTokenizer.from_pretrained(PRETRAINED_MODEL_NAME)`"
             )
         self.vocab = load_vocab(vocab_file)
         self.ids_to_tokens = collections.OrderedDict([(ids, tok) for tok, ids in self.vocab.items()])

src/transformers/tokenization_utils_base.py

@@ -1745,13 +1745,58 @@ def _from_pretrained(
         if tokenizer_config_file is not None:
             with open(tokenizer_config_file, encoding="utf-8") as tokenizer_config_handle:
                 init_kwargs = json.load(tokenizer_config_handle)
+            # First attempt. We get tokenizer_class from tokenizer_config to check mismatch between tokenizers.
+            config_tokenizer_class = init_kwargs.get("tokenizer_class")
             init_kwargs.pop("tokenizer_class", None)
             saved_init_inputs = init_kwargs.pop("init_inputs", ())
             if not init_inputs:
                 init_inputs = saved_init_inputs
         else:
+            config_tokenizer_class = None
             init_kwargs = init_configuration
 
+        if config_tokenizer_class is None:
+            from .models.auto.configuration_auto import AutoConfig
+
+            # Second attempt. If we have not yet found tokenizer_class, let's try to use the config.
+            try:
+                config = AutoConfig.from_pretrained(pretrained_model_name_or_path)
+                config_tokenizer_class = config.tokenizer_class
+            except (OSError, ValueError, KeyError):
+                # skip if an error occured.
+                config = None
+            if config_tokenizer_class is None:
+                # Third attempt. If we have not yet found the original type of the tokenizer,
+                # we are loading we see if we can infer it from the type of the configuration file
+                from .models.auto.configuration_auto import CONFIG_MAPPING
+                from .models.auto.tokenization_auto import TOKENIZER_MAPPING
+
+                if hasattr(config, "model_type"):
+                    config_class = CONFIG_MAPPING.get(config.model_type)
+                else:
+                    # Fallback: use pattern matching on the string.
+                    config_class = None
+                    for pattern, config_class_tmp in CONFIG_MAPPING.items():
+                        if pattern in str(pretrained_model_name_or_path):
+                            config_class = config_class_tmp
+                            break
+
+                if config_class in TOKENIZER_MAPPING.keys():
+                    config_tokenizer_class, config_tokenizer_class_fast = TOKENIZER_MAPPING[config_class]
+                    if config_tokenizer_class is not None:
+                        config_tokenizer_class = config_tokenizer_class.__name__
+                    else:
+                        config_tokenizer_class = config_tokenizer_class_fast.__name__
+
+        if config_tokenizer_class is not None:
+            if cls.__name__.replace("Fast", "") != config_tokenizer_class.replace("Fast", ""):
+                logger.warning(
+                    "The tokenizer class you load from this checkpoint is not the same type as the class this function is called from. "
+                    "It may result in unexpected tokenization. \n"
+                    f"The tokenizer class you load from this checkpoint is '{config_tokenizer_class}'. \n"
+                    f"The class this function is called from is '{cls.__name__}'."
+                )
+
         # Update with newly provided kwargs
         init_kwargs.update(kwargs)
 

tests/test_tokenization_bert_japanese.py

@@ -22,6 +22,7 @@
 from transformers.models.bert_japanese.tokenization_bert_japanese import (
     VOCAB_FILES_NAMES,
     BertJapaneseTokenizer,
+    BertTokenizer,
     CharacterTokenizer,
     MecabTokenizer,
     WordpieceTokenizer,
@@ -278,3 +279,23 @@ def test_tokenizer_bert_japanese(self):
         EXAMPLE_BERT_JAPANESE_ID = "cl-tohoku/bert-base-japanese"
         tokenizer = AutoTokenizer.from_pretrained(EXAMPLE_BERT_JAPANESE_ID)
         self.assertIsInstance(tokenizer, BertJapaneseTokenizer)
+
+
+class BertTokenizerMismatchTest(unittest.TestCase):
+    def test_tokenizer_mismatch_warning(self):
+        EXAMPLE_BERT_JAPANESE_ID = "cl-tohoku/bert-base-japanese"
+        with self.assertLogs("transformers", level="WARNING") as cm:
+            BertTokenizer.from_pretrained(EXAMPLE_BERT_JAPANESE_ID)
+            self.assertTrue(
+                cm.records[0].message.startswith(
+                    "The tokenizer class you load from this checkpoint is not the same type as the class this function is called from."
+                )
+            )
+        EXAMPLE_BERT_ID = "bert-base-cased"
+        with self.assertLogs("transformers", level="WARNING") as cm:
+            BertJapaneseTokenizer.from_pretrained(EXAMPLE_BERT_ID)
+            self.assertTrue(
+                cm.records[0].message.startswith(
+                    "The tokenizer class you load from this checkpoint is not the same type as the class this function is called from."
+                )
+            )

tests/test_tokenization_common.py

@@ -29,7 +29,10 @@
 from huggingface_hub import HfApi
 from requests.exceptions import HTTPError
 from transformers import (
+    AlbertTokenizer,
+    AlbertTokenizerFast,
     BertTokenizer,
+    BertTokenizerFast,
     PreTrainedTokenizer,
     PreTrainedTokenizerBase,
     PreTrainedTokenizerFast,
@@ -3288,6 +3291,41 @@ def test_training_new_tokenizer_with_special_tokens_change(self):
             expected_result = tokenizer.backend_tokenizer.normalizer.normalize_str(expected_result)
         self.assertEqual(expected_result, decoded_input)
 
+    def test_tokenizer_mismatch_warning(self):
+        for tokenizer, pretrained_name, kwargs in self.tokenizers_list:
+            with self.subTest(f"{tokenizer.__class__.__name__} ({pretrained_name})"):
+                with self.assertLogs("transformers", level="WARNING") as cm:
+                    try:
+                        if self.tokenizer_class == BertTokenizer:
+                            AlbertTokenizer.from_pretrained(pretrained_name)
+                        else:
+                            BertTokenizer.from_pretrained(pretrained_name)
+                    except (TypeError, AttributeError):
+                        # Some tokenizers cannot be loaded into the target tokenizer at all and errors are returned,
+                        # here we just check that the warning has been logged before the error is raised
+                        pass
+                    finally:
+                        self.assertTrue(
+                            cm.records[0].message.startswith(
+                                "The tokenizer class you load from this checkpoint is not the same type as the class this function is called from."
+                            )
+                        )
+                    try:
+                        if self.rust_tokenizer_class == BertTokenizerFast:
+                            AlbertTokenizerFast.from_pretrained(pretrained_name)
+                        else:
+                            BertTokenizerFast.from_pretrained(pretrained_name)
+                    except (TypeError, AttributeError):
+                        # Some tokenizers cannot be loaded into the target tokenizer at all and errors are returned,
+                        # here we just check that the warning has been logged before the error is raised
+                        pass
+                    finally:
+                        self.assertTrue(
+                            cm.records[0].message.startswith(
+                                "The tokenizer class you load from this checkpoint is not the same type as the class this function is called from."
+                            )
+                        )
+
 
 @is_staging_test
 class TokenizerPushToHubTester(unittest.TestCase):

tests/test_tokenization_fast.py

@@ -44,6 +44,11 @@ def setUp(self):
         tokenizer = PreTrainedTokenizerFast.from_pretrained(model_paths[0])
         tokenizer.save_pretrained(self.tmpdirname)
 
+    def test_tokenizer_mismatch_warning(self):
+        # We disable this test for PreTrainedTokenizerFast because it is the only tokenizer that is not linked to any
+        # model
+        pass
+
     def test_pretrained_model_lists(self):
         # We disable this test for PreTrainedTokenizerFast because it is the only tokenizer that is not linked to any
         # model