[T5 Tokenizer] Model has no fixed position ids - there is no hardcode… (#16990)

* [T5 Tokenizer] Model has no fixed position ids - there is no hardcoded max length

* [T5 Tokenizer] Model has no fixed position ids - there is no hardcoded max length

* correct t5 tokenizer

* correct t5 tokenizer

* fix test

* Apply suggestions from code review
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

* finish
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

src/transformers/models/t5/tokenization_t5.py

@@ -41,6 +41,8 @@ PRETRAINED_VOCAB_FILES_MAP = {
     }
 }
 
+
+# TODO(PVP) - this should be removed in Transformers v5
 PRETRAINED_POSITIONAL_EMBEDDINGS_SIZES = {
     "t5-small": 512,
     "t5-base": 512,
@@ -151,6 +153,24 @@ class T5Tokenizer(PreTrainedTokenizer):
         self.sp_model = spm.SentencePieceProcessor(**self.sp_model_kwargs)
         self.sp_model.Load(vocab_file)
 
+    @staticmethod
+    def _eventually_correct_t5_max_length(pretrained_model_name_or_path, max_model_length, init_max_model_length):
+        if pretrained_model_name_or_path in T5Tokenizer.max_model_input_sizes:
+            deprecated_max_model_length = T5Tokenizer.max_model_input_sizes[pretrained_model_name_or_path]
+            if init_max_model_length is not None and init_max_model_length != max_model_length:
+                return init_max_model_length
+            elif init_max_model_length is None:
+                warnings.warn(
+                    f"This tokenizer was incorrectly instantiated with a model max length of {deprecated_max_model_length} which will be corrected in Transformers v5.\n"
+                    f"For now, this behavior is kept to avoid breaking backwards compatibility when padding/encoding with `truncation is True`.\n"
+                    f"- Be aware that you SHOULD NOT rely on {pretrained_model_name_or_path} automatically truncating your input to {deprecated_max_model_length} when padding/encoding.\n"
+                    f"- If you want to encode/pad to sequences longer than {deprecated_max_model_length} you can either instantiate this tokenizer with `model_max_length` or pass `max_length` when encoding/padding.\n"
+                    f"- To avoid this warning, please instantiate this tokenizer with `model_max_length` set to your preferred value.",
+                    FutureWarning,
+                )
+
+        return max_model_length
+
     @property
     def vocab_size(self):
         return self.sp_model.get_piece_size() + self._extra_ids

src/transformers/models/t5/tokenization_t5_fast.py

@@ -16,6 +16,7 @@
 
 
 import os
+import warnings
 from shutil import copyfile
 from typing import List, Optional, Tuple
 
@@ -50,6 +51,8 @@ PRETRAINED_VOCAB_FILES_MAP = {
     },
 }
 
+
+# TODO(PVP) - this should be removed in Transformers v5
 PRETRAINED_POSITIONAL_EMBEDDINGS_SIZES = {
     "t5-small": 512,
     "t5-base": 512,
@@ -142,6 +145,24 @@ class T5TokenizerFast(PreTrainedTokenizerFast):
         self.can_save_slow_tokenizer = False if not self.vocab_file else True
         self._extra_ids = extra_ids
 
+    @staticmethod
+    def _eventually_correct_t5_max_length(pretrained_model_name_or_path, max_model_length, init_max_model_length):
+        if pretrained_model_name_or_path in T5TokenizerFast.max_model_input_sizes:
+            deprecated_max_model_length = T5TokenizerFast.max_model_input_sizes[pretrained_model_name_or_path]
+            if init_max_model_length is not None and init_max_model_length != max_model_length:
+                return init_max_model_length
+            elif init_max_model_length is None:
+                warnings.warn(
+                    f"This tokenizer was incorrectly instantiated with a model max length of {deprecated_max_model_length} which will be corrected in Transformers v5.\n"
+                    f"For now, this behavior is kept to avoid breaking backwards compatibility when padding/encoding with `truncation is True`.\n"
+                    f"- Be aware that you SHOULD NOT rely on {pretrained_model_name_or_path} automatically truncating your input to {deprecated_max_model_length} when padding/encoding.\n"
+                    f"- If you want to encode/pad to sequences longer than {deprecated_max_model_length} you can either instantiate this tokenizer with `model_max_length` or pass `max_length` when encoding/padding.\n"
+                    f"- To avoid this warning, please instantiate this tokenizer with `model_max_length` set to your preferred value.",
+                    FutureWarning,
+                )
+
+        return max_model_length
+
     def save_vocabulary(self, save_directory: str, filename_prefix: Optional[str] = None) -> Tuple[str]:
         if not self.can_save_slow_tokenizer:
             raise ValueError(

src/transformers/tokenization_utils_base.py

@@ -1899,9 +1899,19 @@ class PreTrainedTokenizerBase(SpecialTokensMixin, PushToHubMixin):
         if pretrained_model_name_or_path in cls.max_model_input_sizes:
             # if we're using a pretrained model, ensure the tokenizer
             # wont index sequences longer than the number of positional embeddings
+
             model_max_length = cls.max_model_input_sizes[pretrained_model_name_or_path]
             if model_max_length is not None and isinstance(model_max_length, (int, float)):
-                init_kwargs["model_max_length"] = min(init_kwargs.get("model_max_length", int(1e30)), model_max_length)
+
+                model_max_length = min(init_kwargs.get("model_max_length", int(1e30)), model_max_length)
+                # TODO(PVP) - uncomment following line in Transformers v5
+                # init_kwargs["model_max_length"] = model_max_length
+                # TODO(PVP) - remove in Transformers v5
+                # ---
+                init_kwargs["model_max_length"] = cls._eventually_correct_t5_max_length(
+                    pretrained_model_name_or_path, model_max_length, init_kwargs.get("model_max_length")
+                )
+                # ---
 
         # Merge resolved_vocab_files arguments in init_kwargs.
         added_tokens_file = resolved_vocab_files.pop("added_tokens_file", None)
@@ -1983,6 +1993,14 @@ class PreTrainedTokenizerBase(SpecialTokensMixin, PushToHubMixin):
 
         return tokenizer
 
+    @staticmethod
+    def _eventually_correct_t5_max_length(pretrained_model_name_or_path, max_model_length, init_max_model_length):
+        # This method should be deleted in Transformers v5
+        # Its only purpose is to potentially throw a warning
+        # that incorrectly defined max lengths of T5's tokenizer are used
+        # which we will correct in Transformers v5.
+        return max_model_length
+
     def save_pretrained(
         self,
         save_directory: Union[str, os.PathLike],

tests/t5/test_tokenization_t5.py

@@ -223,6 +223,9 @@ class T5TokenizationTest(TokenizerTesterMixin, unittest.TestCase):
             ["I am a small frog" * 1000, "I am a small frog"], padding=True, truncation=True, return_tensors=FRAMEWORK
         )
         self.assertIsInstance(batch, BatchEncoding)
+        # Since T5 does NOT have a max input length,
+        # this test should be changed to the following in Transformers v5:
+        # self.assertEqual(batch.input_ids.shape, (2, 8001))
         self.assertEqual(batch.input_ids.shape, (2, 512))
 
     def test_eos_in_input(self):
@@ -361,6 +364,13 @@ class T5TokenizationTest(TokenizerTesterMixin, unittest.TestCase):
                     ),
                 )
 
+    # overwritten from `test_tokenization_common` since T5 has no max length
+    def test_pretrained_model_lists(self):
+        # We should have at least one default checkpoint for each tokenizer
+        # We should specify the max input length as well (used in some part to list the pretrained checkpoints)
+        self.assertGreaterEqual(len(self.tokenizer_class.pretrained_vocab_files_map), 1)
+        self.assertGreaterEqual(len(list(self.tokenizer_class.pretrained_vocab_files_map.values())[0]), 1)
+
     @slow
     def test_tokenizer_integration(self):
         # fmt: off