[Wav2vec2] Fixed tokenization mistakes while adding single-char tokens to tokenizer (#11538)

* Fixed tokenization mistakes while adding single-char tokens to tokenizer

* Added tests and Removed unnecessary comments.

* finalize wav2vec2 tok

* add more aggressive tests

* Apply suggestions from code review

* fix useless import
Co-authored-by: Patrick von Platen <patrick.v.platen@gmail.com>

src/transformers/models/wav2vec2/tokenization_wav2vec2.py

@@ -24,8 +24,8 @@ from typing import Dict, List, Optional, Tuple, Union
 import numpy as np
 
 from ...file_utils import PaddingStrategy, TensorType, add_end_docstrings
-from ...tokenization_utils import PreTrainedTokenizer
-from ...tokenization_utils_base import BatchEncoding
+from ...tokenization_utils import PreTrainedTokenizer, _insert_one_token_to_ordered_list
+from ...tokenization_utils_base import AddedToken, BatchEncoding
 from ...utils import logging
 
 
@@ -277,6 +277,61 @@ class Wav2Vec2CTCTokenizer(PreTrainedTokenizer):
 
         return (vocab_file,)
 
+    def _add_tokens(self, new_tokens: Union[List[str], List[AddedToken]], special_tokens: bool = False) -> int:
+        """
+        Add a list of new tokens to the tokenizer class. If the new tokens are not in the vocabulary, they are added to
+        it with indices starting from length of the current vocabulary.
+
+        Args:
+            new_tokens (:obj:`List[str]`or :obj:`List[tokenizers.AddedToken]`):
+                Token(s) to add in vocabulary. A token is only added if it's not already in the vocabulary (tested by
+                checking if the tokenizer assign the index of the ``unk_token`` to them).
+            special_tokens (:obj:`bool`, `optional`, defaults to :obj:`False`):
+                Whether or not the tokens should be added as special tokens.
+
+        Returns:
+            :obj:`int`: The number of tokens actually added to the vocabulary.
+
+        Examples::
+
+            # Let's see how to increase the vocabulary of Bert model and tokenizer
+            tokenizer = Wav2Vec2CTCTokenizer.from_pretrained('facebook/wav2vec2-base-960h')
+            model = Wav2Vec2ForCTC.from_pretrained('facebook/wav2vec2-base-960h')
+
+            num_added_toks = tokenizer.add_tokens(['new_tok1', 'my_new-tok2'])
+            print('We have added', num_added_toks, 'tokens')
+            # Note: resize_token_embeddings expects to receive the full size of the new vocabulary, i.e. the length of the tokenizer.
+            model.resize_token_embeddings(len(tokenizer))
+        """
+        new_tokens = [str(tok) for tok in new_tokens]
+
+        tokens_to_add = []
+        for token in new_tokens:
+            assert isinstance(token, str)
+            if not special_tokens and hasattr(self, "do_lower_case") and self.do_lower_case:
+                token = token.lower()
+            if (
+                token != self.unk_token
+                and self.convert_tokens_to_ids(token) == self.convert_tokens_to_ids(self.unk_token)
+                and token not in tokens_to_add
+            ):
+                tokens_to_add.append(token)
+                if self.verbose:
+                    logger.info(f"Adding {token} to the vocabulary")
+
+        added_tok_encoder = dict((tok, len(self) + i) for i, tok in enumerate(tokens_to_add))
+        added_tok_decoder = {v: k for k, v in added_tok_encoder.items()}
+        self.added_tokens_encoder.update(added_tok_encoder)
+        self.added_tokens_decoder.update(added_tok_decoder)
+
+        # Make sure we don't split on any special tokens (even they were already in the vocab before)
+        for token in tokens_to_add:
+            if len(token) > 1:
+                self._additional_special_tokens.append(AddedToken(token))
+                _insert_one_token_to_ordered_list(self.unique_no_split_tokens, token)
+
+        return len(tokens_to_add)
+
 
 class Wav2Vec2Tokenizer(PreTrainedTokenizer):
     """

tests/test_tokenization_wav2vec2.py

@@ -375,6 +375,38 @@ class Wav2Vec2CTCTokenizerTest(TokenizerTesterMixin, unittest.TestCase):
         kwargs.update(self.special_tokens_map)
         return Wav2Vec2CTCTokenizer.from_pretrained(self.tmpdirname, **kwargs)
 
+    def test_tokenizer_add_token_chars(self):
+        tokenizer = self.tokenizer_class.from_pretrained("facebook/wav2vec2-base-960h")
+
+        # check adding a single token
+        tokenizer.add_tokens("x")
+        token_ids = tokenizer("C x A").input_ids
+        self.assertEqual(token_ids, [19, 4, 32, 4, 7])
+
+        tokenizer.add_tokens(["a", "b", "c"])
+        token_ids = tokenizer("C a A c").input_ids
+        self.assertEqual(token_ids, [19, 4, 33, 4, 7, 4, 35])
+
+        tokenizer.add_tokens(["a", "b", "c"])
+        token_ids = tokenizer("CaA c").input_ids
+        self.assertEqual(token_ids, [19, 33, 7, 4, 35])
+
+    def test_tokenizer_add_token_words(self):
+        tokenizer = self.tokenizer_class.from_pretrained("facebook/wav2vec2-base-960h")
+
+        # check adding a single token
+        tokenizer.add_tokens("xxx")
+        token_ids = tokenizer("C xxx A B").input_ids
+        self.assertEqual(token_ids, [19, 4, 32, 4, 7, 4, 24])
+
+        tokenizer.add_tokens(["aaa", "bbb", "ccc"])
+        token_ids = tokenizer("C aaa A ccc B B").input_ids
+        self.assertEqual(token_ids, [19, 4, 33, 4, 7, 4, 35, 4, 24, 4, 24])
+
+        tokenizer.add_tokens(["aaa", "bbb", "ccc"])
+        token_ids = tokenizer("CaaaA ccc B B").input_ids
+        self.assertEqual(token_ids, [19, 33, 7, 4, 35, 4, 24, 4, 24])
+
     def test_tokenizer_decode(self):
         tokenizer = self.tokenizer_class.from_pretrained("facebook/wav2vec2-base-960h")
 
@@ -470,3 +502,55 @@ class Wav2Vec2CTCTokenizerTest(TokenizerTesterMixin, unittest.TestCase):
     def test_pretrained_model_lists(self):
         # Wav2Vec2Model has no max model length => no testing
         pass
+
+    # overwrite from test_tokenization_common
+    def test_add_tokens_tokenizer(self):
+        tokenizers = self.get_tokenizers(do_lower_case=False)
+        for tokenizer in tokenizers:
+            with self.subTest(f"{tokenizer.__class__.__name__}"):
+                vocab_size = tokenizer.vocab_size
+                all_size = len(tokenizer)
+
+                self.assertNotEqual(vocab_size, 0)
+
+                # We usually have added tokens from the start in tests because our vocab fixtures are
+                # smaller than the original vocabs - let's not assert this
+                # self.assertEqual(vocab_size, all_size)
+
+                new_toks = ["aaaaa bbbbbb", "cccccccccdddddddd"]
+                added_toks = tokenizer.add_tokens(new_toks)
+                vocab_size_2 = tokenizer.vocab_size
+                all_size_2 = len(tokenizer)
+
+                self.assertNotEqual(vocab_size_2, 0)
+                self.assertEqual(vocab_size, vocab_size_2)
+                self.assertEqual(added_toks, len(new_toks))
+                self.assertEqual(all_size_2, all_size + len(new_toks))
+
+                tokens = tokenizer.encode("aaaaa bbbbbb low cccccccccdddddddd l", add_special_tokens=False)
+
+                self.assertGreaterEqual(len(tokens), 4)
+                self.assertGreater(tokens[0], tokenizer.vocab_size - 1)
+                self.assertGreater(tokens[-3], tokenizer.vocab_size - 1)
+
+                new_toks_2 = {"eos_token": ">>>>|||<||<<|<<", "pad_token": "<<<<<|||>|>>>>|>"}
+                added_toks_2 = tokenizer.add_special_tokens(new_toks_2)
+                vocab_size_3 = tokenizer.vocab_size
+                all_size_3 = len(tokenizer)
+
+                self.assertNotEqual(vocab_size_3, 0)
+                self.assertEqual(vocab_size, vocab_size_3)
+                self.assertEqual(added_toks_2, len(new_toks_2))
+                self.assertEqual(all_size_3, all_size_2 + len(new_toks_2))
+
+                tokens = tokenizer.encode(
+                    ">>>>|||<||<<|<< aaaaabbbbbb low cccccccccdddddddd <<<<<|||>|>>>>|> l", add_special_tokens=False
+                )
+
+                self.assertGreaterEqual(len(tokens), 6)
+                self.assertGreater(tokens[0], tokenizer.vocab_size - 1)
+                self.assertGreater(tokens[0], tokens[1])
+                self.assertGreater(tokens[-3], tokenizer.vocab_size - 1)
+                self.assertGreater(tokens[-3], tokens[-4])
+                self.assertEqual(tokens[0], tokenizer.eos_token_id)
+                self.assertEqual(tokens[-3], tokenizer.pad_token_id)