Fixing by correctly raising UnicodeDecodeError. (#13449)

src/transformers/models/byt5/tokenization_byt5.py

@@ -237,14 +237,7 @@ class ByT5Tokenizer(PreTrainedTokenizer):
             else:
                 tok_string = bytes([ord(token)])
             bstring += tok_string
-        # XXX: This is most likely incorrect, we want utf-8 errors
-        # to be triggered. However transformers test suite will
-        # try to decode every ID within the tokenizer on their own
-        # meaning it will attempt to try and decode invalid utf-8.
-        # Ignoring errors means passing tests, meanwhile correctly
-        # raising the errors means editing the automated tests to
-        # support that behavior (decoding an arbitrary ID might be invalid).
-        string = bstring.decode("utf-8", errors="ignore")
+        string = bstring.decode("utf-8")
         return string
 
     # ByT5Tokenizer has no vocab file

tests/test_tokenization_byt5.py

@@ -15,9 +15,11 @@
 
 import json
 import os
+import re
 import shutil
 import tempfile
 import unittest
+from typing import Tuple
 
 from transformers import AddedToken, BatchEncoding, ByT5Tokenizer
 from transformers.file_utils import cached_property, is_tf_available, is_torch_available
@@ -50,6 +52,44 @@ class ByT5TokenizationTest(TokenizerTesterMixin, unittest.TestCase):
     def get_tokenizer(self, **kwargs) -> ByT5Tokenizer:
         return self.tokenizer_class.from_pretrained(self.tmpdirname, **kwargs)
 
+    def get_clean_sequence(self, tokenizer, with_prefix_space=False, max_length=20, min_length=5) -> Tuple[str, list]:
+        # XXX The default common tokenizer tests assume that every ID is decodable on its own.
+        # This assumption is invalid for ByT5 because single bytes might not be
+        # valid utf-8 (byte 128 for instance).
+        # Here we're overriding the smallest possible method to provide
+        # a clean sequence without making the same assumption.
+
+        toks = []
+        for i in range(len(tokenizer)):
+            try:
+                tok = tokenizer.decode([i], clean_up_tokenization_spaces=False)
+            except UnicodeDecodeError:
+                pass
+            toks.append((i, tok))
+
+        toks = list(filter(lambda t: re.match(r"^[ a-zA-Z]+$", t[1]), toks))
+        toks = list(filter(lambda t: [t[0]] == tokenizer.encode(t[1], add_special_tokens=False), toks))
+        if max_length is not None and len(toks) > max_length:
+            toks = toks[:max_length]
+        if min_length is not None and len(toks) < min_length and len(toks) > 0:
+            while len(toks) < min_length:
+                toks = toks + toks
+        # toks_str = [t[1] for t in toks]
+        toks_ids = [t[0] for t in toks]
+
+        # Ensure consistency
+        output_txt = tokenizer.decode(toks_ids, clean_up_tokenization_spaces=False)
+        if " " not in output_txt and len(toks_ids) > 1:
+            output_txt = (
+                tokenizer.decode([toks_ids[0]], clean_up_tokenization_spaces=False)
+                + " "
+                + tokenizer.decode(toks_ids[1:], clean_up_tokenization_spaces=False)
+            )
+        if with_prefix_space:
+            output_txt = " " + output_txt
+        output_ids = tokenizer.encode(output_txt, add_special_tokens=False)
+        return output_txt, output_ids
+
     def test_eos_treatment(self):
         tokenizer = self.t5_base_tokenizer
         batch_with_eos_added = tokenizer(["hi</s>", "I went to the gym</s>", "</s>"])