[`TokenizationRoformerFast`] Fix the save and loading (#28527)

* cleanup

* add a test

* update the test

* style

* revert part that allows to pickle the tokenizer

src/transformers/models/roformer/tokenization_roformer_fast.py

@@ -122,15 +122,19 @@ class RoFormerTokenizerFast(PreTrainedTokenizerFast):
             **kwargs,
         )
 
-        pre_tok_state = json.loads(self.backend_tokenizer.normalizer.__getstate__())
+        normalizer_state = json.loads(self.backend_tokenizer.normalizer.__getstate__())
         if (
-            pre_tok_state.get("lowercase", do_lower_case) != do_lower_case
-            or pre_tok_state.get("strip_accents", strip_accents) != strip_accents
+            normalizer_state.get("lowercase", do_lower_case) != do_lower_case
+            or normalizer_state.get("strip_accents", strip_accents) != strip_accents
         ):
-            pre_tok_class = getattr(normalizers, pre_tok_state.pop("type"))
-            pre_tok_state["lowercase"] = do_lower_case
-            pre_tok_state["strip_accents"] = strip_accents
-            self.backend_tokenizer.normalizer = pre_tok_class(**pre_tok_state)
+            normalizer_class = getattr(normalizers, normalizer_state.pop("type"))
+            normalizer_state["lowercase"] = do_lower_case
+            normalizer_state["strip_accents"] = strip_accents
+            self.backend_tokenizer.normalizer = normalizer_class(**normalizer_state)
+
+        # Make sure we correctly set the custom PreTokenizer
+        vocab = self.backend_tokenizer.get_vocab()
+        self.backend_tokenizer.pre_tokenizer = PreTokenizer.custom(JiebaPreTokenizer(vocab))
 
         self.do_lower_case = do_lower_case
 

tests/models/roformer/test_tokenization_roformer.py

@@ -13,6 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import tempfile
 import unittest
 
 from transformers import RoFormerTokenizer, RoFormerTokenizerFast
@@ -71,6 +72,12 @@ class RoFormerTokenizationTest(TokenizerTesterMixin, unittest.TestCase):
     def test_training_new_tokenizer_with_special_tokens_change(self):
         pass
 
-    # can't serialise custom PreTokenizer
     def test_save_slow_from_fast_and_reload_fast(self):
-        pass
+        for cls in [RoFormerTokenizer, RoFormerTokenizerFast]:
+            original = cls.from_pretrained("alchemab/antiberta2")
+            self.assertEqual(original.encode("生活的真谛是"), [1, 4, 4, 4, 4, 4, 4, 2])
+
+            with tempfile.TemporaryDirectory() as tmp_dir:
+                original.save_pretrained(tmp_dir)
+                new = cls.from_pretrained(tmp_dir)
+            self.assertEqual(new.encode("生活的真谛是"), [1, 4, 4, 4, 4, 4, 4, 2])