[LlamaTokenizerFast] nit update `post_processor` on the fly (#23855)

* Update the processor when changing add_eos and add_bos

* fixup

* update

* add a test

* fix failing tests

* fixup

src/transformers/models/llama/tokenization_llama_fast.py

@@ -16,6 +16,8 @@ import os
 from shutil import copyfile
 from typing import Optional, Tuple
 
+from tokenizers import processors
+
 from ...tokenization_utils_fast import PreTrainedTokenizerFast
 from ...utils import is_sentencepiece_available, logging
 from ...utils.versions import require_version
@@ -84,6 +86,8 @@ class LlamaTokenizerFast(PreTrainedTokenizerFast):
         unk_token="<unk>",
         bos_token="<s>",
         eos_token="</s>",
+        add_bos_token=True,
+        add_eos_token=False,
         **kwargs,
     ):
         super().__init__(
@@ -95,10 +99,50 @@ class LlamaTokenizerFast(PreTrainedTokenizerFast):
             eos_token=eos_token,
             **kwargs,
         )
+        self._add_bos_token = add_bos_token
+        self._add_eos_token = add_eos_token
+        self.update_post_processor()
 
         self.vocab_file = vocab_file
         self.can_save_slow_tokenizer = False if not self.vocab_file else True
 
+    def update_post_processor(self):
+        bos = self.bos_token
+        bos_token_id = self.bos_token_id
+
+        eos = self.eos_token
+        eos_token_id = self.eos_token_id
+
+        single = f"{(bos+':0 ') * self.add_bos_token}$A:0{(' '+eos+':0') * self.add_eos_token}"
+        pair = f"{single}{(' '+bos+':1') * self.add_bos_token} $B:1{(' '+eos+':1') * self.add_eos_token}"
+
+        special_tokens = []
+        if self.add_bos_token:
+            special_tokens.append((bos, bos_token_id))
+        if self.add_eos_token:
+            special_tokens.append((eos, eos_token_id))
+        self._tokenizer.post_processor = processors.TemplateProcessing(
+            single=single, pair=pair, special_tokens=special_tokens
+        )
+
+    @property
+    def add_eos_token(self):
+        return self._add_eos_token
+
+    @property
+    def add_bos_token(self):
+        return self._add_bos_token
+
+    @add_eos_token.setter
+    def add_eos_token(self, value):
+        self._add_eos_token = value
+        self.update_post_processor()
+
+    @add_bos_token.setter
+    def add_bos_token(self, value):
+        self._add_bos_token = value
+        self.update_post_processor()
+
     def save_vocabulary(self, save_directory: str, filename_prefix: Optional[str] = None) -> Tuple[str]:
         if not self.can_save_slow_tokenizer:
             raise ValueError(

tests/models/llama/test_tokenization_llama.py

@@ -315,6 +315,39 @@ class LlamaIntegrationTest(unittest.TestCase):
             },
         )
 
+    def test_fast_special_tokens(self):
+        slow_tokenizer = self.tokenizer
+        fast_tokenizer = self.rust_tokenizer
+        slow = slow_tokenizer.encode("A sample test", add_special_tokens=True)
+        assert slow == [1, 319, 4559, 1243]
+
+        fast_tokenizer.add_eos_token = False
+        fast = fast_tokenizer.encode("A sample test", add_special_tokens=True)
+        assert fast == [1, 319, 4559, 1243]
+
+        fast_tokenizer.add_eos_token = True
+        fast = fast_tokenizer.encode("A sample test", add_special_tokens=True)
+        assert fast == [1, 319, 4559, 1243, 2]
+
+        slow_tokenizer.add_eos_token = True
+        slow = slow_tokenizer.encode("A sample test", add_special_tokens=True)
+        assert slow == [1, 319, 4559, 1243, 2]
+
+        fast_tokenizer = LlamaTokenizerFast.from_pretrained(
+            "hf-internal-testing/llama-tokenizer", add_eos_token=True, add_bos_token=False
+        )
+        fast = fast_tokenizer.encode("A sample test", add_special_tokens=True)
+        assert fast == [319, 4559, 1243, 2]
+
+        slow_tokenzier = LlamaTokenizer.from_pretrained(
+            "hf-internal-testing/llama-tokenizer", add_eos_token=True, add_bos_token=False
+        )
+        slow = slow_tokenzier.encode("A sample test", add_special_tokens=True)
+        assert slow == [319, 4559, 1243, 2]
+
+        self.tokenizer.add_eos_token = False
+        self.rust_tokenizer.add_eos_token = False
+
     @slow
     def test_conversion(self):
         # This is excruciatingly slow since it has to recreate the entire merge