[`LlamaTokenizerFast`] Adds edge cases for the template processor (#26606)

* make sure eos and bos are properly handled for fast tokenizer

* fix code llama as well

* nits

* fix the conversion script as well

* fix failing test

src/transformers/convert_slow_tokenizer.py

@@ -1192,32 +1192,8 @@ class LlamaConverter(SpmConverter):
         return None
 
     def post_processor(self):
-        # 3 possible case :
-        # - add_bos and add_eos : '<s>:0 $A:0 </s>:0' and '<s>:0 $A:0 </s>:0 <s>:1 $B:1 </s>:1'
-        # - add_bos: '<s>:0 $A:0' and '<s>:0 $A:0 <s>:1 $B:1'
-        # - add_eos: '$A:0 </s>:0' and '$A:0 </s>:0 $B:1 </s>:1'
-
-        add_bos = self.original_tokenizer.add_bos_token
-        add_eos = self.original_tokenizer.add_eos_token
-        if add_bos or add_eos:
-            bos = self.original_tokenizer.bos_token
-            bos_token_id = self.original_tokenizer.bos_token_id
-
-            eos = self.original_tokenizer.eos_token
-            eos_token_id = self.original_tokenizer.eos_token_id
-
-            single = f"{(bos+':0 ') * add_bos}$A:0{(' '+eos+':0') if add_eos else ''}"
-            pair = f"{single}{(' '+bos+':1') * add_bos} $B:1{(' '+eos+':1') if add_eos else ''}"
-
-            special_tokens = []
-            if add_bos:
-                special_tokens.append((bos, bos_token_id))
-            if add_eos:
-                special_tokens.append((eos, eos_token_id))
-            return processors.TemplateProcessing(single=single, pair=pair, special_tokens=special_tokens)
-
-        else:
-            return None
+        # the processor is defined in the LlamaTokenizerFast class.
+        return None
 
 
 class MarkupLMConverter(Converter):

src/transformers/models/code_llama/tokenization_code_llama_fast.py

@@ -178,12 +178,16 @@ class CodeLlamaTokenizerFast(PreTrainedTokenizerFast):
         """
         bos = self.bos_token
         bos_token_id = self.bos_token_id
+        if bos is None and self.add_bos_token:
+            raise ValueError("add_bos_token = True but bos_token = None")
 
         eos = self.eos_token
         eos_token_id = self.eos_token_id
+        if eos is None and self.add_eos_token:
+            raise ValueError("add_eos_token = True but eos_token = None")
 
-        single = f"{(bos+':0 ') * self.add_bos_token}$A:0{(' '+eos+':0') if self.add_eos_token else ''}"
-        pair = f"{single}{(' '+bos+':1') * self.add_bos_token} $B:1{(' '+eos+':1') if self.add_eos_token else ''}"
+        single = f"{(bos+':0 ') if self.add_bos_token else ''}$A:0{(' '+eos+':0') if self.add_eos_token else ''}"
+        pair = f"{single}{(' '+bos+':1') if self.add_bos_token else ''} $B:1{(' '+eos+':1') if self.add_eos_token else ''}"
 
         special_tokens = []
         if self.add_bos_token:

src/transformers/models/llama/tokenization_llama_fast.py

@@ -145,12 +145,16 @@ class LlamaTokenizerFast(PreTrainedTokenizerFast):
         """
         bos = self.bos_token
         bos_token_id = self.bos_token_id
+        if bos is None and self.add_bos_token:
+            raise ValueError("add_bos_token = True but bos_token = None")
 
         eos = self.eos_token
         eos_token_id = self.eos_token_id
+        if eos is None and self.add_eos_token:
+            raise ValueError("add_eos_token = True but eos_token = None")
 
-        single = f"{(bos+':0 ') * self.add_bos_token}$A:0{(' '+eos+':0') if self.add_eos_token else ''}"
-        pair = f"{single}{(' '+bos+':1') * self.add_bos_token} $B:1{(' '+eos+':1') if self.add_eos_token else ''}"
+        single = f"{(bos+':0 ') if self.add_bos_token else ''}$A:0{(' '+eos+':0') if self.add_eos_token else ''}"
+        pair = f"{single}{(' '+bos+':1') if self.add_bos_token else ''} $B:1{(' '+eos+':1') if self.add_eos_token else ''}"
 
         special_tokens = []
         if self.add_bos_token:

tests/models/llama/test_tokenization_llama.py

@@ -582,6 +582,19 @@ class LlamaIntegrationTest(unittest.TestCase):
         # a dummy prefix space is not added by the sp_model as it was de-activated
         self.assertEqual(tokens, tokenizer.sp_model.encode("▁▁▁", out_type=str))
 
+    def test_fast_post_processor(self):
+        tokenizer = LlamaTokenizerFast(
+            SAMPLE_VOCAB, eos_token=None, bos_token=None, add_bos_token=False, add_eos_token=False
+        )
+        tokenizer.encode(" Hey ")
+
+        with self.assertRaises(ValueError):
+            tokenizer = LlamaTokenizerFast(
+                SAMPLE_VOCAB, bos_token=None, eos_token="<s>", add_bos_token=True, add_eos_token=False
+            )
+        with self.assertRaises(ValueError):
+            tokenizer = LlamaTokenizerFast(SAMPLE_VOCAB, eos_token=None, add_bos_token=True, add_eos_token=True)
+
     @require_jinja
     def test_tokenization_for_chat(self):
         tokenizer = LlamaTokenizer.from_pretrained("huggyllama/llama-7b", legacy=False)