Generation: fix handling of special tokens

src/transformers/generation/utils.py

@@ -1431,23 +1431,6 @@ def _get_cache(self, cache_implementation: str, max_batch_size: int, max_cache_l
             self._cache.reset()
         return self._cache
 
-    def _get_decoder_start_token_id(
-        self, decoder_start_token_id: Union[int, List[int]] = None, bos_token_id: int = None
-    ) -> int:
-        decoder_start_token_id = (
-            decoder_start_token_id
-            if decoder_start_token_id is not None
-            else self.generation_config.decoder_start_token_id
-        )
-        bos_token_id = bos_token_id if bos_token_id is not None else self.generation_config.bos_token_id
-
-        if decoder_start_token_id is not None:
-            return decoder_start_token_id
-        elif bos_token_id is not None:
-            return bos_token_id
-        else:
-            return
-
     def _supports_default_dynamic_cache(self) -> bool:
         """
         Return `True` if current model can use a `DynamicCache` instance when initializing the `past_key_values`.
@@ -1473,25 +1456,32 @@ def _prepare_special_tokens(
         function). However, if called outside `generate`, consider creating a copy of `generation_config` first.
         """
 
-        # Convert special tokens to tensors (if they exist)
-        def _tensor_or_none(token, device=None):
+        # Convert special tokens to tensors (if they exist either in kwargs or in self.config)
+        def _tensor_or_none(token_kwargs, token_self, device=None):
             if device is None:
                 device = self.device
 
+            token = token_kwargs if token_kwargs is not None else token_self
             if token is None or isinstance(token, torch.Tensor):
                 return token
             return torch.tensor(token, device=device, dtype=torch.long)
 
-        # for BC we also try to get `decoder_start_token_id` from model's generation config (#30892)
-        if self.config.is_encoder_decoder:
-            generation_config.decoder_start_token_id = self._get_decoder_start_token_id(
-                generation_config.decoder_start_token_id, generation_config.bos_token_id
-            )
+        bos_token_id = _tensor_or_none(
+            generation_config.bos_token_id, self.generation_config.bos_token_id, device=device
+        )
+        eos_token_id = _tensor_or_none(
+            generation_config.eos_token_id, self.generation_config.eos_token_id, device=device
+        )
+        pad_token_id = _tensor_or_none(
+            generation_config.pad_token_id, self.generation_config.pad_token_id, device=device
+        )
+        decoder_start_token_id = _tensor_or_none(
+            generation_config.decoder_start_token_id, self.generation_config.decoder_start_token_id, device=device
+        )
 
-        bos_token_id = _tensor_or_none(generation_config.bos_token_id, device=device)
-        eos_token_id = _tensor_or_none(generation_config.eos_token_id, device=device)
-        pad_token_id = _tensor_or_none(generation_config.pad_token_id, device=device)
-        decoder_start_token_id = _tensor_or_none(generation_config.decoder_start_token_id, device=device)
+        # for BC we also try to get `decoder_start_token_id` or `bos_token_id` (#30892)
+        if self.config.is_encoder_decoder:
+            decoder_start_token_id = decoder_start_token_id if decoder_start_token_id is not None else bos_token_id
 
         # We can have more than one eos token. Always treat it as a 1D tensor (when it exists).
         if eos_token_id is not None and eos_token_id.ndim == 0:
@@ -1507,6 +1497,15 @@ def _tensor_or_none(token, device=None):
             pad_token_id = eos_token_id[0]
             logger.warning(f"Setting `pad_token_id` to `eos_token_id`:{pad_token_id} for open-end generation.")
 
+        # we can't infer attn mask if pad token is set to be eos token in model's generation config
+        if eos_token_id is not None and torch.isin(elements=eos_token_id, test_elements=pad_token_id).any():
+            if kwargs_has_attention_mask is not None and not kwargs_has_attention_mask:
+                logger.warning_once(
+                    "The attention mask is not set and cannot be inferred from input because pad token is same as eos token."
+                    "As a consequence, you may observe unexpected behavior. Please pass your input's `attention_mask` "
+                    "to obtain reliable results."
+                )
+
         # Sanity checks/warnings
         if self.config.is_encoder_decoder and decoder_start_token_id is None:
             raise ValueError(

tests/generation/test_framework_agnostic.py

@@ -161,6 +161,7 @@ def test_transition_scores_greedy_search(self):
         tokenizer.pad_token = tokenizer.eos_token
 
         model = model_cls.from_pretrained("distilbert/distilgpt2")
+        model.generation_config.eos_token_id = None
         input_ids = tokenizer(articles, return_tensors=return_tensors, padding=True).input_ids
         if is_pt:
             model = model.to(torch_device)
@@ -170,7 +171,6 @@ def test_transition_scores_greedy_search(self):
             input_ids=input_ids,
             max_new_tokens=5,
             pad_token_id=tokenizer.eos_token_id,
-            eos_token_id=None,
             return_dict_in_generate=True,
             output_scores=True,
         )
@@ -197,6 +197,7 @@ def test_transition_scores_greedy_search_normalized(self):
         tokenizer.pad_token = tokenizer.eos_token
 
         model = model_cls.from_pretrained("distilbert/distilgpt2")
+        model.generation_config.eos_token_id = None
         input_ids = tokenizer(articles, return_tensors=return_tensors, padding=True).input_ids
         if is_pt:
             model = model.to(torch_device)
@@ -206,7 +207,6 @@ def test_transition_scores_greedy_search_normalized(self):
             input_ids=input_ids,
             max_new_tokens=5,
             pad_token_id=tokenizer.eos_token_id,
-            eos_token_id=None,
             return_dict_in_generate=True,
             output_scores=True,
         )