🚨🚨🚨 [`Pix2Struct`] Attempts to fix training issues 🚨🚨🚨 (#23004)

* multiple fixes

- add `add_special_tokens` to `True` by default
- remove label smoothing and labels masking

* fix test

src/transformers/models/pix2struct/modeling_pix2struct.py

@@ -1554,10 +1554,9 @@ class Pix2StructTextModel(Pix2StructPreTrainedModel):
         if labels is not None:
             # move labels to correct device to enable model parallelism
             labels = labels.to(logits.device)
-            loss_fct = nn.CrossEntropyLoss(ignore_index=-100, reduction="mean", label_smoothing=0.1)
-            masked_labels = labels.masked_fill(labels == self.config.pad_token_id, -100)
+            loss_fct = nn.CrossEntropyLoss(ignore_index=-100, reduction="mean")
 
-            loss = loss_fct(logits.contiguous().view(-1, logits.size(-1)), masked_labels.contiguous().view(-1))
+            loss = loss_fct(logits.contiguous().view(-1, logits.size(-1)), labels.contiguous().view(-1))
 
         if not return_dict:
             return tuple(

src/transformers/models/pix2struct/processing_pix2struct.py

@@ -49,7 +49,7 @@ class Pix2StructProcessor(ProcessorMixin):
         self,
         images=None,
         text: Union[TextInput, PreTokenizedInput, List[TextInput], List[PreTokenizedInput]] = None,
-        add_special_tokens: bool = False,
+        add_special_tokens: bool = True,
         padding: Union[bool, str, PaddingStrategy] = False,
         truncation: Union[bool, str, TruncationStrategy] = None,
         max_length: Optional[int] = None,

tests/models/pix2struct/test_processor_pix2struct.py

@@ -108,7 +108,7 @@ class Pix2StructProcessorTest(unittest.TestCase):
 
         encoded_processor = processor(text=input_str)
 
-        encoded_tok = tokenizer(input_str, return_token_type_ids=False, add_special_tokens=False)
+        encoded_tok = tokenizer(input_str, return_token_type_ids=False, add_special_tokens=True)
 
         for key in encoded_tok.keys():
             self.assertListEqual(encoded_tok[key], encoded_processor[key])