Switch return_dict to True by default. (#8530)

* Use the CI to identify failing tests

* Remove from all examples and tests

* More default switch

* Fixes

* More test fixes

* More fixes

* Last fixes hopefully

* Use the CI to identify failing tests

* Remove from all examples and tests

* More default switch

* Fixes

* More test fixes

* More fixes

* Last fixes hopefully

* Run on the real suite

* Fix slow tests

src/transformers/configuration_utils.py

@@ -55,7 +55,7 @@ class PretrainedConfig(object):
             Whether or not the model should returns all attentions.
         use_cache (:obj:`bool`, `optional`, defaults to :obj:`True`):
             Whether or not the model should return the last key/values attentions (not used by all models).
-        return_dict (:obj:`bool`, `optional`, defaults to :obj:`False`):
+        return_dict (:obj:`bool`, `optional`, defaults to :obj:`True`):
             Whether or not the model should return a :class:`~transformers.file_utils.ModelOutput` instead of a plain
             tuple.
         is_encoder_decoder (:obj:`bool`, `optional`, defaults to :obj:`False`):
@@ -163,7 +163,7 @@ class PretrainedConfig(object):
 
     def __init__(self, **kwargs):
         # Attributes with defaults
-        self.return_dict = kwargs.pop("return_dict", False)
+        self.return_dict = kwargs.pop("return_dict", True)
         self.output_hidden_states = kwargs.pop("output_hidden_states", False)
         self.output_attentions = kwargs.pop("output_attentions", False)
         self.use_cache = kwargs.pop("use_cache", True)  # Not used by all models