[Trainer] suppress warning for length-related columns (#15421)

* [Trainer] suppress warning for length-related columns

* improve message

* Update src/transformers/trainer.py

src/transformers/trainer.py

@@ -546,15 +546,19 @@ class Trainer:
             self._signature_columns = list(signature.parameters.keys())
             # Labels may be named label or label_ids, the default data collator handles that.
             self._signature_columns += ["label", "label_ids"]
-        columns = [k for k in self._signature_columns if k in dataset.column_names]
+
         ignored_columns = list(set(dataset.column_names) - set(self._signature_columns))
         if len(ignored_columns) > 0:
             dset_description = "" if description is None else f"in the {description} set "
             logger.info(
                 f"The following columns {dset_description} don't have a corresponding argument in "
                 f"`{self.model.__class__.__name__}.forward` and have been ignored: {', '.join(ignored_columns)}."
+                f" If {', '.join(ignored_columns)} are not expected by `{self.model.__class__.__name__}.forward`, "
+                f" you can safely ignore this message."
             )
 
+        columns = [k for k in self._signature_columns if k in dataset.column_names]
+
         if version.parse(datasets.__version__) < version.parse("1.4.0"):
             dataset.set_format(
                 type=dataset.format["type"], columns=columns, format_kwargs=dataset.format["format_kwargs"]