pass langs parameter to certain XLM models (#2734)

* pass langs parameter to certain XLM models

Adding an argument that specifies the language the SQuAD dataset is in so language-sensitive XLMs (e.g. `xlm-mlm-tlm-xnli15-1024`) don't default to language `0`.
Allows resolution of issue #1799 .

* fixing from `make style`

* fixing style (again)

examples/run_squad.py

@@ -219,6 +219,11 @@ def train(args, train_dataset, model, tokenizer):
                 inputs.update({"cls_index": batch[5], "p_mask": batch[6]})
                 if args.version_2_with_negative:
                     inputs.update({"is_impossible": batch[7]})
+                if hasattr(model, "config") and hasattr(model.config, "lang2id"):
+                    inputs.update(
+                        {"langs": (torch.ones(batch[0].shape, dtype=torch.int64) * args.lang_id).to(args.device)}
+                    )
+
             outputs = model(**inputs)
             # model outputs are always tuple in transformers (see doc)
             loss = outputs[0]
@@ -330,6 +335,11 @@ def evaluate(args, model, tokenizer, prefix=""):
             # XLNet and XLM use more arguments for their predictions
             if args.model_type in ["xlnet", "xlm"]:
                 inputs.update({"cls_index": batch[4], "p_mask": batch[5]})
+                # for lang_id-sensitive xlm models
+                if hasattr(model, "config") and hasattr(model.config, "lang2id"):
+                    inputs.update(
+                        {"langs": (torch.ones(batch[0].shape, dtype=torch.int64) * args.lang_id).to(args.device)}
+                    )
 
             outputs = model(**inputs)
 
@@ -635,6 +645,12 @@ def main():
         help="If true, all of the warnings related to data processing will be printed. "
         "A number of warnings are expected for a normal SQuAD evaluation.",
     )
+    parser.add_argument(
+        "--lang_id",
+        default=0,
+        type=int,
+        help="language id of input for language-specific xlm models (see tokenization_xlm.PRETRAINED_INIT_CONFIGURATION)",
+    )
 
     parser.add_argument("--logging_steps", type=int, default=500, help="Log every X updates steps.")
     parser.add_argument("--save_steps", type=int, default=500, help="Save checkpoint every X updates steps.")