MBartForConditionalGeneration (#6441)

* add MBartForConditionalGeneration

* style

* rebase and fixes

* add mbart test in TEST_FILES_WITH_NO_COMMON_TESTS

* fix docs

* don't ignore mbart

* doc

* fix mbart fairseq link

* put mbart before bart

* apply doc suggestions

src/transformers/configuration_mbart.py

@@ -0,0 +1,32 @@
+# coding=utf-8
+# Copyright 2020 The Fairseq Authors and The HuggingFace Inc. team.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+""" MBART configuration """
+
+import logging
+
+from .configuration_bart import BartConfig
+
+
+logger = logging.getLogger(__name__)
+
+MBART_PRETRAINED_CONFIG_ARCHIVE_MAP = {
+    "facebook/mbart-large-en-ro": "https://s3.amazonaws.com/models.huggingface.co/bert/facebook/mbart-large-en-ro/config.json",
+    "facebook/mbart-large-cc25": "https://s3.amazonaws.com/models.huggingface.co/bert/facebook/mbart-large-cc25/config.json",
+}
+
+
+class MBartConfig(BartConfig):
+    model_type = "mbart"
+    """See real config values at https://s3.amazonaws.com/models.huggingface.co/bert/facebook/mbart-large-en-ro/config.json."""