Add mBART-50 (#10154)

* add tokenizer for mBART-50

* update tokenizers

* make src_lang and tgt_lang optional

* update tokenizer test

* add setter

* update docs

* update conversion script

* update docs

* update conversion script

* update tokenizer

* update test

* update docs

* doc

* address Sylvain's suggestions

* fix test

* fix formatting

* nits

README.md

@@ -217,6 +217,7 @@ Min, Patrick Lewis, Ledell Wu, Sergey Edunov, Danqi Chen, and Wen-tau Yih.
 1. **[LXMERT](https://huggingface.co/transformers/model_doc/lxmert.html)** (from UNC Chapel Hill) released with the paper [LXMERT: Learning Cross-Modality Encoder Representations from Transformers for Open-Domain Question Answering](https://arxiv.org/abs/1908.07490) by Hao Tan and Mohit Bansal.
 1. **[MarianMT](https://huggingface.co/transformers/model_doc/marian.html)** Machine translation models trained using [OPUS](http://opus.nlpl.eu/) data by Jörg Tiedemann. The [Marian Framework](https://marian-nmt.github.io/) is being developed by the Microsoft Translator Team.
 1. **[MBart](https://huggingface.co/transformers/model_doc/mbart.html)** (from Facebook) released with the paper [Multilingual Denoising Pre-training for Neural Machine Translation](https://arxiv.org/abs/2001.08210) by Yinhan Liu, Jiatao Gu, Naman Goyal, Xian Li, Sergey Edunov, Marjan Ghazvininejad, Mike Lewis, Luke Zettlemoyer.
+1. **[MBart-50](https://huggingface.co/transformers/model_doc/mbart.html)** (from Facebook) released with the paper [Multilingual Translation with Extensible Multilingual Pretraining and Finetuning](https://arxiv.org/abs/2008.00401) by Yuqing Tang, Chau Tran, Xian Li, Peng-Jen Chen, Naman Goyal, Vishrav Chaudhary, Jiatao Gu, Angela Fan.
 1. **[MPNet](https://huggingface.co/transformers/model_doc/mpnet.html)** (from Microsoft Research) released with the paper [MPNet: Masked and Permuted Pre-training for Language Understanding](https://arxiv.org/abs/2004.09297) by Kaitao Song, Xu Tan, Tao Qin, Jianfeng Lu, Tie-Yan Liu.
 1. **[MT5](https://huggingface.co/transformers/model_doc/mt5.html)** (from Google AI) released with the paper [mT5: A massively multilingual pre-trained text-to-text transformer](https://arxiv.org/abs/2010.11934) by Linting Xue, Noah Constant, Adam Roberts, Mihir Kale, Rami Al-Rfou, Aditya Siddhant, Aditya Barua, Colin Raffel.
 1. **[Pegasus](https://huggingface.co/transformers/model_doc/pegasus.html)** (from Google) released with the paper [PEGASUS: Pre-training with Extracted Gap-sentences for Abstractive Summarization](https://arxiv.org/abs/1912.08777)> by Jingqing Zhang, Yao Zhao, Mohammad Saleh and Peter J. Liu.

docs/source/index.rst

@@ -161,48 +161,51 @@ and conversion utilities for the following models:
 26. :doc:`MBart <model_doc/mbart>` (from Facebook) released with the paper `Multilingual Denoising Pre-training for
     Neural Machine Translation <https://arxiv.org/abs/2001.08210>`__ by Yinhan Liu, Jiatao Gu, Naman Goyal, Xian Li,
     Sergey Edunov, Marjan Ghazvininejad, Mike Lewis, Luke Zettlemoyer.
-27. :doc:`MPNet <model_doc/mpnet>` (from Microsoft Research) released with the paper `MPNet: Masked and Permuted
+27. :doc:`MBart-50 <model_doc/mbart>` (from Facebook) released with the paper `Multilingual Translation with Extensible
+    Multilingual Pretraining and Finetuning <https://arxiv.org/abs/2008.00401>`__ by Yuqing Tang, Chau Tran, Xian Li,
+    Peng-Jen Chen, Naman Goyal, Vishrav Chaudhary, Jiatao Gu, Angela Fan.
+28. :doc:`MPNet <model_doc/mpnet>` (from Microsoft Research) released with the paper `MPNet: Masked and Permuted
     Pre-training for Language Understanding <https://arxiv.org/abs/2004.09297>`__ by Kaitao Song, Xu Tan, Tao Qin,
     Jianfeng Lu, Tie-Yan Liu.
-28. :doc:`MT5 <model_doc/mt5>` (from Google AI) released with the paper `mT5: A massively multilingual pre-trained
+29. :doc:`MT5 <model_doc/mt5>` (from Google AI) released with the paper `mT5: A massively multilingual pre-trained
     text-to-text transformer <https://arxiv.org/abs/2010.11934>`__ by Linting Xue, Noah Constant, Adam Roberts, Mihir
     Kale, Rami Al-Rfou, Aditya Siddhant, Aditya Barua, Colin Raffel.
-29. :doc:`Pegasus <model_doc/pegasus>` (from Google) released with the paper `PEGASUS: Pre-training with Extracted
+30. :doc:`Pegasus <model_doc/pegasus>` (from Google) released with the paper `PEGASUS: Pre-training with Extracted
     Gap-sentences for Abstractive Summarization <https://arxiv.org/abs/1912.08777>`__> by Jingqing Zhang, Yao Zhao,
     Mohammad Saleh and Peter J. Liu.
-30. :doc:`ProphetNet <model_doc/prophetnet>` (from Microsoft Research) released with the paper `ProphetNet: Predicting
+31. :doc:`ProphetNet <model_doc/prophetnet>` (from Microsoft Research) released with the paper `ProphetNet: Predicting
     Future N-gram for Sequence-to-Sequence Pre-training <https://arxiv.org/abs/2001.04063>`__ by Yu Yan, Weizhen Qi,
     Yeyun Gong, Dayiheng Liu, Nan Duan, Jiusheng Chen, Ruofei Zhang and Ming Zhou.
-31. :doc:`Reformer <model_doc/reformer>` (from Google Research) released with the paper `Reformer: The Efficient
+32. :doc:`Reformer <model_doc/reformer>` (from Google Research) released with the paper `Reformer: The Efficient
     Transformer <https://arxiv.org/abs/2001.04451>`__ by Nikita Kitaev, Łukasz Kaiser, Anselm Levskaya.
-32. :doc:`RoBERTa <model_doc/roberta>` (from Facebook), released together with the paper a `Robustly Optimized BERT
+33. :doc:`RoBERTa <model_doc/roberta>` (from Facebook), released together with the paper a `Robustly Optimized BERT
     Pretraining Approach <https://arxiv.org/abs/1907.11692>`__ by Yinhan Liu, Myle Ott, Naman Goyal, Jingfei Du, Mandar
     Joshi, Danqi Chen, Omer Levy, Mike Lewis, Luke Zettlemoyer, Veselin Stoyanov.
-33. :doc:`SqueezeBert <model_doc/squeezebert>` released with the paper `SqueezeBERT: What can computer vision teach NLP
+34. :doc:`SqueezeBert <model_doc/squeezebert>` released with the paper `SqueezeBERT: What can computer vision teach NLP
     about efficient neural networks? <https://arxiv.org/abs/2006.11316>`__ by Forrest N. Iandola, Albert E. Shaw, Ravi
     Krishna, and Kurt W. Keutzer.
-34. :doc:`T5 <model_doc/t5>` (from Google AI) released with the paper `Exploring the Limits of Transfer Learning with a
+35. :doc:`T5 <model_doc/t5>` (from Google AI) released with the paper `Exploring the Limits of Transfer Learning with a
     Unified Text-to-Text Transformer <https://arxiv.org/abs/1910.10683>`__ by Colin Raffel and Noam Shazeer and Adam
     Roberts and Katherine Lee and Sharan Narang and Michael Matena and Yanqi Zhou and Wei Li and Peter J. Liu.
-35. :doc:`TAPAS <model_doc/tapas>` (from Google AI) released with the paper `TAPAS: Weakly Supervised Table Parsing via
+36. :doc:`TAPAS <model_doc/tapas>` (from Google AI) released with the paper `TAPAS: Weakly Supervised Table Parsing via
     Pre-training <https://arxiv.org/abs/2004.02349>`__ by Jonathan Herzig, Paweł Krzysztof Nowak, Thomas Müller,
     Francesco Piccinno and Julian Martin Eisenschlos.
-36. :doc:`Transformer-XL <model_doc/transformerxl>` (from Google/CMU) released with the paper `Transformer-XL:
+37. :doc:`Transformer-XL <model_doc/transformerxl>` (from Google/CMU) released with the paper `Transformer-XL:
     Attentive Language Models Beyond a Fixed-Length Context <https://arxiv.org/abs/1901.02860>`__ by Zihang Dai*,
     Zhilin Yang*, Yiming Yang, Jaime Carbonell, Quoc V. Le, Ruslan Salakhutdinov.
-37. :doc:`Wav2Vec2 <model_doc/wav2vec2>` (from Facebook AI) released with the paper `wav2vec 2.0: A Framework for
+38. :doc:`Wav2Vec2 <model_doc/wav2vec2>` (from Facebook AI) released with the paper `wav2vec 2.0: A Framework for
     Self-Supervised Learning of Speech Representations <https://arxiv.org/abs/2006.11477>`__ by Alexei Baevski, Henry
     Zhou, Abdelrahman Mohamed, Michael Auli.
-38. :doc:`XLM <model_doc/xlm>` (from Facebook) released together with the paper `Cross-lingual Language Model
+39. :doc:`XLM <model_doc/xlm>` (from Facebook) released together with the paper `Cross-lingual Language Model
     Pretraining <https://arxiv.org/abs/1901.07291>`__ by Guillaume Lample and Alexis Conneau.
-39. :doc:`XLM-ProphetNet <model_doc/xlmprophetnet>` (from Microsoft Research) released with the paper `ProphetNet:
+40. :doc:`XLM-ProphetNet <model_doc/xlmprophetnet>` (from Microsoft Research) released with the paper `ProphetNet:
     Predicting Future N-gram for Sequence-to-Sequence Pre-training <https://arxiv.org/abs/2001.04063>`__ by Yu Yan,
     Weizhen Qi, Yeyun Gong, Dayiheng Liu, Nan Duan, Jiusheng Chen, Ruofei Zhang and Ming Zhou.
-40. :doc:`XLM-RoBERTa <model_doc/xlmroberta>` (from Facebook AI), released together with the paper `Unsupervised
+41. :doc:`XLM-RoBERTa <model_doc/xlmroberta>` (from Facebook AI), released together with the paper `Unsupervised
     Cross-lingual Representation Learning at Scale <https://arxiv.org/abs/1911.02116>`__ by Alexis Conneau*, Kartikay
     Khandelwal*, Naman Goyal, Vishrav Chaudhary, Guillaume Wenzek, Francisco Guzmán, Edouard Grave, Myle Ott, Luke
     Zettlemoyer and Veselin Stoyanov.
-41. :doc:`XLNet <model_doc/xlnet>` (from Google/CMU) released with the paper `​XLNet: Generalized Autoregressive
+42. :doc:`XLNet <model_doc/xlnet>` (from Google/CMU) released with the paper `​XLNet: Generalized Autoregressive
     Pretraining for Language Understanding <https://arxiv.org/abs/1906.08237>`__ by Zhilin Yang*, Zihang Dai*, Yiming
     Yang, Jaime Carbonell, Ruslan Salakhutdinov, Quoc V. Le.
 

docs/source/model_doc/mbart.rst

@@ -10,14 +10,14 @@
     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
+MBart and MBart-50
 -----------------------------------------------------------------------------------------------------------------------
 
 **DISCLAIMER:** If you see something strange, file a `Github Issue
 <https://github.com/huggingface/transformers/issues/new?assignees=&labels=&template=bug-report.md&title>`__ and assign
 @patrickvonplaten
 
-Overview
+Overview of MBart
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 The MBart model was presented in `Multilingual Denoising Pre-training for Neural Machine Translation
@@ -31,17 +31,9 @@ on the encoder, decoder, or reconstructing parts of the text.
 
 The Authors' code can be found `here <https://github.com/pytorch/fairseq/tree/master/examples/mbart>`__
 
-Examples
+Training of MBart
 _______________________________________________________________________________________________________________________
 
-- Examples and scripts for fine-tuning mBART and other models for sequence to sequence tasks can be found in
-  :prefix_link:`examples/seq2seq/ <examples/seq2seq/README.md>`.
-- Given the large embeddings table, mBART consumes a large amount of GPU RAM, especially for fine-tuning.
-  :class:`MarianMTModel` is usually a better choice for bilingual machine translation.
-
-Training
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
 MBart is a multilingual encoder-decoder (seq-to-seq) model primarily intended for translation task. As the model is
 multilingual it expects the sequences in a different format. A special language id token is added in both the source
 and target text. The source text format is :obj:`X [eos, src_lang_code]` where :obj:`X` is the source text. The target
@@ -76,6 +68,87 @@ the sequences for sequence-to-sequence fine-tuning.
     assert translation == "Şeful ONU declară că nu există o soluţie militară în Siria"
 
 
+Overview of MBart-50
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+MBart-50 was introduced in the `Multilingual Translation with Extensible Multilingual Pretraining and Finetuning
+<https://arxiv.org/abs/2008.00401>` paper by Yuqing Tang, Chau Tran, Xian Li, Peng-Jen Chen, Naman Goyal, Vishrav
+Chaudhary, Jiatao Gu, Angela Fan. MBart-50 is created using the original `mbart-large-cc25` checkpoint by extendeding
+its embedding layers with randomly initialized vectors for an extra set of 25 language tokens and then pretrained on 50
+languages.
+
+According to the abstract
+
+*Multilingual translation models can be created through multilingual finetuning. Instead of finetuning on one
+direction, a pretrained model is finetuned on many directions at the same time. It demonstrates that pretrained models
+can be extended to incorporate additional languages without loss of performance. Multilingual finetuning improves on
+average 1 BLEU over the strongest baselines (being either multilingual from scratch or bilingual finetuning) while
+improving 9.3 BLEU on average over bilingual baselines from scratch.*
+
+
+Training of MBart-50
+_______________________________________________________________________________________________________________________
+
+The text format for MBart-50 is slightly different from mBART. For MBart-50 the language id token is used as a prefix
+for both source and target text i.e the text format is :obj:`[lang_code] X [eos]`, where :obj:`lang_code` is source
+language id for source text and target language id for target text, with :obj:`X` being the source or target text
+respectively.
+
+
+MBart-50 has its own tokenizer :class:`~transformers.MBart50Tokenizer`.
+
+-  Supervised training
+
+.. code-block::
+
+    from transformers import MBartForConditionalGeneration, MBart50TokenizerFast
+
+    model = MBartForConditionalGeneration.from_pretrained("facebook/mbart-large-50")
+    tokenizer = MBart50TokenizerFast.from_pretrained("facebook/mbart-large-50", src_lang="en_XX", tgt_lang="ro_RO")
+
+    src_text = " UN Chief Says There Is No Military Solution in Syria"
+    tgt_text =  "Şeful ONU declară că nu există o soluţie militară în Siria"
+
+    model_inputs = tokenizer(src_text, return_tensors="pt")
+    with tokenizer.as_target_tokenizer():
+        labels = tokenizer(tgt_text, return_tensors="pt").input_ids
+
+    model(**model_inputs, labels=labels) # forward pass
+
+
+- Generation
+
+    To generate using the mBART-50 multilingual translation models, :obj:`eos_token_id` is used as the
+    :obj:`decoder_start_token_id` and the target language id is forced as the first generated token. To force the
+    target language id as the first generated token, pass the `forced_bos_token_id` parameter to the `generate` method.
+    The following example shows how to translate between Hindi to French and Arabic to English using the
+    `facebook/mbart-50-large-many-to-many` checkpoint.
+
+.. code-block::
+
+    from transformers import MBartForConditionalGeneration, MBart50TokenizerFast
+
+    article_hi = "संयुक्त राष्ट्र के प्रमुख का कहना है कि सीरिया में कोई सैन्य समाधान नहीं है"
+    article_ar = "الأمين العام للأمم المتحدة يقول إنه لا يوجد حل عسكري في سوريا."
+
+    model = MBartForConditionalGeneration.from_pretrained("facebook/mbart-large-50-many-to-many-mmt")
+    tokenizer = MBart50TokenizerFast.from_pretrained("facebook/mbart-large-50-many-to-many-mmt")
+
+    # translate Hindi to French
+    tokenizer.src_lang = "hi_IN"
+    encoded_hi = tokenizer(article_hi, return_tensors="pt")
+    generated_tokens = model.generate(**encoded_hi, forced_bos_token_id=tokenizer.lang_code_to_id["fr_XX"])
+    tokenizer.batch_decode(generated_tokens, skip_special_tokens=True)
+    # => "Le chef de l 'ONU affirme qu 'il n 'y a pas de solution militaire en Syria."
+
+    # translate Arabic to English
+    tokenizer.src_lang = "ar_AR"
+    encoded_ar = tokenizer(article_ar, return_tensors="pt")
+    generated_tokens = model.generate(**encoded_ar, forced_bos_token_id=tokenizer.lang_code_to_id["en_XX"])
+    tokenizer.batch_decode(generated_tokens, skip_special_tokens=True)
+    # => "The Secretary-General of the United Nations says there is no military solution in Syria."
+
+
 MBartConfig
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
@@ -97,6 +170,20 @@ MBartTokenizerFast
     :members:
 
 
+MBart50Tokenizer
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. autoclass:: transformers.MBart50Tokenizer
+    :members:
+
+
+MBart50TokenizerFast
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. autoclass:: transformers.MBart50TokenizerFast
+    :members:
+
+
 MBartModel
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 

docs/source/pretrained_models.rst

@@ -381,6 +381,15 @@ For the full list, refer to `https://huggingface.co/models <https://huggingface.
 |                    +------------------------------------------------------------+---------------------------------------------------------------------------------------------------------------------------------------+
 |                    | ``facebook/mbart-large-en-ro``                             | | 24-layer, 1024-hidden, 16-heads, 610M parameters                                                                                    |
 |                    |                                                            | | mbart-large-cc25 model finetuned on WMT english romanian translation.                                                               |
+|                    +------------------------------------------------------------+---------------------------------------------------------------------------------------------------------------------------------------+
+|                    | ``facebook/mbart-large-50``                                | | 24-layer, 1024-hidden, 16-heads,                                                                                                    |
+|                    |                                                            | | mBART model trained on 50 languages' monolingual corpus.                                                                            |
+|                    +------------------------------------------------------------+---------------------------------------------------------------------------------------------------------------------------------------+
+|                    | ``facebook/mbart-large-50-one-to-many-mmt``                | | 24-layer, 1024-hidden, 16-heads,                                                                                                    |
+|                    |                                                            | | mbart-50-large model finetuned for one (English) to many multilingual machine translation covering 50 languages.                    |
+|                    +------------------------------------------------------------+---------------------------------------------------------------------------------------------------------------------------------------+
+|                    | ``facebook/mbart-large-50-many-to-many-mmt``               | | 24-layer, 1024-hidden, 16-heads,                                                                                                    |
+|                    |                                                            | | mbart-50-large model finetuned for many to many multilingual machine translation covering 50 languages.                             |
 +--------------------+------------------------------------------------------------+---------------------------------------------------------------------------------------------------------------------------------------+
 | Lxmert             | ``lxmert-base-uncased``                                    | | 9-language layers, 9-relationship layers, and 12-cross-modality layers                                                              |
 |                    |                                                            | | 768-hidden, 12-heads (for each layer) ~ 228M parameters                                                                             |

src/transformers/__init__.py

@@ -260,6 +260,7 @@ if is_sentencepiece_available():
     _import_structure["models.camembert"].append("CamembertTokenizer")
     _import_structure["models.marian"].append("MarianTokenizer")
     _import_structure["models.mbart"].append("MBartTokenizer")
+    _import_structure["models.mbart"].append("MBart50Tokenizer")
     _import_structure["models.mt5"].append("MT5Tokenizer")
     _import_structure["models.pegasus"].append("PegasusTokenizer")
     _import_structure["models.reformer"].append("ReformerTokenizer")
@@ -296,6 +297,7 @@ if is_tokenizers_available():
     _import_structure["models.longformer"].append("LongformerTokenizerFast")
     _import_structure["models.lxmert"].append("LxmertTokenizerFast")
     _import_structure["models.mbart"].append("MBartTokenizerFast")
+    _import_structure["models.mbart"].append("MBart50TokenizerFast")
     _import_structure["models.mobilebert"].append("MobileBertTokenizerFast")
     _import_structure["models.mpnet"].append("MPNetTokenizerFast")
     _import_structure["models.mt5"].append("MT5TokenizerFast")
@@ -1391,7 +1393,7 @@ if TYPE_CHECKING:
         from .models.bert_generation import BertGenerationTokenizer
         from .models.camembert import CamembertTokenizer
         from .models.marian import MarianTokenizer
-        from .models.mbart import MBartTokenizer
+        from .models.mbart import MBart50Tokenizer, MBartTokenizer
         from .models.mt5 import MT5Tokenizer
         from .models.pegasus import PegasusTokenizer
         from .models.reformer import ReformerTokenizer
@@ -1419,7 +1421,7 @@ if TYPE_CHECKING:
         from .models.led import LEDTokenizerFast
         from .models.longformer import LongformerTokenizerFast
         from .models.lxmert import LxmertTokenizerFast
-        from .models.mbart import MBartTokenizerFast
+        from .models.mbart import MBart50TokenizerFast, MBartTokenizerFast
         from .models.mobilebert import MobileBertTokenizerFast
         from .models.mpnet import MPNetTokenizerFast
         from .models.mt5 import MT5TokenizerFast

src/transformers/convert_slow_tokenizer.py

@@ -500,6 +500,35 @@ class MBartConverter(SpmConverter):
         )
 
 
+class MBart50Converter(SpmConverter):
+    def vocab(self, proto):
+        vocab = [
+            ("<s>", 0.0),
+            ("<pad>", 0.0),
+            ("</s>", 0.0),
+            ("<unk>", 0.0),
+        ]
+        vocab += [(piece.piece, piece.score) for piece in proto.pieces[3:]]
+        # fmt: off
+        vocab += [("ar_AR", 0.0), ("cs_CZ", 0.0), ("de_DE", 0.0), ("en_XX", 0.0), ("es_XX", 0.0), ("et_EE", 0.0), ("fi_FI", 0.0), ("fr_XX", 0.0), ("gu_IN", 0.0), ("hi_IN", 0.0), ("it_IT", 0.0), ("ja_XX", 0.0), ("kk_KZ", 0.0), ("ko_KR", 0.0), ("lt_LT", 0.0), ("lv_LV", 0.0), ("my_MM", 0.0), ("ne_NP", 0.0), ("nl_XX", 0.0), ("ro_RO", 0.0), ("ru_RU", 0.0), ("si_LK", 0.0), ("tr_TR", 0.0), ("vi_VN", 0.0), ("zh_CN", 0.0), ("af_ZA", 0.0), ("az_AZ", 0.0), ("bn_IN", 0.0), ("fa_IR", 0.0), ("he_IL", 0.0), ("hr_HR", 0.0), ("id_ID", 0.0), ("ka_GE", 0.0), ("km_KH", 0.0), ("mk_MK", 0.0), ("ml_IN", 0.0), ("mn_MN", 0.0), ("mr_IN", 0.0), ("pl_PL", 0.0), ("ps_AF", 0.0), ("pt_XX", 0.0), ("sv_SE", 0.0), ("sw_KE", 0.0), ("ta_IN", 0.0), ("te_IN", 0.0), ("th_TH", 0.0), ("tl_XX", 0.0), ("uk_UA", 0.0), ("ur_PK", 0.0), ("xh_ZA", 0.0), ("gl_ES", 0.0), ("sl_SI", 0.0)]
+        # fmt: on
+        vocab += [("<mask>", 0.0)]
+        return vocab
+
+    def unk_id(self, proto):
+        return 3
+
+    def post_processor(self):
+        return processors.TemplateProcessing(
+            single="en_XX $A </s>",
+            pair="en_XX $A $B </s>",
+            special_tokens=[
+                ("en_XX", self.original_tokenizer.convert_tokens_to_ids("en_XX")),
+                ("</s>", self.original_tokenizer.convert_tokens_to_ids("</s>")),
+            ],
+        )
+
+
 class XLMRobertaConverter(SpmConverter):
     def vocab(self, proto):
         vocab = [
@@ -637,6 +666,7 @@ SLOW_TO_FAST_CONVERTERS = {
     "LEDTokenizer": RobertaConverter,
     "LxmertTokenizer": BertConverter,
     "MBartTokenizer": MBartConverter,
+    "MBart50Tokenizer": MBart50Converter,
     "MPNetTokenizer": MPNetConverter,
     "MobileBertTokenizer": BertConverter,
     "OpenAIGPTTokenizer": OpenAIGPTConverter,

src/transformers/models/mbart/__init__.py

@@ -32,9 +32,11 @@ _import_structure = {
 
 if is_sentencepiece_available():
     _import_structure["tokenization_mbart"] = ["MBartTokenizer"]
+    _import_structure["tokenization_mbart50"] = ["MBart50Tokenizer"]
 
 if is_tokenizers_available():
     _import_structure["tokenization_mbart_fast"] = ["MBartTokenizerFast"]
+    _import_structure["tokenization_mbart50_fast"] = ["MBart50TokenizerFast"]
 
 if is_torch_available():
     _import_structure["modeling_mbart"] = [
@@ -56,8 +58,10 @@ if TYPE_CHECKING:
 
     if is_sentencepiece_available():
         from .tokenization_mbart import MBartTokenizer
+        from .tokenization_mbart50 import MBart50Tokenizer
 
     if is_tokenizers_available():
+        from .tokenization_mbart50_fast import MBart50TokenizerFast
         from .tokenization_mbart_fast import MBartTokenizerFast
 
     if is_torch_available():

src/transformers/models/mbart/convert_mbart_original_checkpoint_to_pytorch.py

@@ -15,19 +15,49 @@
 import argparse
 
 import torch
+from torch import nn
 
-from transformers import BartForConditionalGeneration, MBartConfig
-from transformers.models.bart.convert_bart_original_pytorch_checkpoint_to_pytorch import remove_ignore_keys_
+from transformers import MBartConfig, MBartForConditionalGeneration
 
 
-def convert_fairseq_mbart_checkpoint_from_disk(checkpoint_path, hf_config_path="facebook/mbart-large-en-ro"):
+def remove_ignore_keys_(state_dict):
+    ignore_keys = [
+        "encoder.version",
+        "decoder.version",
+        "model.encoder.version",
+        "model.decoder.version",
+        "_float_tensor",
+        "decoder.output_projection.weight",
+    ]
+    for k in ignore_keys:
+        state_dict.pop(k, None)
+
+
+def make_linear_from_emb(emb):
+    vocab_size, emb_size = emb.weight.shape
+    lin_layer = nn.Linear(vocab_size, emb_size, bias=False)
+    lin_layer.weight.data = emb.weight.data
+    return lin_layer
+
+
+def convert_fairseq_mbart_checkpoint_from_disk(
+    checkpoint_path, hf_config_path="facebook/mbart-large-en-ro", finetuned=False, mbart_50=False
+):
     state_dict = torch.load(checkpoint_path, map_location="cpu")["model"]
     remove_ignore_keys_(state_dict)
     vocab_size = state_dict["encoder.embed_tokens.weight"].shape[0]
+
     mbart_config = MBartConfig.from_pretrained(hf_config_path, vocab_size=vocab_size)
+    if mbart_50 and finetuned:
+        mbart_config.activation_function = "relu"
+
     state_dict["shared.weight"] = state_dict["decoder.embed_tokens.weight"]
-    model = BartForConditionalGeneration(mbart_config)
+    model = MBartForConditionalGeneration(mbart_config)
     model.model.load_state_dict(state_dict)
+
+    if finetuned:
+        model.lm_head = make_linear_from_emb(model.model.shared)
+
     return model
 
 
@@ -42,8 +72,12 @@ if __name__ == "__main__":
         "--hf_config",
         default="facebook/mbart-large-cc25",
         type=str,
-        help="Which huggingface architecture to use: bart-large-xsum",
+        help="Which huggingface architecture to use: mbart-large",
     )
+    parser.add_argument("--mbart_50", action="store_true", help="whether the model is mMART-50 checkpoint")
+    parser.add_argument("--finetuned", action="store_true", help="whether the model is a fine-tuned checkpoint")
     args = parser.parse_args()
-    model = convert_fairseq_mbart_checkpoint_from_disk(args.fairseq_path, hf_config_path=args.hf_config)
+    model = convert_fairseq_mbart_checkpoint_from_disk(
+        args.fairseq_path, hf_config_path=args.hf_config, finetuned=args.finetuned, mbart_50=args.mbart_50
+    )
     model.save_pretrained(args.pytorch_dump_folder_path)

src/transformers/models/mbart/tokenization_mbart50.py

+# coding=utf-8
+# Copyright 2021 The Facebook AI Research Team 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.
+
+import os
+from contextlib import contextmanager
+from shutil import copyfile
+from typing import Dict, List, Optional, Tuple
+
+import sentencepiece as spm
+
+from ...tokenization_utils import AddedToken, BatchEncoding, PreTrainedTokenizer
+from ...utils import logging
+
+
+logger = logging.get_logger(__name__)
+
+SPIECE_UNDERLINE = "▁"
+
+VOCAB_FILES_NAMES = {"vocab_file": "sentencepiece.bpe.model"}
+
+_all_mbart50_models = ["facebook/mbart-large-50-one-to-many-mmt"]
+SPM_URL = "https://huggingface.co/facebook/mbart-large-50-one-to-many-mmt/resolve/main/sentencepiece.bpe.model"
+
+# fmt: off
+FAIRSEQ_LANGUAGE_CODES = ["ar_AR", "cs_CZ", "de_DE", "en_XX", "es_XX", "et_EE", "fi_FI", "fr_XX", "gu_IN", "hi_IN", "it_IT", "ja_XX", "kk_KZ", "ko_KR", "lt_LT", "lv_LV", "my_MM", "ne_NP", "nl_XX", "ro_RO", "ru_RU", "si_LK", "tr_TR", "vi_VN", "zh_CN", "af_ZA", "az_AZ", "bn_IN", "fa_IR", "he_IL", "hr_HR", "id_ID", "ka_GE", "km_KH", "mk_MK", "ml_IN", "mn_MN", "mr_IN", "pl_PL", "ps_AF", "pt_XX", "sv_SE", "sw_KE", "ta_IN", "te_IN", "th_TH", "tl_XX", "uk_UA", "ur_PK", "xh_ZA", "gl_ES", "sl_SI"]
+# fmt: on
+
+
+class MBart50Tokenizer(PreTrainedTokenizer):
+    """
+    Construct a MBart50 tokenizer. Based on `SentencePiece <https://github.com/google/sentencepiece>`__.
+
+    This tokenizer inherits from :class:`~transformers.PreTrainedTokenizer` which contains most of the main methods.
+    Users should refer to this superclass for more information regarding those methods.
+
+    Args:
+        vocab_file (:obj:`str`):
+            Path to the vocabulary file.
+        src_lang (:obj:`str`, `optional`):
+            A string representing the source language.
+        tgt_lang (:obj:`str`, `optional`):
+            A string representing the target language.
+        eos_token (:obj:`str`, `optional`, defaults to :obj:`"</s>"`):
+            The end of sequence token.
+        sep_token (:obj:`str`, `optional`, defaults to :obj:`"</s>"`):
+            The separator token, which is used when building a sequence from multiple sequences, e.g. two sequences for
+            sequence classification or for a text and a question for question answering. It is also used as the last
+            token of a sequence built with special tokens.
+        cls_token (:obj:`str`, `optional`, defaults to :obj:`"<s>"`):
+            The classifier token which is used when doing sequence classification (classification of the whole sequence
+            instead of per-token classification). It is the first token of the sequence when built with special tokens.
+        unk_token (:obj:`str`, `optional`, defaults to :obj:`"<unk>"`):
+            The unknown token. A token that is not in the vocabulary cannot be converted to an ID and is set to be this
+            token instead.
+        pad_token (:obj:`str`, `optional`, defaults to :obj:`"<pad>"`):
+            The token used for padding, for example when batching sequences of different lengths.
+        mask_token (:obj:`str`, `optional`, defaults to :obj:`"<mask>"`):
+            The token used for masking values. This is the token used when training this model with masked language
+            modeling. This is the token which the model will try to predict.
+
+    Examples::
+
+        >>> from transformers import MBart50Tokenizer
+        >>> tokenizer = MBart50Tokenizer.from_pretrained("facebook/mbart-large-50", src_lang="en_XX", tgt_lang="ro_RO")
+        >>> src_text = " UN Chief Says There Is No Military Solution in Syria"
+        >>> tgt_text =  "Şeful ONU declară că nu există o soluţie militară în Siria"
+        >>> model_inputs = tokenizer(src_text, return_tensors="pt")
+        >>> with tokenizer.as_target_tokenizer():
+        ...    labels = tokenizer(tgt_text, return_tensors="pt").input_ids
+        >>> # model(**model_inputs, labels=labels) should work
+    """
+
+    vocab_files_names = VOCAB_FILES_NAMES
+    max_model_input_sizes = {m: 1024 for m in _all_mbart50_models}
+    pretrained_vocab_files_map = {"vocab_file": {m: SPM_URL for m in _all_mbart50_models}}
+    model_input_names = ["input_ids", "attention_mask"]
+
+    prefix_tokens: List[int] = []
+    suffix_tokens: List[int] = []
+
+    def __init__(
+        self,
+        vocab_file,
+        src_lang=None,
+        tgt_lang=None,
+        eos_token="</s>",
+        sep_token="</s>",
+        cls_token="<s>",
+        unk_token="<unk>",
+        pad_token="<pad>",
+        mask_token="<mask>",
+        **kwargs
+    ):
+        # Mask token behave like a normal word, i.e. include the space before it
+        mask_token = AddedToken(mask_token, lstrip=True, rstrip=False) if isinstance(mask_token, str) else mask_token
+
+        super().__init__(
+            src_lang=src_lang,
+            tgt_lang=tgt_lang,
+            eos_token=eos_token,
+            unk_token=unk_token,
+            sep_token=sep_token,
+            cls_token=cls_token,
+            pad_token=pad_token,
+            mask_token=mask_token,
+            **kwargs,
+        )
+
+        self.sp_model = spm.SentencePieceProcessor()
+        self.sp_model.Load(str(vocab_file))
+        self.vocab_file = vocab_file
+
+        # Original fairseq vocab and spm vocab must be "aligned":
+        # Vocab    |    0    |    1    |   2    |    3    |  4  |  5  |  6  |   7   |   8   |  9
+        # -------- | ------- | ------- | ------ | ------- | --- | --- | --- | ----- | ----- | ----
+        # fairseq  | '<s>'   | '<pad>' | '</s>' | '<unk>' | ',' | '.' | '▁' | 's'   | '▁de' | '-'
+        # spm      | '<unk>' | '<s>'   | '</s>' | ','     | '.' | '▁' | 's' | '▁de' | '-'   | '▁a'
+
+        # Mimic fairseq token-to-id alignment for the first 4 token
+        self.fairseq_tokens_to_ids = {"<s>": 0, "<pad>": 1, "</s>": 2, "<unk>": 3}
+
+        # The first "real" token "," has position 4 in the original fairseq vocab and position 3 in the spm vocab
+        self.fairseq_offset = 1
+
+        self.sp_model_size = len(self.sp_model)
+        self.lang_code_to_id = {
+            code: self.sp_model_size + i + self.fairseq_offset for i, code in enumerate(FAIRSEQ_LANGUAGE_CODES)
+        }
+        self.id_to_lang_code = {v: k for k, v in self.lang_code_to_id.items()}
+        self.fairseq_tokens_to_ids["<mask>"] = len(self.sp_model) + len(self.lang_code_to_id) + self.fairseq_offset
+
+        self.fairseq_tokens_to_ids.update(self.lang_code_to_id)
+        self.fairseq_ids_to_tokens = {v: k for k, v in self.fairseq_tokens_to_ids.items()}
+        self._additional_special_tokens = list(self.lang_code_to_id.keys())
+
+        self._src_lang = src_lang if src_lang is not None else "en_XX"
+        self.cur_lang_code_id = self.lang_code_to_id[self._src_lang]
+        self.tgt_lang = tgt_lang
+        self.set_src_lang_special_tokens(self._src_lang)
+
+    @property
+    def vocab_size(self) -> int:
+        return len(self.sp_model) + len(self.lang_code_to_id) + self.fairseq_offset + 1  # Plus 1 for the mask token
+
+    @property
+    def src_lang(self) -> str:
+        return self._src_lang
+
+    @src_lang.setter
+    def src_lang(self, new_src_lang: str) -> None:
+        self._src_lang = new_src_lang
+        self.set_src_lang_special_tokens(self._src_lang)
+
+    def __getstate__(self) -> Dict:
+        state = self.__dict__.copy()
+        state["sp_model"] = None
+        return state
+
+    def __setstate__(self, d: Dict) -> None:
+        self.__dict__ = d
+        self.sp_model = spm.SentencePieceProcessor()
+        self.sp_model.Load(self.vocab_file)
+
+    def get_vocab(self) -> Dict:
+        vocab = {self.convert_ids_to_tokens(i): i for i in range(self.vocab_size)}
+        vocab.update(self.added_tokens_encoder)
+        return vocab
+
+    def _tokenize(self, text: str) -> List[str]:
+        return self.sp_model.EncodeAsPieces(text)
+
+    def _convert_token_to_id(self, token: str) -> int:
+        """ Converts a token (str) in an id using the vocab. """
+        if token in self.fairseq_tokens_to_ids:
+            return self.fairseq_tokens_to_ids[token]
+        spm_id = self.sp_model.PieceToId(token)
+
+        # Need to return unknown token if the SP model returned 0
+        return spm_id + self.fairseq_offset if spm_id else self.unk_token_id
+
+    def _convert_id_to_token(self, index: int) -> str:
+        """Converts an index (integer) in a token (str) using the vocab."""
+        if index in self.fairseq_ids_to_tokens:
+            return self.fairseq_ids_to_tokens[index]
+        return self.sp_model.IdToPiece(index - self.fairseq_offset)
+
+    def convert_tokens_to_string(self, tokens: List[str]) -> str:
+        """Converts a sequence of tokens (strings for sub-words) in a single string."""
+        out_string = "".join(tokens).replace(SPIECE_UNDERLINE, " ").strip()
+        return out_string
+
+    def save_vocabulary(self, save_directory: str, filename_prefix: Optional[str] = None) -> Tuple[str]:
+        if not os.path.isdir(save_directory):
+            logger.error("Vocabulary path ({}) should be a directory".format(save_directory))
+            return
+        out_vocab_file = os.path.join(
+            save_directory, (filename_prefix + "-" if filename_prefix else "") + VOCAB_FILES_NAMES["vocab_file"]
+        )
+
+        if os.path.abspath(self.vocab_file) != os.path.abspath(out_vocab_file):
+            copyfile(self.vocab_file, out_vocab_file)
+
+        return (out_vocab_file,)
+
+    def get_special_tokens_mask(
+        self, token_ids_0: List[int], token_ids_1: Optional[List[int]] = None, already_has_special_tokens: bool = False
+    ) -> List[int]:
+        """
+        Retrieve sequence ids from a token list that has no special tokens added. This method is called when adding
+        special tokens using the tokenizer ``prepare_for_model`` method.
+
+        Args:
+            token_ids_0 (:obj:`List[int]`):
+                List of IDs.
+            token_ids_1 (:obj:`List[int]`, `optional`):
+                Optional second list of IDs for sequence pairs.
+            already_has_special_tokens (:obj:`bool`, `optional`, defaults to :obj:`False`):
+                Whether or not the token list is already formatted with special tokens for the model.
+
+        Returns:
+            :obj:`List[int]`: A list of integers in the range [0, 1]: 1 for a special token, 0 for a sequence token.
+        """
+
+        if already_has_special_tokens:
+            if token_ids_1 is not None:
+                raise ValueError(
+                    "You should not supply a second sequence if the provided sequence of "
+                    "ids is already formatted with special tokens for the model."
+                )
+            return list(map(lambda x: 1 if x in [self.sep_token_id, self.cls_token_id] else 0, token_ids_0))
+        prefix_ones = [1] * len(self.prefix_tokens)
+        suffix_ones = [1] * len(self.suffix_tokens)
+        if token_ids_1 is None:
+            return prefix_ones + ([0] * len(token_ids_0)) + suffix_ones
+        return prefix_ones + ([0] * len(token_ids_0)) + ([0] * len(token_ids_1)) + suffix_ones
+
+    def build_inputs_with_special_tokens(
+        self, token_ids_0: List[int], token_ids_1: Optional[List[int]] = None
+    ) -> List[int]:
+        """
+        Build model inputs from a sequence or a pair of sequence for sequence classification tasks by concatenating and
+        adding special tokens. An MBART-50 sequence has the following format, where ``X`` represents the sequence:
+
+        - ``input_ids`` (for encoder) ``[src_lang_code] X [eos]``
+        - ``labels``: (for decoder) ``[tgt_lang_code] X [eos]``
+
+        BOS is never used. Pairs of sequences are not the expected use case, but they will be handled without a
+        separator.
+
+        Args:
+            token_ids_0 (:obj:`List[int]`):
+                List of IDs to which the special tokens will be added.
+            token_ids_1 (:obj:`List[int]`, `optional`):
+                Optional second list of IDs for sequence pairs.
+
+        Returns:
+            :obj:`List[int]`: List of `input IDs <../glossary.html#input-ids>`__ with the appropriate special tokens.
+        """
+        if token_ids_1 is None:
+            return self.prefix_tokens + token_ids_0 + self.suffix_tokens
+        # We don't expect to process pairs, but leave the pair logic for API consistency
+        return self.prefix_tokens + token_ids_0 + token_ids_1 + self.suffix_tokens
+
+    def prepare_seq2seq_batch(
+        self,
+        src_texts: List[str],
+        src_lang: str = "en_XX",
+        tgt_texts: Optional[List[str]] = None,
+        tgt_lang: str = "ro_RO",
+        **kwargs,
+    ) -> BatchEncoding:
+        self.src_lang = src_lang
+        self.tgt_lang = tgt_lang
+        return super().prepare_seq2seq_batch(src_texts, tgt_texts, **kwargs)
+
+    @contextmanager
+    def as_target_tokenizer(self):
+        """
+        Temporarily sets the tokenizer for encoding the targets. Useful for tokenizer associated to
+        sequence-to-sequence models that need a slightly different processing for the labels.
+        """
+        self.set_tgt_lang_special_tokens(self.tgt_lang)
+        yield
+        self.set_src_lang_special_tokens(self.src_lang)
+
+    def set_src_lang_special_tokens(self, src_lang: str) -> None:
+        """Reset the special tokens to the source lang setting. prefix=[src_lang_code] and suffix=[eos]."""
+        self.cur_lang_code_id = self.lang_code_to_id[src_lang]
+        self.prefix_tokens = [self.cur_lang_code_id]
+        self.suffix_tokens = [self.eos_token_id]
+
+    def set_tgt_lang_special_tokens(self, tgt_lang: str) -> None:
+        """Reset the special tokens to the target language setting. prefix=[tgt_lang_code] and suffix=[eos]."""
+        self.cur_lang_code_id = self.lang_code_to_id[tgt_lang]
+        self.prefix_tokens = [self.cur_lang_code_id]
+        self.suffix_tokens = [self.eos_token_id]

src/transformers/models/mbart/tokenization_mbart50_fast.py

+# coding=utf-8
+# Copyright 2021 The Facebook AI Research Team 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.
+
+import os
+from contextlib import contextmanager
+from shutil import copyfile
+from typing import List, Optional, Tuple
+
+from tokenizers import processors
+
+from ...file_utils import is_sentencepiece_available
+from ...tokenization_utils import AddedToken, BatchEncoding
+from ...tokenization_utils_fast import PreTrainedTokenizerFast
+from ...utils import logging
+
+
+if is_sentencepiece_available():
+    from .tokenization_mbart50 import MBart50Tokenizer
+else:
+    MBart50Tokenizer = None
+
+
+logger = logging.get_logger(__name__)
+
+VOCAB_FILES_NAMES = {"vocab_file": "sentencepiece.bpe.model", "tokenizer_file": "tokenizer.json"}
+
+_all_mbart50_models = ["facebook/mbart-large-50-one-to-many-mmt"]
+SPM_URL = "https://huggingface.co/facebook/mbart-large-50-one-to-many-mmt/resolve/main/sentencepiece.bpe.model"
+tokenizer_URL = "https://huggingface.co/facebook/mbart-large-50-one-to-many-mmt/resolve/main/tokenizer.json"
+
+# fmt: off
+FAIRSEQ_LANGUAGE_CODES = ["ar_AR", "cs_CZ", "de_DE", "en_XX", "es_XX", "et_EE", "fi_FI", "fr_XX", "gu_IN", "hi_IN", "it_IT", "ja_XX", "kk_KZ", "ko_KR", "lt_LT", "lv_LV", "my_MM", "ne_NP", "nl_XX", "ro_RO", "ru_RU", "si_LK", "tr_TR", "vi_VN", "zh_CN", "af_ZA", "az_AZ", "bn_IN", "fa_IR", "he_IL", "hr_HR", "id_ID", "ka_GE", "km_KH", "mk_MK", "ml_IN", "mn_MN", "mr_IN", "pl_PL", "ps_AF", "pt_XX", "sv_SE", "sw_KE", "ta_IN", "te_IN", "th_TH", "tl_XX", "uk_UA", "ur_PK", "xh_ZA", "gl_ES", "sl_SI"]
+# fmt: on
+
+
+class MBart50TokenizerFast(PreTrainedTokenizerFast):
+    """
+    Construct a "fast" MBART tokenizer for mBART-50 (backed by HuggingFace's `tokenizers` library). Based on `BPE
+    <https://huggingface.co/docs/tokenizers/python/latest/components.html?highlight=BPE#models>`__.
+
+    This tokenizer inherits from :class:`~transformers.PreTrainedTokenizerFast` which contains most of the main
+    methods. Users should refer to this superclass for more information regarding those methods.
+
+    Args:
+        vocab_file (:obj:`str`):
+            Path to the vocabulary file.
+        src_lang (:obj:`str`, `optional`):
+            A string representing the source language.
+        tgt_lang (:obj:`str`, `optional`):
+            A string representing the target language.
+        eos_token (:obj:`str`, `optional`, defaults to :obj:`"</s>"`):
+            The end of sequence token.
+        sep_token (:obj:`str`, `optional`, defaults to :obj:`"</s>"`):
+            The separator token, which is used when building a sequence from multiple sequences, e.g. two sequences for
+            sequence classification or for a text and a question for question answering. It is also used as the last
+            token of a sequence built with special tokens.
+        cls_token (:obj:`str`, `optional`, defaults to :obj:`"<s>"`):
+            The classifier token which is used when doing sequence classification (classification of the whole sequence
+            instead of per-token classification). It is the first token of the sequence when built with special tokens.
+        unk_token (:obj:`str`, `optional`, defaults to :obj:`"<unk>"`):
+            The unknown token. A token that is not in the vocabulary cannot be converted to an ID and is set to be this
+            token instead.
+        pad_token (:obj:`str`, `optional`, defaults to :obj:`"<pad>"`):
+            The token used for padding, for example when batching sequences of different lengths.
+        mask_token (:obj:`str`, `optional`, defaults to :obj:`"<mask>"`):
+            The token used for masking values. This is the token used when training this model with masked language
+            modeling. This is the token which the model will try to predict.
+
+    Examples::
+
+        >>> from transformers import MBart50TokenizerFast
+        >>> tokenizer = MBart50TokenizerFast.from_pretrained("facebook/mbart-large-50", src_lang="en_XX", tgt_lang="ro_RO")
+        >>> src_text = " UN Chief Says There Is No Military Solution in Syria"
+        >>> tgt_text =  "Şeful ONU declară că nu există o soluţie militară în Siria"
+        >>> model_inputs = tokenizer(src_text, return_tensors="pt")
+        >>> with tokenizer.as_target_tokenizer():
+        ...    labels = tokenizer(tgt_text, return_tensors="pt").input_ids
+        >>> # model(**model_inputs, labels=labels) should work
+    """
+
+    vocab_files_names = VOCAB_FILES_NAMES
+    max_model_input_sizes = {m: 1024 for m in _all_mbart50_models}
+    pretrained_vocab_files_map = {"vocab_file": {m: SPM_URL for m in _all_mbart50_models}}
+    model_input_names = ["input_ids", "attention_mask"]
+    slow_tokenizer_class = MBart50Tokenizer
+
+    prefix_tokens: List[int] = []
+    suffix_tokens: List[int] = []
+
+    def __init__(
+        self,
+        vocab_file,
+        src_lang=None,
+        tgt_lang=None,
+        tokenizer_file=None,
+        eos_token="</s>",
+        sep_token="</s>",
+        cls_token="<s>",
+        unk_token="<unk>",
+        pad_token="<pad>",
+        mask_token="<mask>",
+        **kwargs
+    ):
+        # Mask token behave like a normal word, i.e. include the space before it
+        mask_token = AddedToken(mask_token, lstrip=True, rstrip=False) if isinstance(mask_token, str) else mask_token
+
+        super().__init__(
+            vocab_file,
+            src_lang=src_lang,
+            tgt_lang=tgt_lang,
+            tokenizer_file=tokenizer_file,
+            eos_token=eos_token,
+            sep_token=sep_token,
+            cls_token=cls_token,
+            unk_token=unk_token,
+            pad_token=pad_token,
+            mask_token=mask_token,
+            **kwargs,
+        )
+
+        self.vocab_file = vocab_file
+
+        self.add_special_tokens({"additional_special_tokens": FAIRSEQ_LANGUAGE_CODES})
+        self.lang_code_to_id = {
+            lang_code: self.convert_tokens_to_ids(lang_code) for lang_code in FAIRSEQ_LANGUAGE_CODES
+        }
+
+        self._src_lang = src_lang if src_lang is not None else "en_XX"
+        self.tgt_lang = tgt_lang
+        self.cur_lang_code_id = self.lang_code_to_id[self._src_lang]
+        self.set_src_lang_special_tokens(self._src_lang)
+
+    @property
+    def src_lang(self) -> str:
+        return self._src_lang
+
+    @src_lang.setter
+    def src_lang(self, new_src_lang: str) -> None:
+        self._src_lang = new_src_lang
+        self.set_src_lang_special_tokens(self._src_lang)
+
+    def get_special_tokens_mask(
+        self, token_ids_0: List[int], token_ids_1: Optional[List[int]] = None, already_has_special_tokens: bool = False
+    ) -> List[int]:
+        """
+        Retrieves sequence ids from a token list that has no special tokens added. This method is called when adding
+        special tokens using the tokenizer ``prepare_for_model`` method.
+
+        Args:
+            token_ids_0 (:obj:`List[int]`):
+                List of ids.
+            token_ids_1 (:obj:`List[int]`, `optional`):
+                Optional second list of IDs for sequence pairs.
+            already_has_special_tokens (:obj:`bool`, `optional`, defaults to :obj:`False`):
+                Whether or not the token list is already formatted with special tokens for the model.
+
+        Returns:
+            :obj:`List[int]`: A list of integers in the range [0, 1]: 1 for a special token, 0 for a sequence token.
+        """
+
+        if already_has_special_tokens:
+            if token_ids_1 is not None:
+                raise ValueError(
+                    "You should not supply a second sequence if the provided sequence of "
+                    "ids is already formatted with special tokens for the model."
+                )
+            return list(map(lambda x: 1 if x in [self.sep_token_id, self.cls_token_id] else 0, token_ids_0))
+        prefix_ones = [1] * len(self.prefix_tokens)
+        suffix_ones = [1] * len(self.suffix_tokens)
+        if token_ids_1 is None:
+            return prefix_ones + ([0] * len(token_ids_0)) + suffix_ones
+        return prefix_ones + ([0] * len(token_ids_0)) + ([0] * len(token_ids_1)) + suffix_ones
+
+    def build_inputs_with_special_tokens(
+        self, token_ids_0: List[int], token_ids_1: Optional[List[int]] = None
+    ) -> List[int]:
+        """
+        Build model inputs from a sequence or a pair of sequence for sequence classification tasks by concatenating and
+        adding special tokens. The special tokens depend on calling set_lang.
+
+        An MBART-50 sequence has the following format, where ``X`` represents the sequence:
+
+        - ``input_ids`` (for encoder) ``[src_lang_code] X [eos]``
+        - ``labels``: (for decoder) ``[tgt_lang_code] X [eos]``
+
+        BOS is never used. Pairs of sequences are not the expected use case, but they will be handled without a
+        separator.
+
+        Args:
+            token_ids_0 (:obj:`List[int]`):
+                List of IDs to which the special tokens will be added.
+            token_ids_1 (:obj:`List[int]`, `optional`):
+                Optional second list of IDs for sequence pairs.
+
+        Returns:
+            :obj:`List[int]`: list of `input IDs <../glossary.html#input-ids>`__ with the appropriate special tokens.
+        """
+        if token_ids_1 is None:
+            return self.prefix_tokens + token_ids_0 + self.suffix_tokens
+        # We don't expect to process pairs, but leave the pair logic for API consistency
+        return self.prefix_tokens + token_ids_0 + token_ids_1 + self.suffix_tokens
+
+    def prepare_seq2seq_batch(
+        self,
+        src_texts: List[str],
+        src_lang: str = "en_XX",
+        tgt_texts: Optional[List[str]] = None,
+        tgt_lang: str = "ro_RO",
+        **kwargs,
+    ) -> BatchEncoding:
+        self.src_lang = src_lang
+        self.tgt_lang = tgt_lang
+        return super().prepare_seq2seq_batch(src_texts, tgt_texts, **kwargs)
+
+    @contextmanager
+    def as_target_tokenizer(self):
+        """
+        Temporarily sets the tokenizer for encoding the targets. Useful for tokenizer associated to
+        sequence-to-sequence models that need a slightly different processing for the labels.
+        """
+        self.set_tgt_lang_special_tokens(self.tgt_lang)
+        yield
+        self.set_src_lang_special_tokens(self.src_lang)
+
+    def set_src_lang_special_tokens(self, src_lang: str) -> None:
+        """Reset the special tokens to the source lang setting. prefix=[src_lang_code] and suffix=[eos]."""
+        self.cur_lang_code_id = self.convert_tokens_to_ids(src_lang)
+        self.prefix_tokens = [self.cur_lang_code_id]
+        self.suffix_tokens = [self.eos_token_id]
+
+        prefix_tokens_str = self.convert_ids_to_tokens(self.prefix_tokens)
+        suffix_tokens_str = self.convert_ids_to_tokens(self.suffix_tokens)
+
+        self._tokenizer.post_processor = processors.TemplateProcessing(
+            single=prefix_tokens_str + ["$A"] + suffix_tokens_str,
+            pair=prefix_tokens_str + ["$A", "$B"] + suffix_tokens_str,
+            special_tokens=list(zip(prefix_tokens_str + suffix_tokens_str, self.prefix_tokens + self.suffix_tokens)),
+        )
+
+    def set_tgt_lang_special_tokens(self, tgt_lang: str) -> None:
+        """Reset the special tokens to the target language setting. prefix=[src_lang_code] and suffix=[eos]."""
+        self.cur_lang_code_id = self.convert_tokens_to_ids(tgt_lang)
+        self.prefix_tokens = [self.cur_lang_code_id]
+        self.suffix_tokens = [self.eos_token_id]
+
+        prefix_tokens_str = self.convert_ids_to_tokens(self.prefix_tokens)
+        suffix_tokens_str = self.convert_ids_to_tokens(self.suffix_tokens)
+
+        self._tokenizer.post_processor = processors.TemplateProcessing(
+            single=prefix_tokens_str + ["$A"] + suffix_tokens_str,
+            pair=prefix_tokens_str + ["$A", "$B"] + suffix_tokens_str,
+            special_tokens=list(zip(prefix_tokens_str + suffix_tokens_str, self.prefix_tokens + self.suffix_tokens)),
+        )
+
+    def save_vocabulary(self, save_directory: str, filename_prefix: Optional[str] = None) -> Tuple[str]:
+        if not os.path.isdir(save_directory):
+            logger.error("Vocabulary path ({}) should be a directory".format(save_directory))
+            return
+        out_vocab_file = os.path.join(
+            save_directory, (filename_prefix + "-" if filename_prefix else "") + VOCAB_FILES_NAMES["vocab_file"]
+        )
+
+        if os.path.abspath(self.vocab_file) != os.path.abspath(out_vocab_file):
+            copyfile(self.vocab_file, out_vocab_file)
+
+        return (out_vocab_file,)

src/transformers/utils/dummy_sentencepiece_objects.py

@@ -47,6 +47,15 @@ class MarianTokenizer:
         requires_sentencepiece(self)
 
 
+class MBart50Tokenizer:
+    def __init__(self, *args, **kwargs):
+        requires_sentencepiece(self)
+
+    @classmethod
+    def from_pretrained(self, *args, **kwargs):
+        requires_sentencepiece(self)
+
+
 class MBartTokenizer:
     def __init__(self, *args, **kwargs):
         requires_sentencepiece(self)

src/transformers/utils/dummy_tokenizers_objects.py

@@ -164,6 +164,15 @@ class LxmertTokenizerFast:
         requires_tokenizers(self)
 
 
+class MBart50TokenizerFast:
+    def __init__(self, *args, **kwargs):
+        requires_tokenizers(self)
+
+    @classmethod
+    def from_pretrained(self, *args, **kwargs):
+        requires_tokenizers(self)
+
+
 class MBartTokenizerFast:
     def __init__(self, *args, **kwargs):
         requires_tokenizers(self)

tests/test_tokenization_mbart50.py

+# Copyright 2021 The HuggingFace Team. All rights reserved.
+#
+# 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.
+
+import os
+import tempfile
+import unittest
+
+from transformers import SPIECE_UNDERLINE, BatchEncoding, MBart50Tokenizer, MBart50TokenizerFast, is_torch_available
+from transformers.file_utils import is_sentencepiece_available
+from transformers.testing_utils import require_sentencepiece, require_tokenizers, require_torch
+
+from .test_tokenization_common import TokenizerTesterMixin
+
+
+if is_sentencepiece_available():
+    SAMPLE_VOCAB = os.path.join(os.path.dirname(os.path.abspath(__file__)), "fixtures/test_sentencepiece.model")
+
+
+if is_torch_available():
+    from transformers.models.mbart.modeling_mbart import shift_tokens_right
+
+EN_CODE = 250004
+RO_CODE = 250020
+
+
+@require_sentencepiece
+@require_tokenizers
+class MBartTokenizationTest(TokenizerTesterMixin, unittest.TestCase):
+    tokenizer_class = MBart50Tokenizer
+    rust_tokenizer_class = MBart50TokenizerFast
+    test_rust_tokenizer = True
+
+    def setUp(self):
+        super().setUp()
+
+        # We have a SentencePiece fixture for testing
+        tokenizer = MBart50Tokenizer(SAMPLE_VOCAB, src_lang="en_XX", tgt_lang="ro_RO", keep_accents=True)
+        tokenizer.save_pretrained(self.tmpdirname)
+
+    def test_full_tokenizer(self):
+        tokenizer = MBart50Tokenizer(SAMPLE_VOCAB, src_lang="en_XX", tgt_lang="ro_RO", keep_accents=True)
+
+        tokens = tokenizer.tokenize("This is a test")
+        self.assertListEqual(tokens, ["▁This", "▁is", "▁a", "▁t", "est"])
+
+        self.assertListEqual(
+            tokenizer.convert_tokens_to_ids(tokens),
+            [value + tokenizer.fairseq_offset for value in [285, 46, 10, 170, 382]],
+        )
+
+        tokens = tokenizer.tokenize("I was born in 92000, and this is falsé.")
+        self.assertListEqual(
+            tokens,
+            # fmt: off
+            [SPIECE_UNDERLINE + "I", SPIECE_UNDERLINE + "was", SPIECE_UNDERLINE + "b", "or", "n", SPIECE_UNDERLINE + "in", SPIECE_UNDERLINE + "", "9", "2", "0", "0", "0", ",", SPIECE_UNDERLINE + "and", SPIECE_UNDERLINE + "this", SPIECE_UNDERLINE + "is", SPIECE_UNDERLINE + "f", "al", "s", "é", "."],
+            # fmt: on
+        )
+        ids = tokenizer.convert_tokens_to_ids(tokens)
+        self.assertListEqual(
+            ids,
+            [
+                value + tokenizer.fairseq_offset
+                for value in [8, 21, 84, 55, 24, 19, 7, 2, 602, 347, 347, 347, 3, 12, 66, 46, 72, 80, 6, 2, 4]
+            ],
+        )
+
+        back_tokens = tokenizer.convert_ids_to_tokens(ids)
+        self.assertListEqual(
+            back_tokens,
+            # fmt: off
+            [SPIECE_UNDERLINE + "I", SPIECE_UNDERLINE + "was", SPIECE_UNDERLINE + "b", "or", "n", SPIECE_UNDERLINE + "in", SPIECE_UNDERLINE + "", "<unk>", "2", "0", "0", "0", ",", SPIECE_UNDERLINE + "and", SPIECE_UNDERLINE + "this", SPIECE_UNDERLINE + "is", SPIECE_UNDERLINE + "f", "al", "s", "<unk>", "."],
+            # fmt: on
+        )
+
+
+@require_torch
+@require_sentencepiece
+@require_tokenizers
+class MBartOneToManyIntegrationTest(unittest.TestCase):
+    checkpoint_name = "facebook/mbart-large-50-one-to-many-mmt"
+    src_text = [
+        " UN Chief Says There Is No Military Solution in Syria",
+        """ Secretary-General Ban Ki-moon says his response to Russia's stepped up military support for Syria is that "there is no military solution" to the nearly five-year conflict and more weapons will only worsen the violence and misery for millions of people.""",
+    ]
+    tgt_text = [
+        "Şeful ONU declară că nu există o soluţie militară în Siria",
+        'Secretarul General Ban Ki-moon declară că răspunsul său la intensificarea sprijinului militar al Rusiei pentru Siria este că "nu există o soluţie militară" la conflictul de aproape cinci ani şi că noi arme nu vor face decât să înrăutăţească violenţele şi mizeria pentru milioane de oameni.',
+    ]
+    expected_src_tokens = [EN_CODE, 8274, 127873, 25916, 7, 8622, 2071, 438, 67485, 53, 187895, 23, 51712, 2]
+
+    @classmethod
+    def setUpClass(cls):
+        cls.tokenizer: MBart50Tokenizer = MBart50Tokenizer.from_pretrained(
+            cls.checkpoint_name, src_lang="en_XX", tgt_lang="ro_RO"
+        )
+        cls.pad_token_id = 1
+        return cls
+
+    def check_language_codes(self):
+        self.assertEqual(self.tokenizer.fairseq_tokens_to_ids["ar_AR"], 250001)
+        self.assertEqual(self.tokenizer.fairseq_tokens_to_ids["en_EN"], 250004)
+        self.assertEqual(self.tokenizer.fairseq_tokens_to_ids["ro_RO"], 250020)
+        self.assertEqual(self.tokenizer.fairseq_tokens_to_ids["mr_IN"], 250038)
+
+    def test_tokenizer_batch_encode_plus(self):
+        ids = self.tokenizer.batch_encode_plus(self.src_text).input_ids[0]
+        self.assertListEqual(self.expected_src_tokens, ids)
+
+    def test_tokenizer_decode_ignores_language_codes(self):
+        self.assertIn(RO_CODE, self.tokenizer.all_special_ids)
+        generated_ids = [RO_CODE, 884, 9019, 96, 9, 916, 86792, 36, 18743, 15596, 5, 2]
+        result = self.tokenizer.decode(generated_ids, skip_special_tokens=True)
+        expected_romanian = self.tokenizer.decode(generated_ids[1:], skip_special_tokens=True)
+        self.assertEqual(result, expected_romanian)
+        self.assertNotIn(self.tokenizer.eos_token, result)
+
+    def test_tokenizer_truncation(self):
+        src_text = ["this is gunna be a long sentence " * 20]
+        assert isinstance(src_text[0], str)
+        desired_max_length = 10
+        ids = self.tokenizer.prepare_seq2seq_batch(
+            src_text,
+            max_length=desired_max_length,
+        ).input_ids[0]
+        self.assertEqual(ids[0], EN_CODE)
+        self.assertEqual(ids[-1], 2)
+        self.assertEqual(len(ids), desired_max_length)
+
+    def test_mask_token(self):
+        self.assertListEqual(self.tokenizer.convert_tokens_to_ids(["<mask>", "ar_AR"]), [250053, 250001])
+
+    def test_special_tokens_unaffacted_by_save_load(self):
+        tmpdirname = tempfile.mkdtemp()
+        original_special_tokens = self.tokenizer.fairseq_tokens_to_ids
+        self.tokenizer.save_pretrained(tmpdirname)
+        new_tok = MBart50Tokenizer.from_pretrained(tmpdirname)
+        self.assertDictEqual(new_tok.fairseq_tokens_to_ids, original_special_tokens)
+
+    # prepare_seq2seq_batch tests below
+
+    @require_torch
+    def test_batch_fairseq_parity(self):
+        batch: BatchEncoding = self.tokenizer.prepare_seq2seq_batch(
+            self.src_text, tgt_texts=self.tgt_text, return_tensors="pt"
+        )
+        batch["decoder_input_ids"] = shift_tokens_right(batch.labels, self.tokenizer.pad_token_id)
+
+        for k in batch:
+            batch[k] = batch[k].tolist()
+        # batch = {k: v.tolist() for k,v in batch.items()}
+        # fairseq batch: https://gist.github.com/sshleifer/cba08bc2109361a74ac3760a7e30e4f4
+        # batch.decoder_inputs_ids[0][0] ==
+        assert batch.input_ids[1][0] == EN_CODE
+        assert batch.input_ids[1][-1] == 2
+        assert batch.labels[1][0] == RO_CODE
+        assert batch.labels[1][-1] == 2
+        assert batch.decoder_input_ids[1][:2] == [2, RO_CODE]
+
+    @require_torch
+    def test_tokenizer_prepare_seq2seq_batch(self):
+        batch = self.tokenizer.prepare_seq2seq_batch(
+            self.src_text, tgt_texts=self.tgt_text, max_length=len(self.expected_src_tokens), return_tensors="pt"
+        )
+        batch["decoder_input_ids"] = shift_tokens_right(batch.labels, self.tokenizer.pad_token_id)
+        self.assertIsInstance(batch, BatchEncoding)
+
+        self.assertEqual((2, 14), batch.input_ids.shape)
+        self.assertEqual((2, 14), batch.attention_mask.shape)
+        result = batch.input_ids.tolist()[0]
+        self.assertListEqual(self.expected_src_tokens, result)
+        self.assertEqual(2, batch.decoder_input_ids[0, 0])  # decoder_start_token_id
+        # Test that special tokens are reset
+        self.assertEqual(self.tokenizer.prefix_tokens, [EN_CODE])
+        self.assertEqual(self.tokenizer.suffix_tokens, [self.tokenizer.eos_token_id])
+
+    def test_seq2seq_max_target_length(self):
+        batch = self.tokenizer.prepare_seq2seq_batch(
+            self.src_text, tgt_texts=self.tgt_text, max_length=3, max_target_length=10, return_tensors="pt"
+        )
+        batch["decoder_input_ids"] = shift_tokens_right(batch.labels, self.tokenizer.pad_token_id)
+        self.assertEqual(batch.input_ids.shape[1], 3)
+        self.assertEqual(batch.decoder_input_ids.shape[1], 10)
+        # max_target_length will default to max_length if not specified
+        batch = self.tokenizer.prepare_seq2seq_batch(
+            self.src_text, tgt_texts=self.tgt_text, max_length=3, return_tensors="pt"
+        )
+        batch["decoder_input_ids"] = shift_tokens_right(batch.labels, self.tokenizer.pad_token_id)
+        self.assertEqual(batch.input_ids.shape[1], 3)
+        self.assertEqual(batch.decoder_input_ids.shape[1], 3)