tokenization_marian.py: use current_spm for decoding (#10357)

* Fix Marian decoding

Tokenizer's decode and batch_decode now accepts a new argument (use_source_tokenizer) which indicates whether the source spm should be used to decode ids. This is useful for Marian models specificallly when decoding source input ids.

* Adapt docstrings

Co-authored-by: Sylvain Gugger <sylvain.gugger@gmail.com>

src/transformers/models/marian/tokenization_marian.py

@@ -159,7 +159,7 @@ class MarianTokenizer(PreTrainedTokenizer):
         return self.encoder.get(token, self.encoder[self.unk_token])
 
     def remove_language_code(self, text: str):
-        """Remove language codes like <<fr>> before sentencepiece"""
+        """Remove language codes like >>fr<< before sentencepiece"""
         match = self.language_code_re.match(text)
         code: list = [match.group(0)] if match else []
         return code, self.language_code_re.sub("", text)
@@ -170,12 +170,62 @@ class MarianTokenizer(PreTrainedTokenizer):
         return code + pieces
 
     def _convert_id_to_token(self, index: int) -> str:
-        """Converts an index (integer) in a token (str) using the encoder."""
+        """Converts an index (integer) in a token (str) using the decoder."""
         return self.decoder.get(index, self.unk_token)
 
+    def batch_decode(self, sequences, **kwargs):
+        """
+        Convert a list of lists of token ids into a list of strings by calling decode.
+
+        Args:
+            sequences (:obj:`Union[List[int], List[List[int]], np.ndarray, torch.Tensor, tf.Tensor]`):
+                List of tokenized input ids. Can be obtained using the ``__call__`` method.
+            skip_special_tokens (:obj:`bool`, `optional`, defaults to :obj:`False`):
+                Whether or not to remove special tokens in the decoding.
+            clean_up_tokenization_spaces (:obj:`bool`, `optional`, defaults to :obj:`True`):
+                Whether or not to clean up the tokenization spaces.
+            use_source_tokenizer (:obj:`bool`, `optional`, defaults to :obj:`False`):
+                Whether or not to use the source tokenizer to decode sequences (only applicable in sequence-to-sequence
+                problems).
+            kwargs (additional keyword arguments, `optional`):
+                Will be passed to the underlying model specific decode method.
+
+        Returns:
+            :obj:`List[str]`: The list of decoded sentences.
+        """
+        return super().batch_decode(sequences, **kwargs)
+
+    def decode(self, token_ids, **kwargs):
+        """
+        Converts a sequence of ids in a string, using the tokenizer and vocabulary with options to remove special
+        tokens and clean up tokenization spaces.
+
+        Similar to doing ``self.convert_tokens_to_string(self.convert_ids_to_tokens(token_ids))``.
+
+        Args:
+            token_ids (:obj:`Union[int, List[int], np.ndarray, torch.Tensor, tf.Tensor]`):
+                List of tokenized input ids. Can be obtained using the ``__call__`` method.
+            skip_special_tokens (:obj:`bool`, `optional`, defaults to :obj:`False`):
+                Whether or not to remove special tokens in the decoding.
+            clean_up_tokenization_spaces (:obj:`bool`, `optional`, defaults to :obj:`True`):
+                Whether or not to clean up the tokenization spaces.
+            use_source_tokenizer (:obj:`bool`, `optional`, defaults to :obj:`False`):
+                Whether or not to use the source tokenizer to decode sequences (only applicable in sequence-to-sequence
+                problems).
+            kwargs (additional keyword arguments, `optional`):
+                Will be passed to the underlying model specific decode method.
+
+        Returns:
+            :obj:`str`: The decoded sentence.
+        """
+        return super().decode(token_ids, **kwargs)
+
     def convert_tokens_to_string(self, tokens: List[str]) -> str:
-        """Uses target language sentencepiece model"""
-        return self.spm_target.DecodePieces(tokens)
+        """Uses source spm if _decode_use_source_tokenizer is True, and target spm otherwise """
+        if self._decode_use_source_tokenizer:
+            return self.spm_source.DecodePieces(tokens)
+        else:
+            return self.spm_target.DecodePieces(tokens)
 
     def build_inputs_with_special_tokens(self, token_ids_0, token_ids_1=None) -> List[int]:
         """Build model inputs from a sequence by appending eos_token_id."""

src/transformers/models/wav2vec2/tokenization_wav2vec2.py

@@ -486,6 +486,7 @@ class Wav2Vec2Tokenizer(PreTrainedTokenizer):
         token_ids: List[int],
         skip_special_tokens: bool = False,
         clean_up_tokenization_spaces: bool = True,
+        **kwargs
     ) -> str:
         """
         special _decode function is needed for Wav2Vec2Tokenizer because added tokens should be treated exactly the