Shared vocabulary with EncoderDecoderModel
# 🚀 Feature request
Currently, two separate models are instantiated as encoder/decoder when using this model class. It would be useful in a lot of fine-tuning applications (i.e. summarization) to share the same embeddings between the encoder / decoder classes -- is this something that could be supported with the library?
I believe the `EncoderDecoderConfig` class has an argument `tie_encoder_decoder` which can be used to share weights between the encoder and decoder.

Is this what you're looking for?

@patrickvonplaten <|||||>Thanks @LysandreJik; it's close enough to what I'm looking for. Closing this issue.<|||||>Hey @bayanbatn, 

We are currently working on a function (see #8224)  that automatically ties encoder and decoder word embeddings only in an automatic fashion...for now what one can do is to simply set it yourself via

```python
model.decoder.word_embeddings = model.encoder.word_embeddings
```