Deprecation warning when using torch 1.8

[egpbos]

While trying to fix warnings, I stumbled upon a new warning that only comes up since pytorch 1.8: UserWarning: Using a non-full backward hook when the forward contains multiple autograd Nodes is deprecated and will be removed in future versions. This hook will be missing some grad_input. Please use register_full_backward_hook to get the documented behavior.

The warning is triggered in the basic and transformer tests:

platalea/basic.py:39: in cost
    speech_enc, image_enc = self.forward(item['audio'], item['audio_len'], item['image'])
platalea/basic.py:34: in forward
    speech_enc = self.SpeechEncoder(audio, audio_len)
../../../sw/miniconda3/envs/platalea/lib/python3.8/site-packages/torch/nn/modules/module.py:914: in _call_impl
    self._maybe_warn_non_full_backward_hook(input, result, grad_fn)

(Note: I added the forward function in SpeechImage as a test, this call to SpeechEncoder is the actual troublemaker, and it was in SpeechImage.cost() before.)

I frankly have no idea what a backward hook is, let alone a non-full one. Anyone have any clue?

My best guess is that it has something to do with the multiple inputs and multiple outputs and some kind of missing element regarding autograd somewhere. I tried to search the other models/experiments (asr, mtl) for hints in this direction, but couldn't really find anything.

[egpbos]

It seems that the warning is gone now. Testing on Torch 1.8.1 now, so the issue may have been with 1.8.0 specifically.