AutoConfig.from_pretrained("model", return_unused_kwargs=True) returns "_from_auto": True field against specification

[GabrielKP]

System Info

- `transformers` version: 4.17.0
- Platform: Linux-5.13.0-40-generic-x86_64-with-glibc2.34
- Python version: 3.9.7
- PyTorch version (GPU?): 1.11.0+cu102 (False)
- Tensorflow version (GPU?): not installed (NA)
- Flax version (CPU?/GPU?/TPU?): not installed (NA)
- Jax version: not installed
- JaxLib version: not installed

Who can help?

@sgugger

Small bug in which for some cases {"_from_auto": True} is returned against specification.

Seems to originate here and/or here

Information

• The official example scripts
• My own modified scripts

Tasks

• An officially supported task in the examples folder (such as GLUE/SQuAD, ...)
• My own task or dataset (give details below)

Reproduction

Replicable with

>>> from transformers import AutoConfig
>>> config, kwargs = AutoConfig.from_pretrained("bert-base-uncased", return_unused_kwargs=True)
>>> kwargs
{'_from_auto': True}

Expected behavior

There should be no "_from_auto": True field in returned dict.

>>> from transformers import AutoConfig
>>> config, kwargs = AutoConfig.from_pretrained("bert-base-uncased", return_unused_kwargs=True)
>>> kwargs
{}

[sgugger]

I can reproduce, thanks for flagging and for taking the time to give us a clear example of code that fails!
I will try to dive into this and have a fix ready later today.