Support QuestionAnswering Module for ModernBert based models.

[bakrianoo]

What does this PR do?

This PR introduces a new feature: ModernBertForQuestionAnswering, which extends the ModernBERT model to support Question-Answering tasks.

This addresses a gap in the current implementation of ModernBERT and enables its use for tasks requiring answer extraction from long texts.

Evaluating

I made an experiment to fine-tune a QnA ModernBert based model. I used this script to produce this model.

Dependencies

• No new dependencies were introduced.
• The model was tested using the existing Hugging Face transformers library. Please check a QnA fine-tuned model here rankyx/ModernBERT-QnA-base-squad

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you read the contributor guideline,
  Pull Request section?
• Was this discussed/approved via a Github issue or the forum? Please add a link
  to it if that's the case.
• Did you make sure to update the documentation with your changes? Here are the
  documentation guidelines, and
  here are tips on formatting docstrings.
• Did you write any new necessary tests?

Current Status

Although I was be able to finetune a QnA Modern Bert model, I am still having an issue to complete the PR.

1)

Applying make fixup produces this error

Traceback (most recent call last):
  File "/usr/local/lib/python3.10/dist-packages/jax/_src/xla_bridge.py", line 430, in discover_pjrt_plugins
    plugin_module.initialize()
  File "/usr/local/lib/python3.10/dist-packages/jax_plugins/xla_cuda12/__init__.py", line 85, in initialize
    options = xla_client.generate_pjrt_gpu_plugin_options()
AttributeError: module 'jaxlib.xla_client' has no attribute 'generate_pjrt_gpu_plugin_options'
Traceback (most recent call last):
  File "/content/transformers/utils/check_docstrings.py", line 1060, in <module>
    check_docstrings(overwrite=args.fix_and_overwrite, check_all=args.check_all)
  File "/content/transformers/utils/check_docstrings.py", line 978, in check_docstrings
    for modified_file_diff in repo.index.diff(repo.refs.main.commit):
  File "/usr/local/lib/python3.10/dist-packages/git/util.py", line 972, in __getattr__
    return list.__getattribute__(self, attr)
AttributeError: 'IterableList' object has no attribute 'main'

I tried to reinstall jaxlib==0.4.13 but it does not help.

I appreciate your help here.

[Rocketknight1]

Hi @bakrianoo, thanks for the PR!

1. I think the reason you can't load the model with AutoModelForQuestionAnswering is that you've added an extra line in the MODEL_FOR_TOKEN_CLASSIFICATION_MAPPING_NAMES? Can you make sure the model is only included in the question answering mapping? Once it's in there I believe it should be loadable with the autoclass.

2. The repo-consistency error is because the new class isn't added to docs/source/en/model_doc/modernbert.md. If you add an autodoc section there, the error should go away!

[bakrianoo]

Hi @Rocketknight1
Your advice solved my issues. Thank you.
I now have a new issue, can you check the updated PR description?

---

Applying make fixup produces this error

Traceback (most recent call last):
  File "/usr/local/lib/python3.10/dist-packages/jax/_src/xla_bridge.py", line 430, in discover_pjrt_plugins
    plugin_module.initialize()
  File "/usr/local/lib/python3.10/dist-packages/jax_plugins/xla_cuda12/__init__.py", line 85, in initialize
    options = xla_client.generate_pjrt_gpu_plugin_options()
AttributeError: module 'jaxlib.xla_client' has no attribute 'generate_pjrt_gpu_plugin_options'
Traceback (most recent call last):
  File "/content/transformers/utils/check_docstrings.py", line 1060, in <module>
    check_docstrings(overwrite=args.fix_and_overwrite, check_all=args.check_all)
  File "/content/transformers/utils/check_docstrings.py", line 978, in check_docstrings
    for modified_file_diff in repo.index.diff(repo.refs.main.commit):
  File "/usr/local/lib/python3.10/dist-packages/git/util.py", line 972, in __getattr__
    return list.__getattribute__(self, attr)
AttributeError: 'IterableList' object has no attribute 'main'

I tried to reinstall jaxlib==0.4.13 but it does not help.