Fix modular model converter unable to generate Processor classes

[tonywu71]

What does this PR do?

Modular 🤗 transformers is awesome, but a typo in the code prevents the user to generate a processing_xxx.py file from modular_xxx.py. This PR solves this problem.

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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• Was this discussed/approved via a Github issue or the forum? Please add a link
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• Did you write any new necessary tests?

Note: I believe the last 3 checks don't apply to my PR. Feel free to correct me if I'm wrong!

Who can review?

• @ArthurZucker → follow-up of your previous PR Modular transformers: modularity and inheritance for new model additions #33248
• @yonigozlan → who's been helping me with the integration of ColPali in 🤗 transfomers (see Add ColPali to 🤗 transformers #33736)

E2E Test

Before:

❯ python utils/modular_model_converter.py --files_to_parse src/transformers/models/colpali/modular_colpali.py
Converting src/transformers/models/colpali/modular_colpali.py to a single model single file format
Traceback (most recent call last):
  File "/Users/tony/Documents/illuin-repositories/transformers/utils/modular_model_converter.py", line 781, in <module>
    converted_files = convert_modular_file(file_name, args.old_model_name, args.new_model_name)
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/tony/Documents/illuin-repositories/transformers/utils/modular_model_converter.py", line 726, in convert_modular_file
    wrapper.visit(cst_transformers)
  File "/Users/tony/Documents/illuin-repositories/transformers/.venv/lib/python3.11/site-packages/libcst/metadata/wrapper.py", line 204, in visit
    return self.module.visit(visitor)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/tony/Documents/illuin-repositories/transformers/.venv/lib/python3.11/site-packages/libcst/_nodes/module.py", line 89, in visit
    result = super(Module, self).visit(visitor)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/tony/Documents/illuin-repositories/transformers/.venv/lib/python3.11/site-packages/libcst/_nodes/base.py", line 227, in visit
    _CSTNodeSelfT, self._visit_and_replace_children(visitor)
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/tony/Documents/illuin-repositories/transformers/.venv/lib/python3.11/site-packages/libcst/_nodes/module.py", line 74, in _visit_and_replace_children
    body=visit_body_sequence(self, "body", self.body, visitor),
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/tony/Documents/illuin-repositories/transformers/.venv/lib/python3.11/site-packages/libcst/_nodes/internal.py", line 227, in visit_body_sequence
    return tuple(visit_body_iterable(parent, fieldname, children, visitor))
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/tony/Documents/illuin-repositories/transformers/.venv/lib/python3.11/site-packages/libcst/_nodes/internal.py", line 193, in visit_body_iterable
    new_child = child.visit(visitor)
                ^^^^^^^^^^^^^^^^^^^^
  File "/Users/tony/Documents/illuin-repositories/transformers/.venv/lib/python3.11/site-packages/libcst/_nodes/base.py", line 236, in visit
    leave_result = visitor.on_leave(self, with_updated_children)
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/tony/Documents/illuin-repositories/transformers/.venv/lib/python3.11/site-packages/libcst/_visitors.py", line 71, in on_leave
    updated_node = leave_func(original_node, updated_node)
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/tony/Documents/illuin-repositories/transformers/utils/modular_model_converter.py", line 681, in leave_ClassDef
    self.files[key][class_name] = {"insert_idx": self.global_scope_index, "node": updated_node}
    ~~~~~~~~~~^^^^^
KeyError: 'processor'

After, with the proposed fix:

❯ python utils/modular_model_converter.py --files_to_parse src/transformers/models/colpali/modular_colpali.py
Converting src/transformers/models/colpali/modular_colpali.py to a single model single file format

[ArthurZucker]

Good job! Indeed, would you like to ad an example in the examples? 🤗 seeing as a model will use it, let's go!

[tonywu71]

Good job! Indeed, would you like to ad an example in the examples? 🤗 seeing as a model will use it, let's go!

I think I'll finish my ColPali integration PR first, then open a new PR to showcase the modular transformers in the examples. Wdyt? 😉

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[ArthurZucker]

Sounds good!