Fix LightningCLI saving hyperparameters breaking change

[mauvilsa]

What does this PR do?

Changes the LightningCLI's load_from_checkpoint support such that the hparams are not saved with the class_path and init_args structure, since this constitutes a breaking change which we failed to notice in #18105.

Fixes #19977

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📚 Documentation preview 📚: https://pytorch-lightning--20068.org.readthedocs.build/en/20068/

[adamjstewart]

Thanks for the quick fix @mauvilsa. This seems very specific to init_args and ignores dict_kwargs. I also seem to be missing many class parameters with default values that are not listed in the YAML file, and/or optional values that default to None.

EDIT: It's possible no special handling is needed for dict_kwargs.

[adamjstewart]

Steps to reproduce are identical to #19977 (comment), but replace model.py with:

from lightning.pytorch import LightningModule


class Model(LightningModule):
    def __init__(self, learning_rate, step_size=None):
        super().__init__()
        self.save_hyperparameters()
        assert 'learning_rate' in self.hparams
        assert 'step_size' in self.hparams

    def training_step(*args):
        pass

    def configure_optimizers(*args):
        pass

The code will fail because step_size is not defined in self.hparams. Note that this code does not fail if the default value is 2 instead of None.

[mauvilsa]

I also seem to be missing many class parameters with default values that are not listed in the YAML file, and/or optional values that default to None.

Indeed, there was a bug.

It's possible no special handling is needed for dict_kwargs.

It is needed. It is now fixed and I added a new unit test based on your code snippet which includes dict_kwargs.

@adamjstewart please check again.

[adamjstewart]

Passes all TorchGeo tests now, thanks for the quick fix!

[awaelchli]

Thank you @mauvilsa, very appreciated!

[awaelchli]

Thanks @mauvilsa @adamjstewart for the help here 🚀

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82%. Comparing base (50af052) to head (6df8678).
Report is 63 commits behind head on master.

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HEAD has 380 uploads less than BASE

Flag	BASE (50af052)	HEAD (6df8678)
cpu	106	21
lightning_fabric	19	0
pytest	59	2
python3.11	41	3
lightning	74	16
python3.8	36	6
python3.10	29	12
gpu	5	2
pytorch2.1	35	13
pytest-full	52	21
pytorch2.2	8	4
pytorch2.3	9	4
pytorch_lightning	18	7

Additional details and impacted files

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  Files         266      263      -3     
  Lines       22942    22891     -51     
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- Hits        20722    18670   -2052     
- Misses       2220     4221   +2001