Automatic Optimization should be a property of the LightningModule, not the Trainer

[ananthsub]

🚀 Feature

https://pytorch-lightning.readthedocs.io/en/latest/optimizers.html#manual-optimization
To switch between manual and automatic optimization, we need to toggle this flag on the Trainer. However, all of the user code for optimization is inside the LightningModule. If we had this flag for automatic_optimization on the LightningModule instead, we'd keep all the user-facing optimization pieces in one place.

Pitch

Define a property method for automatic_optimization inside the LightningModule. this would be another model hook

By default:

@property
def automatic_optimization(self) -> bool:
    return True

Then we can set the corresponding properties on the trainer/training loop based on the LightningModule and deprecate the automatic_optimization flag on the Trainer

[williamFalcon]

this makes sense to me! good catch

[titamar]

Please also update the docs regarding this change at: https://pytorch-lightning.readthedocs.io/en/1.0.1/new-project.html