Cannot use `torch.jit.trace` to trace `LightningModule` in Lightning v1.7

🐛 Bug

When I use torch.jit.trace to trace a LightningModule, I got RuntimeError: XXX(LightningModule class name) is not attached to a Trainer.

This because in lightning 1.7.0, property trainer will raise an RuntimeError if the module doesn’t attach a Trainer.

https://github.com/Lightning-AI/lightning/blob/12a061f2aaefaa9ed9ccf81ab6f378835b675a7e/src/pytorch_lightning/core/module.py#L179

but in torch.jit, it will justify each attr by hasattr,

https://github.com/pytorch/pytorch/blob/de0e03001d31523ef86c3d7852c87cdad6d96632/torch/_jit_internal.py#L749

and in hasattr docstring, Return whether the object has an attribute with the given name. This is done by calling getattr(obj, name) and catching AttributeError.

To Reproduce

Initialize any LightningModule under Lightning v1.7.0, and trace it by torch.jit.trace without attach trainer to the lightning module.

To Fix

Replace RuntimeError by AttributeError.

This fix is work for me, but I don’t know will this cause other problems.

Environment

• Lightning Component (e.g. Trainer, LightningModule, LightningApp, LightningWork, LightningFlow): LightningModule
• PyTorch Lightning Version (e.g., 1.5.0): 1.7.0
• PyTorch Version (e.g., 1.10): 1.10
• Python version (e.g., 3.9): 3.7.12

cc @carmocca @justusschock @awaelchli @borda @ananthsub @ninginthecloud @jjenniferdai @rohitgr7