[JIT] Provide more info when attribute fails to convert (#50870)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/50870
**Summary**
Module attributes whose types cannot be determined based on annotations
or inference based on their values at script time are added to the
concrete type of the corresponding module as "failed attributes". Any
attempt to access them in scripted code produces an error with a message
explaining that the attribute could not be contributed to a
corresponding attribute on the TorchScript module. However, this error
is not more specific than that.
This commit modifies `infer_type` in `_recursive.py` so that it returns
`c10::InferredType` instead, which allows more information about typing
failures to be communicated to the caller through the `reason()` method
on this class. This information is appended to the hint added to the
module concrete type for failed attributes.
**Testing**
This commit adds a unit test to `test_module_containers.py` that checks
that extra information is provided about the reason for the failure
when a module attribute consisting of a list of `torch.nn.Module` fails to convert.
Test Plan: Imported from OSS
Reviewed By: pbelevich
Differential Revision: D26091472
Pulled By: SplitInfinity
fbshipit-source-id: fcad6588b937520f250587f3d9e005662eb9af0d
