Vision: Nightly build failure on Windows

[peterjc123]

Starting from Jan.11, the nightly build started to fail. (commit: 61763fa)
See https://dev.azure.com/pytorch/778b86d3-09b9-4636-a34b-315646862684/_apis/build/builds/18418/logs/122.

[fmassa]

I suspect the failure in torchvision is due to a change somewhere in PyTorch, because there has been no changes in torchvision C++ files since then that could potentially be the culprit.

[peterjc123]

https://github.com/pytorch/vision/blob/master/torchvision/csrc/vision.cpp#L20 Maybe we should add a PyInit__C function here?

[fmassa]

Maybe, but I wonder what has changed since https://github.com/pytorch/vision/pull/1348 , so because CI was passing back then.
Could you try sending a PR to see if it fixes it?

[asears]

The integration with PIL 7.0 VERSION API change is breaking some dependencies. I can see these are fixed in Linux / Mac releases.

Doesn't look like Windows version has been published to pypi? https://pypi.org/project/torchvision/0.5.0/#files

Last release appears to be
https://pypi.org/project/torchvision/0.4.1/#files

References #1759 #1712 #1718 #1726

[peterjc123]

@asears Your issue doesn't seem to be related to mine. Would you please open a new one?

[asears]

Added #1774

[peterjc123]

Well, I think I figured out what happened here. It was caused by the removal of the static library _C.lib at the PyTorch side in https://github.com/pytorch/pytorch/pull/31161. Before that change is merged, building torchvision._C uses the init function PyInit__C from PyTorch, which is actually not correct. We should define our own version of that. ~Actually, this problem is not Windows only. But I don't know how to fix for other platforms.~
Update: Well, it is simply because _custom_ops is now called _C.

[fmassa]

Thanks a lot for the investigation and the fix @peterjc123 !