Fixes #20124 (#20203)
Summary:
Fixes #20124
Description:
Code wraps `optimizer.step()` method to detect whether user is following new pattern or old pattern. In case of old pattern detected, a UserWarning is raised. Documentation is also updated to reflect the change:
cc SsnL, bado-lee
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20203
Differential Revision: D15543060
Pulled By: ezyang
fbshipit-source-id: 3605e1afdb6ffc2dfd5e75e92e01b967c4d065b5
