Currently the following interpolation modes are allowed

Since torch==1.11.0 (pytorch/pytorch#64501 of @vfdev-5 to be exact), torch.nn.functional also supports mode="nearest-exact":

Mode mode='nearest-exact' matches Scikit-Image and PIL nearest neighbours interpolation algorithms and fixes known issues with mode='nearest'. This mode is introduced to keep backward compatibility. Mode mode='nearest' matches buggy OpenCV's INTER_NEAREST interpolation algorithm.

Given that we are aligning more with PIL and "nearest" is described as "buggy", can we add support for "nearest-exact"?

If yes, we should also think about changing all our default values to it. That might be a bit cumbersome for the users, but we could also remap its name. Meaning after the whole deprecation period is through, "nearest" just maps to "nearest-exact" of interpolate and we have a "nearest-legacy" or the like that maps to "nearest". We already do a name mapping for other interpolation modes:

Deprecation process could look like this where r denotes the current release.

• r+1: add "nearest-exact" as valid interpolation mode and deprecate not passing a value explicitly. Plus, this should add a "nearest-legacy" that aliases the current "nearest". We also need to warn if "nearest" is passed that the behavior will change in the future.

  def foo(..., mode=None):
      if mode is None:
          warnings.warn("Not passing a default value is deprecated.")
          mode = "nearest-legacy"
      elif mode == "nearest":
          warnings.warn(
              "Nearest is deprecated. Use nearest-legacy for the current behavior "
              "or nearest-exact for the future behavior"
          )

• r+2: fail if interpolation mode is not passed explicitly or "nearest" is passed.

• r+3: re-introduce "nearest" as default value for the interpolation mode, but map it internally to "nearest-exact".

cc @vfdev-5 @datumbox