`canonicalize` should fill in `NoTangent()`?

[vpuri3]

Currently cacnonicalize fills in properties not present in the input tangent with ZeroTangent(). I would think if the package author has not added a field to Tangent{P}(...), then its tangent would not exist, like for traits and indices. And ZeroTangent() is used for cases where the tangent exists, but is vanishing.

[mzgubic]

Both can be true: the non-existent field being a NoTangent() or ZeroTangent(), depending on the use case. And we had to pick a default. One could argue that ZeroTangent() is the more appropriate choice, but it is probably not worth the effort to change it at this point, unless you have a concrete use case in mind? (In practice, the behaviour of ZeroTangent() and NoTangent() should be interchangeable.)

[vpuri3]

no i was just curious. thanks for the answer