The question is the subject, but anyway I’ll repeat it here: Why URL
doesn't have fileReferenceURL and isFileReferenceURL, but NSURL has? Is
it by design? If it’s a bug I can create an issue in https://bugs.swift.org.
It seems this is intentional, see SR-2728: https://bugs.swift.org/browse/SR-2728.
Tony Parker wrote in a comment there:
"Note that it is expected behavior that `struct URL` does not support file reference URLs.
The unfortunate part here is that we don't have a mechanism to keep `NSURL.fileReferenceURL` from being imported as returning `struct URL` instead of `NSURL`. We probably need to add an ObjC thunk in the overlay and mark the API as `NS_REFINED_FOR_SWIFT` in the NSURL.h header. However, that would be a source breaking change."