extension outside of file declaring generic struct 'AnyArrayBuffer' prevents automatic synthesis of 'move(by:)'

[ProfFan]

AnyArrayBuffer+Differentiable.swift:18:1: error: extension outside of file declaring generic struct 'AnyArrayBuffer' prevents automatic synthesis of 'move(by:)' for protocol 'Differentiable'
extension AnyArrayBuffer: Differentiable where Dispatch: DifferentiableArrayDispatch {
^

@BradLarson have you encountered this? I think this is a new rule added to the Swift compiler, but I don't know when or how.