By experimentation, I have figured out that the module can be made to build by removing the conformances to SearchableBidirectionalCollection and its inherited BidirectionalPattern from Data and several of String’s view types (which defeats the purpose). What these types appear to have in common is that SubSequence == Self and/or that Element is concrete. The other types that appear to successfully conform either have a distinct SubSequence or have conditional conformance based on a generic Element (e.g. Array where Element: Equatable).