Update: @nnnnnnnn found a great workaround and we are even able to declare the associated type default without breaking any tests. See [NOMERGE] Make Sequence be a typealias for Collection by dabrahams · Pull Request #17220 · apple/swift · GitHub
Update: @nnnnnnnn found a great workaround and we are even able to declare the associated type default without breaking any tests. See [NOMERGE] Make Sequence be a typealias for Collection by dabrahams · Pull Request #17220 · apple/swift · GitHub