@krzyzanowskim @helge It’s a known issue that’s fixed by https://github.com/swiftlang/swift/pull/80595 which is not included in Swift 6.1.0. It’s an accidental crash on a code path where the compiler should emit a warning about a missing `any`. You can resolve the crash by adding `any` or `some` in front of `Collection` depending on which one you meant.