After upgrading Xcode to 7.3, I just found that some modules are stricken out while importing, like in this screenshot:
But after adding the module (so just pressing enter) everything is fine. What does that mean? The module here is written in Swift and works fine.
This is a bug. We have fixed it in 218010af, which should be included in the Swift 2.2.1 release and is included in the 2016-04-12-a developer snapshot.