Xcode 7.3 beta 3:
Apple Swift version 2.2 (swiftlang-703.0.6.5 clang-703.0.21)
Also affects Snapshot 2016-02-08:
Apple Swift version 3.0-dev (LLVM a7663bb722, Clang 4ca3c7fa28, Swift 1c2f40e246)
Returning nil from a failable initializer of an NSObject subclass results in a runtime crash in swift_deallocPartialClassInstance call. This doesn't happen if a class method is used instead of a convenience initializer, or if the class doesn't inherit from NSObject. The issue does not depend on optimization level. This is a regression from Swift 2.1 / Xcode 7.2 where the same setup doesn't crash.