Apple Swift version 2.1.1 (swiftlang-700.1.101.15 clang-700.1.81)
Define a protocol that contains a static function on it. Then write a protocol extension for said protocol that implements a function of the same name but without the static modifier.
When marking a class or struct as conforming to the protocol, the compiler will crash without letting the developer know the cause of the problem.
I ran into this issue by forgetting to add the modifier to the protocol extension. Moreover, the compiler wouldn't tell me that my conforming class wasn't implementing the specified method.
See the attached playground for an example.
If the function in the protocol extension has a different name, the compiler will catch it and let the developer know that the conforming class is missing said function.
Here is the stack trace that Xcode outputs: