Swift compiler crashes on associatedtype in @objc protocol

Question

This code sample breaks Swift compiler:

import Foundation

@objc protocol Some {
    associatedtype W
}

extension Some {
    func takeW(w: W) -> Void {
    }
}

Output:

0  swift                    0x0000000104f583ad PrintStackTraceSignalHandler(void*) + 45
1  swift                    0x0000000104f57b56 SignalHandler(int) + 790
2  libsystem_platform.dylib 0x00007fffe7eadbba _sigtramp + 26
3  libsystem_malloc.dylib   0x00007fffe7e21258 malloc + 24
4  swift                    0x0000000101f8cd32 llvm::Value* llvm::function_ref<llvm::Value* (unsigned int)>::callback_fn<swift::irgen::emitArchetypeWitnessTableRef(swift::irgen::IRGenFunction&, swift::CanTypeWrapper<swift::ArchetypeType>, swift::ProtocolDecl*)::$_0>(long, unsigned int) + 530
...

While emitting IR SIL function @_TFE4mainPS_4Some5takeWfT1wwx1W_T_ for 'takeW' at main.swift:11:5

Is mixing @objc and associatedtype is inherently wrong, or is it plain compiler bug?

swiftc --version
Apple Swift version 3.0.2 (swiftlang-800.0.63 clang-800.0.42.1)
Target: x86_64-apple-macosx10.9

Answer 1

Associated types are Swift-only feature, not visible to Objective-C, so there should be compiler error.

Filed a bug https://bugs.swift.org/browse/SR-3850